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thegats1 · 07-12-2021, 06:59 PM

OK I admit I have no clue if I am even able to ask this question properly.

I have a 2019 Tiffin Allegro Red 340 that has a Cummins ISB6.7 with a Allison 2500MH. It was bought new in August of 2020.

It had a very small oil leak from Day 1. While in Red Bay getting some warranty work items taken care of, they looked at it and referred me to Cummins Coach Care. Again, it is a very small leak that only leaks while the engine is operating. Once the engine is off, it leaks about a 1/2 or maybe a full teaspoon on the ground then stops. Until today, I could not tell where it was leaking from. Mainly due to the wind blowing the oil backwards and dirt accumulating all over the area. Doesn't help that there is spray on insulation all over the place giving a nice texture to an otherwise smooth engine surface. Never has caused an issue with engine oil level.

OK, I called Cummins here in Houston. Apparently they are busy. Waiting on a call back. It is under warranty. In the meantime, today I crawled under there and cleaned the entire area with brake cleaner and rags. Got it nice and clean. Ran it for a while, drove it around the storage lot. It took about 45 minutes for it to appear.

There is a part, that I believe is the transfer case between the engine and the transmission. I suppose it gears down or up, not sure. The oil is coming from the mating area of the transfer case and the transmission. It is ever so slight, but it does appear and does "flow", although very slowly. In looking at the engine, transfer case, transmission, and all supporting systems around it, there is no way it would be a good idea to separate all of this to reseat the transfer case to the transmission (my opinion). Seems I'd be opening a whole other can of worms with more leaks sure to follow.

My questions are the following:
1.) Is this component that connects the engine to the transmission in fact a transfer case?
2.) Am I thinking correctly that it isn't worth fixing unless it is a larger oil leak (given the scope of the job)?
3.) Is there a fixed quantity of oil (like many vehicles) in the transfer case where I need to worry about the level? I'm concerned this may be a fixed amount and now could be low. See #4 next and why I'm thinking it may not be a fixed reservoir of oil in the transfer case.

4.) There appears to be oil cooler inlet and outlet lines coming out of the transfer case. Is this circulating only transfer case oil? It doesn't seem like a large volume of oil in the transfer case to justify pretty large diameter oil cooler hoses, so I am wondering if all of the engine oil flows through that cooler. Not sure that makes sense either.

Clearly I'm not a mechanic. I know enough to be dangerous. Thanks for any help offered.

Tom

**Lt Dan** · 07-12-2021, 07:12 PM

There is no transfer case on these engines. What you are looking at is probably the bell housing that encloses the torque converter for the transmission. It sounds like what you have is a leaking "rear" seal for the engine. Keep in mind the engine sets in the chassis backward so the seal toward the front of the coach is actually the rear engine seal. It could also be a front seal on the transmission and Cummins should be able to trace it out.

Bruce Anthon · 07-13-2021, 07:20 AM

In my experience, if the rear engine seal or front transmission seal is leaking, the oil leak is most prevalent coming out of the inspection hole at the bottom of the transmission bell housing. On my coach the leak at the joint between the bell hosing and engine actually came from the valve cover gasket. The engine slopes slightly from the rear to front of the coach. The valve cover gasket leaked and the oil pooled at the back of the head and then ran down the back of the engine coming out at the bottom between the rear of the engine and the transmission bell housing. It was very hard to see from the bottom of the coach. When I opened the bedroom engine access panel, it was easy to see the path the oil ran from the top of the engine.

All leaks no matter how slight need to be investigated. Whether you fix it or not, you need to know for sure what fluid is leaking and why. Since it has done it from your first day on, it might be something as simple as a hose connection, leaking sending unit, etc. Being under warranty, I would be sure to have a qualified Cummins tech look it over for you. It may be a very simple fix. Let us know what you find out. Good luck!

jacwjames · 07-13-2021, 07:52 AM

Need to get it fixed as it will only get worse.

