The Stovebolt Site Forums The Shop Area Engine Shop Fluctuating Oil Pressure

I just got my new transmission installed so I was feeling pretty happy about my truck. I noticed today that the oil pressure has begun to fluctuate. Whenever I start the motor, the oil pressure is usually around 60 psi or more then backs down to about 40 or so when warm. This morning I noticed that everytime I accelerated, the oil pressure would go down; the opposite of what you would think. I also noticed that if I drove at a steady speed, the oil pressure would fluctuate from 20 to 60. My guess is that there is something inside the tube that runs from the motor to the mechanical guage on the dash that is blocking it. Perhaps when I press the accelerator, it puts more pressure on some peice of dirt that closes off the line. I was just wondering if any of you guys have had this problem before? Thanks.

It could be in the gauge, but the gauge going down when you give it the gas is not a good sign. Either low on oil, pump sucking air or a bearing spinning. I would check the oil and make sure you are getting an accurate reading. False readings often come from oil splashed up in the dipstick tube. If you are sure you have enough oil, put a master gauge on the galley where the pressure tube screws in. Verify the pressure. If it is indeed fluctuating like your gauge in the dash, drop the pan immediately and see what's going on before before something bad happens.

The oil pressure of an engine is established by the clearances that exist in the engine (bearings/galleries/etc). Oil pressure is affected by oil viscosity, oil pump efficiency, oil supply, temperature, and the oil pump relief valve.
I recommend starting with the easiest things first......OIL SUPPLY, then install a new gage at any access point in the output side of the pump (block) and check the readings. Oil pressure should remain relatively constant once the engine reaches operating temperatures,with only slight increase as RPM's are increased. If the same high irratic condition is found using a new gauge you have an internal engine problem. Start again with the easiest....the oil filter (if equipted) the new spin on filters actually has a relief bypass built inside the housing and may be malfunctioning. Next check for ample flow of oil at the rocker shaft assembly, make sure the system lines shaft etc are not clogged up causing excess back pressure. Next the pump and relief valve assembly, clean, inspect, and replace if found worn. Finally, the bearings, mains, rods and cam shaft........yikes I hope you don't get this far!(these are NOT likely) as bearing surfaces wear, the restrictions (space for oil flow within the engine widens) and oil pressure dcreases (usually in worn engines). Most likely something is plugged up somewhere!!

Thanks for putting so much effort into writing this guys. I am lucky in that it was only a faulty gauge reading. I'm usually not this lucky. Thanks for the info anyway, it is good to know what can go wrong. The engine only has about 19,000 miles on it, I wouldn't expect it to be worn out already even though I did have a head gasket blow out a few miles back. I can't believe I have put this many miles onto it; it seems like yesterday when I was putting my freshly rebuilt motor into my truck.

CHANGE THE OIL FILTER RIGHT NOW!!! Your oil pressure fluctuation is not just the gauge. I had this exact same thing happen on my race engine (355 Chevy). The filter started to fall apart. At low RPM I'd have good pressure, but when you revved it up the extra volume flowing through the filter would move pieces of it around and the pressure would fall right off. I changed the filter and I was back in business. It was a Fram filter that did it to me. Haven't bought one since. Now I only use WIX or Napa Gold.

Will do, better safe than sorry.

I had an old ford engine that did this - it was the cam bearings - the previous owner thought you only changed the oil when you changed the tires & junked the engine.

When the oil is cold the viscosity is up (thick) so you get good oil pressure - when it gets hot it gets thinner so you lose it.

I sure hope it was your filter - otherwise it is a rebuild.

No worries, it's working good now. I'm getting 60 or so when cold and 40-45 when warm.