Oil pressure drops as RPM increases

[JMD]

I have a mild build 454 in my ‘68 K10. It’s a Mark IV block with Edelbrock heads, hydraulic lifters, roller rockers, and a high volume oil pump. Should be pushing about 400hp at the crank. The engine was professionally rebuilt by an upstanding shop about 2000 miles ago with no issues. I have 4.10 gears and a TH400 so cruising speed keeps the engine at about 2900 rpm. Oil pressure at that speed is around 70lbs, and at idle it’s about 20lbs

Yesterday after driving for about 1/2hr at highway speeds I heard a loud clacking noise that I believe was coming from the valvetrain. I noticed that the oil pressure was 13lbs so I immediately turned the engine off and coasted to a stop. The engine ran for probably a total of 7 seconds with low pressure before I shut it off.

The coolant temp was a normal 180*, and there was plenty of oil in the pan. No leaks or any visible signs that something was wrong. I waited about 45 minutes and started it back up to drive it on a trailer. No weird noises, and the oil pressure at idle was normal. However I did notice that if I revved the engine to about 2500rpm the oil pressure would climb and then drop to about 20lbs.

At this point IÂ’m thinking either the oil pickup tube is blocked or cracked, the pump is going out, or oil filter is messed up. IÂ’m running synthetic 10w30, but I donÂ’t think viscosity or oil level is the culprit since I havenÂ’t had a problem in over 1600 miles.

The only thing I changed leading up to this event was about 50 miles ago I reinstalled the oil dipstick tube with a new O-ring after it had developed a nasty leak, and I added a quart of oil to replace what had leaked out.

Today I plan to take the valve covers off and look for anything weird as well as do an oil/filter change and cut open the old filter to look for any carnage. Has anyone seen this type of thing before? Is there something specific I should be looking for? The engine has to come out in order to drop the pan, so IÂ’d like to rule everything else out before I dive that deep. Thanks.

[AussieinNC]

Make sure the oil pressure reading on the gauge is accurate by testing on another gauge.

Overfill the engine with an extra quart and see if the problem persists...if it doesnt, the pick up tube has fallen out of the oil pump. I have seen this happen literally on over 50 engines I have had to repair. I usually tig weld a sheet metal bracket to the tube and secure it under a pump cover bolt.

You can validate this by draining the oil from the engine and using a cheap video probe to look inside the pan....

There are aftermarket brackets available,,make sure you use Loctite on the bracket bolts and the clamp boly.

https://www.summitracing.com/parts/p...SABEgLm5PD_BwE

I do not recommend welding the tube directly into the pump housing, as the housing is cast and the tube is steel...

I have also found the bypass valve in the oil filter housing can act up....these are easy to check and replace if necessary.

[JMD]

Thanks for the reply, I’ll overfill it and see what happens. I forgot to mention that I removed the bypass valve before I broke the engine in, so we can rule that out as the culprit.

I removed the valve covers and started her up. Oil pressure was normal for a cold engine, all the rockers were getting oil and everything seemed normal so I’ll do an oil and filter change and see if anything changes.

[JMD]

It would make sense that the pickup tube fell off since the noise I heard seemed to match crankshaft rotation. Is it possible that the crank was contacting the pickup tube in the bottom of the pan?

[AussieinNC]

Anything is possible, but they usually lay flat on the bottom of the sump...but it is like being inside a hurricane of oil splash inside a running engine.

[JMD]

Changing the filter and adding a quart didn’t help. Oil looked clean though, no glittery stuff. While I had all the oil drained I hit the bottom of the pan with a rubber mallet to see if I could hear anything rattle around but no dice. I guess I’ll be pulling the engine this week to see what’s going on.

At this point I highly doubt the gauge is reading wrong since it definitely makes more valve train noise when the pressure drops off at higher rpm, but I’ll throw a new sender in there just to make sure.

[cadillac_al]

When you get the pan off, double check that the dipstick is at the correct level. It sounds like low oil level or a pick up problem.

