not getting oil to rockers

not getting oil to rockers

Postby grumpyvette » February 6th, 2011, 8:19 am

What would cause 70lbs of oil pressure at idle and none to the push rods? Gauge is good. I put in a new hv oil pump and still no oil. HELP!!!!!!!!"

just a tip guys, any ELECTRIC DRILL is going to have a difficult time spinning an oil pump priming tool , without heating up and at least potentially or eventually burning out ,simply because electric drills cool with air flow and spinning as slow as an oil pump priming tool with that much resistance to the rotation its not going to be spinning fast enough to get the required air flow to cool properly.
the correct oil pump primer tool duplicates the distributor body and seals the oil passages
there IS a simple solution for anyone who can fabricate that has access to air tools
you simply modify an old distributor similar to this picture then weld on a 3/8" drive socket to the top and your your AIR RATCHET to spin the primer tool which will not overheat and burn up.

anytime your tracking down a problem you need to isolate and test,each potential source, think logically!
I know some of you would rather be boiled in oil than read links I provide...but you might be amazed at the info they contain

Id suggest two quick checks first, replace your oil filter, as they can be defective and block flow,while its off inspect the spin on oil filter adapter plate

and verify your oil levels at the correct level on the dipstick,
then loosen ALL the rocker arms until they are loose enough to click at idle, and use a pre-luber to furnish the oil pressure without putting any wear on the bearings as you have a friend slowly rotate the crank to allow oil to flow easily



READ THESE threads, a clogged oil passage or cam or main bearing oil feed hole, bearings full of crud from a previous failed cam, lifter,or bearing failure, or bits of silicone gasket material or the wrong oil filter or oil pump pick-up can be a problem source. If you find a single lifter or cylinder clicking, obviously youll want to verify clearances and adjust the rocker, if the ticking continues you might have a worn cam lobe but do some testing and checking, Assuming youve located the lifter tick to a single cylinder location, do this quick test, look carefully for an exhaust gasket leak, if you don,t find one .swap a couple rocker arms that are NOT near each other and see if the problem stays with the lifter or rocker arm location
a good many lifter ticks are rocker related



viewtopic.php?f=54&t=2187 ... pumps.aspx





because it FORMS a wall in the lower lifter gallery oil passage

if you use a pre-oiler or oil pump drive like these below, theres a huge internal leak and youll never get much oil flow



theres also a plug that can be incorrectly installed



PLUG BLOCKING OIL PASSAGE which may be your issue
the plug is not sideways, or missing, if it was theres no difference in oil pressure, you just have most of the oil bye-pass the filter
if you had both oil pressure and flow for over 1200 miles for the cam break in, its not likely the plug, personally Id inspect the oil pump and pick-up that will require a tool like this one below or pulling the oil pan


the tool I bought saves me a ton of work

think logically!

(1) if hes got 70 psi at idle theres only a few potential problems

(2)he can,t have a major oil passage plug out of place other than the one I linked too being placed too deeply, so it blocks most or all of the oil to the lifter gallery passages.

(3) he states the GAUGE is correct(I tend to doubt that a bit because even a high volume oil pump will rarely reach 70psi at idle) but because oil is not compressible yes its entirely possible
while your engines running theres several gallons of oil per minutes circulating thru your blocks oil pump and the blocks internal oil passages, if you have any crud suspended in that oil like particles of sealant or micro bits of bearing or cam lobe, metallic crud from a wiped cam lobe etc, its pumped, thru the oil system along with the oil flow until its trapped by the oil filter, or gets trapped and blocks the oil passages.
all that extra silicone sealant that gets squeezed out off the gaskets tends to get carried by the oil flow into the oil pan where some of its trapped in the oil filter during each successive trip thru the engine, but bits that get trapped in the oil passages can rapidly reduce oil flow and destroy bearings, cam lobes and rockers and lifters.


there are many oil leakage points(100) in a standard Chevy engine.
16 lifter to push rod points
16 push rod to rocker arm points
32 lifter bores 16 x 2 ends
10 main bearing edges
9 cam bearing edges
16 rod bearing edges
2 distributor shaft leaks
1 distributor shaft to shim above the cam gear(some engines that have an oil pressure feed distributor shaft bearing.)




