Low Oil Pressure
Thread Starter
Cruising
Joined: Sep 2009
Posts: 14
Likes: 0
From: Wadsworth Ohio
Low Oil Pressure
I have a 75 corvette stingray. just changed the oil in it. There are no oil leaks, it doesn't appear to be burning oil, but the pressure will not stay up. I will be driving it and it drops to 20 on the gauge. any ideas?
Race Director
Joined: Apr 2009
Posts: 19,294
Likes: 2,753
From: Charlotte NC
Did you have this issue BEFORE you changed the oil???
How many miles on the engine????
A lot may be in the grade of oil you used..depending on the engine itself. May require different viscosity to compensate for bearing clearances that may be larger..due to age and wear. I do not know...so that is why I am asking. NOT every car uses 5w-30 or 10w-30 oil...some older aged, weathered engines may need an oil a bit heavier in viscosity.
I would verify this issue my installing another gauge and seeing if it reads the exact same. I would get a gauge that is NOT electric...but uses the tube to transfer the oil to the gauge ...like the earlier years had. If it reads differently...then it can possibly be in the sending unit. I have seen and experienced some crap or a sliver of RTV or something that plugs or partially blocks the opening of the sending unit.
Not knowing what you oil pressure is when you crank it up COLD...first thing in the morning....it is hard to tell.
DUB
Thread Starter
Cruising
Joined: Sep 2009
Posts: 14
Likes: 0
From: Wadsworth Ohio
The pressure will not stay up WHEN??? At Idle, under a load...which is it???
Did you have this issue BEFORE you changed the oil???
How many miles on the engine????
A lot may be in the grade of oil you used..depending on the engine itself. May require different viscosity to compensate for bearing clearances that may be larger..due to age and wear. I do not know...so that is why I am asking. NOT every car uses 5w-30 or 10w-30 oil...some older aged, weathered engines may need an oil a bit heavier in viscosity.
I would verify this issue my installing another gauge and seeing if it reads the exact same. I would get a gauge that is NOT electric...but uses the tube to transfer the oil to the gauge ...like the earlier years had. If it reads differently...then it can possibly be in the sending unit. I have seen and experienced some crap or a sliver of RTV or something that plugs or partially blocks the opening of the sending unit.
Not knowing what you oil pressure is when you crank it up COLD...first thing in the morning....it is hard to tell.
DUB
Did you have this issue BEFORE you changed the oil???
How many miles on the engine????
A lot may be in the grade of oil you used..depending on the engine itself. May require different viscosity to compensate for bearing clearances that may be larger..due to age and wear. I do not know...so that is why I am asking. NOT every car uses 5w-30 or 10w-30 oil...some older aged, weathered engines may need an oil a bit heavier in viscosity.
I would verify this issue my installing another gauge and seeing if it reads the exact same. I would get a gauge that is NOT electric...but uses the tube to transfer the oil to the gauge ...like the earlier years had. If it reads differently...then it can possibly be in the sending unit. I have seen and experienced some crap or a sliver of RTV or something that plugs or partially blocks the opening of the sending unit.
Not knowing what you oil pressure is when you crank it up COLD...first thing in the morning....it is hard to tell.
DUB
Drifting
Joined: Jun 2010
Posts: 1,781
Likes: 15
From: Oxford Ohio
Dub asked the pertinent questions. Mileage and oil and verify pressure. Usually the pressure is an indicator of bearing ware if all other particulars are the same.
Original engine mileage and service intervals would be good to know. Verify the pressure with a mechanical gauge if you can.
Original engine mileage and service intervals would be good to know. Verify the pressure with a mechanical gauge if you can.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,117
From: Crossville TN
If it drops all the way to zero, you likely have an intermittant short in the signal line to the meter. That would force the meter to read zero.
If it just drops part of the way, then comes back to normal pressure, you probably have a bad oil filter. The filter has an overpressure bypass valve in it. If that valve is bad, it could be bleeding off pressure when it should not. Since you just changed oil, that would be my choice of problem 'cause'.
Just install another filter (preferably WIX....not Fram
) and see if the problem goes away.
