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1999 firebird 3.8L low oil pressure at idle only when hot
My 99 firebird with just over 100,000 miles has a similar issue, when driven for maybe 30 minutes, the oil pressure at idle will drop to around 40 psi and be good, mid range above idle. I also see a slight fluxuation once the pressure is lower at idle. The needle jumps around maybe a 5 psi flux,(35-40). Anyone have any ideas what could be causing that? Also there is a noticable dent in the oil pan, but I would think if this was restricting the oil pick up it would cause problems when cold as well and at higher rpm. Any thoughts, ideas, suggestions please email me and or post here.
Thanks,
John
Re: 1999 firebird 3.8L low oil pressure at idle only when...
Your oil pump does that on purpose - more noticeable with a dented oilpan as pressure is slightly increased. nothing to do until it goes (if it goes) unless you want to throw parts at your car anyways.
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Are you idling or is it doing 10 PSI driving it? If it has many miles on it it could be just getting worn out and that would be low oil pressure at idle when hot.
If the idle speed drops to a low enough point when the oil is hot, then the oil pressure light will come on because the oil pump, which is driven by the engine, is not turning fast enough to maintain proper pressure. You'll need to find out why the idle is dropping and almost dying. It could be a bad IAC valve, dirty throttle valve or something like a vacuum leak. It would be helpful if you had a scan tool to monitor IAC (idle air control valve) counts as this is happening as it would help you find the cause. This may be a job for a shop, but don't let them sell you an oil pump until the low idle problem is fixed.
It is not a problem that it gets low. The older engine only needs five psi's to lubricate. When the engines get higher miles, the wear in the bearings allow the oil to pass too easily witch lowers the pressure. the oil gets hot and it gets thinner thus lowering the pressure. Next oil change switch to a higher viscosity. like 10W40. Also it would help to put a can of a good engine oil supplement in.
Re-new the engine oil and see if the problem persists.
Low oil pressure at idle is usually a sign of a worn motor - worn camshaft and crank bearings allowing excessive oil to pass.
I would have to say your engine is probably shot. The bearings are probably gone. It is possible, i suppose, that your oil pump is faulty. As soon as the oil warms up, and becomes thin, the rods and lifters start to rattle. The same goes for the oil pump, as oil becomes hot, and thin, it may not be pumping properly. I would try a used oil pump, and see if there is any difference before i wrote the engine off.
if your car has the 2.7 litre you have to change the oil every 5oookm or 3000 miles and use the exact grade as per the book.
the 2.7 has small oil galleries.
you have low oil pressure and or idle speed.check the rpm and it should be 700 unloaded at warm temp.if the iac controller is bad and there is low idle,really low rpm could trigger the oil light to come on and the transmission vacuum controls will be causing strange behavior.
30-40 psi of oil pressure is fine for many vehicles including your GMC. I am assuming that the truck has more than 100,000 miles on it and still has the original engine in it. By rule of thumb you only need 10 psi per 1000 rpms in a typical street driven engine to give adequate oil pressure to keep the bearings from oil starvation. The oil pressure is typically higher when initial start up occurs because it is more viscous due to the temperature of the oil as the engines oil warms up the visconsity thins out and the oil flows more smoothly. The drop in oil pressure is a normal occurance. Above 45 is more than required for a daily driven street engine. I believe that the specs on that engine only list 30- 45 psi.
The sensor can show high pressure when that is not the case, they fail high not low, take the sender out and plug in a mechanical guage to verify this, that is the only way to be 100% sure.
Depending on the amount of miles, maintenance records, or how hard the car has been driven either by a previous owner, or by yourself. The engine's main crankshaft bearings or the connecting-rod bearings could be excessively worn.
Also, it could very well be a wiring problem to the sensor and/or computer causing the problem.
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