Did something bad happen? Low oil pressure

I agree with plugging in another gauge first off. Easiest thing to rule out of the equation and could save the trouble of tearing into a job that didn't need done (if the gauge turns out to be faulty).

Does that engine have a high volume oil pump in it? With pressure like that (60 psi), I would think it possible.

 

Air in the line to the gauge will cause false readings. Air is compressible. This is the reason that you bleed your brake lines. The pressure to the fitting will not be the same as what the engine is producing. That being said, it would be wise to check the pressure using a different gauge for comparison. I would also want to know where the 2 quarts of oil went.

 

Isn't there a write up about the high volume oil pumps on these engines having problems?

The oil system is not a closed system. every time you shut off the engine some of the oil will drain away from the point where the tube is plumbed into the oil gallery and you will always have some bubbles. We are also talking PSI in a fairly low range as compared to brake lines. what happened to the 2 quarts of oil?

 

The gauge is mechanical. I did bleed the air out of it. I'll try a different gauge tomorrow and see what happens. When I built this v6 a couple years ago, I put a 60 psi oil pump relief spring in it. I did pull the pump apart and checked that all out. Everything was ok in it.

 

It probably used it. It doesn't leak at all. I did an oil change in February and haven't put that many miles on it since then. I did find another oil gauge and put it on. Still pretty low. It doesn't get above 20 psi when I drive it. I'm going to change the oil tomorrow and saw the old filter in half to see what gold I find in there....

 

lame

 

"Increasing spring tension (assuming you can do that to the V6 relief) will increase oil pressure and of course less tension = less oil pressure."

As I understand these things, that spring controls the maximum pressure at higher rpms, by "blowing off" excess oil above the 60psi rating. The spring cannot "increase" the lesser pressure the pump generates at warm idle, which normally is too low to activate the relief at all.

Am I mistaken?

 

True, gases are compressible. But the air will compress in the capillary tube only until the pressures are equalized throughout, and the gauge will read true. Air compressors have pressure gauges, right?

A brake pedal has limited travel, and so can't generate the volume needed to fully compress the air bubbles, but the gauge capillary has an effectively infinite supply of 'pressure' from the oil pump.

 

I had the same argument with my boss when I was 16 (in my 40s now). Couldn't wrap my brain around the fact that the air makes no difference. So, we checked the pressure with the air and then after bleeding, no difference. Think of it this way: After a night of drinking beer, the next day there is liquid and gas, and they both exit with the same PSI, none compressed more than the other.

 

leave it to a yooper to compare things to beer..hahahah

 

A late chime-in. Yes, the bypass spring shouldn't have been an issue unless it was near non-functioning. I run a big block pump in my B with a 60 psi spring and that is where the oil pressure stays except on start up when it can go a lot higher if you gun it. The filter analysis is probably key but if the oil pump checks out, I suspect you did increase the bearing clearance somewhere.

 

I sawed open the old filter after doing an oil change. Saw no metal in it, so I guess I'll run it. It doesn't knock or anything.

 

The difference is how the gauge reacts to the pressure. Think of the oil as as a stick and the air bubble as a sponge. When you push on the stick, it takes additional time for the sponge to compress and transmit the correct pressure reading to the gauge. If the oil pressure is constant, the oil and air will equalize, but the gauge reaction time is slower. Due to the lower pressures and hopefully constant pressure, a small bubble may not be an issue. The purpose of the gauge is to give you an idea what pressure is being produced and if the pressure is rising or dropping.

Air should not be entering the line in a system that is installed properly. Once the line is bleed and sealed, the oil does not run back out of the tube after the engine is cut off. This is why you can pick up water with a straw by putting your finger over the top of the straw. The oil also does not absorb the air when the line is pressurized. It just squeezes the air into a smaller volume as the pressure increases.

In any case, he has a bigger issue than the air in the line feeding the gauge. If the gauge is correct, then he has a 50 psi difference from where he started. A true reading of 5 to 10 PSI is problem that needs to be fixed. If another gauge reads that low, then it is time to pull the oil pan and hope that the engine is not damaged.

 

Slightly off topic, but when I get around to completing my 53, I'm going all electric on the gauges. It's a useable build as opposed to a restore, especially with the 70s repop tub with tool indents, glovebox etc. I've had more than one mechanical oil gauge pop the tube, especially if you're using that cheap nylon, and squirt oil all over the place. To each his own on air in the line. Personally, I'd put a quality gauge at the block source, or as close as practical, and take real time readings from there. Often times the dash gauge's accuracy is off, and I have always used them more as a reference point than an accurate certainty.