if crud blocks most of these leakage points pressure will rapidly increase until the pumps bye-pass circuit opens to limit pressure to 65-70 psi





did you do what I suggested and loosen every rocker until it clicks, the reason is that its entirely possible to cold adjust rockers so the lifter seat can,t move far enough up to fill the lifter with oil,when its on the base of the cam lobe when the rockers not placing spring loads on the lifter seat so that no or darn little oil gets under the push rod seat consequentially, no-or very little oil moves up the push rods
Image because any missing plug would severely reduce the oil pressure.
if your not getting oil to the lifters this process of loosening all the lifters to maximize the lifter push rod seat movement is a mandatory first step in locating the source of the problem.

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Re: not getting oil to rockers

Postby grumpyvette » May 17th, 2011, 4:34 pm

"hey grumpyvette?

Priming motor, have oil to all rockers except one
Ever see this before? I have my drill on my priming tool, gauge reads 60psi. Initially took about 2 minutes to get oil to flow to the top end, but now they all flow within 5 seconds of turning the drill on. Except for #6 exhaust. No oil comes out. Push-rod is clear and so is the rocker arm adjuster. I have rotated the engine over 90* increments several times, but nothing. Tried for over 5 minutes steady.
All rockers/pushrods have great flow otherwise. What's the deal here? If it does not flow after 5 minutes of 60psi, I don't think it will flow if I fire it up.
Same block as last time. Swapped lifters from Crane rollers to Isky EZX.
Look at this thing, it is bone dry"


IF your not getting oil flow at the rockers, do a few basic tests, don,t assume anything, ARE you 100% sure the push rod feed holes line up with the oil feed holes in the rockers at some point in the engines rotation, can you stick a small paper clip wire thru the oil feed hole in the rocker tip so it goes into the tip of the push rod, and have you used solvent and air pressure to flush out the interior of the push rods to verify oil can travel up thru them?
try backing off on the adjustment nut as the engine idles to the point the rocker clicks noticeably then slowly tighten just to the point the noise stops , then add only a 1/4 turn, and see if that doesn,t cure the oil feed issue
There is an oiling hole in the tip of the rocker that feeds from the lifter to the rocker, as the lifter rides up the cam lobe the spring compressed the oil trapped in the lifter, forcing it up the push rod, that oil in the push rod has to, at some point, line up with the hole in the push rod to rocker oil feed hole. Maybe its not lining up and thats why theres no oil coming out, it can,t, if the holes don,t line up at some point in the rotation.

I find threads like this a bit amusing..MOST,automotive problems are best solved by a isolate and verify process,I'M going to assume you've verified the valve train clearances and geometry and that the push rod was clear, and rocker oil holes are not blocked and you inspected the lifter before installing it?
make sure the push-rod guide plates or the cylinder head clearance slot don,t touch the push-rod anyplace during the full 720 degree cycle because if they bind, the push-rod tip feed hole to lifter seat or push-rod to rocker oil hole alignment may be preventing oil flow
.logic says that if all but one rockers is getting oil theres obviously something different with that rocker,push rod or lifter,the first test is to loosen the rocker adjustment to allow the rocker to have a bit more slack or lash as it might just be its too tightly lashed, if thats not the cure, now it should be obvious that the fastest and easiest test would be to swap push-rods and see if the push rod change caused the problem to stay at that location or move with the push-rod, if it moves its obviously a defective push rod, if not you still have the lifter and rocker, so you move the rocker next, same deal, it either moves the problem or it stays in that case if it moves its the rocker, if it stays its the lifter and you, remove and inspect and clean or replace the defective lifter, if thats not the problem that only leaves the cam lobe ... 39313_0_0_







you might be amazed at the crud that can get trapped in the an engines valve train components and oil passages if the parts are not soaked in a solvent and blown out with high pressure air and then lubed before they get installed







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Re: not getting oil to rockers

Postby grumpyvette » July 25th, 2011, 1:19 pm

I have 1966 CHEVELLE SS clone that I am installing a original, 1966 big block engine into, but its been rebuilt, "the 396 bbc engine". I Purchased a 396 big block with the correct casting numbers from a farmer who had it in his barn for over 20 years, said it had been gone through but he didnt know what had been done , Long story short, I installed it, because it looked fine but I didnt have any oil to the rockers when I primed it or briefly started it? now what.

