oil pressure

[racer88]

I recently bought a 97 GMC 6.5 turbo. The peerson i bought it had no maintenance history. So i changed oil and filter (15w40 rotella), and now my oil pressure at idle is at approx 5lbs which causes the check gauge light to com on. At 2000rpm it is at 20lbs. When cold however it reads 40lbs and 20lbs. What happened? does anyone have an answer to this problem? thanks alot

[Jim Brzozowski]

Anyone who doesn't take the time to document maintenence probably didn't have the time to do any. That may well be the truck's first oil change. Verify the pressure with an auxillary gauge to be sure the gauge is showing correct pressure, if its only running 20 psig, I'd probably start checking bottom end bearing clearances, if its not not knocking like it spun a bearing on the crank, then its probably worn so badly that there is too much clearance and the pump can't supply enough pressure because the oil is escaping faster than it can supply it over 20 psig. If the bearings are alright, replace the oil pump with a high volume pump and drive it.

[David Proske]

Like he said it may be pretty well worn. The guy you bought it from may have put in a super thick oil so the motor could make oil pressure long enough for him to sell it.

This may not be the case but sure looks like it since the issue appeared when you changed the oil.

Similar to thick oil in the trans to make it shift or sawdust in a rear end to make it quiet.