1931 Buick-87 oil pressure drops to 5psi as rpms increase

[Duane Meyers]

As my increase in rpms - like over 25mph my oil pressure drops to 5psi. 
when I drop below 25 mph or just idle motor it raise back to 25 psi?

Any one have any experience with this?

[Larry Schramm]

Maybe a stupid question, but do you have enough oil in the engine?  Sounds like you could be sucking air somewhere.

[Duane Meyers]

Oil  is full

[auburnseeker]

Is the pickup on the pump clean?  Sludge in the oil pan? I would look at restricted flow as a first step. 

[Duane Meyers]

The car has less than 300 miles on the complete restore/overhaul. 
i’ve had a car over 10 years but up until I recently retired never had a chance to do anything with it other than to take up for short drives. But this has been an ongoing problem. I probably need to pull the pan.

It’s never ran enough to get the oil dirty although I have changed it twice once I went with 30 weight oil last time I went with 20. 
No change

[auburnseeker]

I would start with the pan as you mentioned and make sure everything looks good in there.  Did you restore the car yourself? Did you rebuild the engine or did a shop?  Can't hurt to check things over either way? I've known more than a few people that bought a restored car or a fresh looking engine that was actually worn out with a nice cosmetic restoration.  (me included) 

 

Did you unscrew the factory gauge and  try an aftermarket one right on the block?  Just to be sure it isn't a gauge issue , before you tear too deep into the engine.  That would be the first thing I would do. 

[Duane Meyers]

The car was done as a complete restore well over 35years ago.  Hired By the previous owner (I knew him well).  He started at the frame Wheels brakes tires. Then went to the  motor drivetrain interior and finished with the body. It was about an eight year restore project.

The restore had been done at least 16 years that I know of before I bought it. Actually It was an in town car , probably never been taken over 25 miles an hour, And seldom drove, before I bought it. I have all the receipts very little money was spared Parts were available  were much cheaper and so was labor costs. 

But yes I will check the gauge out first Thank you!

[EmTee]

Maybe the pickup has loosened...?

[auburnseeker]

A friend has always urged me to go most basic simple things first.  Even stuff you think might be right double check, even if a shop did it.  They can screw things up just as easy as a regular guy.  We have often dug deep into things only to find out later it was something much more simple we had overlooked thinking no way it could be that or that's new so it can't be that. 

[Duane Meyers]

This is just what I need

SOME GOOD IDEAS😀

[32buick67]

46 minutes ago, auburnseeker said:

I would start with the pan as you mentioned and make sure everything looks good in there.  Did you restore the car yourself? Did you rebuild the engine or did a shop?  Can't hurt to check things over either way? I've known more than a few people that bought a restored car or a fresh looking engine that was actually worn out with a nice cosmetic restoration.  (me included) 

 

Did you unscrew the factory gauge and  try an aftermarket one right on the block?  Just to be sure it isn't a gauge issue , before you tear too deep into the engine.  That would be the first thing I would do. 

Agree with Auburnseeker, always confirm your feedback via gauges and measurements first with a known good gauge or sensor, it will save effort, and you feel very relieved to have potentially avoided many hours of unnecessary and disruptive work.

 

Does anyone know if the 1931 engines have two oil valves like 1932?

Relief valve and bypass valve?

 

I had to clean these in my 32-60 because of debris- I think it was a 7/8" brass nut to remove, and I cleaned the springs and plunger/piston and then blew out the oil lines with air (40-50psi as to not stress the piping and fittings with normal 120psi from a shop compressor).

I also blew out the oil gauge line.

Oil = water + solids, and after sitting many years, water evaporates, leaving solids which can easily clog the tiny oil gauge line.

What a difference it made!

[Robert Engle]

Your oil viscosity is too low.  20 weight is okay for below freezing temperatures, but too low when the engine is up to temperature.  I would suggest 20-50 multi viscosity and see how your oil pressure holds up.  It may not be the cure, but it surely won't hurt to try.  Theses old cars function well with multi viscosity oils which are so superior over anything offered in the 30's.

 

Bob Engle

[Duane Meyers]

I will start with the gauge.

Then remove the pan.

Check out and clean anything needed for the oil pump.
And definitely put in multi viscosity oil. 
Thank you everyone for all the suggestions

[Robert Engle]

One other word of caution.  The oil line from the filter to the block is a small line.  Many people going to a new canister type oil filter install a larger oil line.  This delivers too much oil to the rocker assemblies and reduces oil pressure on the entire system.  

