I just bought a 1990 f-150. Apparently the main bearings are bad and need to be replaced, because my oil pressure shows the classic signs of high when cold and very very low when warm. I've eliminated all the other possibilitis (oil pickup being clogged, oil pump, sending unit etc.) I don't have the time or money to fix them right now and will probably just find a donor motor to do the job in the future.
My question is...how can I squeeze just a little more life out of this block. Would changing from 10w-40 to say 20w-50 be a good idea? Oil additives? High pressure oil pump (to replace the new regular one that I just put in). Any ideas?
By the way am I correct in my thinking ... oil pressure is really the resistance that the bearings/engine put on the the oil flow right? So is it correct to assume that the oil flow is still pretty strong and the top end is still getting a good soaking of oil but the bearings aren't resisting the flow (because they are worn) and getting the nice cushion of oil that they need to avoid wear? I wondered about this because I bought the truck despite erroneous oil pressure readings because the top end wasn't ticking and clanging like they do when they are not getting oil. (I thought that it was a short in the oil pressure sending unit...come to find out on this board about ford's sweet idea of a "dummyguage".)

 

The dash mounted oil gauge is misleading.. so don't trust it. Get an aftermarket gauge, put it on the engine and find out what your actual oil pressure is under normal operating conditions. IF that indicates you actually do have a problem.. then pick up a donor motor and drive this one until it quits. Chances are though once you have a backup in the garage, it will never fail.

 

i had the same problem with an 86 302. mine had a factory gauge. the guage was in acurate as well as the other gauges on the instrument panel. i bought aftermarket gauges andd they showed a world of difference. something about a egulator on the dash panel. Didn't fix my oil problem though. turns out it was the distirbutor. tHE SHAFT WAS wollerd out where the oil pump plugged in to it. also i did use heavier oil and it seemed to work. Might look at that

 

The way all bearings work, is they have an "oil wedge" that the shaft rides on/or against in the case of thrust bearings. If this wedge is unable to be maintained, due to a loss of babbit of whatever, then the shaft willl be hitting the bearing material, getting hot. And sooner or later theyre going to weld to each other(IE seize). So the oil wedge not only reduces the friction, but removes the heat.

If as already stated, your only indication is the stock gauge, then youre probably alright. Get a real oil pressure gauge, swap out the sending units and look at it. You should have 15-20@idle(warmed up) and 40-50@running speed, ie 2000-2500rpm's. The gauge should track up and down as you accelerate/decelerate. If the engine sounds good, thats a good thing. They tend ot make a heck of a racket when theyre oil starved.

 

Sorry, I failed to mention that I have replaced the gauge with a mechanical one. I get 40 psi dead cold, which quickly drops to about 5-10 psi when warm. When at operating temperature I would estimate that it puts out about 4 or 5 psi per 1000 rpms. Not good. So what things will help the put the oil "wedgie" (Can we call it a wedgie, just for fun? back in my bearings? thicker oil, and if so what number, oil additives, high pressure oil pump etc. By the way what engines blocks will go into my truck with little trouble.? I think I only need the bottom end of the motor because the top end sounds ok.

 

You are in the exact same boat that I am in. I have about 8 psi at hot idle and the highest the guage gets hot on the highway is a roughly 18 psi at 2100 rpms.


From my past I know you can run full synthetic oil in a heavier weight (it will help some) and a high volume (not high pressure) oil pump could get you a few more miles out of it (though it will be a pain to install).

Kenny

 

Dunno what oil has been run in it, but I swear by Castrol GTX 20W-50, unless you've elected for a synthetic. I've never run the synthetic, because to me, there's just something inherently wrong with not changing the oil. I find the GTX to be good high temp oil with little break-down between changes. I've run it since day dot in my 92 5.0L. To this day, no noise, and not a drop used between changes. All original factory seals/gaskets (with the exception of a plenum gasket installed last weekend). I did more work on my engine last weekend than it's had in the past 14 years, and still did it all in one day. I'm the original owner, so I know. The amount of blow-by on the engine is nearly non-existant. I pulled the PCV out when I had the plenum off, and it's clean as a whistle. The truck gets a lot of highway mileage, so I normally change at 4000 miles. ALWAYS put a new filter on, otherwise, you're keeping about a quart of dirty oil. I now have 136K on the truck, and ZERO leaks or oil related issues. The Castrol is a little more expensive than some other brands, but remember, you get what you pay for. Try a heavier oil to see if it bumps your pressure up.

I also have a 1970 Beetle Baja with some pretty serious mods made that make it want to cook oil like a deep fryer. The Castrol stands up. When I pull the valve covers for valve adjustment, they're just as clean as the day I built the engine. I've had some engine failures on the VW, but NEVER one that was lubrication related. Most of the failures required me digging my toenails out of the main bearings after over-revving or getting a little too cheeky with the timing and blowing a piston.

 

I agree, synthetic is pretty good(I run it in my 8.1 Burb cause it has piston slap, and even then I dont know it will help at all) but have always run valvoline in my 5.0 stang and 4.9 f150, with never an issue. The key, is clean oil.

If youre still at 8-10, I would move up to the 20w-50, as stated. But, I would start saving for a rebuild kit. And at least replace the rod/main bearings and inspect the oil pump.

 

Well I replaced the 10W-40 with 20w-50 and even added in a little Rislone ring sealer in it too to increase the viscosity a bit. The pressure is up a little more. At highway speeds I get 15-20 psi. Still not great, but it's enough that I don't feel guilty driving it here and there. It is also alot smoother on startup, no more loud noises for the one to two seconds when it doesn't get oil.