Advice Needed- '76 Mercedes 240D (OM616) Oil Leak + Blow by

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Greetings,

I recently purchased a '76 240D Automatic. The car has 157K miles on the odometer and has been reasonably well cared for (the first owner for 35+ years was an lady who drove it locally). The car has no rust, is beautiful and really made me want to own and restore it.

Aside from rotten window seals, the car's only issue is oil blow by and associated oil leak. (See video of the dancing oil cap test I recently did).

https://www.youtube.com/watch?v=sxIhj7KDb6Y&feature=youtu.be

I just drove the car from the East Coast to the Mid West, over 1000 highway miles, with 2 Bottles of Auto RX mixed with Rotella T engine oil + new filter. I also used Diesel Kleen for each diesel fill up. The car ran well but loses about a quart of oil approximate every 300+ miles.

I plan to run the Auto RX for another 2000 odd miles, as instructed, before swapping out the engine oil but thought I'd ask for any suggestions before I continued on. Should I be worried with that rate of oil loss? Should I top up the Auto Rx in the same proportion as the oil that I replace? All experience based advice is welcome!

 
Originally Posted By: Screwdriver
The car ran well but loses about a quart of oil approximate every 300+ miles.


Blue smoke, or marking your territory wherever it's parked?
 
Will replacing the liners solve this issue? I guess I'm looking for best next steps and am not the most mechanically inclined
 
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Originally Posted By: Screwdriver
Marking my territory. Hardly any smoke outside of a small white puff on start up


Ok, then -- here's the solution.

http://amzn.com/B000NVW1LM - You'll need two bottles.
Mystik JT-8 15w-50 - This will be available locally at attractive pricing, and provides the additional viscosity that's welcome here.

Keep using Diesel Kleen, but stop with AutoRx -- you're wasting money there.
Report back after the change.
 
157K seems like very low mileage for a Mercedes Diesel to be worn to the point of needing a full overhaul. I would get the valve stem seals changed first. This can be done with the head in place and the originals are likely hard as a rock by now. I changed them on the OM617.951 that I had in my '81 300SD about 12 years ago and the originals were very brittle and certainly not doing their job any longer. I do remember that my oil consumption dropped after this.

Andrew S.
 
I wouldn't bet on valve stem seals with the oil coming out of the engine and hitting the ground.

That will come down to either a very effective sealer, or more appropriately, a set of new gaskets or seals wherever the leaks are coming out.

Where the dancing oil cap is concerned, the first thing you want to do is make sure that you didn't end up with burnt piston rings due to a fueling issue, and the next step is a rebuild. The rebuild will solve all of your problems you have.

It's not a cheap or pretty deal, but there's likely not a way around it.
 
Originally Posted By: DoubleWasp
I wouldn't bet on valve stem seals with the oil coming out of the engine and hitting the ground.

That will come down to either a very effective sealer, or more appropriately, a set of new gaskets or seals wherever the leaks are coming out.

Where the dancing oil cap is concerned, the first thing you want to do is make sure that you didn't end up with burnt piston rings due to a fueling issue, and the next step is a rebuild. The rebuild will solve all of your problems you have.

It's not a cheap or pretty deal, but there's likely not a way around it.


I agree that bad valve stem seals aren't going to help external oil leaks, but they might help overall consumption like they did on my '81 300SD. It had external oil leaks and blow by as well.
 
Starts easy and runs at 70mph without breaking a sweat. No smoke. Compression test is my logical next step...
 
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Originally Posted By: Screwdriver
Wouldn't burnt piston rings exhibit more signs? Blue smoke perhaps? Hesitation?


Every time I have gone shopping for for a Ram diesel, I come across some with piston rings so smoked, that oil shoots out of the dipstick tube when pulled. Most exhibit little smoke, even under acceleration, and run like an assaulted primate.

Dancing oil cap alone is not a death sentence, however. Half of our NPRs have been doing that for the past 150k miles, and never seem to care, some approaching or past 300k miles.
 
Originally Posted By: Screwdriver
Marking my territory. Hardly any smoke outside of a small white puff on start up
That's a good looking old merc. Expect JRZH2 to comment. I think He has one of a similar vintage. Interestingly, your photo host site is blocked by Malwarebytes for adult content.
 
Originally Posted By: Screwdriver
Starts easy and runs at 70mph without breaking a sweat. No smoke. Compression test is my logical next step...

Thats a good sign right there, when these things get really tired they are hard to start cold because of low compression.

IIRC these used the engines vacuum pump to draw a vacuum for the breather (diesels don't create a vacuum like a gas engine) and uses quite a lot of hoses and connections.
check every hose for being clogged or broken and make sure the vacuum pump is working 100%.

This crankcase blowby can create pressure which can cause external leaks at gaskets and seals.
I don't have a book for this if you don't have one get one. This might turn ut to be a simple enough problem as the pumps are rebuildable for cheap money.
 
Interestingly, the car does appear to have vacuum related issues. The central locking is vacuum based and does not function on this car. That may be worth investigating but I doubt it could cause such substantial oil loss, could it?
 
Sure it could. I uses vacuum created by the pump to draw the gases out of the crank case.
If there is no vacuum pressure can build and force oil out of gaskets and seals.
You dancing cap indicates there maybe some pressure buildup that is more than the openings themselves can overcome without the help of vacuum.

Seeing as there is a lot of vacuum operated controls in this car inc the door locks any issue could indicate a bad or weak pump.
Check it out in the service manual, i only have basic data for this car not the actual manual, the ones i have start a little later than yours.

BTW Look at the lines and hoses going to the oil cooler, they are usually a braided hose, they have a habit of leaking when they get older and can be a source of the sort of consumption your having.
 
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