The Stovebolt Site Forums The Shop Area Engine Shop 261 oil pressure too high

i just started the 261 in my 51 chevy and it runs great.. when i got this engine it had sat for many years, so i got a new gasket set and pulled the head and oil pan off.. i pulled the rod caps and main caps all looked good someone had just did alot of work on the engine because it had new rods, pistons,and oil pump.. i put the engine back together with dual carbs and exhaust.. it started good but the oil pressure is too high..i have a 80 PSI gauge and it pegs it even after the engine gets warm.. i have blown 2 oil filters apart.. the only thing i can think of is the relief valve in the oil pump is somehow stuck..i am not wanting to pull the pan back off so i was hoping someone here might have a idea on something else it could be that dont involve pulling the pan back off

http://s202.photobucket.com/user/rcplumley/library/51%20chevy%20project

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Well, since the oil pump is inside the oil pan, and the bypass spring is inside the oil pump inside the oil pan, you have no choice but to drop the pan.

Do you have a full flow oil filter setup? If you do and you are using one of the old style bypass canisters, it would need to be modified. It has a restriction built in, usually a hole around 1/16' in diameter.

hi truckermix.. i had already converted it to a spin on type filter..but had to remove that because it burst 2 filters already..i have made a solid copper line to replace the filter, then installed a 300psi gauge and run the engine again..after it warms to operating temp the oil pressure did drop.. it idled at 50psi but jumped to 160 psi at part throttle.. the original full flow (not a bypass) filter on the engine did not have a restricted canister. instead the canister has a by-pass built into it. i am hoping that running the engine a few times and cycling it though a few hot and cool-down cycles it will improve the high pressure situation.. i am thinking of sand blasting and painting the original filter canister if i can find a filter and a place to mount it.. at least i dont think it will blow apart at higher rpm and pressure.. i just never ran into this problem before usually it is a low pressure situation on these engines.. i also installed another gauge at the plug on the head leading to the rockershaft feed..it reads 50psi cold idle and drops to 5-10 psi hot... i think i will make a video next time i start the engine. so ya'll can see what i am talking about

I am surprised by the lack of replies here but there is no way that it should be able to reach 160 psi ! I am wondering about the relief valve in your oil pump.

yea trucker.. i am very surprised about the pressure also..in fact when i first started the engine with the filter bypassed and a 300psi gauge on it. when i raised the rpm with engine still cold the gauge read over 230psi at the pump and 80psi at the head.. i have never heard of a chevy 6 putting out that kind of pressure.. if i get time to start it today i will see if i can get a video of it both cold and hot

whisky runner,

Presumably, you have a 58-63 261 that is set-up for a full-flow oil filtration system?

Do you now have any oil filter on your engine?

If yes, is it a by-pass filter?
It should not be a by-pass (restricted inlet) filter - that would restrict the flow of oil (and may be the cause of the high pressure readings)? I am clutching at straws.

since the oil pump is a positive displacement pump im inclined to say what releif valve what goes in the pump must come out. if it cant come out a excessive build up of pressure occurs. hence the reason for the relief valve. since you were able to verify the readings, if it were me id start by looking into the pump and discharge lines and go from there.

I agree with Mike (51 ashton) and truckernix, a stuck relief valve (pressure control valve).

sorry i got busy with other projects..but i started the car almost every day and let it get warmed up, but it never did change.. i shot a short crappy video of it running with a shot of both the gauge i had connected at the head and one connected at the oil line feeding oil filter.. it would drop pressure and run 45 lbs at a idle when hot , but up the rpms just a little and it would still peg the 300psi gauge.. so i had to finally admit that it wasnt going to fix itself and i pulled the pan off today.. after i got the oil pump apart i had to use a hammer to get the relief valve out. i cleaned everything with some 360 emery to where it will slide easy, and put the oil pump back in.. i will restart it tomorrow ..after i get a new pan gasket.. i am really sure that was the problem.. i will try to post another video of it holding normal oil pressure tomorrow.."LESSON LEARNED" even with a fresh rebuilt engine if it has set around the shop very long.."COMPLETELY" disassemble it before you install it in your project ha ha ha ha

[IMG]http://i202.photobucket.com/al...vy%20project/51chevywindows021.jpg[/IMG]

[IMG]http://i202.photobucket.com/al...vy%20project/51chevywindows021.jpg[/IMG]

here is a link the complete build album if anyone is interested..

http://s202.photobucket.com/user/rcplumley/library/51%20chevy%20project

I am going to say its not the relief valve. At idle, the motor is not generating enough RPMs to push enough oil to create an 80+PSI back pressure. Remember... pumps create FLOW. restrictions create PRESSURE.

At idle the relieve valve would never lift even in a properly working motor, as the normal oil pressure, at idle, is less than 10PSI (some trucks simply say 'any' pressure is OK.