If your concerned about which stock performance camshaft...3904362? or 3863143?
the #143 has the groove for the 65/66 BBC lifter oiling system. the #362 does not , both are listed as replacement cams,and if the groove not present in the early block,it can not be used in a 65/66 BBC without having a machine shop cut the groove in the rear cam journal
the 1965 and 1966 big block 396 had unique rear cam bearings and required a grooved rear cam journal, most cams you buy currently are not grooved, the groove can be cut on a lathe its about .188 wide and .125 deep

its best to have both the correct cam mods and rear cam bearing
the rockers should be checked as they tend to have the problem first as the lifters and bearings usually get at least some oil, but don,t run it until youve verified thats the problem or youve located the problem.
any decent machine shop can groove your rear cam bearing journal cheaply
.188-.200 wide and .125- 3/16" deep is usually fine

Small Block Chevy Oil & Lubrication Systems
The Chevy smallblock lubrication system is very reliable and presents no design defects to worry
about. Just keep everything clean. Change the oil and filter on a regular basis, and it will provide good
service for more than one hundred thousand miles. If the recommended main and rod bearing and
rod side clearances are maintained, a stock volume oil pump is all that is required. A high-volume or
high-pressure pump or an oil pump from a bigblock Chevy are not needed in most street applications.
These other pumps take additional horsepower to run and add more strain on the cam/distributor
drive gears and drive shaft. Checking the operating clearances on the stock oil pump and optimizing
them if necessary, will ensure adequate oil pressure. The clearance between the pump gears and the
pump gear cover should be .002" to .0025". If there is more clearance, take a sheet of 400-grit
sandpaper and some oil, then move the main pump body in a figure-8 motion over the wet sandpaper
to remove material until the clearance is correct. If there is less than the minimum clearance, you can
sand the pump gears. Remember to Loctite the pump cover bolts when you put the pump back
Stock small block oil pump Oil pump drive shafts compared

The stock standard volume smallblock oil
pump will give excellent service in most
applications. Make sure that the pickup screen
you use fits the depth of the oil pan and that
the pickup tube is welded or bolted to the
pump body.
The oil pump drive shaft on the left fits any
Gen. I smallblock except the 400. The 400
shaft on the right is necked down in the center
portion to clear the wider main caps found on
the 400.

Oil pump pressure relief spring
You can increase the operating oil
pressure in a standard volume oil
pump by changing the pressure relief
spring to the Z-28 302 spring offered
under (PN-3848911, color-coded
white). With this high-pressure spring,
there is no need for washer shims or
carb jets. Operating pressures will be
65 to 70 pounds.

Two different oil pump intermediate drive shafts have been used in Gen. I blocks. All Gen. I blocks
except the 400 use a drive shaft that is 53⁄4" long overall and is the same shaft diameter its entire
length up to where the plastic or metal coupling sleeve attaches. The 400-style shaft is the same
length, but the diameter is necked down in a portion of the shaft to clear the wider journal 400 main
caps. The oil pump drive shaft for a Chevy bigblock is longer (61⁄2" overall) and is not
interchangeable. Gen. II engines that have a front-mounted OptiSpark distributor use an oil pump
drive shaft stub, which connects the gear on the rear of the cam to the oil pump. If you have a Gen. II
long-block and elect to use a Bowtie four-barrel carburetor aluminum intake and a rear-mounted
distributor, you must change the oil pump stub drive shaft to the conventional intermediate drive shaft
found on Gen. I motors.

Have the oil pump screen and pickup tube welded to the pump body. Remove the pump’s pressure
bypass spring in the pump before you do any welding to prevent heat damage to the spring. There
are some aftermarket pickup screens and tubes that will bolt to the pump and give positive retention
of the pickup instead of welding.

Make sure that you prime the oil pump before you install it. Squirt some oil into the pump or stick the
pickup down into some oil and turn the pump shaft by hand to coat the pump gears. This ensures that
the pump will move oil as soon as the new motor is turned over the first time you start it. It’s also a
good practice to use a priming tool on an assembled motor, before it is started for the first time. Oil
can then be pumped throughout the engine.
Continue to use the priming tool until you see oil come out of all of the rocker arm oiling holes.
Check that there is 1⁄4" to 3⁄8" clearance between the lowest point of the pickup screen and the
bottom of the oil pan.

