Oil Pressure gauge possible incorrecto readings?

[vetteboy86]

71 BB coupe. The motor runs fine, and sounds great. However, I have noticed that the oil pressure gauge reads low. I was going to hook up an external gauge to verify, but wanted to ask first.

Is it possible that the gauge is 20 psi low across the range of the gauge? The reason I think it may be, is because on cold start up the oil pressure is around 40, but when the motor is fully warmed up the gauge drops to 0? I am imagining that under cold start up the oil pressure would be 60 ish, which would bring the warm idle to 20 which seems correct.

The plastic tube that goes to the oil pressure gauge has been replaced in the past, and it is somewhat see through, and I can see constant oil in the tube while the reading is 0. Mechanically is it possible to be off a tooth or something? During warm idle if I touch the pedal slightly the gauge will increase.

 

[LT4man]

Yes, the readings could be off in a linear fashion.

Your idea of attaching a mechanical gauge is spot-on! Then you will know exactly what your pressure is.

With my years of experience working on GM products I have found the following to be true.

Some of their oil pressure mechanical gauges read more like an "idiot lite" than not. I have viewed many which show the same amount of pressure whether the engine is cold or hot.

At least yours shows a difference in pressure according to temperature.

SAVE THE GOSH DARN

 

[Drummer72]

Yes, the readings could be off in a linear fashion.

Your idea of attaching a mechanical gauge is spot-on! Then you will know exactly what your pressure is.

With my years of experience working on GM products I have found the following to be true.

Some of their oil pressure mechanical gauges read more like an "idiot lite" than not. I have viewed many which show the same amount of pressure whether the engine is cold or hot.

At least yours shows a difference in pressure according to temperature.

SAVE THE GOSH DARN

Hi Guys,
i experience exactly the same phenomenon. My 71 coupe suffered low pressure which made me believe the crankshaft bearings were shot. Replaced them and installed a new oil pump as well. Pressure went consequently op to a promising 40 psi, however kept dropping to zero at idle when warm. Engine runs purrfect and sounds very sweet. Knocker arms are also sufficiently lubed so there is oil pumped around.
Before tossing in 20W50 instead of the current 25W40 I'll try to install a new gauge.
Keep you posted.

 

[Kid_Again]

Interesting post.

I had my #match 427 rebuilt and I constantly complained about low oil pressure. I confirmed the pressure with a second gauge and the rebuilder (and my buddy who sent me to that guy) said, well big blocks run lower oil pressure than a small block, no problem

the engine seized and i'm now driving a zz440 bullet

live and learn i suppose

what makes matters worse is the small block that he rebuilt for me at the same time runs 60-80 psi ALL the time, hot cold, whatever (the dash gauge was compared to a hand-held gauge)

 

[73shark]

FWIW when I took my new '68 GTO in shortly after I got and complained about the oil pressure gauge not reading what the engine was spec'd at and was told that GM gauges were indicators, not accurate gauges.

If you're ever in doubt about a reading, you should always verify with a known good gauge or meter.

 

[GerryLP]

Interesting post.

I had my #match 427 rebuilt and I constantly complained about low oil pressure. I confirmed the pressure with a second gauge and the rebuilder (and my buddy who sent me to that guy) said, well big blocks run lower oil pressure than a small block, no problem

the engine seized and i'm now driving a zz440 bullet

live and learn i suppose

what makes matters worse is the small block that he rebuilt for me at the same time runs 60-80 psi ALL the time, hot cold, whatever (the dash gauge was compared to a hand-held gauge)

Oucchhhh! It looks like you were another victim of "Bubba". Which is pretty common...like back in 2002, I went to SharkFest week at BG without my Vette, for falling victim to a mechanic as well (except that I was able to rescue my matching-numbers block and components). And worse, his hobby was messing with Fords at the track, which should have given me a huge clue...:L