[TP32]

I had the same problem with my 32 ser. 60 exactly. I took the oil pan off and checked the oil pump. The piston check that controls the bypass was wore and gouged A new one was made in the lathe and made .001 “ larger on the OD to compensate for internal wear . A small washer was installed behind the piston spring . After a long run on a hot dat the oil pressure runs at 35/38 PSI at 45/50 MPH and 10/15 at idle  I don’t know if this will help anyone but that cured mine TP32 

[Grant L. Meredith]

Things to look for , restrictions in pickup screen, some guys use lots of silicone to seal things and it gets to the oil pan and plugs the screen. Does this engine have lots of blow by?  Seen this before where badly worn rings pressurized the crankcase and oil can’t return. Bought a car once that had that problem( I knew it needed it’s motor done) and starved it of oil pressure. Can the oil return to the oil pan?  Again if returns are plugged and slowing the return of oil can starve oil pump. Is oil pump healthy? Is it’s pressure relief spring weak?

Just some things I have found in any kind of engine. 
I hope you get this fixed.  It’s a sick feeling when the gauge drops off

[nzcarnerd]

Assuming everything else is good you need to use a good quality oil intended for 'classic' cars.

[1wonton]

On 2/21/2022 at 7:34 AM, 32buick67 said:

Agree with Auburnseeker, always confirm your feedback via gauges and measurements first with a known good gauge or sensor, it will save effort, and you feel very relieved to have potentially avoided many hours of unnecessary and disruptive work.

 

Does anyone know if the 1931 engines have two oil valves like 1932?

Relief valve and bypass valve?

 

I had to clean these in my 32-60 because of debris- I think it was a 7/8" brass nut to remove, and I cleaned the springs and plunger/piston and then blew out the oil lines with air (40-50psi as to not stress the piping and fittings with normal 120psi from a shop compressor).

I also blew out the oil gauge line.

Oil = water + solids, and after sitting many years, water evaporates, leaving solids which can easily clog the tiny oil gauge line.

What a difference it made!

There's a possibility that if the oil pump was taken apart the two valves or springs were not re-installed correctly.  One spring is longer than the other and one valve has a small hole in it, the other does not.

[Century Eight]

I agree with 1wonton.  A friend of mine did his own 64 Lesabre engine over and had the same issue, also its a totally different engine. He found out that something was installed backwards (no, I dont know what it was) and when the engine was revved, the oil pressure dropped way too low, because it couldn’t return.  He had to take it apart and it was an easy, but labor intensive fix..  Better than burning up the engine..

[Duane Meyers]

Can anybody tell me what the compression is supposed to be on a 1931 Buick straight eight 344Cu.In?

All eight cylinders of mine read 65psi and it runs terrible, It won’t hardly pull itself especially when it’s warm

Edited June 4, 2023 by Duane Meyers
Miss print (see edit history)

[Duane Meyers]

correction: it won’t hardly pull itself

especially when it’s warm

[EmTee]

Don't quote me, but I'd guess something like 90 psi.  Have you checked the valve lash?  If valves are too tight they will not seal properly (especially when hot) and compression will be lost.

[Duane Meyers]

I did check and adjusted. This car used to run just fine. Once it’s warm, it backfires as well as when I put a vacuum gauge on the intake manifold when I speed up the motor it drops to 5 to 10.

Edited June 4, 2023 by Duane Meyers (see edit history)

[Robert Engle]

Compression ratio should be 89  to 99 psi.

 

Check that the camshaft to crankshaft timing is correct.  

 

squirt some 50 weight oil into the cylinders and check if compression increases.  

 

Set the valve lash to .008" cold engine.

 

Carb and ignition issues should only be addressed once the correct compression, valve timing and lash are achieved.

 

Bob Engle

 

 

 

 

[Duane Meyers]

Thank you for responding😀.

This motor was overhauled in 1978. It has 2260 miles on it since the overhaul.  It ran great!! (Sometimes the oil pressure would drop low)

It was 50 mile an hour car easy!! It

started giving me trouble about a year ago.

I pretty much parked it until this year when I retired.  It does run better when it’s cold,  as it warms up it runs horrible. It requires the choke to be pulled 1/2 way out when  up to temp. 
When it’s cold, the vacuum on the intake manifold runs about 15 to 19.

once it warms the only time it is 19

is when it is idling otherwise drops clear down to 5–10. 