[JMD]

Originally Posted by cadillac_al

When you get the pan off, double check that the dipstick is at the correct level. It sounds like low oil level or a pick up problem.

I do have a cheap aftermarket dipstick so I donÂ’t REALLY know where the oil level should be at. However, I havenÂ’t had any issues up until this point and the dipstick hasnÂ’t moved.

What are the dangers of having too much oil in the pan? Heat and aeration, right? Would it be a bad idea to add another quart or two? I have 6 quarts exactly in it right now, and it’s right at the “full” mark on the dipstick. Now that I think about it, 6 quarts doesn’t seem like enough for a 454 with a “truck” pan.

[JMD]

Originally Posted by cadillac_al

When you get the pan off, double check that the dipstick is at the correct level. It sounds like low oil level or a pick up problem.

I do have a cheap aftermarket dipstick so I donÂ’t REALLY know where the oil level should be at. However, I havenÂ’t had any issues up until this point and the dipstick hasnÂ’t moved.

What are the dangers of having too much oil in the pan? Heat and aeration, right? Would it be a bad idea to add another quart or two? I have 6 quarts exactly in it right now, and it’s right at the “full” mark on the dipstick. Now that I think about it, 6 quarts doesn’t seem like enough for a 454 with a “truck” pan.

[AussieinNC]

Most 454's with a truck pan take 7 quarts...some take 8 quarts....

Put the extra quart in it and try it...

[JMD]

I called the shop who built the engine for me and he said he wanted to cut open the filter before I did anything more. He called me back tonight and said that the filter was jammed full of some kind of paper/gasket material...

I can’t for the life of me figure out how something that big would have made its way into the engine. The only thing I’ve done since the engine was built was install a Holley Sniper throttle body and a different distributor. So I guess it’s possible that something fell into the intake or the distributor hole.

I’m in the process of dropping the oil pan to see what the pickup screen looks like.

[JMD]

Found the problem. The oil pan gasket got pinched and the inner half of it fell into the pan.

[Greasey Harley]

Ouch!!
Hopefully, no hard parts were damaged.
You might take a quick look at the bearings.
(((Fingers crossed)))

[JMD]

My engine builder said there was no glitter anywhere in the filter so I think I caught it in time. I’m just glad it wasn’t anything major and that I didn’t have to pull the motor to drop the pan! I was able to lift the engine up just enough to unbolt the crossmember and slide it out of the way.

[AussieinNC]

Ok...not as bad as it could be...I use these one piece gaskets all the time...they dont break up and are reusable....

https://www.summitracing.com/parts/f...SABEgLvWfD_BwE

Have to admit, I have never seen so much "gasket" material from a pinched gasket....check the sump rail is not bent up around the bolt holes...if it is, flatten the rail out before you re-assemble....

Now, if the filter was full of paper, it means the oil pump has ingested the paper, ground it up and pushed it into the filter....

Suggest new pump, plus add that retainer bracket I sent you the details of earlier in the post....

Pop off a couple of bearing caps and check bearings for scoring....sometimes the filter does its job and stops down stream issues...

You absolutely did the right thing by looking at this issue as soon as you did.

Just a thought...ask your engine builder if they used a nylon faced cam gear?

[JMD]

Everything checked out fine as fair as bearings go. I removed the oil pump and thoroughly cleaned it as well as the pickup tube. I didn’t find any scoring on the pump gears or inside the housing, so I decided to reuse the pump. The distributor gear matches the cam, so I’m not worried about that as a source of the problem.

It was 100% oil pan gasket on the pickup screen. When I removed the pan most of the gasket was still RTVd to the pan, except for a couple spots near the front where the inside half of the gasket was missing. I assumed those pieces were stuck to the block, but I found the the block had no gasket material whatsoever stuck to it.

A few days before all of this happened I noticed a small leak from the pan gasket and a couple of the bolts were only finger tight, so I grabbed a wrench and snugged them all up. I think I over tightened the bolts, which caused the gasket to split in half and fall into the pan.

I bought a FelPro one piece rubber gasket and buttoned everything back up. No leaks (finally) and oil pressure is back to normal...