Generally, the rule of thumb for oil pressure is 10 pounds of pressure for every 1,000 rpm. For
example, you should have 40 pounds of hot oil pressure at 4,000 rpm, 50 pounds at 5,000 rpm and
60 pounds at 6,000 rpm. Chevrolet makes a high-pressure relief spring (PN-3848911). It is color
coded white and will provide a maximum of approximately 70 pounds of oil pressure. This spring is
used in high-performance oil pump (PN-3848907). You can add this spring to a stock standard
volume oil pump for increased line pressure.
(PN-3848907) is a standard volume oil pump with Z-28 pressure relief spring.

(PN-3848911) is a pressure relief spring; Z-28; 70psi.

(PN-3855152) oil pump pickup screen and tube is used with (PN-465220) Z-28 oil pan and standard
volume Z-28 pump.

(PN-10046007) is an oil pump mounting bolt.

(PN-3998287) is an oil pump / distributor drive shaft, use with plastic retainer / connector
(PN-3764554 or 10105879)
If you do use a high-volume or high-pressure oil pump, use a pump drive shaft that has a metal
coupler instead of using the stock plastic coupler. The LS1 Gen. III 350 uses a front-mounted gerotor
oil pump that is driven by a gear on the crank snout. A long pickup tube is routed from the pump to
the pickup screen in the Gen. III cast aluminum pan.
Oil Pans
First make sure that whichever oil pan you intend to use will fit inside your engine compartment
without hitting the front suspension crossmembers. Also determine on which side of the engine the
dipstick will go. It must match the dipstick location in the block and the oil pan. If you mistakenly put an
oil pan with a passenger side dipstick location on to a block with a driver’s side dipstick location, you
can develop an oil leak. Check these things before you build the engine and certainly before you
install the engine into the vehicle.

Over the years, two-piece rear main oil seal pans used two different thicknesses of seals between the
front oil pan surface and the timing chain cover. Here’s how to tell which front pan gasket to use. On
engines from 1955 to ’74, a 1⁄4" thin gasket was used; and from 1975 to ’85, a 3⁄8" thick gasket was
used. Take the oil pan you’re going to use and place a straightedge across the pan rails over the
front gasket half-moon opening. Measure the distance from the seal surface to the bottom of the
straightedge. If the distance is 21⁄4" use the 1⁄4" thin seal. If the distance is 23⁄8", use the 3⁄8" thick
seal. You can use a two-piece seal oil pan with a thick gasket on a block that originally used a thin
gasket and pan, if you must. Just make sure you use the appropriate front pan seal and that the pan
has the dipstick location that matches the block and location that you need.
A Moroso deep sump oil pan
A Moroso deep sump oil pan. Note
the trap door baffle to keep oil
around the oil pump pickup screen
and the curved portion of the pan
rail to accommodate a driver’s side
dipstick and tube.

Also, make sure that you use a pan for a two-piece rear main oil seal with a block that has the
two-piece rear seal. Likewise, a one-piece rear main seal block and crank requires an oil pan suited
for this application. Chevy and some aftermarket suppliers do make adapters to mount a two-piece
seal crank into a one-piece seal block and use the appropriate pan. Make sure you figure this all out
and make your parts selection before you build the motor.
Moroso deep sump oil pan
Make sure that the type of pan
you have chosen will fit in the
engine compartment of your
vehicle. This type of deep sump
pan oil fits most vehicle

(PN-359942) is a 5-quart oil pan with trap door baffles and a bigger sump. It was used on Gen. I
engines in Corvettes with a two-piece rear oil seal block; driver’s side dipstick position. This pan will fit
pre-’86 Corvettes, but may not fit your application due to crossmember clearance problems with the
larger sump.

(PN-360866) is a Corvette 4-quart Gen. I oil pan with a driver’s side dipstick and is used with two-
piece rear main oil seals.