The valve lash is definitely not the problem I am 100% sure of that. I ran a compression test with both warm and cold engine.  I’ve squirted some 10 weight oil into the cylinders and no change in compression.
 65psi is constant. 
Do I have to tear it apart to check the camshaft and crankshaft timing?

[Morgan Wright]

Are you saying manifold vacuum is 5 or are you saying oil pressure is 5 like in the thread title? 

[Duane Meyers]

Vacuum 

[Morgan Wright]

If your vacuum tester says "In Hg Vac" or something that means inches Hg vacuum. Hg means mercury.

 

Atmospheric pressure is 29.92 inches of mercury at sea level so 5 inches of vacuum is really 24.92 inches of pressure, they don't measure vacuum in psi because gauge pressure of 0 psi is atmospheric pressure, and 5 psi of vacuum would be -5 psi gauge pressure which is minus pressure which is confusing so they don't do it that way. Vacuum is measured in inches of mercury below atmospheric. (The most vacuum you can ever have is 29.92 inches which is a perfect vacuum, can't get less than that.)

 

Atmospheric pressure is 14.7 psi so you can't have "15-19" psi of vacuum, that's impossible. Those are inches.

 

14.7 psi = 29.92 inches.

[Duane Meyers]

I don’t think I referenced vacuum gauge as a psi reading , but if I did, I certainly didn’t mean to. 
 

[Robert Engle]

I don't think your issue can be cam and crank timing.  If it ran well before then the cam and crank timing is correct.  There is a fiber gear on the cam shaft.  If there is damage to the fiber gear the engine won't run as it would get way off timing.  The generator is driven off of the fiber gear also and the distributor is driven off of the generator.  

 

The oil pump is driven off of a gear on the center of the camshaft.

 

One thing to consider would be a loss of oil to the lifter assemblies.  you should see a good flow of oil at the rocker arms and oil flowing out the front going down to the cam and crank gears.  loss of oil to the top can lead to valves sticking and could cause the compression loss.  

 

Bob Engle

[Morgan Wright]

OK so your oil is 5 psi and your vacuum is 5 inches. Sorry I misunderstood.

[EmTee]

6 hours ago, Robert Engle said:

valves sticking and could cause the compression loss.

Valves sticking is one of the possibilities I am thinking about.  I'm still not 100% convinced that valve lash is not involved.  I'd rather hear some light ticking than dead quiet from the valves; at least that would indicate they are not being held open.  So, is the vacuum at fast idle 19ish to start, then drops to 5 as you hold throttle steady?  If so, that is the classic symptom of an exhaust restriction.  If the car was in prolonged storage maybe some rodents took up residence in the muffler.  Have you noticed and debris coming from the tailpipe?

[1wonton]

Duane;

  Sine you've said this problem has always been present even though the engine was supposedly rebuilt I will again suggest the issue is with the oil pump.  I've rebuilt several model 90 oil pumps and will tell you that the springs and plungers must be installed correctly, or you will experience the problem you describe.  The springs are different length, and one plunger has a little hole in it.  It would have been easy for the rebuilder to get these parts installed incorrectly since they will all fit interchangeably.  You would be best advised to pull the pump and inspect it before you go to any further analysis, that way you could eliminate this possibility as the cause of the low oil pressure at speed.

[Duane Meyers]

Thank you so much Bob for the timing information. That would be a considerable amount of work only to find the gears in god shape

[Duane Meyers]

1 wonton

 THANK YOU!

it wasn’t until I started this “second problem”  conversation it makes sense my two problems may be ONE.

(especially when I look at the date of my last oil pressure post)

Removing the oil pan is where I will go next. Thanks Again. 

[1wonton]

Before you pull the pan you might want to check the oil lines from the oil filter, one line has a special fitting that restricts the oil flow.  I would temporarily plug the input line {to the filter, from the pump), then run the engine to see if anything changes.

[Duane Meyers]

It will be this evening before I get a chance, but I will get back to you on what happens

[Robert Engle]

The oil filter only provides oil to the valve train.  It is restricted with a small tube to the rocker arms.  Oil to the rods and mains is not filtered oil.  excess oil to the valve train flow out the front and down to the timing gears.  No oil to the valve train means no oil to the timing gears.

 

Low compression occurs from valves timing or not seating or lack of piston seating ( worn or damaged rings).  If it is a ring problem, you should see a lot of  air blowing out the crankcase vent tube.  

 

Bob Engle

[Oldtech]

I'm with EmTee. Check exhaust before you get too involved. 

[EmTee]

A leakdown test would identify the source of the problem.