I have a 92 F250 7.5L automatic trans. Bought the truck several months ago with quite a few issues. Seem to have most repaired... however I changed the oil and put 10w 40 syn. Don't know if this issue pre exists or was a result of oil change.. I am loosing about a quart of oil every 100 miles. Don't know where it is going. It doesn't smoke ,,,except black when I kick in the passing gear. It is wet between the trans and engine. Figure that to be either pan gasket or rear seal. The engine shows 173th miles. When I stop driving I park on a cement slab and have yet to see any oil leak greater than a quarter. Lately I don't see any oil leak drippin onto the concrete at all. Where can it be going? How do I stop it?

 

My guess would be if it's not leaking, it's burning. But 1 qt per hundred is a lot. That's like an oil change after 500 miles. Wow, I'm surprised you haven't found a leak or see smoke.

If it were a qt every 3000, I'd say run it until it dies unless you really want to dive into the motor now. Seeing as how it uses so much and costs you A LOT in oil, I'd pull the motor...that's just me.

 

I did that once many years ago. Pulled the engine and replaced it in a ford fairlane. Then found out it was just a $20.00 piece that was bad. Once I find out what the problem is then I'll decide what action to take. Thanks for the advice. It might be what I end up doing. I pulled the spark plugs and all were clean except #6. It wasn't fouled just a little carbon around the inside of the plug... not at all around the tip.

 

Yeah, obviously cheaper is better, I'd just hate for you to be 100 miles from home and your engine takes a crap. Good luck.

 

Is the rest of the undercarriage wet with oil? Could be losing it out the valve cover gaskets and rear main while it's running going down the road. Otherwise I'd check the coolant to see if there's any oil in it. 1 qt per 100 miles is pretty extreme.

 

Get the synthetic oil out & see what happens. Running synthetic oil in an old truck with unknown history is crazy in my opinion.
Just run a good grade & brand of oil & filter.

Craig

 

I'd like to learn...what's the deal with synthetic? How is it not as good as 'real' oil? I've heard not to mix them either.

 

The issue with synthetic oil is that is much thinner than regular oil. Putting synthetic in a high mileage vehicle that has never had it before can result in lower oil pressure and mainly leaks. All the seals that were "ok" with regular oil will most likely leak with synthetic simply because it can go through smaller spaces and clearances much easier. Now, when it comes to choosing oil for a fresh rebuild or new engine, synthetic is much better. Lasts longer and lubricates better. If you start an engine on synthetic and keep it that way, it is great. When you try and transfuse it into an old, used engine that used normal oil all its life you will most likely have issues.

 

I put synthetic in my 86 F250 4x4 with a 460/C-6 once. After about an hour the oil was running out the oil pan gaskets like water running out a faucet. I tighten up the bolts & it slowed to a slower leak. Went back to Dino oil & it never leaked a drop. This truck only had 135,000 at the time.
So go figure. I just stay the hell away from that crap on older vehicles.
Now my 99 Dodge 2500 4x4 requires a special synthetic oil in the transmission which is an NV 4500 5 speed manual, because it has some kind of carbon fiber sycros. Dodge recommends synthetic gear oil in the limited slip rear end. Other than those two things I run dino oil.

Craig

 

Check the air filter housing for blow-by through the valve cover vent. A quart every 100 miles would be an awful lot to be in the housing, but it's another thought.

 

Evan, I agree with you. But having said that I have driven well over a million miles on dino oil & I can't tell you how many vehicles I have owned in my life but a bunch & I never saw any real world proof that synthetic engine oil does anything better. It never saved me one gallon of gas never saved me one penny in cost of anything. I keep pretty close details of cost. Being an old mechanic it was drilled into me PREVENTATIVE MAINTENANCE is the easiest way to save money. Working in an industry that down time cost thousands of dollars an hour in many cases. mistakes were looked upon as good for you job security.
We bought a new 04 Trailblazer 4x4 & the dealer paid for the first oil change. They put in Mobil 1 & we stayed with it until we traded it in with 75,000 miles.
Now Gears is a complete different story. I saw a reduction in rear end heat running synthetic gear oil in my 86 F250 4x4. But the problem was the seals new would not hold the oil from seeping onto the brakes. So it cost me new seals twice & a complete brake job once in 60,000 miles, so not any savings there. That was on a Sterling 12.5 Rear End. I checked hubs for size etc & yet new high dollar seals would not work with synthetic.
Yet when working in the drilling business as a mechanic the best gear oil out was Lubrication Engineers oils. Kind of a stick red oil. It cut our gear issues in both Rigs, & Drill units in half. We used it in all our trucks, front & rear diffs, T/C etc. We had over fifty Ford F250s, some 2x4 & some 4x4 in our division, from new to a few years old. This was in the 70s.

Craig

 

That is one of the first places I looked for issues. Strangely the rest of the under parts are dry except the one as previously mentioned. If it were just leaking surely it would drip onto a concrete parking slab. Nothing there. I will remove the oil and try a non synthetic oil.

 

You still have the cat. converter?
Catalytic conv. will burn and mask much of the traditional blue smoke you would see on a straight piped rig.
Is the aircleaner crankcase breather element puking out oil?......if yes, thats a clear sign of bad crank-case blow-by and a real tired motor.

And I agree, get that syn. oil out of there.

 

I have seen where the transmission crank case cover has put a rub hole at thr top of the oil pan on some trucks w high miles. Sounds just like that to me. It was described almost word for word like your description.

 

The oil cooler is a common failure point on 460s. Pull the radiator cap off and see if your radiator is full of sludge.