(PN-465220) is a 1969 Z-28 Camaro oil pan with better baffling, for use with two-piece rear seals. This
pan has a 4-quart capacity and a driver’s side dipstick for use with Gen. I blocks.
(PN-465221) is the standard production Gen. I 4-quart oil pan. Chevy windage trays will not fit this
pan. It is used with two-piece rear seals and has a driver’s side dipstick location.

(PN-10055765) is a 1986 and newer Corvette 5-quart Gen. I and II pan for use with one-piece rear
main seals. It has a passenger side dipstick location.

(PN-10066039) is a 4-quart pan for two-piece rear seals and is used on the Gen. I Goodwrench
350/190hp, 350/285hp crate motors. It will clear and fit most front crossmembers

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Re: not getting oil to rockers

Postby grumpyvette » March 10th, 2013, 5:22 pm

"GRUMPY? why does the hydraulic lifter preload matter, 1/4 turn, 3/4 turn, I don,t see any reason it maters and does less preload result in less valve lift or more valve lift, Id figure that the more preload the less lifter plunger moves and the more valve lift?"




I don,t think you have a firm grasp on whats going on,during the mechanics of the lifters operation, the lifter seat is FULLY compressed to its seat as the cam lobe ramp spinning under the lifter base lifts the lifter off the cams base circle,and the lifters push-rod seat is compressed against the valve spring, oil trapped between the lifter, is forced up the push-rod until the lifters push-rod seat reaches its fully depressed location in the lifter body, this takes time and depending on the rpm levels it may not reach its full depressed seat location in the lifter body before peak valve lift, keep in mind that at 6000rpm the lifter is cycling from seated to fully open 50 times a second.
the lifter seat is forced back to its full upper location by a combo of engine oil hydraulic pressure and a small spring, this also takes time, hydraulic lifters will at some point in the upper rpm band fail to fully cycle, but generally continue to cycle once the rpms drop again.
the factory suggests 3/4 turn as it allows more compensation for wear in the valve train, and anything from 1/4-3/4 works but you get more valve spring cooling with 1/4

at low and mid rpms the lifter push-rod seat is fully depressed during the lash ramp and has little or no effect on total valve lift (see green line)this is mandatory as its how oil is forced up the push rods to lube the valve train,
at high rpms the lack of time to bleed oil up thru the push rods, and allowing the seat to fully seat might add insignificant lift, at very high rpms the lifter seat can,t collapse the plunger fully and it can cause the valves not to fully seat

Ive helped break in many dozens of engines, over the years , reading thru these threads, and sub links in them, will give you a great deal of useful info














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Re: not getting oil to rockers

Postby grumpyvette » June 20th, 2013, 6:24 pm

Diagnosing Oil Pressure Problems

By Larry Carley

Larry Carley

Every engine requires a certain amount of oil flow to keep the bearings, camshaft, valvetrain and other moving parts lubricated. Oil forms a barrier that prevents metal-to-metal contact and reduces friction and wear within the engine.

In the bearings, it forms a wedge that actually lifts and supports the crankshaft and camshaft as they rotate. Oil also serves as the primary means of cooling the bearings as well as the pistons. What’s more, oil also serves as a hydraulic fluid inside hydraulic lifters and lash adjusters to maintain proper valve lash. On some late model engines with variable valve timing, oil also moves the adjuster mechanism that advances and retards cam timing.

With so many important jobs to do, it’s obvious that the engine needs a steady supply of oil. But how do we know if the bearings and other moving parts are being adequately lubricated? Since there’s no simple way of measuring oil flow inside an engine, we use oil pressure as a means of gauging oil flow and lubrication.

Oddly enough, oil pressure by itself doesn’t give us the complete picture of what’s really going on inside the engine. It only tells us the oil is encountering resistance as it circulates through the engine.

Understanding oil pressure
Oil pressure is created when the positive displacement oil pump sucks up oil from the pan and pushes it through the filter into the engine’s main oil gallery. The oil is then routed to where it is needed: the main bearings, rod bearings, cam bearings, upper valvetrain and timing chain or tensioner.

The oil’s viscosity makes it thick and slows the flow as it passes through the passages and bearings. The amount of pressure created thus depends on the bearing clearances as well as the oil’s viscosity. Tighter clearances and/or heavier viscosity equal more pressure.

