Oil leak after 120 miles with a synthetic blend, - PeachParts Mercedes-Benz Forum

BoostnBenz · #1 03-23-2003, 08:39 PM

Hi all,
I put a synthetic blend (Castrol Truck 15w40, CH-4) in my 83 300D (183k miles) to help it turn on those cold days, it has now became my daily driver and to my surprise today I found some engine oil under it. Looks like it is dripping off of the torque converter (rear main seal?). What do you think I should do, drain it and put some cheap crap back in there or just live with it and hope it softens the seal back up enough to stop the leak?

Applicable info:
Around 2,300 miles the car's front main seal leaked.
I have receipts showing Castrol GTX 15w40 about every 4k miles. (I was assured by the previous owner that is doesn't burn any oil (liar).)
This is my first 120 miles driving this car, it has had the oil in it for a couple months now.
It didn't leak before this oil change.

The only reason I care that it leaks is that there is good chances I'll be selling this car soon and would like to say it doesn't leak.... I'm still contemplating trying some Rotella synthetic in the 84 just because the motor in it doesn't burn, just leaks.

Just out of curiosity, how much work is required in changing the rear main seal? Would it be a motor rebuild or just a nice weekend project?

Thanks.

Diesel 924 · #2 03-23-2003, 09:52 PM

FWIW, the same thing has happened to me. I switched to Rotella SB 10w40 synthetic blend in December after the car wouldn't start with 15W40 in it. It was the only 10W40 diesel rated oil I could find. I figured since it wasn't a pure synthetic, maybe the oil leak problem wouldn't crop up. It DID make the car turn over faster but my rear main seal started weeping too, just enough to be annoying and leave a spot in the driveway. When I bought the case of oil, the distributor said that oil leaks from synthetic were a myth....that stopped years ago.

Not an old-wives tale I guess.

#3 03-23-2003, 10:03 PM

I'm sure the leak is coming from the oil filter housing, this is an easy fix. I just replaced mine the other day, and it is nice to not have it leaking anymore. As for fast starts in cold weather, try switching over to the updated starter if you havn't already done so. I did this last week, and it makes a huge difference on starting for me, even in 38 degree weather.

Steve300 · #4 03-23-2003, 11:43 PM

Thats why I never use synthenic oils (both engine or transmission). They tend to leak easily than regular oils.

#5 03-23-2003, 11:49 PM

Synthetics are supposed to swell seals and gaskets and help stop minor oil leaks if used for several thousand miles. If you have a major oil leak, then you are throwing away your money. Now that I have some of my major leaks fixed, I might switch back to a synthetic. Also all diesels will burn a little bit of oil, I don't care what anyone says. I think now that I got my leaks fixed, it should burn about a quart of oil every 3,000 miles, but I will have to wait and see.

engatwork · #6 03-24-2003, 06:52 AM

Quote:

Just out of curiosity, how much work is required in changing the rear main seal?

It is alot of work. Pull the engine, turn it over, remove the "main" oil pan (not the little one that can be removed with the engine in the car), unbolt/remove the crank and replace the seal. The rear main is like "packing" and the crank has to be moved out of the way to replace the "upper" half of this seal. I would rate this a pretty good job.

#7 03-24-2003, 09:13 AM

The main seal is a lot of work, I hope mine isn't leaking, because I was going to have mine replaced when I had the transmission replaced in my car, but the shop said it was fine

. I should know in a few days

rwthomas1 · #8 03-24-2003, 12:42 PM

Oy Vey!! Synthetic oils do not cause leaks!!! They do however leak/flow much more easily than conventional oil. If you have a leak after converting to synthetic you have three options. Fix the leak, live with it, or go back to dino. The leak was either about to occur before the change or it was very small and you didn't notice it. RT

ewstan · #9 03-24-2003, 12:56 PM

I've switched two cars to Mobil 1 15W50; an '83 300D with 150K, and an '87 300D with 170K.

The '83 leaks less than it did on dino. The '87 doesn't seem to leak more or less.

ewstan

BoostnBenz · #10 03-24-2003, 02:45 PM

I did see a little amount of oil on the outside of the filter housing this morning, so I changed the big o-ring (again). I get home and now instead of having one mediocre size puddle (overnight), I have like 7+ little drips (within a minute). So I'm going to take the cover off again and see what the deal is with this. I also looked at my 84's leak. Looks like it is leaking from this same o-ring and possibly from the little metal line in back on the bottom. I will take that cover off as well and change the o-ring again.

123c- you had to change the whole housing or just a seal? I'm wondering if my housings are damaged, this time I'm going to get real in depth with the leak see why that new seal isn't doing its job.

Sounds like if the rear main seal ever leaks it is going to stay that way!

Oh and as a side note minutes ago I was sitting here and my brother told me someone was looking at my car, apparently someone has been admiring my cars for a while now and stopped in. A local sheriff is interested in buying the 83.

#11 03-24-2003, 02:53 PM

Quote:

Originally posted by BoostnBenz
123c- you had to change the whole housing or just a seal? I'm wondering if my housings are damaged, this time I'm going to get real in depth with the leak see why that new seal isn't doing its job.

I just changed two gaskets, there is one for the oil pressure sending unit, then there is the one that goes from the housing to the block. I also changed the seals on the cooler lines into the housing. It looks like I still have a leak somewhere, but I am going to check it out today.

BoostnBenz · #12 03-24-2003, 03:03 PM

Are there o-rings on the ends of the lines?

BoostnBenz · #13 03-24-2003, 07:42 PM

Well I think I just fixed the leak in the 83, let it run for a few minutes and nothing at all came out so.... Thanks to everyone who chimed in here.

I'd appreciate any advice or experiences with this other leak too. I have a pretty big leak on the 84, starts at the filter housing with the oil feed line (light), it soaks the tranny (medium), the rear passenger side of the block is coated with (heavy) 'fresh' oil. The camshaft cover seals perfectly and the block is soaked as far up as I can see (upto the exhaust mani, only on one nut, shields, and the other manifolds are clean) and remains somewhat wet until the motor mount. Is there any way that the head can be leaking the oil out or is this just the oil feed line for the turbo? Maybe it has a VERY small hole where that bracket bolts it to the head? And if this helps, it drips onto the steering rack then whatever underneath it.

Thanks a lot.

#14 03-24-2003, 07:47 PM

Check the oil feed line, this might be where it is leaking.

BoostnBenz · #15 03-24-2003, 08:27 PM

Guess I can pull the bracket off or move it over to look, I **REALLY** doubt it is leaking at the ends, as it is such a incline. I want to change the oil before starting it up again though, may just try some delo dino this time.