I have an 86 F-250 with a 302. The engine was rebuilt about 10,000 miles ago, and has been consuming oil ever since. I followed the break in specs to a tee. It burns about a quart every 200 miles. I broke it in with 10W-30 oil and have continued to use it ever since. One person recently told me to try a thinner oil, but I think if anything, that made it worse. I may try a 10W-40 next.

The question is, what's causing the oil consumption? The engine has plenty of power, and does not smoke excessively on start-up. I checked the plugs, and they acutally look OK. Some were a little white and one had a little carbon build-up. I just replaced the radiator because it was heating up on the highway. That probably caused the white on the plugs.

The truck does have a high volume oil pump, and the oil pressure always runs high. Also, when the truck first was started up, it lost oil pressure immediately. One of the freeze plugs had popped out of the core.

Is it possible that the high oil pressure is blowing by the valve seals or oil rings? Also, are there any freeze plugs that located against the exhaust manifold?? If there is, and one let go, oil could be blowing directly into the exhaust.

One more thing, the exhaust doesn't smoke constantly. Sometimes on idle I see no smoke. At other times, usually when it's warmed up, it will smoke constantly at idle, and the RPMs will bump up to about 1500. Any thoughts???

 

Normally oil comsumption after a rebuild is due to the rings not seating properly. If the cylinders were not properly honed (cross-hatched marks), new rings will not seat properly. Valve guide seals do not have oil pressure on them, and there is only coolant behind the freeze plugs. Years ago, I remember hearing about a technique to use Bonami in a water into the intake to try and seat new rings. The Bonami has alumina, which is an abraisive, that will help the rings seat. I've never tried this technique, and I would only use it as a last resort....

 

What is Bonami?? A glass cleaner?

 

Bonami is an abrasive cleaner. People sometimes use it to break the glaze on a cylinder bore.
Don't do it. For a start, the scratches it will put on your cylinder wall will be in the wrong direction and it will wear out your rings and pistons and bore.
It's the same as tipping sand into your carb, would you do that?

It sounds like the rings are broken or incorrectly installed or the valve guides.
1 qt per 200 miles is a lot! I would expect it to smoke badly. Maybe it's leaking out?

Either way, did you get a warranty with the rebuild?

 

That's what gets me. Can't find a leak and it doesn't smoke a lot. I'd expect that the plugs would foul if it was burning that much oil, and they look fine.

When the motor was rebuilt, the valves, guides and seals were not replaced. Is there any way to determine whether its the rings or the valve seals??

Also, no warranty. The motor was rebuilt about three years ago and I have put less than 10,000 miles on it since then. It doesn't get driven very much.

 

You say it doesn't smoke constantly, but at idle, warmed up, it smokes. That's a good indication the valve seals are shot. How many miles were on it before the rebuild?

It's probably time to get the heads done(guides and seals, lap the valves, replace any weakened springs, etc).

If possible, check and see if your cam was replaced when the engine was rebuilt as well. If you're going to have the heads off, and it wasn't, you may as well install a new cam and lifters while you're in there.

 

When you say it uses 1 quart per two hundred miles does that mean you put in 1 quart every time you check it at around 200 miles? Have you had to add more then 1 quart? The reason I ask is I have had a few engines that will always run a quart low on the dipstick, if you fill them up to the full mark they will throw it out, burn it or do something but once down to the 1 quart low mark they never lost anymore. Just a thought.