I was talking to my Uncle the other day and he is having problems with his F150. Its a 302, I'm guessing mid to late 80's.

Anyway he says it has normal oil pressure up unitil the engine is warm. Then the pressure starts dropping. He also said the oil pump is relatively new. I was thinking that it might be a gasket or something somewhere that maybe opens up once the block gets hot, or possibly something that simply causes the pressure to drop once the oil is thinned enough by the heat.

Is there a common cause for this in this engine? How would you go about troubleshooting this?

I don't think he is willing to rebuild the motor, as the rest of the truck may not be worth the effort. Is there any likely causes that do not require a rebuild?

Thanks!

I'm havin' that same symptom. Mine is the fact that I have 330,000 miles on my block. But the actual reason for me is the crank bearings from what I've been told. They just warm up and the area around them bein' so worn won't keep the pressure up...hth some. Phil

It is common and really nothing major to worry about. The problem isn't usually the oil pump, it's "excessive" clearances with the main and rod bearings. Fairly easily replaced, but most of the time it is not warranted to go through the trouble. As long as your keeping roughly 10psi per 1000 RPMs, your good to go. Hell, I've had a couple that dropped to 4 or 5 psi at idle, but sticks around just fine at cruise.

Thanks! I'll pass on the advice.

i finally stuck an oil pressure gauge on my truck cause the stock one dropped out. thought i was gonna have to replace the oil pump. at startup my pressures 55 - 60 driving. After it warms up driving it stays around 45. at idle in park its 25. in gear it drops to 18. Glad it wasen't the oil pump

Is this also a comon problem with 351's?

TIA

Klaus

its common for all engines that are well worn..


my current ho idles at 6 psi hot.. its only got a bit over 230k on it. the last one i ran 20/50 oil in to keep the psi @10-15 at idle..after 2500 miles it would drop under 10 and i would change it. both engines will/would hold at least 30 at highway cruise @2200-2800 rpm. and it was @ 350 k when the last one broke in half. and these were not leisure miles either.


bearings will put it back to stock readings and if you live in real cold climate and the compression is still in spec in all cylinders i have seen alot of people successfully just put bearings in. but that thought just doesnt sit too well with me. some guys just install high volume pumps...but the bearings are beat and they need replacing cause the proper surfaces are gone.

This was a freshly rebuilt longblock. Thanks again,

Klaus

pay no attention to stock "guage". my '87 reads all over the place. it's a liar.

the 351 that I am told destroys bearings quickly is the 351M. I had one that had ZERO oil pressure at idle, and about 30-35 at cruise once warm, and themotor only had 98K on it.

the 351 that I am told destroys bearings quickly is the 351M. I had one that had ZERO oil pressure at idle, and about 30-35 at cruise once warm, and themotor only had 98K on it.

I heard from a lot of people that have 351M or 400s with hardly any oil pressure, and they are still running..

I guess it is pretty common with the M style motors.

From all the post's I went through, it seems the 351'? have the same problem as the 302, but with a lot less miles. I really appreciate all the help, and info. Not a Newb to the EB, Just looking out for a co-worker with a 351 swap. Once again, you people kick ass.

Thanks again,

Klaus

my brand new 393 storker does the same thing. i run 65 lbs for the 1st 15 min then i hit 27-30 at idle. i am not worried about it. the motor turned 1,200 mi tonight so all is going good. *knocks on wood*