I am purchasing a 1978 Bronco with a 351M, and the oil pressure gauge indicates that the pressure is very low (nearly no pressure). The engine started up perfectly, and runs like a top, there is no fluctuation in idle speed, or no hesitation to rev. There are no abnormal engine noises, and the engine was cold before I started it up, so I should have been able to hear a rod knock if there was one. Could the oil pressure sending unit or the pressure gauge be the cause of the low oil pressure reading, or would something internal, such as a worn out oil pump, or loose engine tolerances be the cause of the apparently low oil pressure? :confused:

Thanks in advance

351M's are notorious for low oil pressure, I've owned two and both had good pressure at startup (with an aftermarket guage) but die down to 5psi or less at idle when they warm up. Something about narrow oil passages in the block.. Anyway both ran fine, in fact the one in my 81 F250 is my daily driver at the moment.

get used to it, mine has been that way since i got it, even got worse since i spun the main bearings :flipoff2: but it still runs strong and gets enough oil to keep it going i guess, from what im told this thing ran with low oil presure almost its whole life and it has about 350k on it right now. gunna try to improve my oil presure when i rebuild it this summer. but dont be scared of it

Thanks for the replys. I was hoping it wasn't a problem, and now I won't have to worry about the engine. :D

Now for an off-topic, newbie question, are the "genuine gear" (I think that's the company) lockers any good? I'll need to tear down the rear axle eventually to replace some leaking seals, and I'd like to get a locker or a true-trac type device in there when I do. I've only got about $4-500 to spend on the rear-end seals and modifications, so I need to make a good choice.

i got a mini-spool and chromoly pin (pin was never used) for a ford 9" if thats what ya want, ill sell it for $40 + shipping, mini-spool is 31 spline and only has maybe 700 miles on it

You will learn not rely solely on those factory gauges to indicate certain levels. They are good at providing approximate settings. Also, if you ever have to perform lower engine work, you might want to install a high volume oil pump for security.

i got a mini-spool and chromoly pin (pin was never used) for a ford 9" if thats what ya want, ill sell it for $40 + shipping, mini-spool is 31 spline and only has maybe 700 miles on it

I need something that will let the wheels have a little speed difference, since this will be my daily driver, so the spool wouldn't work for me, Thank you for the offer though.

ford issued a tsb on these engines for oil pressure problems. don't worry about it unless it starts sounding like is diesel, then rebuild it.

As others have said, the oil pressure is a problem. THIS IS BECAUSE THE BEARINGS ARE WORN OUT- IN MOST CASES. I have serviced many of these. I recommend using a mechanical gauge first to confirm the low oil pressure, THEN REPLACE THE MAIN AND ROD BEARINGS AND INSTALL A HIGH PRESSURE, HIGH VOLUME OIL PUMP and check the screen for cleanliness. If you do nothing it will blow up as others have mentioned. Many of those engine will go 300,000 miles if the bearings are replaced when needed... which may be every 60k to 80k on a 3/4 or 1 ton rig w/manual trans, cause they go fast when the engine is lugged.

I need something that will let the wheels have a little speed difference, since this will be my daily driver, so the spool wouldn't work for me, Thank you for the offer though.


whats the problem with a mini-spool in a DD? my rig is a DD and i just welded up the 14b im dropping in, only ever hear a lil tire chirp when going around 90* turns :flipoff2:

I have run a 351m for 12 years and about every 2 years put in new main and rod bearings in it. The oil psi just keep getting lower and lower. The Cam bearings are the problem. The high valume oil pump will wear out the distor gear with in 3 years, I've been there. This is what I've learned with my motor.

You only get 2 years out of the bearings? Wouldn't it be easier and cheaper to pull the whole engine out and fix the problem in the first problem?

I have run a 351m for 12 years and about every 2 years put in new main and rod bearings in it. The oil psi just keep getting lower and lower. The Cam bearings are the problem. The high valume oil pump will wear out the distor gear with in 3 years, I've been there. This is what I've learned with my motor.


you got bigger issues, my buddies 351m was rebuilt top toi bottom 4 years ago and his oil pressure is normal with a hiugh volume pump. we just did a new cam in it and bearings looked fine.

#1 main reson for really low oil pressure is main bearings, once they are shot the oil just runs thru them and decreases the oil pressure (as im told) and i believe this is right cuz right after i spun my main bearings by my ex running the motoro hot when a freeze plug blew my oil pressure went to shit, i just have yet to fix the problem. but as stated before once it starts sounding like a diesel its time to rebuild, mine has about 350k on it and sounds like my bosses mack when im at crusing speeds above 2500RPM but im just to lazy and short on money to pull the motor yet

Hay NET,run straight lucus oil.I have and it helps.Dont throw a rod in that 400 or your stuck with that 300/6 forever.

Hay NET,run straight lucus oil.I have and it helps.Dont throw a rod in that 400 or your stuck with that 300/6 forever.


400 and 300 were both pulled today, i managed to get the 300 running after 4 years of it sitting, ran strong but rear main seals leaking, but i think it swelled back up and stopped. the 400 is getting totally redone and bored .030 over and hot tanked, scoped, heads are getting ported and polished, then i gotta find out what ima run in it

Well,dont build it to much.I overbuilt my 466 and now regreat it.I am going from a 6k pound mud truck to a jeep for rock crawling.Before I put the 460 in the jeep,ittl get a smaller cam and some things like that to settel it doun a bit.Its hard to crawl rocks with a lopy idle.

Hmm... I've got the 351M and my oil pressure never goes below 40.

The 351M thats currently in my '79 has virtually no oil pressure. The mains are completly gone, infact it knocks so bad that it sounds like the crank is hitting the block. These motors seem to wear main bearings out fairly bad, I've heard of many doing it.

I'm going to try putting straight 50w oil in mine and see what happens, hope it runs long enough to get me through this next trail ride. Then I'm ripping the piece of crap out, throwing it in the land fill, and getting this GT-40 351w built up thats sitting on my engine stand. Can anyone tell I despise modified series motors?

The 351M thats currently in my '79 has virtually no oil pressure. The mains are completly gone, infact it knocks so bad that it sounds like the crank is hitting the block. These motors seem to wear main bearings out fairly bad, I've heard of many doing it.

I'm going to try putting straight 50w oil in mine and see what happens, hope it runs long enough to get me through this next trail ride. Then I'm ripping the piece of crap out, throwing it in the land fill, and getting this GT-40 351w built up thats sitting on my engine stand. Can anyone tell I despise modified series motors?


:rolleyes: :rolleyes: :shaking: A good "m" is just fine.........even for Abusers like me:D

:jester: