oil weight queston

[oswego37]

I recently installed a rebuilt 37 motor in my car. when we fire it up the oil pressure goes up to 20lbs. or so and after it warms up the gauge reads only reads a few lbs. the sending unit is the 50lb one and I used 10w30 oil. seems like 2-3 lbs. is low . Is this normal? Wrong oil? Thanks

[JSeery]

Your best bet is to install a mechanical oil pressure gauge to double check the pressure (assuming you are taking the current reading on the original gauges). If the pressures are actually that low, it is a bigger concern/issue than adding heavier viscosity oil.

[Bursonaw]

If you have a remote bypass style oil filter, check to see if you have the .065” oil feed restrictor inline with the filter.

The symptoms you are describing are similar to what they would be without it an oil pressure reducer installed in a bypass filter installation.


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[G.M.]

Try Castrol 20/50 I think that will fix your problem. G.M.

[Talkwrench]

recently rebuilt..?At start up you should be seeing about 60 lbs straight up end of story. as said try a mechanical gauge.. Something is a miss..

[drolston]

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Could be the oil pressure relief in the valve galley is broken or incorrectly installed.
If the mechanical gauge confirms the way-low oil pressure, first eliminate the oil filter flow reducer as the problem by disconnecting the pressure line from the back of the block and plugging it. If you find nothing wrong with the filter or pressure relief, that leaves the oil pump. Ask you re-builder about the pump.

Do not run that engine very long with pressure that low. My tired 59AB with rods knocking and shot main bearings would pull over 30 PSI at speed and almost 10 PSI at idle.

[DD931]

I agree with GM's recommendation to shift to 20W-50 oil. I've been using it for years and still have great oil pressure. I think 10W-30 is too light.

[Ford Freak]

Originally Posted by DD931

I agree with GM's recommendation to shift to 20W-50 oil. I've been using it for years and still have great oil pressure. I think 10W-30 is too light.

Its been 20W-50 oil for me for years in both my flatty V8's .

[Ol' Ron]

10/30 is the proper oil for a rebuilt engine. Adding a heaver oil, doesn't fix the problem. Could be the oil pump

[alanwoodieman]

take off the intake and check the relief valve, put in a new spring or a washer or just stretch it out==it worked for me

[rotorwrench]

Rebuilt or overhauled engines should have at least factory recommended clearances on the cam, main, and rod bearings. If not, it won't have good oil pressure from the get go. This is why I overhaul my own engines since I can only kick myself if problems arise. Motor oil does have a tendency to thin some after warm up but the modern oils with expanding polymers should keep a fair viscosity when at operating temperature. A person can expect a 15 psi drop in pressure after complete warm up but it shouldn't be much more than that. If a person wants 45 PSI then cold start pressure should be pegged out on a 50 psi gauge at initial start up with new oil. Always use a mechanical gauge to test a newly overhauled engine. A calibrated one would be best but this isn't the norm unless you are in aviation like I am.

The engine should be test run for relief valve checks and a person has to keep in mind that the intake manifold may have to be removed to do this. If a worn relief valve spring is reinstalled then a new one should be installed if psi is low. If the pressure can not be increased with the relief valve, I would suspect bearing clearance or oil pump gear clearance problems.

[DD931]

Opinions are like noses. Everybody has one!!!

[Ken/Alabama]

On a rebuilt engine you should see good oil pressure even when it's hot with 30 wt motor oil. Somethings not right. As already mentioned, install mechanical gauge and disconnect oil filter if you have one. If the problem is still there your gonna need to investigate it on the inside.

[countrysquire]

I like the thicker oil because it doesn't spread as far as it drips onto the garage floor...

[Ford Freak]

Originally Posted by countrysquire

I like the thicker oil because it doesn't spread as far as it drips onto the garage floor...

Yes , or on the driveway ! That is the main reason I use it .

[tubman]

"2 or 3 lbs" of oil pressure being too low for a rebuilt engine is a fact, not an opinion.

[revkev6]

My fresh 8ba has 60 going down the road... drops to 15 or 20 hot idle

[Ford Freak]

My 1952 never rebuilt 8BA has 45 going down the road , drops to 5 @ hot idle .
Still runs great ! ( And quiet ! )
However , like the guys above have stated , there is something wrong w/yours if the engine was just redone . Most likely your oil pump is bad . - F F

[Ken/Alabama]

Originally Posted by Ford Freak

My 1952 never rebuilt 8BA has 45 going down the road , drops to 5 @ hot idle .
Still runs great ! ( And quiet ! )
However , like the guys above have stated , there is something wrong w/yours if the engine was just redone . Most likely your oil pump is bad . - F F

Or too much clearance in the bearings.

[Ol' Ron]

THINK ABOUT WHAT CAUSES OIL PRESSURE?. Resistance to flow. If you've ever seen the oil pump, pump out oil, the flow is fantastic. At idle the flow is about 10 feet, and the pressure is zero. I have a friend with a 284 ci Ardun, has about 10 lbs at idle and 30 in cruise. So far the bottom end is just fine.

[Talkwrench]

So Ron I take it you're saying there's a difference ..there's flow and then there's pressure...? So why do we need the 'pressure' is it just to tell us the oil is there and we can see it on a gauge..? I could be wrong but would I be right in saying that floating bearings don't need as much 'pressure'? .. Curious, as I too have always had low oil pressure at idle HOT, always have 60psi on start up. The problem I have [and why Im building another engine] is that when HOT at high speed my oil pressure drops off below the 10 psi per 1000rpm. But its been like that for 5 years of almost daily driving...

[flatheadmurre]

As long as you got oil in the bearing it will work...you need a bit of "starting" pressure in the bearing after that the rotation does the job to create a cushion of oil in the bearing.
Flow is needed to make sure fresh cool oil is fed to the bearing...if pressure only and no flow heat will kill the oil and bearing.
What you don´t want going for a heavier oil is to thick at cold start...not much of an issue today with modern oils...
When the pressure drops that means you don´t have enough flow in the pump to maintain oilpressure...so either the bearing clearances needs to be less...or the pump needs attention.

[Talkwrench]

Well I assume that in my situation that it would be clearances... Always good oil pressure till you hit around that 20 minute mark when the oil is getting hot and its down hill from there.. The normal too and fro' doesn't worry me its when hot outside temps and high speed freeway driving that causes me a concern.

[oswego37]

I appreciate all the input, will post my findings