1997 Ford F150, V6, 4.2, 2WD, 137K miles. Oil pressure is fine until warmed up and then begins to drop with lower idle (significant drop). Oil pump has been replaced with no change. Any ideas ??
The only other thing that can cause this in an engine is, excessive clearances in the rod/main bearings.
What are you using to determine oil pressure? If the dash gauge indicates low pressure then have the oil pressure checked with a calibrated oil pressure gauge. If it’s still low then you may have worn bearings. What are you considering as low oil pressure?
Did you think it would last forever? Worn engines can have difficulty maintaining “normal” oil pressure at idle. You need 10 psi for every 1000 RPM. If you are using 5w-20 oil, try 10/40 and see if that helps a little.
On many Fords with oil pressure gauges, the “gauge” does not read oil pressure at all, the needle just goes to the center of the scale using the same circuit as the idiot light. Maybe trucks have a real gauge…Have you replaced the oil pressure sender? Sometimes those can fail and give false readings…
Thanks, Tester. After speaking to a local mechanic, similar to you, he felt that it was definitely a “clearance” problem in the engine. Of course the question that probably can’t be answered is how long and what will the last signs (as it gets worse and the engine dies) ??
Was using 5Wx30 - but could definitely give 10Wx40 a shot.
There may be a knocking from the lower end of the engine, or the lifters might start clacking from the lack of oil pressure, or the engine might sieze. Hard to say when an engine displays this.
I once bought a Ford from a guy that had worn engine bearings. I was able to drive it to the shop in fifteen minutes. As soon as I pulled into the shop the engine siezed up. If the engine was allowed to cool off, the engine would restart and idle for thirty minutes before it siezed up.
A pretty good indication, after the truck sits for a couple of days, listen to the engine as you start it. When they get real loose, you will hear the rods knocking a little before the oil pressure comes up. Then that thump-thump-thump sound should stop instantly. When you start hearing that sound with the engine warm and idling, you know the end is near…But that progression can take a long time…
Now a silly question : Are there any oil additives that can prolong the inevitable ??
What happened to “Restore”??
Right now, just try the 10/40 and see how that works. Then try 20-50…When it’s on life support, 20/50 and a jug of Lucas Oil Treatment…
But as long as it holds decent oil pressure at road speed, don’t worry about it. Idle oil pressure is not that critical…Remember, 10 PSI for every 1000 RPM…
Well? I’d put Restore in the engine before I’d put a heavier oil in the engine. At least the Restore isn’t going to hurt anything. The heavier weight oil will build pressure quicker, but doesn’t flow as fast on a cold start up. And if you want to wear out a worn out engine faster, use a heavy oil where it gets cold.
The reason there is low oil pressure is because the flow-rate is way to high through the loose bearings, like you said…