GT-40 Oil Pressure

1997 GT-40

I'm having some interesting oil pressure swings,

    Cold start -   40 right on the dot
    at temp (160 F)
          at idle -   20 ish
          at 1500 rpm or better - 50 -70 ish

replaced the sending unit and everything is the same so I've got something else going on..   I'm also getting the "save the engine" sensor at 3200 rpm kicking in, verified it was the oil sensor by pulling wire and it went away ..    oil pump is not tied to crankshaft from what I understand so why would it have these swings with rpm?

Some background:
Using 10w-40.

Last year I had a failure of the exhaust manifold and ended up with quite a bit of water in the oil (brown milkshake anyone ?? ). I was able to get new headers on, went through about 8-10 oil / filter flushes and the oil looks great now.   I do have a bit of a valve chatter since this time also.    

While not "tied to the crankshaft" directly,your oil pump does does change rpm with the crank. Most here are using 20w-50 VR1. If you suspect oil pressure problems it's always best to temporarily install a quality mechanical gauge. What oil are you using?

I'd do what Gary and Pete said.

Put in a temporary high quality press gauge.

Your numbers are a little confusing. Do you mean it's constantly bouncing from 50-70 or was that a generalization that at 2000 rpm it might be 55 and at 3000 rpm it's 65 for example.

Did you replace the sending unit for the oil pressure gauge or was it the sensor for the engine's protective system?

And....what was "normal" before the water in the oil issue?

I'd be more worried about having a rock steady 40# no matter what the speed or engine temp than the changes you're seeing now.
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Your pressure numbers seem pretty OK to me.

I'd still DEFINITELY put in a mechanical gauge temporarily and replace the oil press switch for sure.

Don't have a clue what your noise sounds like so no wild guesses about engine damage or not.

Gary's 20w50 or some 15w40 diesel oil would be my oil choice though, for the zinc levels if for no other reason

Well, for only the 3rd time in recent memory, I find myself thinking like Pete.

I saw a shrink those other two times and called for another appointment this morning ASAP

But anyways, doing a search,it seems like a number of people have GT40's that run about 40-45 # under all conditions like yours did originally. The oil pump relief on a GT 40 must be set at 40-45# to do this

I think that to get the numbers you're seeing your relief must not be fully seated properly. It doesn't seem as if it would be fully open or you'd never get 50-70 # at higher RPM.. Piece of crud in the seating surface, stuck partially open etc.

Looser bearing clearances don't seem like they would make your hot high speed pressure go up.

Like MrMcD said, your 20# and 50-70# are OK as long as you don't have any oil related engine noises.

Maybe you could put a video on here so the noises can be heard.

Since you re[placed the manifolds, are you sure you don't have an exhaust gasket leak and tightening the bolts could make it go away?

This exhaust leak just came up recently and the poster put a video or 3 or 4 up for some help and he solved his problem

Maybe your noise could be as easy........maybe not

KENO wrote: Well, for only the 3rd time in recent memory, I find myself thinking like Pete. I saw a shrink those other two times and called for another appointment this morning ASAP

Ken,
I suggest making multiple appointments with that doctor!

"Sorry I was not clear

Oil pressure prior to the water event - rock solid 40 +/- regardless of the rpm, hot / cold

Replaced the pressure gauge sending unit not the engine protection sensor (meant to replace sensor but they shipped me the wrong one)

warm oil pressure at high rpm, I'll watch a little closer but does not seem to change with rpm at 70 ish just as long as I'm not at idle.   

Thank you for the input, I'm really hoping it is not the bearings as I'm not set up to lift motor."
Since the oil pressure changed it sounds like your pressure relief is stuck. As mentioned above it does not take much to stick the piston in a pressure relief valve.
Your oil pressures are not a problem as they currently are, I would run it and hope it pops loose on its own. I would run it a long time before pulling the pan to fix it as long as your pressure stays as is.   This still does not fix the new noise you have though.
Keep us posted.