HOWEVER...I noticed that once the oil gets nice and hot the pressure begins to dip after about 3500rpms. Not much, it goes from about 60lbs to 50lbs, but it’s still an issue.

So, assuming the pickup tube is no longer clogged, I’m guessing it’s either windage caused by too much oil in the pan and no windage tray, or too little oil in the pan and it’s not draining back to the pan fast enough to supply the pump with enough oil. I’m going to mess with the oil level this afternoon and I’ll report back with what I find.

[AussieinNC]

Originally Posted by JMD

Everything checked out fine as fair as bearings go. I removed the oil pump and thoroughly cleaned it as well as the pickup tube. I didn’t find any scoring on the pump gears or inside the housing, so I decided to reuse the pump. The distributor gear matches the cam, so I’m not worried about that as a source of the problem.

It was 100% oil pan gasket on the pickup screen. When I removed the pan most of the gasket was still RTVd to the pan, except for a couple spots near the front where the inside half of the gasket was missing. I assumed those pieces were stuck to the block, but I found the the block had no gasket material whatsoever stuck to it.

A few days before all of this happened I noticed a small leak from the pan gasket and a couple of the bolts were only finger tight, so I grabbed a wrench and snugged them all up. I think I over tightened the bolts, which caused the gasket to split in half and fall into the pan.

I bought a FelPro one piece rubber gasket and buttoned everything back up. No leaks (finally) and oil pressure is back to normal...

HOWEVER...I noticed that once the oil gets nice and hot the pressure begins to dip after about 3500rpms. Not much, it goes from about 60lbs to 50lbs, but it’s still an issue.

So, assuming the pickup tube is no longer clogged, I’m guessing it’s either windage caused by too much oil in the pan and no windage tray, or too little oil in the pan and it’s not draining back to the pan fast enough to supply the pump with enough oil. I’m going to mess with the oil level this afternoon and I’ll report back with what I find.

What weight oil of you have in the engine? 50lbs at 3500 plus should be ok, most performance engines look for 10 psi per 1000 rpm...

When you cleaned out the oil pump, did you clean and free up the bypass valve in the pump? Check its spring was ok...?

[JMD]

I’m running 10w30 full synthetic for oil. And no I did not clean out the bypass or look at the spring… I only remove the gears and looked for any scoring. How would a faulty spring affect pressure only at certain RPMs? And only when the oil is hot? I’m not doubting your expertise, I’ve just never gone this deep into an oiling system and I guess I have a lot to learn

[AussieinNC]

The bypass system is designed to provide a certain maximum oil pressure to an engine before releasing (bypassing) the extra pressurized oil back out. The valve is a simple round metal plug with a spring sitting against it, retained in the pump housing by a pin.

If the spring has been heat cycled with contaminated oil, the tension of the spring may be compromised. As the oil warms up it thins out a little which may be enough to drop the pressure.

If the engine was built to tight specs, 10W30 oil should be fine....however, we dont know the bearing clearances the engine was built with....IMHO, I would up the oil to 20W50 and try it.

Oil pressure drop above a certain RPM could also indicate that too much oil is being retained out of the sump.

Some street strip big blocks can retain up to a quart or more of oil around the crank itself simply by the spinning of the crank in the enclosed crankcase.

Does the engine have a crank scraper system on it? or a windage tray?

I would be upping the oil viscosity first...some may disagree here, but some aftermarket additive may do the trick with the oil you have in there now. This is not a plug, I use Lucas Oil Treatment. I have had success with older engines, like an LS I have in a 2001 Sierra that has 300,000 miles on it...and it retains 50 lbs oil pressure at 65 mph.

BTW...I dont see you as doubting my expertise...you are asking honest and viable questions to which you are entitled to my best knowledge.

[cadillac_al]

Cold oil pressure is always higher than hot oil pressure.

[BigRandy]

Originally Posted by cadillac_al

Cold oil pressure is always higher than hot oil pressure.

I think the OP is saying that with hot oil the pressure drops if the engine goes above 3500RPM.