As the pressure builds up in the oil system, it has to go somewhere. A spring-loaded pressure relief valve built in the oil pump (or next to the pump) opens when pressure exceeds a certain limit and either reroutes oil back into the pump’s inlet or the oil pan. This prevents a dangerous build-up of pressure that could rupture the oil filter or blow out pressed in oil gallery plugs. Most relief valves are set to open when oil pressure exceeds about 50 psi.

At idle, most oil pumps do not produce enough flow to force open the relief valve. Oil pumps that are camshaft driven only turn at half engine speed so output isn’t great at idle and low rpm. Even pumps that are crankshaft driven and turn at engine speed (or double engine speed in a few instances) don’t pump enough oil to overcome the relief valve spring. The relief valve generally only comes into play at higher rpms when the pump’s output pushes more oil into the system than it can handle. Then the relief valve opens to vent oil and limit maximum oil pressure until engine returns to idle or a lower rpm.

Low oil pressure
The first indication of low oil pressure is usually a flickering oil warning lamp at idle, or a lower-than-normal gauge reading. Unfortunately, most warning lamps won’t come on until the oil pressure is really low, like 4 to 5 psi. If the warning isn’t noticed or heeded, the next indication may be valve clatter as the hydraulic lifters or lash adjusters run out of oil. If the loss of oil pressure continues much longer, the next sound will be the rods knocking followed by silence as the bearings seize.

Low oil pressure is bad news because it usually means the engine isn’t getting enough oil, and that can lead to serious trouble very quickly for the rod and main bearings, as well as upper valvetrain components (especially overhead camshafts). For this reason, any indication of low oil pressure should not be ignored and should be diagnosed and dealt with immediately!

In a high mileage engine, low oil pressure is often due to a combination of worn bearings and a worn oil pump. The oil pump is a high wear component in all engines because it draws in unfiltered oil. The pickup screen on most engines is relatively coarse and will only stop relatively large chunks of debris from entering the pump. Yet the internal clearances in many pumps is only a few thousandths of an inch between the gears and between the gears and cover. What’s more, many pickup screens have a relatively large bypass valve or slots that allow unfiltered oil to enter the pump when the oil is cold and thick, or if the oil filter pickup screen itself becomes plugged with debris.

When an oil pump ingests debris, it can wear or damage the gears. As wear increases over time, clearances increase causing the pump to work less efficiently. As the pump gets weaker, oil pressure drops. The cure here is to replace the worn pump with a new one.

Sometimes an oil pump will suck in something that causes it to lock up. This usually breaks the pump drive and totally starves the engine for oil. Unless the engine is shut off almost immediately, it’s the end of the road for the bearings, too.

Installing a high volume oil pump can increase oil pressure somewhat at idle because the larger gears will displace more oil. But high volume oil pumps are designed primarily for high rpm, performance applications where increased bearing clearances and/or the use of a remote filter or dry oil sump requires more oil flow. A high volume oil pump is not a substitute for overhauling or replacing a worn engine.

As for high pressure oil pumps, installing one usually won’t make any difference in idle pressure because the relief valve doesn’t come into play until higher rpms. All this type of pump does is raise maximum oil pressure at higher rpms. If you replace an oil pump, always replace the pickup, too.

Swishing an old pickup in some solvent may only loosen the crud that has accumulated over the years inside the screen, allowing it to be sucked into the new pump as soon as the engine is started. Priming the pump prior to starting the engine is also a good idea so there’s no delay in oil reaching the bearings. Also, use care when installing a pickup tube and screen so that it is properly mounted and does not leak.

As for worn bearings, increased clearances allow the oil to leak out of the bearings at a faster rate. Only about .001˝ of wear in the main bearings can reduce oil pressure up to 20%! Wear also increases the amount of oil splash inside the crankcase, which can overwhelm the rings and cause the engine to burn more oil. Excessive bearing clearances will also increase engine noise and pounding, which will eventually lead to bearing fatigue and failure.

The only fix for worn bearings is to replace them or the entire engine. Installing a set of standard sized bearings (assuming the crankshaft is still within acceptable tolerances) can help restore normal oil pressure at idle, but the amount of improvement will depend on wear elsewhere in the engine, too. Bearings alone can’t rejuvenate a tired engine that may also have low compression and worn valvetrain components.

