The Stovebolt Site Forums The Shop Area Engine Shop 327 and oil pressure

I recently installed the line for the oil pressure gauge in my 1959 panel truck.
It measures fine cold but after the engine warms up and at idle the pressure
goes down. It picks up again to normal with a little acceleration.
Is this normal to the old gauge or is my oil too hot? Possibilities?

How much pressure drop do you have???

A little drop is normal going from cold to running full operating temp. If it's got some wear and tear you can expect a bit more drop in pressure like experienced with the I-6's, but usually not as much.

What are your numbers???

Dan

EDIT - As this conversation is engine related, I have moved it to the Engine Shop for further discussion.

Thanks for the move. I was unsure being its a 327 and not a stove.
Crank up and idle at 30, so middle of the gauge.
After warm up it drops to just above 0 but slight acceleration brings it back to 30.

Put a real gauge on it- - - -at least for diagnosis- - - -don't trust the dash gauge to be more than a wild-donkey guess about what's going on, especially at hot idle. The idiot light on a 327 and most other small block V8s turned on at 7 PSI or less. That's one reason the factory stopped putting gauges on vehicles in the late 1950's- - - -they really didn't want people to see how low the pressure was going.

Small block Chevys with some mileage on them tend to wear out camshaft bearings, which causes a pretty good pressure loss at hot idle. Unfortunately, it takes a full engine teardown to a bare block to swap cam bearings. If you drop the oil pan and install a high volume oil pump you can avoid the appearance of zero or very low pressure at idle- - - -but it's like taking an aspirin for the headache caused by a brain tumor- - - -it's treating the symptom ,not the real cause of the problem.
Jerry

Just for comparison, I just put in a three gauge set in my LCF, decent gauges, AutoMeter. My 283 runs 40 psi cold at 1500 RPM, hot idle is 20 PSI. Original dash gauge does not have the small increments that the AutoMeter has but they do agree.

I just completed the break in period with the 327 so not much mileage.
I would imagine its been this way with the pressure since I got it running. About 4 months now.
I don`t know. I do know I am about to run another oil pressure line
for my 58 with a 327. Its a fresh break in too. This time a copper line.
Not that it matters. I`ll see how the old gauge on it works.
Note on the 59, its only 1/2 quart low and 10w 30.

If the pressure is that low on a fresh rebuild, there has been a massive error made somewhere on some bearing clearances. I'd suggest at least a partial teardown and a check of the rod and main bearing clearances to find the source of the pressure drop. A slightly open pressure relief valve in the oil pump could also be the cause.
Jerry

I like the slightly open pressure relief valve theory. It's the cheapest theory!

As HRL stated, first thing to do is measure with a KNOWN GOOD gauge, then take appropriate action. If you have several gauges, try them all and compare the results, get rid of the one/ones that are reading far from the average.

I agree with Jerry, if the pressure is really that low you need to talk to your engine builder. That much drop cold to warm tends to indicate excessive bearing clearance somewhere in the system and that should not be the case on a recent rebuild.

Was this an actual rebuild or just a ring and bearing job? The reason I ask is that I have seen this before, the engine had a lower end rebuild but the cam bearings were not replaced. The wear on the cam bearings really showed up once the engine was run in.

Far as I know a complete rebuild from five star engine.

There was a company in Nashville that got a pretty bad reputation for cranking out fast, poor quality rebuilds. "Master Built Motors" earned a pretty well-deserved nickname that the PC Patrol wouldn't appreciate. It had to do with "self-pleasuring"! Last I heard, they moved to a location in north Alabama, not far from where I've lived for the past 40 years. Not all engine rebuilders work to the same quality standards, for either parts or labor.
Jerry

I hooked an oil line to the 58 with a 327. Same type old stock gauge.
It reads real high, past the meter (60) with some gas. Acts like a tach.
At warm idle it reads 30, normal. If anything ,too high. I just wonder about these older model gauges.
I hope my new engine in my 59 panel is OK. That would probably ruin me.

The 327 in the black 58 has dino records recently that we can
access to check what the oil pressure was then (3 months).
But the gauge reads in the truck 70-80. 1/2 of that would be good.

I have a vague recollection that early SBC distributors had a flat machined to allow oil to one bank or the other. If a distributor without the flat was installed or if the distributor was rotated that bank would run dry. Anyway I think the lifters would run dry and not pump up causing a racket. If you had solids, though and you had plumbed the gauge into the plugged gallery in the manifold you might get an erroneous reading. This might be a wild goose chase with too much poor memory so be aware.

1955-57 265 engines. The distributor housing had a flat milled on it to align with the passenger's side lifter oil gallery when the distributor was clocked correctly. Get the #1 cylinder plug wire a couple of positions off on the cap and rotate the housing to get the firing order right, and the right bank lifters would collapse. In 1959, the flat was replaced with a groove all the way around the housing- - - -clocking problem solved!
Jerry

I have a better new mechanical pressure gauge and think I may
have found an oil port above the timing chain cover passenger side.
Is that a possibility?
I can run a short line to it.

That one is on the front end of the passenger's side lifter oil gallery. It will read several pounds lower than the port beside the distributor housing. Be aware that on some later model 327 engines, that the port above the timing cover DOES NOT have a passage drilled all the way to the lifter gallery- - - -it's just a dead end hole threaded for a 1/8" NPT pipe plug. You will get very low, or no oil pressure on a gauge connected to that port. It was originally used for 1955 only 265 engines that used a bypass oil filter. 56 and later engines had a full flow filter provision cast into the block back by the driver's side bell housing area.
Jerry

Thanks Jerry. Then the only other one is down by the oil filter?
I am using the one under the DIST. Which is a pain in the behind to get to
on these Apaches.

Ok dino records show the 327 in the black truck was idle at 57-60lbs and 80 and 5000rpm.
High volume oil pump was used here.
We feel the other 327 has a low volume oil pump. But other things might be going on.
Gonna check some things out this week. slightly open pressure relief valve.

Try installing a short brass 1/8" NPT pipe nipple and a 45 degree elbow beside the distributor (with the distributor removed) to make the port easier to reach. I do that on a lot of the small block engines I build when I use a mechanical oil pressure gauge. The port down beside the oil filter doesn't give an accurate pressure reading for some reason on a lot of engines. I learned that on a dyno run about 20 years ago.
Jerry

I did add a tall adapter that made that port taller but straight up for the brass tube.