I am trying to figure out the low oil pressure problem I am having on my car. When the engine starts cold it has good oil pressure 40psi, when the engine is warmed up and I drive it regular the oil pressure drops down to about 15psi at idle and if I rev the motor up the oil pressure starts to increase. If I put a load on the engine like a wide open throttle run or just like a higher rpm run when I come to a stop the oil pressure goes low like around 6psi and sometimes it goes into the red and the check gauges light comes on, if I rev the motor the oil pressure comes back. I have checked the oil and it is full, no leaks from the engine and I have used a mechanical gauge to check the instrument cluster gauge and they were reading the same at idle warm (15psi). I was wondering if it is possible that at wot or under heavy acceleration if the computer is dumping in so much fuel that it is washing the cylinder walls down with fuel and making the oil pressure go low because of the gas in the oil and that at idle the pump doesn't have enough rpm to push the diluted gasy oil around. Once the gas evaporates the oil pressure comes back and it is okay again until I go WOT or do any heavy acceleration. If I rev the engine at idle when the pressure goes low the additional rpm give the pump enough strength to pump the diluted oil. I think it is a bit of a stretch but I don't know what else might be causing the condition to happen. The oil doesn't have any bearing material or copper in it and the engine is not noisey like it would be if a bearing was gone. The car smells like it is running rich and when I pull the dipstick out and smell it I think I can smell fuel. I am going to the dyno on Friday to have it tuned, hopefully they will be able to get to the bottom of it. In the mean time I think I will do another oil change and use 20w50. Any suggestions would help, sorry for the long post.

 

Wow...... maybe a new record for the longest single paragraph post...... . Really hard to read something like that.

Have you considered the possibility that the oil pump pickup has fallen off? That is a fairly common cause when the oil pressure drops to near zero on a hard stop.

The idea of WOT diluting the oil with excess fuel and then evaporating seems a bit out in left field..... the fuel would thin the oil and it would stay that way for a fairly long period of time. It isn't going to evaporate the fuel in a matter of seconds. If you can smell fuel in the oil, there's a good chance you have thinned it out, reducing the pressure. But I'd still be suspicious of the drop to near zero on a hard stop.

 

Injuneer:

Would it make sense that if the oil pick up fell off that by just revving the motor to 2000rpms that the pressure would pick back up?

By the way would a high volume pump be more apt to cause a lower pressure at idle - I believe the pump that is in the car is a Melling high volume pump.

 

OK you say you have 15psi hot on an idle right?
Is your oil gauge the one in you cluster on the first mark?
If so then that is normal.
So if this is the case then one problem is solved.
Don't know about the rest if I get any ides I will let you know.


Chris G.

 

Get some REAL oil in it. Kendall GT1 40 weight and see what happens.
Some of the synthetics don't like being hot and loose fitting brg's.

Fuel or water won't mix with it.