Funny oil pressure on 330 GTC

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Enzo Bertaggia
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Funny oil pressure on 330 GTC

Post by Enzo Bertaggia »

I am having problems with the oil pressure on my 330 GTC. After the engine is at normal operating temperatures, if I am running the engine at a steady 4000 rpm, the oil pressure is at 5 kg/cm2. If I step on the gas, the oil pressure goes down to about 3 kg/cm2 for several seconds. After getting to about 4500 rpm the oil pressure goes up to 6 kg/cm2. If I return to a steady 4000 rpm, the oil pressure returns to 5 kg/cm2. If I release the gas, the oil pressure momentarily goes up to about 6 kg/cm2 for several seconds.

Normally I expect the oil pressure to go up at higher rpm and the oil pressure to go down at lower rpm. What can be wrong?

Thanks,

Enzo
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Yale
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Post by Yale »

May I posit, broken gauge or something not correct in the feeding of the pressure to the gauge. -caveat- I know nothing, it's just a thought.
Yale
Ex - 1964 330GT #6097
1963 Abarth Monomille
1970 Porsche 911S
1974 BMW 2002turbo
John Vardanian
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Post by John Vardanian »

Enzo,

I would fix a temporary gauge at the pick-up point to see if it behaves the same way as the car's gauge. If it does, I would then look into the pressure relief valve.

john
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grumpy2
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oil

Post by grumpy2 »

My car is very sensetive to oil level . but I would look at the gauge and then the relief valve.
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63 250 GTE s/n 4157 (apart for now)
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330GT
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Post by 330GT »

Assuming that the oil gauge is original, it is a simple mechanical one, driven by oil pressure fed through a tube from the rear of the engine.

This eliminates all electical/sender issues. Since the gauge does read something, it should be relatively accurately, i.e. higher pressure, higher reading but not necessarily the exact right numbers.

So I would suspect either the oil pressure regulator or possibly a partially clogged filter causing a bypass thus changing the pressure oddly.
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tyang
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Post by tyang »

Cars that are sensitive to oil level should have their oil pick ups looked at. There is a short section of rubber hose that can crack and leak that I think connects the oil pick up to the pump.

Tom
'63 330 America #5053
John Vardanian
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Post by John Vardanian »

Enzo,

Tom Y is onto something. That could very well be your problem: a leaky hose.

john
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Stephanm
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Post by Stephanm »

Does this happen upon accelerating while driving the car or just while it is sitting still? Tom is correct in pionting to the rubber hose at the oil pick up, often the people who have rebuilt the cars use standard radiator hose that cannot withstand the constant bathing in oil so they harden and crack. Maybe the baffling that contains the oil in the pick up area has come undone or someone forgot to install it.
I have seen a few cars where the dip stick was wrong because the solder that sets how far the stick goes into the sump let go.
330Jim
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Post by 330Jim »

Enzo,

Did you have any luck with your oil pressure problem? My oil pressure also increases about 20 psi when I decelerate (I haven't noticed anything on acceleration but I have not checked either).

Tom’s suggestion about the rubber hose made a lot of sense to me so I dropped my lower oil pan. The hose does not appear to be split but it is hard and only held on with wire (bailing wire wrapped around the hose and twisted) instead of hose clamps. It seems like it would be a wise idea to replace it but the tube is attached to the oil pump directly above the cross member so there is no access. Where you able to get at the rubber hose on your oil pick up tube? How did you do it?

Anybody else have any suggestions?

Cheers Jim
66 330GT 2+2
Jimmyr
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Post by Jimmyr »

The rubber pickup hose may very well be part of the problem as can the pressure regulator that controls the bypass, check the spring and piston in that assembly for dirt or sludge. Another possibility for oil pressure dropping when you let off of the gas is main bearing wear. Excess clearence in the main bearing area causes the crank to move during unloading, and a dip in oil pressure.
330Jim
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Post by 330Jim »

Wear on the main bearings was my first thought but I would rather not go there. I liked the rubber hose theory much better. Anyway I will pull one or two main caps tonight just to make sure.

I have had the pressure regulator apart, there was some minor scoring on the piston that I cleaned up. Cleaning the piston up took care of a slight erratic oil pressure problem I was having but did not cure the issue of the oil pressure increasing with deceleration. I can not think of a situation were the pressure regulator could cause the oil pressure to increase with deceleration. However since it is easy to get to I will go through it again anyway just to be sure.

I will also check the dipstick calibration while I am at it to make sure a low oil level is not causing my problem.

Thanks Jim
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David Booth
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Post by David Booth »

Hint: any time Jim Riff, who posts in this forum as jimmyr, voices an opinion on a mechanical mystery, write it down, go and do it, and you will most likely be rewarded. 'Nuff said.
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Yale
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Post by Yale »

Chris Coios gave me some old Ferrari (FCA) club magazines which I have been lovingly reading. Jim Riff are those pictures of you smoking a pipe in some of the club gatherings in the late '70's? Best Yale
Ex - 1964 330GT #6097
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1970 Porsche 911S
1974 BMW 2002turbo
330Jim
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Post by 330Jim »

I pulled the #5 and #6 main caps off last night. The bearings are fine. They still have a nice layer of white metal on them and are not worn down to the copper. Cutting apart the oil filter, it is clean with no signs of a bearing coming apart. So the oil pressure problem is not related to the main bearings.

Comparing the rubber hose to the oil level it appears that it is hose sits just above the oil or partially submerged. Perfect location to cause the oil pressure changes I have been seeing. Putting a little air pressure on the end of the pick up tube it I can hear a hissing sound from the end of the oil pan with the hose in it. I can also hear some oil gurgling through the lines. Loosing the oil pick up tube clamps you can move the tube around in the rubber hose without to much difficulty so it is not clamped up solid. Unfortunately the only way I see to change the rubber hose is to pull the engine since the rubber hose is above the frame crossmember. I tried pulling the fuel pump to see if there was access that way but no luck. Anybody have any tricks for changing the rubber hose?

Cheers Jim
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Post by Jimmyr »

Yale, never smoked a pipe or anything else for that matter!
As for the oil hose, try to just tighten the clamps and see if that stops the hissing.
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