Oil pressure dilema

[jimTN]

37 engine, 46-8 spring in top relief, pump with relief also. Starts with 60 lbs pressure and drops to near nothing after about 20 min when it gets good and hot and begins to rattle. Had pan off to replace plugs in the rails that were leaking coolant but did not pull any rod caps. Going to pull the engine again and replace rod bearings. Anyone got other recommendations?

[alanwoodieman]

change cam bearings, check clearances on main bearings-how many miles since overhaul? smokes? uses oil--then it needs a rebuild

[jimTN]

No history on engine. Has good compression and runs well.

[G.M.]

With the pan off inject oil under pressure in through
the fitting of the oil sender. I did this on a Lincoln V/12
and found the problem was the bypass spring in the oil
oil pump. You may still have the problem with the spring
you replaced. try a shim made of 1/8th inch pipe on the
top of the spring, start with 5/16" long and adjust to get
50 lbs. If you have an oil pump with a bypass valve that can
be the problem and fixed with the same type shim. You can
test the oil pressure by removing the spark plugs, install a
mechanical gauge and spin the engine with 12 volts. The oil
pressure you see will be what you get at 45 MPH. You can do
this with the engine in the car or sitting on the floor. G.M.

[grumppyoldman]

It could also be the sending unit mine did about the same thing, I installed a mechanical gauge under the original sending unit. Getting 80# on start-up runs at 20# after warm-up, you could avoid pulling engine if it's only the sending unit. Al

[JSeery]

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Always a good idea to use a separate modern gauge to double check readings.

[40cpe]

Originally Posted by jimTN

Starts with 60 lbs pressure and drops to near nothing after about 20 min when it gets good and hot and begins to rattle.

These engines shouldn't rattle if they have just a little oil pressure. After you verify actual pressure you will have to find the excessive tolerances. You are right there at the mains when you replace the rod bearings so I would check them, too.

[jimTN]

Thanks all, somewhere I have a chamber I made to put oil in under pressure, will take GM's advice and also check the mains while I am at it.

[Kurt in NJ]

the pressure pot should have adjustable pressure, if you put pressure higher than the relief(full air hose pressure) valve you will have a lot of oil spraying -won't be able to tell where it is all coming from---the bearings should only drip, a steady stream usually is the pressure loss/excessive clearance ----start with low pressure, increase it till you get relief valve open---that way you check that pressure too

[Talkwrench]

I take it that this is while driving and not on a stand?
Its not uncommon for the earlier ones to get near zero at idle when hot mines been doing it for years, but rattle NO ...
So do you have a later oil pump in it?

[jake197000]

id ck with gauge. and if low and rattling id say too much clearance some where.did this come up all at once?.i alwasys say if its quiet its got enough preasure unless your talkin race type engine.