Since this motor is new to you, and has had extensive internal work "i pulled the rod caps and main caps all looked good someone had just did alot of work on the engine because it had new rods, pistons,and oil pump

Sounds to me like something was wrong (you don't replace all that stuff for kicks and giggles) and is still wrong.

Somethings off the top of my head:
Are the bearing in right (oil holes not covered)?
Are the cam bearings in right (oil holes not covered)?
Is any oil making it to the lifters? A late model 261 is going to be fed oil via the lifter galley.. DO YOU HAVE THE RIGHT LIFTERS IN?????

So basically you pump is working fine, the relief valve would never lift at idle on a working motor... that leaves clogged/blocked oil galleys.

When you find out what's blocked, let us know.

Going to disagree with you to some extent pfarber. If the engine is still pretty new, then at idle (depending on idle speed) it will have more than 10psi even when hot. My old 261 would hold around 30psi at hot idle with appx 20,000 miles on it. Would peg the gauge when cold. At highway speeds would hold about 45psi when hot.

The relief valve in the oil pump does much more work than you might think. With the oil pump and new bearings throughout the engine, it can build lots of pressure on the system in a hurry so the relief valve helps to "dump" the excess oil (and lowers the pressure) back into the pan rather than forcing it through the engine at such an extreme pressure.

I bet when he gets the relief valve working properly his oil pressure problem will be fixed. His engine should be set up for full flow filtration so he also needs to make sure he uses full flow filtration.

If the bearings (especially rod and main bearings) were not installed correctly the engine likely wouldn't turn over. Even if it did start, it wouldn't run long without obvious signs of troubles.

If any of the oil passages were blocked due to dirt or sludge then the engine would also show signs of bearing troubles very early in the run cycle. Rod and main bearings just don't do well without a steady supply of oil.

The oil pump in the engine isn't that different to a hydraulic pump on a machine. Just pumps a different kind of oil for a different purpose.

pfarber, what year and engine are you referring to?

This discussion is about a high-pressure 261 (high-pressure with 261 is redundant, but used here for emphasis).

Look this over and then educate us. I am not a trained mechanic but I have worked on 1940s 216s through 1960s 261a - I might not know what I read in manuals and I am ALWAYS ready to learn (and, I am am often apologizing for my mistakes, by thanking people for educating me).

All I know is you need to stop running it until you find the problem. You are going to break something or get hurt. It is obvious the relief valve isn't working, and it is also apparent the oil isn't going anywhere. You are going to have to drop the pan, because either you have a pump with no relief valve, or someone has plugged off the hole where it goes, the bearings are in upside down or something. I am pretty sure it has something to do with your "conversion". It is also apparent there is something you aren't telling us. And when you do find the problem you are going to just cry most likely.....

Ok, what if I told you the OFFICIAL 1954 spec guide for 235/261cu/in engines says that at 1150-1200 engine RPM the oil pump is rated at 4.3GPM (hot oil, 20W) and the OIL PRESSURE AT 1170-1200 engine RPMs is also 45PSI?

AT IDLE, the pump WILL NOT, BY DESIGN pump enough oil (remember, pumps create FLOW, RESTRICTIONS create PRESSURE. Say that second part again) to lift the relief valve? So, at 400-450RPM idle, the pump is, by design, NO WHERE NEAR 45PSI... most ppl seem to agree on 15PSI, but other say less, WHY WOULD A CLOGGED RELIEVE VALVE EVER OPEN? You could weld the relief port shut, and at IDLE, the pump will never spin fast enough to create a system back pressure of 45PSI+ THE FLOW/RPMs are not there to do it.

So, that means, that something AFTER the pump is clogged, as AT IDLE, and UP TO about 1000RPMs the pump WILL NOT generate more than 45PSI to lift the relief valve.

The OP said the pressure "it idled at 50psi but jumped to 160 psi at part throttle" while the relief valve MAY NOT be lifting, its not the reason WHY the system is seeing 80PSI+.

Something is blocking the oil. There are only 4 things in the path of the oil: cam bearings, main bearings, rod bearings and lifters.

One of those, or the galleys themselves, is blocked.

Hows that for explaining my position???


Edit 10:16 - OP said he had to bang out the relief valve with a hammer... but has not reported back if the pressures are normal. I agree that at high RPM the relief valve is a definite culprit... but not at idle, on a summers day with 30wt oil.

Sorry I am late to the party. I have read all the post and by chance have you confirmed this high reading with another gauge? Are you sure the gauge is not giving false readings?

If you have, I think you need to have a very close look of the engine to see what the issue is.