JMD does the oil pressure return to 60 when you drop below 3500?

[JMD]

AussieinNC, I already have pretty high oil pressure at cold idle and what I would call excessive pressure if I try driving it before the oil is warmed up. The gauge is pegged past 80psi if I bring up the rpms on a cold engine. Would upping the viscosity risk damaging a cold engine? I’m worried that the cold oil would take to long to pump up the lifters and get to the top end of engine. I already noticed a couple of the rockers weren’t getting much oil when I did a cold start with the valve covers off.

Also, there is no windage tray or scraper system.

BogRandy, yes the pressure does return to 60 or more as soon as I drop below 3500. It seems to hover right around 40 lbs after 3500 unless I really get on it and bring it up past 5000. Then it slowly drops until I chicken out and let off the throttle.

The problem seems much more pronounced if the engine is under load and I’m accelerating. If I just rev it in neutral or hold the transmission in 1st while I slowly accelerate, the drop in psi isn’t nearly as rapid. Any clue what that means?

[geezer#99]

Originally Posted by JMD

The problem seems much more pronounced if the engine is under load and I’m accelerating. If I just rev it in neutral or hold the transmission in 1st while I slowly accelerate, the drop in psi isn’t nearly as rapid. Any clue what that means?

That tells you the pickup tube is starving for oil.
Under heavy acceleration the oil is climbing up the back of the pan.
I had a 70 LS6 did that. It was a loosely set up motor that used a quart every 700 miles. Drop in pressure said ‘time to add some oil’.

Add an extra 1/2 quart to test.

Did you measure pickup tube to bottom of pan clearance When you had it apart?

[JMD]

Originally Posted by geezer#99

That tells you the pickup tube is starving for oil.
Under heavy acceleration the oil is climbing up the back of the pan.
I had a 70 LS6 did that. It was a loosely set up motor that used a quart every 700 miles. Drop in pressure said ‘time to add some oil’.

Add an extra 1/2 quart to test.

Did you measure pickup tube to bottom of pan clearance When you had it apart?

Ah I forgot to mention that I did add another quart of oil and it made no difference whatsoever. I haven’t tried removing a quart yet, but doing so would only leave 5 quarts in the pan and I’m fairly certain a big block requires more than that.

I did not measure pickup tube clearance. I thought for sure the clogged pickup tube was my only problem so I cleaned it and slammed everything back together. The weird thing is that I don’t believe this was ever a problem until recently when the pickup tube got clogged. So in my mind, things like pickup tube height and oil viscosity shouldn’t be the problem because they haven’t changed since the engine was built and operating like normal.

[Ironangel]

One of the problems with overfilling is aeration of the oil. Air compresses and oil doesn't. One of the problems with big blocks are those open holes down the center of the lifter valley allowing oil from the heads to drain right back down on cam (which is good) and also back onto the rods and crank. That causes copious amounts of oil to get airyated before running back into the pan. You might try a 10w-30 oil such as Valvoline VR-1 or Lucas Hot Rod Oil containing zinc. Many of the full synthetics have properties that resist shear meaning they will readily trap air bubbles before releasing them in the pan and sump before getting sucked up into the pump. Many big block performance guys (myself included) epoxy a stainless steel screen mesh over those lifter valley openings serving a dual purpose. The second being catching fragments from a shelled out rocker or spring problem. Another trick David Vizard advises doing is drilling one or two extra oil drains in the back of the lifter Valley next to the distributor shaft, and enlarging the drain hole at the front dumping oil right on the timing set. When that motor winds up the oil fills with tiny air bubbles compromising the pressure from the pump... Try 5 quarts of old school zinc ladened 10w-30 and see if the pressure drop still persists...I run a high volume pump in an 8 quart pan with no tray or wiper. I also use a billet adaptor in the oil filter opening to filter 100% of the oil. I cut lifter bore grooves and use EDM solid lifters to oil the cam lobes...I also drill 3/64" holes in the galley plugs to purge any air that likes to stay in the ends of the lifter oil galley ways...Good luck!