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www.fixya.com/cars/t7880379-oil_pressure_drops_zero_idle_2002_gmc Jan 18, 2011 - You could have three possable problems that I can think of. 1) Your oilviscosity is too low and you need to change it to a higher level. A 5w/30 .
A comparatively quiet engine is often a worn out engine.( Much of the knocking sound in an engine is caused by compression and expansion of gasses, which in a worn out engine is reduced due to leakage of gasses beyond the piston rings or valves.)
You will first have to have the engine pressure tested on each cylinder to ascertain the overall condition. Usually there are one of two reasons for a low oil pressure warning light or gauge reading.
No.1: The engine is badly worn and oil pressure can leak beyond the piston rings and into the cylinder.
No.2: The oil pump is close to failing or has already failed.
There is also the slight possibility that both of these faults have occurred at the same time.
How many miles are on the engine? Have you tried to replace the oil pressure switch? is the engine making any type of noise due to low pressure reading?
Since the oil pressure reads fine when cool or not at idle, the problem is probably the oil pressure sending unit. The easiest way to check is by replacing it, and it is fortunately not an expensive part.
Let's hope that is the correct fix.....
Think about how you noticed the problem....was it a gradual thing, with the gauge reading lower and lower until it was at zero, or one day it suddenly just happened? If it was a sudden thing, the sending unit is the probable cause. If it was gradual, there are several other possibilities, one being the oil pump itself. When an engine warms up, the oil thins, and a worn oil pump cannot deliver as much pressure. This can be fixed for a relatively low cost by a do-it-yourselfer in an afternoon or so, by replacing the oil pump. This requires removing the oil pan, and in some (not all) cases the engine must be unbolted and jacked up enough to allow the oil pan to be removed. A worst case scenario would be if the loss of oil pressure at idle is caused by worn main engine bearings. This would require major engine service.
If you really do not want to put any money into your van and just need it to last a little while longer, if the problem turns out to be main bearings, you can alternatively add an oil thickening agent like "STP" or "Motor Honey" to the oil and thicken it up enough to build up some extra pressure. Please be advised that this is not a "fix", but it will get you a few more miles out of your van in a pinch....eventually the bearings will fail. This will also help a worn oil pump build pressure, but it depends on how worn it is. This about covers "best case", "middle case" and "worst case" scenarios. There are some in-betweens, but unless you have noticed strange engine noises you do not have to worry about them as much.
Stay positive and go for the oil pressure sending unit first!
how did you clean the gasket off of the head? if you used a sanding disc the grit will eat up the bearings. are you reading pressure with a mechanical gauge? you have replaced all bearings??
6 psi @ 1000 RPM 18 psi @ 2000 RPM 24 psi @ 4000 RPM this is chevrolet specs on oil pressure in your truck so you are within the range.
describe your idle problem more and i will try and help you with that
It sounds like oil pressure switch is bad. You said you changed? To clarify, your oil pressure switch is also a safety item that shuts down ignition when oil pressure drops. Try an oil pressure gauge (hand held) to relieve your nerves about engine seizure. Make sure you're not getting to much fuel in engine also, that will dilute oil to a thin viscosity and show low oil press.
The 4.3 engine should have 20 to 30 psi at idle cold and around 50 to 60 psi running down the road. Has this engine had regular oil changes? If not the problem could be sludge build up. The oil pressure sending unit could be the problem. If in question about the sending unit install a mechanical gauge and watch the pressure.
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