Oil Leak - Odd

[swexlin]

I have an odd leak. Noticed a good spot of oil under the truck today, and looking under, I'm noticing that there is a bracket on the passenger side that bolts to the transmission bellhousing. It "appears" that this is where the leak is coming from. Also, the blowby tube is fairly wet, but never had much seepeage from there.



I checked the oil level, it is in the normal range, and smells normal (no diesel smell), so I cannot see where else this leak is coming from. I looked from the top and bottom, and see nothing. Oil filter is tight, no leakage there.



Any ideas? Thanks in advance.

 

[BHanna]

Check the valve cover gasket. If you can feel oil on the back of the head, that's probably it. Also maybe a rear main seal? You could take off the cover on the bottom of the bellhousing and get a look in there.

 

[rbattelle]

Also be sure to check the rocker box gasket (o-ring, really)! It's very common for the o-ring to be deformed slightly at the back of the engine, resulting in oil leaking down in a way that can look like leaks coming from many other places (such as the rear main).

To check it, reach all the way in the back of the engine from the top and run your hand along the back edge of the rocker box. If your hand returns with fresh oil all over it, that's your problem.

Ryan

 

[swexlin]

Ryan, please pardon my ignorance, but I'm not sure where the rocker box is? I looked in the engine from the top, and stuck my hand down as far as it could go, as everything seems dry.



Everything on top of the engine is dry as well - oil filter, lines, hoses, etc, as far as I can see.



P. S - What exactly is the rear main seal? I'm learning slowly about these trucks as it ages, so please bear with me.

 

[rbattelle]

Swexlin, sorry about that! I should've attached a link to this thread.

The rocker box is located between the valve cover and the cylinder head. Moving down from the top of the engine, you have a plastic trim piece, followed by the aluminum valve cover, then the rocker box, and finally the head. Gaskets are located between the valve cover and the rocker box, and between the rocker box and the head. [We say "gasket", but these are really more like o-rings].

Anyway, if yours is dry we'll have to look elsewhere. Can you post a photo of the transmission member that is getting wet? Is this an automatic or manual transmission?

The rear main seal is a circular oil seal that sits at the very back of the crankshaft. Its job is to prevent oil from leaking past the crankshaft when rotating. They do occasionally go bad, but it's been my casual observance around here that it's not particularly common on the Cummins trucks.

Now, we should also bear in mind that all dynamic seals leak to some degree, by design. Oil seal life is inversely proportional to leak rate, since a little oil seepage lubricates the seal, and a complete lack of lubrication would quickly overheat and destroy the seal. All I'm saying is a little bit of seepage past a rotary seal is not abnormal. Swexlin, your leak sounds excessive.

Ryan

 

[swexlin]

Ryan, thanks. I did a search, and actually found another thread that linked with what you provided. In my search, I found a few threads about people with symptoms like mine.



Looking at your photos, I inspected the engine, ran my hand down the back, looked and felt for any seepage, and found none. Only thing I could find was some seepage at the oil pan bolts, but this truck has 53,000 miles, and most of this is probably road grime, oil from the blowby, and remnants of the oil that leaked from the brass fitting in my aftermarket oil gauge from some months back (since disconnected and long cleaned up).



I have an automatic, by the way. Only thing I could see is maybe blowby form the tube is accumulating on the bottom of the bellhousing, and finally after 5+ years, there is enough for it to drip a bit.



I'm going to monitor the situation for a couple days, and see whats what. I reached up from the under the truck, found hoses, etc, and looked for wetness and oil trails, and found nothing.



This appears to be something that happens while the engine is running. Check the oil again this morning, cold, after the truck sat overnight, and it is exactly in the middle of the "safe" range, and smells and looks normal.



THanks for your continuing help and suggestions.



Scott

 

[rbattelle]

If it were me, I'd wash the underside carefully with a decent degreaser (Simple Green). Just spray on the degreaser, let it sit for awhile, and hose off. Very simple.

Then monitor it. Starting with a clean slate will improve the chances of a successful diagnosis.

Ryan

 

[macdaddy]

Ryan, thanks. I did a search, and actually found another thread that linked with what you provided. In my search, I found a few threads about people with symptoms like mine.



Looking at your photos, I inspected the engine, ran my hand down the back, looked and felt for any seepage, and found none. Only thing I could find was some seepage at the oil pan bolts, but this truck has 53,000 miles, and most of this is probably road grime, oil from the blowby, and remnants of the oil that leaked from the brass fitting in my aftermarket oil gauge from some months back (since disconnected and long cleaned up).



I have an automatic, by the way. Only thing I could see is maybe blowby form the tube is accumulating on the bottom of the bellhousing, and finally after 5+ years, there is enough for it to drip a bit.



I'm going to monitor the situation for a couple days, and see whats what. I reached up from the under the truck, found hoses, etc, and looked for wetness and oil trails, and found nothing.



This appears to be something that happens while the engine is running. Check the oil again this morning, cold, after the truck sat overnight, and it is exactly in the middle of the "safe" range, and smells and looks normal.



THanks for your continuing help and suggestions.



Scott

I just helped another member fix this same oil leak, as I went through the same thing. I short it's your Oil Pan Gasket.



All you have to do is remover the the 10mm Oil Pan bolts where you see a drip accumulating and using a generous of brake cleaner clean the threaded hole very well. Then using a good quality high temp silicone sealant fill the hole, and threads of the pan bolt with silicone.



I had the same leak on mine and thought it might be the Main Seal. I ended up cleaning and resealing all of the rear pan bolts. You want to remove the 10 mm pan bolts and clean the bolts and the threaded holes one day and allow the block to cool over night before sealing the next day.



I allowed the sealant to cure for 24 hours before driving it. The leak is seeping out around the hole. Mine quit leaking completely. When I read you thread it was identical to mine and the other member I told. If you want do a search on my threads and you'll find it.



Mac