If the rig is still under warranty I'd let Cummins take care of it. Don't let them blow you off, they may make a general comment that "this is normal".

twinboat · 07-13-2021, 07:55 AM

What Bruce said !!!

thegats1 · 07-13-2021, 08:36 AM

Quote:

Originally Posted by Lt Dan

There is no transfer case on these engines. What you are looking at is probably the bell housing that encloses the torque converter for the transmission. It sounds like what you have is a leaking "rear" seal for the engine. Keep in mind the engine sets in the chassis backward so the seal toward the front of the coach is actually the rear engine seal. It could also be a front seal on the transmission and Cummins should be able to trace it out.

Lt Dan, yes it does appear to be the mating surface between the torque converter housing and engine (bottom). I incorrectly assumed the torque converter housing as a separate transitional piece between the engine and transmission. I guess it is sort of, but the torque converter is obviously part of the transmission. I now see and understand why your first inclination was the rear main seal. Although there are potential other sources (as mentioned by Bruce Anthon above), I suspect it is the rear main seal. Will be nice if it were something simpler.

Today I will chase Cummins down. I don't believe they are avoiding me. I understand they have a single scheduler and he is swamped (according to the nice lady that answered the phone). I may just have to hop in my truck and drive the 26 miles and go in person to discuss this.

I posted a pic showing the location of the leak. No oil in the pic since I wiped it off yesterday while troubleshooting. The engine has to be running and I suppose oil has to be warm before it appears.

Tom

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wolfe10 · 07-13-2021, 08:43 AM

Yup, if engine oil (black vs clear and red if from transmission) it is the engine rear main seal.

thegats1 · 07-13-2021, 08:59 AM

Quote:

Originally Posted by Bruce Anthon

In my experience, if the rear engine seal or front transmission seal is leaking, the oil leak is most prevalent coming out of the inspection hole at the bottom of the transmission bell housing. On my coach the leak at the joint between the bell hosing and engine actually came from the valve cover gasket. The engine slopes slightly from the rear to front of the coach. The valve cover gasket leaked and the oil pooled at the back of the head and then ran down the back of the engine coming out at the bottom between the rear of the engine and the transmission bell housing. It was very hard to see from the bottom of the coach. When I opened the bedroom engine access panel, it was easy to see the path the oil ran from the top of the engine.

All leaks no matter how slight need to be investigated. Whether you fix it or not, you need to know for sure what fluid is leaking and why. Since it has done it from your first day on, it might be something as simple as a hose connection, leaking sending unit, etc. Being under warranty, I would be sure to have a qualified Cummins tech look it over for you. It may be a very simple fix. Let us know what you find out. Good luck!

Bruce, is the red plug in this picture I posted above the inspection hole you are referring to? I'm not necessarily planning to do this, but it seems to me the red housing should be empty correct? If so, then removing that plug should reveal no fluids. The mating occurs within this housing, but I don't believe there are any parts needing lubrication in this housing. Anyway, I am not confident enough to remove this plug to test my theory. Wondering if this is what Cummins will do. Thanks for your help.

Bruce Anthon · 07-13-2021, 09:19 AM

Yes that is the inspection plug. You can remove it to check, but I would wait and have cummins look it over. A trip to the shop to talk to them and setup an appointment may be time very well spent. You need to get to know your local service contacts… especially with DEF and DPF units. You can print a picture of this to share with them. Let them tell you what it might be. It will also give them an idea of which mechanic they would want to assign the job to. The picture you sent is perfect.

thegats1 · 07-23-2021, 09:40 AM

Coach is at Cummins. They have verified the rear main seal is leaking. Will be replacing it under warranty. Big job. Hopefully I will have it back next week and running correctly. Thanks for everyone's help diagnosing this. I had no idea how serious this was. Thought it was a simple gasket leak.

vito.a · 07-23-2021, 06:18 PM

This is a big job. To repair a rear main seal leak they will have to remove either the transmission or engine, which ever is easiest.

thegats1 · 07-24-2021, 04:46 AM

Quote:

Originally Posted by vito.a

This is a big job. To repair a rear main seal leak they will have to remove either the transmission or engine, which ever is easiest.

Yes, they are removing the transmission. To me it looks like they won't have to do anything from the top. I'm hoping they won't need to access the engine from the bedroom.