View Full Version : Dropping oil pressure

09-27-2016, 05:18 PM
The engine in my 56 truck, which has just gone back on the road after an unknown period of hibernation (at least 10 years) is exhibiting some weird oil pressure readings. Engine is a Canadian built 259 from a 63 Daytona. When it starts from cold the pressure shows 50 psi. After idling for a bit it will drop to a steady 40. In gear it will show 30 to 40 while driving around till it gets to operating temp (170-180) then it begins to drop into the 20's both at idle in gear, its got a gm 700r4, and going down the road at 40 or so. When I pull into the driveway to park it, I put it in park, blip the throttle, and she it settles to idle it will show 30/35 psi. Oil is old and a pint low, no visible leaks, no nasty noises. Going to do a change and filter tomorrow. But wondered what the great minds here might come up with in regard to this fluctating pressure.

09-27-2016, 09:49 PM
Anything above 5 lbs at idle is acceptable, and 10 lbs for every 1000 rpm is usually the goal. Anything above 35lbs on the road should be good enough to prevent any unpleasantries.

09-28-2016, 07:42 AM
Your idle oil pressure is good if it is in the low 20's at idle. I do recommend cleaning the oil pressure relief valve as a sticking or plugged valve has a big effect on oil pressure. Bud

09-28-2016, 09:12 AM
Advise to check with a known gage..... otherwise, sounds good to me. I was thinking bearing disintergration, but your idle pressure sounds too good for that (cam)...