If it just drops part of the way, then comes back to normal pressure, you probably have a bad oil filter. The filter has an overpressure bypass valve in it. If that valve is bad, it could be bleeding off pressure when it should not. Since you just changed oil, that would be my choice of problem 'cause'.
Just install another filter (preferably WIX....not Fram
) and see if the problem goes away.
Race Director
Joined: Apr 2009
Posts: 19,294
Likes: 2,753
From: Charlotte NC
HOW MANY MILES ON THIS ENGINE????
What viscosity/grade of oil did you put into your engine???
Does the new oil smell like fuel...and the oil level getting higher on the dip stick????
Depending on how much fuel you had in your oil...you may need to change it a few times to get all of the fuel/oil mix out of the engine.
And when all is said and done....a heavier viscosity oil may be required.
Fuel in the oil can occur by a carburetor that is dripping fuel...running into the intake and int the cylinders....weeping past the rings and getting into the oil.
Head gaskets can not cause fuel to get into the oil.
DUB
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Le Mans Master
Joined: Jan 2006
Posts: 6,506
Likes: 139
From: Butler Pa
If it just drops part of the way, then comes back to normal pressure, you probably have a bad oil filter. The filter has an overpressure bypass valve in it. If that valve is bad, it could be bleeding off pressure when it should not. Since you just changed oil, that would be my choice of problem 'cause'.
Burning Brakes
Joined: Feb 2014
Posts: 1,045
Likes: 226
From: Cape Neddick Maine
2020 C3 of the Year Finalist - Modified
My car has 78,000 on it I did the oil change and used synthetic(not that it matters) 10w30 oil pressure was 40 lbs hot or cold before I did the oil change. I was not sure how long the oil had been in the motor from the previous owner so that's why I changed it and it still was clean looking.
Anyway after I changed the oil it started getting lower and lower pressure no knocking sound it did hit 0 on the gauge once at idle and scared the crap out of me. I changed the sender but ir made no real difference.
Sorry for the long story but I will get to the point now. I put 15w50 in and the pressure stays right at 40 Yeah I know I am only buying time and a rebuild is in the future but a heavier oil may be what you need.
if your oil was fuel diluted you may have started to wipe a bearing check the filter
Anyway after I changed the oil it started getting lower and lower pressure no knocking sound it did hit 0 on the gauge once at idle and scared the crap out of me. I changed the sender but ir made no real difference.
Sorry for the long story but I will get to the point now. I put 15w50 in and the pressure stays right at 40 Yeah I know I am only buying time and a rebuild is in the future but a heavier oil may be what you need.
if your oil was fuel diluted you may have started to wipe a bearing check the filter
Le Mans Master
Joined: May 2007
Posts: 5,021
Likes: 1,120
From: North tonawanda NY
My car has 78,000 on it I did the oil change and used synthetic(not that it matters) 10w30 oil pressure was 40 lbs hot or cold before I did the oil change. I was not sure how long the oil had been in the motor from the previous owner so that's why I changed it and it still was clean looking.
Anyway after I changed the oil it started getting lower and lower pressure no knocking sound it did hit 0 on the gauge once at idle and scared the crap out of me. I changed the sender but ir made no real difference.
Sorry for the long story but I will get to the point now. I put 15w50 in and the pressure stays right at 40 Yeah I know I am only buying time and a rebuild is in the future but a heavier oil may be what you need.
if your oil was fuel diluted you may have started to wipe a bearing check the filter
Anyway after I changed the oil it started getting lower and lower pressure no knocking sound it did hit 0 on the gauge once at idle and scared the crap out of me. I changed the sender but ir made no real difference.
Sorry for the long story but I will get to the point now. I put 15w50 in and the pressure stays right at 40 Yeah I know I am only buying time and a rebuild is in the future but a heavier oil may be what you need.
if your oil was fuel diluted you may have started to wipe a bearing check the filter
you should have at least 10psi for every 1,000rpm when the engine is fully warmed up.
I had a pressure sender fail on me right after replacing a head gasket and valve seals on a jeep 4.0...scared the crap out of me.
Last edited by augiedoggy; Aug 4, 2014 at 05:55 PM.