Engine oil leak from rear main seal?

[Nickaru]

I have a M1008. I'm new to the MV stuff, but I'm excited to work on it. I noticed I have some oil dripping and it looks like the rear main seal is leaking. Is this common on these 6.2 diesels? If it is the seal, is the repair possible without pulling the engine?

I'm trying to get up to speed on these 6.2 engines. Thanks for any help you can give me.

 

[WillWagner]

Remember to start looking high for the leak. They all end up at the rear of the pan. It would suck to pull the trans/t-case only to find it was a valve cover

No, you don't need to pull the engine, just the t-case and trans. The t-case is heavy.

 

[Matt65]

Exactly, be sure of where she's leaking. My IP slowly leaks diesel, and I thought it was the rear main. Below is good information from the CUCV wiki / FAQ.

List your truck model in your signature, this will always help.

Welcome to the forum!


Autozone rear main ~ $22
Autozone oil pan seals ~ $12

Here are the steps I took:

1. Jack up front end frame, to raise frame slightly off axle. Even an inch will help.
2. Drain oil, remove filter.
3. Unplug batteries
4. Remove starter
5. Remove bottom access for bell housing, tricky since tranny cooling lines have to be pushed over a bit, no need to remove the lines though
6. Pull oil pan, may need to loosen a line for the front axle breather from frame rail, tends to block access to front bolts on oil pan. Use a screwdriver to gently pry the pan loose from the engine block if it sticks; which it should if RTV was used.
7. Remove oil pump/pickup
8. Remove rear main bearing cap
9. Remove old seal
10. Install new seal, carefully. I had a helper and with 4 hands we were able to hold it in place while applying pressure to push it in the grove. Take note of placement, mine was labeled which side points out. TM shows a shim which can be made to assist in seal install. I'd be wary though as you don't want to damage the seal.
11. Following the TM, use anaerobic sealing compound on the rear main cap as specified, install rear main cap and torque to spec.
12. Reinstall oil pump/pickup
13. Clean old gasket from oil pan and engine block. RTV oil pan gasket to oil pan, let sit for 10 minutes, RTV top of gasket, let sit a few minutes; then reinstall oil pan while trying not to get RTV places it should not be.
14. Reinstall bell housing access cover and air breather line for front axle if removed.
15. Reinstall starter
16. Install oil filter
17. Fill oil, check level, etc.
18. Reconnect batteries
19. Start it up, recheck oil level after idling for a few minutes and verifying no leaks.

That is about it! If anyone sees a step I missed, please edit this. As long as you have another vehicle to drive in case the job takes longer than you hoped; you'll be fine to try it yourself. It took me two days, maybe 7hrs total. First day, I setup doing steps 1-5. Once you pull the oil pan, you will want to finish through step 13.

 

[ralbelt]

Ditto on above. I would also inspect carefully the flex plate, if I have the trans out, and replace it if you see worn teeth or cracking around the mount bolts.

 

[Chaski]

My rear main went from a weep to a leak last week after a hard 120 mile round trip run.

Now it it is time to do the rear main.

 

[HETvet]

Check crank shaft for groove! Over this that seal WILL rub a groove in to the crankshaft. If/when that happens and you develop a leak, you will never get it to fully stop leaking. at that point your looking at a possible crank replacement.

 

[Drock]

The original seal is a piece of rope. Mine leaked a little at first, then let go big time. When I pulled it apart the pieces of rope that were left would disintegrate between your figures. You mite want to mark it on your calendar that you'll have to replace it in another 30 years.

 

[Mg84648]

Like Will said, look high first. Probably 50% of our "rear main" leaks are misdiagnosed IP leaks. The throttle shaft seals weep into the valley back to a drain hole that exits just above the camshaft plug. Along its journey down to the crank shaft seal area it picks up 30 year old dirt and grime and no longer looks or smells like diesel. It will accumulate or drip from the flexplate cover and certainly look like dirty oil.
If this is the case then you probably have hard starting issue also?

 

[Abbylind]

If you notice the leak while the engine is running its most likely the IP pump seals. The O rings on the IP accelerator shaft dry out (especially if the truck sat) they leak down the center gallery the out the back of the engine when its running.

 

[cucvrus]

Rear main seals leak when the engine is running also. That analogy is poor. I don't think the oil sets in the pan that deep that the rear main would leak when parked. And if the throttle shaft seals are leaking that bad the driver will have other problems also. Hard starting and a burning eye sensation from hot fuel. Have a great day enjoy the nice weather. Winter is coming on fast.

 

[Abbylind]

"Rear main seals leak when the engine is running also. That analogy is poor. I don't think the oil sets in the pan that deep that the rear main would leak when parked. And if the throttle shaft seals are leaking that bad the driver will have other problems also. Hard starting and a burning eye sensation from hot fuel"

Sorry didnt mean to step on any toes, just passing along my experiences . Mine ran OK just leaked fuel out the back of the gallery. I traced it back to the IP pump. Replaced the O rings solved the problem! Maybe I leave the diagnosis on this one to the experts...

 

[cucvrus]

Your not stepping on my toes. No problem. I have steel tips on as much as I take a beating. I understood your statement was wanting to make sure others not so knowledgeable get the point also.

 

[Chaski]

Double groin kick.
1) My 6.5 crate has a one piece main seal, have to pull the engine or the transmission to do it.
2) Main bearings look ugly - real ugly.

 

[cucvrus]

I would pull the engine anyway. It makes the whole job easier and you can go wild and change everything while you have it out. It is always less expensive and trouble free to do the job right the first time. More work? But once and done. Get an eyeball on everything. It's a simple task.

 

[Chaski]

Got it back together and drove it today.

New rear main seal
New main bearings (std & .013mm under)
New rod bearings (.026mm under)
New fan clutch.
Put my other rebuilt transfer case in.

The TM and parts listing saved my bacon on the odd sized bearings. A short evilbay search with the correct part numbers got me the bearings I needed. A little over .002" clearance on everything, slightly more oil pressure than before.

Also I splurged and got ARP 3/8-16 bolts for the adapter to transfer case (1.25") and bellhousing to engine block bolts (1.5"). I had broken the bolt that secures the transfer case support rod, if I do it with the ARP bolt I must be doing something else wrong. About $3 each from Mcmaster Carr.

So if you have a reman or crate 6.5 in your rig identify what seal it has before you tear it apart...

 

[Hank Baer]

Very helpful info, thanks to all.