Troubleshooting low pressure
Start by checking the oil level on the dipstick. If the oil level is low, the engine may be leaking and/or burning oil. Adding oil may temporarily restore normal oil pressure, but unless the oil level is maintained the problem will return.

If the engine is leaking oil, recommend new gaskets or seals to fix the leak. If the engine is burning oil, the valve guides and seals are probably worn, and the rings and cylinders might be worn, too. A wet compression test and/or leakdown test can help isolate the wear and determine the best course of action.

Also note the condition of the oil and make sure it is the correct viscosity for the vehicle and prevailing weather conditions. For most late model vehicles, the crankcase should contain 5W-30 or 10W-30. For older high mileage engines, 10W-40, 20W-50 or even straight 30W or 40W oil can help maintain good oil pressure in hot weather. But 20W-50 and straight 30 and 40 are too thick for cold weather driving and may cause start-up lubrication problems especially in overhead cam engines. Light viscosity oils such as 5W-20 and straight 10W can provide good lubrication in cold weather but may be too thin for warm weather or high mileage engines.

If the oil level is OK, the next thing to check would probably be the oil pressure sending unit. Disconnect the unit and check the warning lamp or gauge reading. If the warning light remains on with the sending unit disconnected, there’s probably a short to ground in the warning lamp circuit. Likewise, if there’s no change in a gauge reading, the problem is in the instrumentation, not the engine.

Bad oil pressure sending units are fairly common. But if the warning lamp is still on after replacing the unit, guess what? A sending unit has just been replaced unnecessarily. A better approach is to unscrew the sending unit, hook up a pressure gauge to the fitting on the block and take an actual pressure reading with the engine running.

If oil pressure reads low at idle, check for a plugged oil filter. Is the filter OK? Then you’ll probably have to drop the oil pan to inspect the oil pump, pickup screen and bearings.

With a crankcase mounted pump, you can remove the pump cover and check the pump’s internal clearances for wear or damage. If the pump appears to be in good condition, that leaves the bearings. Check the clearances on the main bearing closest to the pump (since this has the greatest effect on pressure), and clearances on the furthest rod bearing (since this will show the greatest wear). If the bearings are worn, your customer either needs a new set of bearings, more extensive machine work and/or a rebuilt engine. But don’t install any bearings until you’ve carefully measured the crankshaft journals with a micrometer. If you find excessive wear, taper, out-of-round or any damage, the crank will also have to be reground or replaced.

Other checks might include camshaft end play, and/or pulling a valve cover or the intake manifold to check the cam bearings and lifters. Remember, excessive clearances or leaks anywhere in the engine’s oil supply system can contribute to low oil pressure.

Erratic oil pressure
If the oil pressure seems fine one minute, then suddenly drops, it usually means air is being sucked into the oil pump. This can be caused by a low oil level, an improperly mounted oil pickup (too high in the oil pan), leaks between the pickup and pump, or too much oil in the crankcase. In the case of too much oil in the crankcase, windage from the spinning crankshaft whips the oil into foam. A missing or loose windage tray inside the oil pan may be a contributing factor.

If the oil pressure surges at higher rpms, it may be the result of air being drawn into the pump for any of the just mentioned reasons or a sticking pressure relief valve. Sometimes an engine can run out of oil at higher rpm if the return passages in the head and block are restricted and don’t allow the oil to drain back into the pan quickly enough.

Too much oil pressure
Though less common, too much oil pressure can also create problems. The most likely cause here is a stuck relief valve in the oil pump. If the pressure valve fails to open, pressure can reach dangerously high levels and may rupture the oil filter or force out oil gallery plugs. Replace the pump or valve (if separate) to cure this condition.

On 1995-’97 General Motors 2.3L and 2.4L engines, the OEM oil pump relief valve can stick causing pressure to shoot up to 125 psi or higher. GM says pressure should not exceed 85 psi at 3,000 rpms on these engines. GM’s fix for the problem is a revised oil pump (p/n 24576315).

Other causes of excessive oil pressure can include a restriction or blockage in the main oil gallery, or a combination of tight bearing clearances, high rpm operation and using an oil viscosity that’s too thick.

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