When my 261 is cold, the oil pressure will peg my gauge in the truck, (still running the 30 psi stock gauge). Only after some longer driving will the oil pressure drop down to 15 psi at idle.

if he ever reports back it will be an interesting learning experience to see to what extent the relief valve actually affects things. I wouldn't think it would be able to produce pressures of that magnitude in a normally clearanced engine, given the volume of oil lost in all the bearings and what not. Lets just hope he doesn't leave us hanging.

i worked on the car yesterday. after i cleaned the oil pump and polished the relief valve till it just fell in and out of the bore with just gravity. i put it all back together. had to wait on a new pan gasket so i dint get it all buttoned back up till late afternoon yesterday.. will go to the shop today and finish up with a few more things and restart the engine.. i hope all is well!!!!.. i did make a 1/4 line than i ran from the remote filter line to the oil port in the center of the head "just because we always did that when i was young" my father and uncles have raced these engines since the 40's.. i started this thread because i was surprised at the high oil pressure the engine was running. this is far from my first time working on a chevy stovebolt just my first experience with a modified 261. for those who think that a 261 full flow can not develop over 50psi at cold idle i have to differ. after installing 3 different gauges 1-50psi next a 80 psi and the last a 300psi all with high pressure at idle and pegging at 2000 rpm i am fairly certain of true readings.. i will try to make another video today after i fire it back up and will post the results.. thanks to all who have read this and offered their opinions

i got the engine started this afternoon.. i am happy to say it held 50psi at a cold idle and 35psi after hitting operating temp.. at 2000 rpm it did rise slightly to 55-60 psi.. so i am happy.. i guess i will not use the 30psi original gauge in the dash cluster i will install a 80psi gauge in the clock housing.. it sure is surprising how a stuck relief valve can give me such grief..from now on anytime i have a pan off a used engine i will check the oil pump ..probably will never run into that again, but something like that sure sticks in your mind..ha ha ha ha ..

thanks for getting back to us, I wouldn't have thought that, but there ya are. I will have to say the clearances are pretty tight....

yes when i plasti gauged the bearings they were all at 3 thou. or a little less..the rocker shaft had typical wear on the rocker bushings and was losing oil on the ones nearest the center..thats why i installed the extra oil line..but other than that the engine looked great

thats why the stuck relief valve had me baffled at first. the engine looked so good and had a new oil pump..but things happen to a engine even in dry storage.. i will probably never take anything for granted after this..ha ha ha ha ..the joys of old cars and trucks ..gotta love em

What weight oil are you using? Manual says 20 weight (all my 40s TMs use 30 weight).

Using something like 15W40 is like molasses at start up... will show higher pressure, but its still much to thick.

I always used 10-30 in my 261 and never had any problems.

An old trick to increase oil pressure is to run thicker oil (10W40). That's why I asked what the OP used. If he stuck 10W40 in the motor it will be like mud till warmed.

If I run 30 weight in my L134 pressure at idle is < 5psi. If I switch to 10W40 I get 15psi at idle. The gauge shows pressure is 'good' but oil is not flowing as it really needs to.

at cold start up, 10W30 should "act" thinner than straight 30 at cold start up, and the same as 10W40
https://en.wikipedia.org/wiki/Motor_oil#Grades

Bill

I have put on my wading boots.

10W40 and 15W40 are thinner at startup than any 20W or 30W oil at the same temperature.

i have a 10-30 in it right now... it was the relief valve causing the high pressure..i fixed that and now it runs 45 or so hot idle and 60 at higher rpm..here is a video i made today..

link.. http://s202.photobucket.com/user/rcplumley/media/51%20chevy%20project/MVI_8742.mp4.html

Looks good.

the real trick is making 10-40 thicker than straight 30 weight when it is cold.

just get a 0-60 to replace your existing 0-30. that what i did in my dump. i cant stand to see a gage pegged all the time unless its accuarate and then i really cant stand it

ha ha ha youre right 51ashton nothing worse than a pegged gauge.. thats why i started this thread.. my 300psi gauge being pegged was a trip..:)

Congratulations, whiskey runner

I put that in backwards... Used 30 weight straight as per the manual, but was seeing less than 5psi on the gauge... put in 15W40 (Rotella) and got 15psi at idle.

Simple typo... heaven forbid you make a mistake in the internet.

thats alright pfarber... i made a mistake once myself..ha ha ha ha ha ... if i had a dollar for every mistake i ever made i could probably hire someone to build these old trucks for me..:)

just wanted to catch up on here about the old car. have been working on other projects past few months plus the weather has been keeping things slow around here.. since i fixed the relief valve in the oil pump it has been acting perfect still a bit too high to use the original dash gauge. so i have a universal just hung under the dash for now..but the old car fires right up and drives good with alot more power than i was expecting.:) and the sound of the spit fenton headers and dual carbs is really great. am going to take it to a shop to get the headliner done and finally get this out of the shop in a few weeks.. so now i am back on my 50 3600 with a 56model 325 and will be taking the cab offa it soon to do rust repair. will be sure to come back if i run into any problems with it..ha h ha ..thanks for all the advice and support ya'll gave me .. happy motoring