Posi12Bolt Posted September 4, 2008 Report Posted September 4, 2008 '99 GMC sierra 4x4 with a ton(200k+) of highway miles... engine has never been apart. its hit or miss whether it will have oil pressure or not, take it for a drive and it'll have 35-45 #'s and the engine is super quiet. Next time you drive it, its got 0-15 #'s with some valvetrain noise... what the hell, how is it so erratic? I thought you either had oil pressure or you didnt... do oil pumps go out like this? thanks Brian Quote
misterp Posted September 4, 2008 Report Posted September 4, 2008 '99 GMC sierra 4x4 with a ton(200k+) of highway miles... engine has never been apart. its hit or miss whether it will have oil pressure or not, take it for a drive and it'll have 35-45 #'s and the engine is super quiet. Next time you drive it, its got 0-15 #'s with some valvetrain noise... what the hell, how is it so erratic? I thought you either had oil pressure or you didnt... do oil pumps go out like this? thanks Brian Can't be the oil pump. Since you are getting valvetrain noise I'm going to agree the guage & sending unit are accurate. If it were anyone else I'd say check the dipstick and make sure it's not low on oil, but I'm sure you've already done that. Spun cam bearing was another guess, but since the motor is not making death rattle noises that's 99.9% not it. The oil system has got to have a blowoff/dump valve in the pump, maybe it's sticking? We used to clean-out high-mileage demolition derby car motors by substituting 2 quarts ATF in the engine oil, the extremely high detergent content in Dexron-III will wash anything sticky out of the engine, be sure to change the filter & oil after 400-500 miles because the filter will be plugged solid. Others have used Marvel Mystery Oil with similar results. Sorry for nothing more than wild-assed guesses... Mr. P. Quote
Posi12Bolt Posted September 4, 2008 Author Report Posted September 4, 2008 If it were anyone else I'd say check the dipstick and make sure it's not low on oil, but I'm sure you've already done that. yeah, i checked it first thing... was bout 3/4 quart low... its good now. its due for an oil change, maybe I'll try the atf trick. its strange how it'll act just fine one second and not the next. never seen anything like it Quote
Fireman31 Posted September 5, 2008 Report Posted September 5, 2008 Just out of curiosity, what kind of oil filter is on it? Quote
zippy Posted September 8, 2008 Report Posted September 8, 2008 Quite possibly an oil pump problem. There is a check valve in the oil pump that can gum up after years of use and if it sticks you'll get very eratic oil pressure. Quote
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