BreauxBridgeKid

At idle my oil pressure drops to almost zero, then goes up as i accelerate. While cruising maintains around 35 40. Is this right? I'm really not sure and dont know who to ask.

Thanks.

gerry72

No, that's not normal. As to the cause, it could be the gauge itself, the cam bearings, the rod or crank bearings, a worn pump, a stuck bypass...it's a long and troubling list. Assuming the gauge is reading true, your idle and 2k rpm oil pressure should be very close to the same. Your pressure readings with a cold and warm engine will vary a bit but a tight engine will be within 10psi. Broad ranges between idle and 2k rpm or cold and hot usually indicate worn cam bearings(this is where pressure is primarily built). If it really is a zero or nearly zero reading usually means that it can't build pressure so either the pump isn't spinning fast enough to account for wear in the pump or you have oil being dumped from a leak (bypass, galley plugs) before it can pressurize the galleys.

Hard to say but to me it sounds like your cam bearings are shot, but that's only my guess.

Matt Gruber

replace the pump

ram82fire

What he said

Geo

Graemeinvette

!st things 1st. When was the last time you changed the oil and filter?
You need good oil in there with a clean good quality filter. If its still at zero on idle, try the pump, if its not that you are heading into rebuild territory, sorry!

Paul Borowski

Before I'd make any call, I'd go to AutoZone or the like and get a simple oil pressure gauge. Disconnect yours, then temporarily install this new gauge then make a judgement call. Had a friend whose gauge quit working on one of his C3s. He thought he also had a "motor" problem. We disconnected his factory gauge, installed my remote $20 AutoZone gauge and saw that it was in fact his gauge on his car. His motor & oil pressure were fine. One thing I've learned about problems with C3s, seems like most of the time it's the "simple" problems that are most often overlooked.

Steve's74

yup!

68BLUEVETTE

I havethe same problem, drops to ~10 - 15 psi at idle and up to 30 - 35 at speed.

SharkAttack

It's normal for the factory gauge to vary with speed, but not that much. As mentioned above, check the gauge first. Remember these are old cars with technology that was cutting edge at the time they were designed and built.

den(thevetteman)78

Got the same problem only when i drives it hard for a while and go from fast to a stop, the pressure go down and come back when i raise the rpm ,i asked a friend who work at GM dealer as a mecanic and it said it was normal. He said that the oil get so hot that it hard to build pressure. I don't know ,but it still scary . But it run like that now for a decade and no problem.

BreauxBridgeKid

Should I be using something other than 10w30?

timbo79

These guages are old.. I relocated mine from the top tee on manifold to lower boss.. runs about 5lbs on average lower now..

Anyway,at idle and warm, it will drop a bit.. should rise as engine rpm rises... As i recall reading in one of Smokey Yanuck's build up books.. 10lbs pressure for every 1000 rpm... Just something I always have believed in...

0 pressure is BAD.. if it is not the guage..maybe cam. or crank.. I once had main bearings go and I lost pressure.. (ouch!)

Good Luck

JoeRags

With my brand spankin new 383, I was noticing the same thing. The needle on my '70 would drop nearly to zero. I called my builder, he actually was with me when we fired it the first time, and he told me that it is ok. The gauge is in 15 psi incriments, and from what he told me, it is perfectly normal for small block GM engines to run around 7 psi at idle speed. Thats half way to the first line on the gauge. As soon as you touch the gas, it jumps right up. Oh yea, I'm running 10w30.

Joe

joe73vette

I picked up 5 psi by switching to single viscosity SAE30 oil. No need for the 10W in a summer car. Joe

den(thevetteman)78

Nice 68 Firebird ,if i can afford a second dream car it would be a 67 or 68 , i found they do look a lot better than the 69 with the pontiac lemans frond end.

glen242

I have a 29 year old motor, including oil pump, and if the oil pressure was nearly zero at idle, I would be very concerned. My GM 'vette spec form says "normal oil pressure is 32-40 psi @ 2000 rpm". I was, at one point, concerned about high oil pressure. Bought an aftermarket mechanical gauge and found the stock electric gauge was off by a lot. At the least, I would spend the +/- $15 and try an aftermarket gauge to verify your readings. At idle I have about 40# with hot oil and it does not rise much with RPM.

Did your "builder" tell you what the bearing clearances were on the engine? I have to believe they were very loose, compared to stock, to have that kind of pressure.

Matt Gruber

i've found 20w50 is worth 11psi over 10w30.
29 went to 40 @65mph

mvftw

Same problem here If the idle went below 700 (normally at 900 it is a 20*) it will go to zero. Even with a mechanical gauge. I replaced the the pump with a Melling 55A (high pressure, stock volume). Now my cold pressure is 70+ but it still goes to zero went hot and idle goes low. I think it's bearings. I use 20w-50. I'm going to let it go till I here knocking. Motor still runs strong.

Gage

Same issue with mine. Replaced gauge, even hooked up mech gauge from autozone to verify. They all read about 0 at idle with hot engine. Picks up to about 25 psi while cruising. Has been that way for over a year, no knocking noises, no problems, runs great. I have to think if it was a bad thing that something would have broke by now after 3K miles runnning like this....

Aflac

Never over look the obvious! Always start at the easiest and simplest thing possible. Will save you a lot of headaches and money in the long run!