I recently switched to Mobile 1 at 100,000. Wich was about 1,200 mile's ago. Now I have a pretty good leak at what seem's like the front and rear main's. Admittatly, there was a leak at the front before, but it was fixed by the dealer. How ever, it was not this bad of a leak. I have been keeping an on the repair and hadn't noticed it when I changed the oil at 100,000. Any thought's. Thank's.

 

Synthetic oils have much more cleaning ability than dino oil. If you compare an engine that has ran on synthetic oil for 200k miles and an engine that has ran on dino oil for 200k miles, the engine that ran synthetic will still look like "new" inside, and the engine ran with dino oil will have some "tar" like buildups and will not be nearly as clean. The synthetic oils are also smaller molecules, and can seep past gaskets and seals that dino oil can't. When you start using an oil, after 100k miles, that cleans much better and gets into smaller spaces, you will probably have some leaks. I switched over to Rotella 5w-40 synthetic at 130k miles and I didn't get any leaks. This might be because it isn't a true synthetic. It is just a super refined dino oil.

 

Synthetic does leak more than dino oil.

 

If the dealer fixed that leak under warranty and now it leaks again, I think I would have to wonder if they really fixed it or just poured some stop leak in it and sent it home.

 

on the leak repair its a bad deal... most of the time....my buddy has 04 rubicon w/55k on it, his rear main started leaking, took it in they has a S.B. on it so they fixed it for free! no dedutable one week later guess what? its back! the deal is they replaced the failed seal w/ another same type "factory" seal ...when it fails it usually cuts a little faint groove in the shaft (all the old gasser guys probably remember the micro sleeve for the front seal on a 350?) thats why felpro uses a doubel lip in place of most factory singel lip seals to move back on fresh metal....but its not OEM they wont install it under warrenty

of my soap box now!

 

I have not had any significant problems with synthetic oil causing leaks. Our Chevy van has 106 K and is dry, the engine has never been washed. So far the Dodge has no leaks at 18.5 K. It also has very low oil consumption less than 1qt in 12K. None of my power equipment has had seal or gasket leaks. My old Peugeot does drip a bit (from the head gasket) but it's total oil consumption is less than 1 qt in 5-6K miles. I have been using it since 1979 in most of my vehicles, could never use it in the 6.9IH due to lots of oil consumption (>1quart/1K). It had about 50K on it when I bought it and the oil use pattern was already established. I had a 7.3L IH that was tight and stayed tight with synthetic.
I ran it in my chev 454 in a class A MH for 7 years and had great performance, very low consumtion (about 6-7K/qt) and only very minor oil weeps from valve covers.
I park all of my rigs inside on conctete so leaks do not go unnoticed.

That said changing to synthetic a 100K might agrivate an existing condition due to the varnish removing ability of synthetic. I have not seen any polls on at what mileage that the Cummins typically begins to leak. Some of the long time owners could give some insite on that issue. I would hope that it would be more age related than miles but have no idea.

Front seals are more likely to leak if the rig is operated in dusty conditions. As smokin05 mentioned if the shafts get worn where the seal runs it quickly damages the seal, dust and mud speed up this process.

I hope that you get your problem(s) resolved, leaks are a PIA.

Regards,

JimB

 

I'm a fan of synth oil but when I used Mobil 1 0W-30 one winter in my 2000 gasser I noted some leaking at the front main seal. When the weather warmed up I went back to the 15W-50 (still Mobil 1) I'd been using. The leak stopped. Sure did start nice on cold mornings w/ that 0W, though.

 

The camaro forums pretty well documented this a few years ago.
regular joe's were selling 100k mile DD camaro's, and the hot rod guys were souping them up, and putting synthetic in.

the LT1's have a high internal back pressure, and they were leaking like a loose diaper.

there were long winded technical webpages that told about the smaller molecular size mentioned above, and that was supposed to be part of the problem

so yeah, i'd guess the Syn leaks better than Dino.

 

So what should I do about it. Let it leak, switch back to dino or maybe try some stop leak.

 

Hi, BRJ,

Well, you could let it leak a while and see if it stops. I guess I'll find out, too, because today, at 43K, I changed it to Valvoline Blue Extreme, which is what Cummins in Jacksonville recommended if I wanted synthetic. The local Advance Auto guy said they'd start carrying it if I'd buy it from them.

This oil was supposed to have 5500 miles on it, and it came out very CLEAN. The fuel filter, though, was nasty and blackened.

NOBODY in this little town, including China-Mart, is carrying the Mobile One Truck & SUV, or I would have gone with that.

 

I was told or read that synthetic oil doesn't make gaskets expand like dino oil does. Not sure if this is cork or neoprene dependent.

I'm guessing that synthetic doesn't clean any better than dino. However, it never produces the tar, gunk, varnish in the first place because it has very little friction and has a very high burn temp. Then gunk never forms.

 

Before jumping back to dino, I'd try another brand of syn oil first. There are lots of 15W-40 diesel syn out there waiting to be tried. Nothing to lose, other than large spots on driveway.....

Been there done that with syn oil finding leaky seals. My old volvo never recovered.

 

It has been my experience that oil leaks tends to leak oil. If it leaks one type more than another...it's largely a temporary condition that will be rectified......... as soon as you switch back to old faithfull...it will start leaking too.

Joking aside...are you running M1 in a CTD?

 

After reading your post agian...it's not the oil. I've run M1 in every vehicle I've owned (except my CTD), some well over the 150k mile mark. An oil that can't deal with soot as effectivey as one that carries the rating, will not eat your seals.

 

I'm using the "Mobil 1 Truck and SUV for gasoline and Diesel engine's".

Are you guy's saying there is something wrong with this in the Cummins.