Geez, could it at least try to keep some oil in the crankcase...

[65skyturbo]

I'm new here but have been reading posts for a few months to learn about the 6.2 diesel. I purchased a 85 C10 Suburban with the 6.2 about 7 months ago and have been slowly fixing it up. When I first purchased the truck it did not leak a drop of oil. About a month later it would leave a single dime size drip, no big deal. Yesterday I drove it about 20 miles and looked under this morning and counted 15 drips with the smallest being about 1" and the largest being 6-7 inches. It appears to be between 1/2 quart and 1 quart low on oil (just checked it on monday and it was full). I know it is not leaking from the top as I just changed my intake to a J code and everything on top is completely dry. It is wet inside the inspection cover but it is not dripping off the flexplate or torque converter. I imagine that it is the rear main seal but I would expect the flexplate to be wet. Whatever is leaking appears to happen while cruising because with the inspection cover off it is not dripping, however I have oil spray all the way back to the gas tank. Oil pressure when hot is about 45-50 psi on the factory gauge. Truck mileage just rolled over and it has at least 200K if not 300K or 400K. Do rear main seals dump that much oil or has something else sprung a leak? I changed the oil around 1000 miles ago and it seems worse since then. Don't know what the previous owner had in it but I put Delo 400 15-40 in it. CDR valve was just replaced. The truck drives great and gets 23-24 mpg in town (no highway driving yet due to bad tires), it fires right up the first time and doesnt even try to overheat (I'm in Phoenix). It does have blowby but it runs so well I can't imagine that it would be considered excessive. I just can't figure out how I would end up with the bottom of my truck covered in oil and there not be any on the flexplate and torque converter, seems like it is squirting out too fast to be the seal... Sorry for the long post, just wanted to give plenty of info. Thanks.

[DmaxMaverick]

Welcome aboard!

Before blaming the rear main seal, verify your oil source is not from the filter, vacuum pump, or oil cooler lines.

The CDR does not prevent excessive pressure, but prevents excessive crankcase vacuum under high RPM's. It's normally open, then closes as intake vacuum increases. Some blowby is normal. With the engine up to operating temp, remove the oil filler cap. It should huff a bit of vapor, but shouldn't billow out.

If the rear main seal is original, it is a "rope" type. They are generally OK, but can leak a lot with excessive crankcase pressure or an overfill (normal fill is 7 to 7.5 qts). If the vehicle sits unused for a long time, the rope seal can dry up, then take quite a while to fully seal again. Your oil choice is first rate, so that's not the problem. The good news is, the seal isn't hard to replace. It can be done in-frame (drop pan and rear main cap, push/pull out old seal, insert new 2-piece rubber/steel seal).

[65skyturbo]

Thanks for the welcome. I've been using Delo for years in all my older non-roller cam cars ever since I learned the hard way about the lower levels of ZDDP in the modern oils. Filled it with up with 7 quarts. I checked the valve covers, vacuum pump seal and oil sending unit first and everything is dry. Oil cooler lines are dry too. I'm pretty sure that it is the rear main seal or the rear pan seal but I've heard of people having issues with the oil galley plugs and even the cam plug. As far as the blowby is concerned, I definitely think it is more of a steady flow than a light puff. I believe this truck was only driven something like 2000 miles in 8 years so I wouldn't be surprised if the rings are a little gummed up and the rear main seal is dry. If I do have an excessive amount of crankcase pressure, would a vented type oil cap possibly help at the expense of making the CDR useless? I would hate to spend the time and effort on changing the rear main seal or oilpan gasket if my engine has so much pressure that it is just going to leak again. Are there any proven additives that soften up the rope seals without doing damage to the other gaskets? On the 2wd trucks, how many inches is it necessary to lift the engine up to gain clearance to drop the oil pan?

[DmaxMaverick]

I do not recommend a vented oil filler cap. It won't help, and will have no effect on the function of the CDR. The CDR manages crankcase VACUUM, not pressure. It is, and remains, fully open under pressure. It only restricts excessive vacuum at higher engine RPM's. Crankcase vacuum isn't your problem, and venting may make it worse. Let the intake pull as much as it can.

I don't know of any additive to help a rope seal. There's no rubber to soften or swell. The rear crank baffle/channel will usually manage most oil in the area, as long as there isn't too much pressure. Roller/cam issues are almost non-existent on these engines, regardless of oil choice. Red bottle STP will help with any ZDP/ZDDP concerns. It doesn't take much.

There may be some cause attributed to the low mileage over a long period of time. To start with, it's over 26 years old. Short, infrequent trips can certainly cause issues with the rings, and seals. Some more frequent use and proper care may remedy that. Maybe try some MMO (Marvel Mystery Oil). Gallery and cam plugs are aren't an issue, that I've heard of.

No gasket on the pan. It's sealer only. Same with the valve covers. If you remove either, true the sealing surfaces and clean them before reinstall. Gaskets are available, and included in most gasket sets, but WILL leak after a while.