250 I6 Oil Leak Help

[RPIcka]

I'm looking at purchasing a '67 K20 with straight 6 250. The owner says it leaks a bit of oil. A couple drops only overnight but drips while running and then stops once the motor is shut off. The leak is to the rear of the motor closer to the transmission. Any ideas? Is it a sign of something wrong or an easy fix? Thanks.

[Fldawg]

probably the rear main seal,

[RPIcka]

Is that a lot of work to repair?

[Wrenchbender Ret]

The rear main seal would be a lot of work to fix. Often it is the valve cover leaking at the rear. It runs down & apears to be leaking at the rear seal. Or it can be the side cover.These are easy repairs. Have a mechanic take a look at it for you. These are simple easily assesable engines.

[50bomb]

Rear main seal and make sure the oil pan gasket is good. I hate those 4 piece oil pan gaskets. I couldnt get the rear rubber near transmission to stay on so I made my own out of cork. Seems to be good now.

[PanelDeland]

I'll say it's some work but more like eating an elephant.Do it one step (or bite) at a time.If you're not comfortable learning and doing this repair then one of these trucks could get expensive quickly.It's over 40 years old so unless someone has really kept it up or restored it right,it will need some work and it will definitely need more upkeep than a later model daily driver.Not trying to discourage you,just want you to be informed when you make the decision.

[RPIcka]

What does replacing the rear main seal entail?

[martindc1]

Since it is a K20 IMO the job is easier than if it were a C10. You'll have to support the engine and take out the crossmember, then drop the oil pan, take off the rear main cap, work out the top half of the old seal and work the new one in, put the new bottom half in the rear main cap and reassemble. Not too bad - it beats working on a modern car.

Now, another thing to consider is whether the 45 year old engine has a rear main seal leak that is compounded by excessive crank case pressure. My truck was like this because it had a "closed" PVC system. This means that the PVC valve hose goes to the intake manifold. An "open" system on the other hand has the PVC hose going to the manifold, plus there is an additional hose going from the valve cover to the air cleaner. IMO the "open" system is better because under high vacuum it lets clean air go into the crank case from the air filter and under scenarios where the crank case pressure exceeds the amount that the pvc system can pull (low vacuum or a worn out engine), the second hose provides a place for the pressure to go.

If there isn't a vent, excessive crank case pressure can cause more oil to blow out of the rear main seal. You can make your closed system an open system by getting a breather to go in the oil fill hole.

When I got my 67 the engine was so worn out that a breather caused the cab to fill with crank case fumes, so I got a breather cap with a 1/2" nipple off the side then ran a hose from that down between the inner fender and frame rail. After I overhauled the engine, I maintained this "open" pvc system by getting an aircleaner downpipe from a 292 and running the hose from the oil fill breather nipple to the nipple on the aircleaner downpipe.

The reason of getting the 292 downpipe is because they had an open pvc system by having a hose run from the nipple on the downpipe to a hole in the side of the valve cover below the oil fill hole.

[geezer#99]

Jack up the motor 4", pull off the pan, pop off the rear cap, replace the seal and then reverse order.
If you're lucky the seal will slide out without looking for a seal puller or loosening the main caps.
About a 4 hour job if you've done it before.
Much longer if you haven't.

[martindc1]

It could be the valve cover gasket too though. When the engine is cold reach around and feel the back of the head to see if it is wet with oil. If that is the case it can be fixed in a half hour.

Another sign that it is the rear main seal is the clutch can get "grabby" and also there is usually a hole in the bottom of the fly wheel cover and you would see it wet with oil.

I envy you, I wish I still had my 67 K20. I ended up falling in love with that old 250 too. That old truck was surprisingly good on gas.

[pat 70/71]

I would recommend changing all the gaskets that could leak, valve cover, oil pan, rear main seal, (as stated above can be done with trans in place and nothing that the average guy couldn't finish in one weekend) cheers, Pat
Posted via Mobile Device

[RPIcka]

Thanks guys

[PanelDeland]

You might try cleaning everything with a couple cans of degreaser and the quater car wash.I found the leak on mine was at the valve cover and one of the side/lifter covers.About a 30 min fix.

[Daner]

Clean all the suspect areas good. Back of valve cover/head, side cover, flywheel cover. Then take it for a short drive. When you stop and let it cool you will be able to tell where your oil is coming from. Always start top down or easiest to hardest oil only runs down.

[RPIcka]

Using a degreaser I guess I better find a spot where I can collect all the drips