I'v got a 1988 f150 4x4 351w EFI that has low oil pressure. when I bought it, the pump screen was plugged 90% and the previous owner had driven it that way for 3 MONTHS OR MORE!

I got a good deal on the truck, so I had the pump and screen replaced and had my mech check the bearings, he said that they were so-so (his words).

Oil pressure is better, but once it gets warmed up the pressure at Idle is about 2-5 psi. I know, not good. I think the bearings are worn from the previous owner. The whole truck has only 79K miles on it.

So, my questions are : Can I have my mech replace just the rod and main bearings? Will It last 80K more miles? can I have him use bearings that are .001 thicker?

My mech is very proficent, but somtimes uses parts that are only mediocore. He can also do the bearings with the engine in the truck which saves me alot of money.

Any problems doing it this way?

Thanks in advance, I also posted this in the performance and general rebuilding forum because I am going to get this done soon. (before I spin a bearing or worse).

 

If I were you, I honestly wouldn't give them a whole bunch of thought right now. Oil pressure is always a baseline on how to determine what kind of shape your engine is in. More importantly, but not as odten discussed, is the volume of oil being pumped. If you're having low oil pressure, but there's no knock or other nasty noise coming from the internals of the engine, I'd say you're still in good shape. I had a mud truck that ran for a long time with dang near negative oil pressure, but it never came apart, even after several trips to the 6k rpm god.

 

Well, that is the problem I ran into. I bought a 66 ford f100 with a 351w. The teflon coating on the timing gears had shreaded and clogged the screen up. Had all of that replaced. Still had no oil pressure. Then it started rattling and was getting worse.

If you start getting a rattling from the engine, that is the time to get them replaced immediately.

What kind of Oil Pressure guage do you have? Is it stock or do you have an after market guage? If it is an after market guage, take a look at the plastic line going to it. See if it has any air in the line. Will just be blank places in the oil going through it. It is possible that you have an air leak in the line and it may need to be redone.

 

Thanks for the reply.

It's not knocking yet (knock on wood), but just concerns me.

I don't have any air in the gauge line and pretty sure that its accurate. So as long as I have volume, the pressure means less?
It is not a hi-volume pump, Is that still OK? Should I run a thicker oil, 10W30 in it right now?

 

I don't see why not. It sounds like your oiling is sufficient. Just keep the oil level up to par and keep an ear on the engine. Heck, even a knocking motor can last a while.

 

I had a 1982 E350 ext. Club Wagon with a 351, it knocked all the time. Dump a bottle of dura lube in it it quieted the mains, and helped on cold start.

 

Heck, if it's already knocking, I don't see why you wouldn't try dang near anything to get the thing to shut up. Dura lube, marvel mystery oil, 90 wt gear oil...

 

I talk to my mech and he seems to think that since the pump screen was 90% plugged that the cam bearings are shot. no oil to the top end. It never did have any lifter tap.

Can you replace the cam bearings without disassembling the whole engine? And what would happen in the long run if I kept running it?

It is making a sound,(hard to describe, bear with me), but only above 3800 RPM. Its not a knock, (if it is, very small one) but kinda sounds like valves, kinda like the valve rattle in a worn out 300-I6, but not as loud as that. engine runs good, alittle on the weak side, and has a hard time rapping up to above 4200 RPM in passing gear going up a semi steep hill. I know that this a heavy truck, but I thought IT should be doing a little better than that. I have to let off the gas to let the trans shift into 3rd. its not a tranny problem. the fluid is clean and clear red. not burnt. shifts real good and firm (not hard).

Maybe the cam lobes are worn flat from lack of OIL?

Just trying to get a better idea of what I might be faced with or possible problems running for extended times on the engine.

Oh, It has 20psi runing down the highway @65 warmed up and 38-40 cold @ idle.

 

It wouldn't be a flat cam. If your cam was flat, it wouldn't want to run at all, and certainly not up to 4200 rpm. It is entirely possible that your mechanic is correct. No, it's not difficult to change out the cam; I'm not sure about the bearings. I know my neighbor's cam went flat in his truck and they changed it out in an afternoon. The bearings might be a whole different story. Who knows; maybe you just need a new cam. It sounds like your oiling problems are solved from the pressure you posted.

 

No, the original problem was no pressure at Idle, I have pressure at running speeds just not very much. 20 psi @ 3000rpm is not much when it is supposed to be around 45 or more. Cold pressures never get above 40, should be 60. Still have a problem, not sure how to solve though.

Oh yeh, my mech said that the original problem (screen plugged) was caused by a rubber one piece oil pan gasket that had deteriated and crumbled into the oil pan. Thats what he found pluging the screen. Just FYI, use the paper or cork gasket. The rubber may seal better, but at what price?

 

Well boys (and girls , politically correct you know), The bearings have finally worn out. I have a knock hot @ Idle , just one rod. not sure which one though. doesn't matter though.

Now, I need serious help making up my mind what to do next.

Should I replace the rod and main bearings soon and hope that it lasts until march( tax refund), and put a new short block in, or moth ball it until next spring?

Here's some more info,

The lifters never did tap and power was decent. No other noises from the engine. have put 2500 miles on truck since mid june.

If the cam bearings were not getting oil, would the lifters still pump up?

Was my mechanic wrong and bearings were more worn than he thought?

Please give your opinion on as many of my questions as you can, As this is my work truck, and don't have another. Moth balling it would entail coming up with a ride to work or a very cheap small car.

thanks in advance

Marc.

 

Pull the pan and see what bearings are causing the knock. Check the crank jounals for damage. If it is just a little nicked (very little) you can get away with using a fine emory cloth to dress it up. Check the rods for damage, you may need to replace one or more. Buy a set of +1 bearings and slap it in and check the clearance with plastiguage. If one or more has too much clearance buy the appropriate bearings to make up for it and check again.

You may be able to get it back to health this way without causing any more damage.

I wouldn't run it until you have done this because you could (if not already) damage the crank beyond repair, costing you alot more than necessary.

I myself have a knock/rattle, but only when revved. I had surgery so I can't finish pulling that pan.

Question for ya. - How loud is it? Is it a heavy metal sound? I'm just trying to compare yours with mine.

Good luck.

 

I know how it goes guys . I'm building a 400 horse 358w because my old tired 351 is about to give up. The rods are getting so bad that when there is no load and all the windows open you can here them clatter away over my long tubes and flows. I went from 15w-40 to strait S.A.E 40 year round and it helped a lot. But still only have 5 p.s.i. pressure at hot idle. About 20 going down the road at 55.

 

Listen, I have a 93 302 and I had low oil pressure. It started out having good oil pressure until the oil warmed up and then it would drop to about 2 psi at idle. At first when I would accelerate it would go up to about 55-60 psi. So at this point I was not worried. After a while of driving like this, the oil pressure would no longer go up when accelerating. Then I started to worry. I had already changed the oil pump and this did not help. I decided to check out the main bearings and crankshaft endplay. Everything was shot! I had about .025 slop in the thrust bearing and everything else was sloppy also (rod and other mains). The crankshaft was non repairable so I got another one that was machined down .010 and put on oversized bearings. I put it all back together and fired the truck up and the oil pressure jumped right to 65 psi and stays there whenever the truck is running. That was 5000 kms ago so...................

 

That is a very good post, You described my problem to a 'T'.

Now That I know what I'm in for, How much was the Crank?, machine work? Did you machine the rod journals too? Any bad rods?

What made the Crank non-repairable? thrust surfaces? journals themselves?


Any advice for getting a good crank from junkyard?

thanks a bunch!