W123 cracked head or something more nefarious?
 

First of all, the vehicle in question is a 1981 240D. I have a good cylinder head with valves waiting to be installed. The assumption is that I have a cracked head. However, I want to be sure before I tear everything apart.

1. The car consistently starts on the first tick of the starter, no matter how long it sat, how cold it is, or how weak the battery gets.

2. The car is 'fast' and revs smoothly.

3. The engine sounds healthy, the oil cap bounces ever so slightly, and almost no smoke is leaving the valve cover when the cap is off.

4. All filters are clean.

5. I drained the oil and found no coolant. I drained the coolant and found no oil.

6. The radiator hoses do not pressurize until it reaches operating temp of 80 C and I see no exhaust in the radiator.

7. When the car hits 80 C, I get a ton of white, sweet smelling smoke and the engine starts to struggle for a few seconds before stalling.

8. Brand new oil pump and full oil pressure at start up and idle. I looked online and didn't find a procedure for bleeding the oil pump. I just installed it and got full pressure right away.

I lose no perceptible level of coolant, and the engine cannot idle. I can drive it this way slowly, but the car loses almost all power and stalls when dropping back to idle.

My current view is that a crack has developed in the head, allowing some coolant into at least one cylinder. The coolant doesn't seem to reach the oil, apparently burning off as steam at a quick pace. I think if the car didn't stall, I would be finding coolant in the oil. I am also surmising that the coolant is entering the cylinder faster than the fuel from the injectors. The IP has never been timed to my knowledge and the chain shows 6 degrees of stretch, thus the fueling is retarded and the coolant is steady, leading to the stalling.

My fear is that I will do all this work replacing the head and it won't help. I am downright dreading the job because I have three other cars I'm sorting out now and keep pushing this one back.

My question is, would there be any other reason for a seemingly healthy motor to behave this way?

Part of me wants to believe I'm missing something simple here, or trying to make it more complicated than it is.

If coolant is getting into a cylinder it typically cleans out the carbon so you might be able to confirm your diagnosis by sticking a boroscope into each cylinder. Personally, the problem is so odd, I wouldn't replace the head without a more definitive diagnosis.

Have you confirmed it is getting fuel when it stalls? Does it lock up after it stalls? Have you sent an oil sample to Blackstone to test for coolant in the oil?

white smoke clouds have plagued others here and they gave up. Jimmy L had one case. It's exceedingly rare for a 616/617 head to crack, but I don't have other advice.

Actually if coolant is getting into the cylined pulling the Injectors and looking in side and at the bottom of the Injectiors might show some differeance in color.

In order to use a borescope you need to remove the Injectors, Glow Plugs and the Pre-combustion Chambers.

Head Gasket issue?

You might drain out the Coolant and save it and fill it with Water and see if the sweet smell of the smoke goes away. If the smell goes away or changes you know coolant was getting into the Engine.

Since when is it uncommon for a OM617 cylinder to crack?

I have two in my possession (one of these days I'll get around to stripping them out and junking them:o) which have cracks in the combustion chamber areas. I have replaced probably 15 or 20 OM617 cylinder heads over the years. Over-heating is the cause.

There a few threads here on the board covering this very circumstance.

http://www.peachparts.com/shopforum/diesel-discussion/373938-85-300tdt-just-pulled-my-head-need-some-encouragement.html

I have the injectors in my 75 240D now and they looked normal when I did the swap. The glow plugs also looked normal when I inspected them. I also did the valve stem seals and there was no lateral play on any of them.

Also, the car does not lock up when it stalls. I think if there's coolant in the cylinders, it drains into the exhaust pipe somehow. I only need to let it sit a few minutes before it starts again.

Start with a compression test.

It's OM617 not M617. "M" denotes a gasoline engine. "OM" denotes a diesel engine. The Germans are quite specific about this, it avoids confusion.Are you a professional MB mechanic? If you've replaced 15 or 20 that's a record for anyone on this forum ever. No one other than a person who does this for a living has even come close to that figure, and I think it's an exaggeration. My MB indie and pros here tell a far different story that yours; please don't get pissy with this- I'm just relaying what is known and true. The later engines - OM 603 and it's variants- and others- are far more likely to have cracked head issues. There are literally dozens of stories of running out of coolant and still driving for 30 minutes or more and not having head issues with the OM616/617. An iron block and an iron head means less cracked head issues.

A few things:

Many times a head gasket is blamed for engine ills when it isn't involved, proper diagnosis is the key.

What is the history of this car?

If you are not consuming coolant you don't have a leak between the combustion chamber and cooling system ( cracked head / bad head gasket ) .

The only way to test for combustion to coolant leak is a leak down test, all else is folly. This is where you pull a glow plug / injector / spark plug , put the piston at top with bolt valves closed then pump in about 100 PSI. With the rad cap off you look for the level to rise / bubble / spray out. Search my screen name and leakdown or leak down.

Generally a crack / head gasket will leak all the time though it is possible to be affected by heat so do the leak down with a hot engine.

I'd suspect the breather system is allowing oil to enter the air intake, pull the hose and have a look.

Any water in the fuel filter?

Oops, thank you for pointing out my fumble-fingers. Corrected.

I stand by my count. Most of these vehicles were of the "Well, it's a Mercedes, they run for a gadzillion miles without any maintenance" type of owners. Not all of them were OM617's. There were a few OM615's and OM616's in the mix.

I suppose my location could add to the number of these incidents I have seen. Drivers are less likely to stop when the next available place is 50 miles away in 115 F temperature. Probably 90% of the heads I replaced were in the era before cell phones were common.

From just this forum: https://www.google.com/search?q=OM617+cylinder+head+cracks&rlz=1C1PRFB_enUS651US651&oq=OM617+cylinder+head+cracks&aqs=chrom e..69i57.23381j0j7&sourceid=chrome&ie=UTF-8#q=OM617+cylinder+head+cracks+site:www.peachparts.com

From various forums: https://www.google.com/search?q=OM617+cylinder+head+cracks&biw=1280&bih=894&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwjCqf 2roabSAhVI-mMKHQNxA6MQ7AkIJg#imgrc=BWw4ra-jWLHL0M:

Pretty much forget the head or head gasket for now.

Sweet smell as you know is usually anti freeze. Yet you are not loosing any.


Make sure the valve pan vent hose is clear. Also you state the car has to sit for a minute or so before a restart. Try taking the oil filter cap off as soon as it quits and see if it restarts.

Some anti freeze getting into a cylinder while driving is not going to shut down an engine I suspect.

One other thing is perhaps a faulty operating egr valve might do this. It opens as soon as the conditions that allow it to occur. Then if it does not close when it should. Until you let the car cool down a little. The combustion gases it lets in stop the fuel from burning and you get the white clouds of unburnt fuel and quitting engine.


Part of your description does not fit a head gasket or cracked head issue I feel. Or just not what would be my first suspicion. Also if your coolant level is not dropping I would do a rethink. A leakage as heavy as you describe would probably blow the coolant out of the rad with the cap off.


Remember never to remove a rad cap on a warmed up engine without taking precautions. You could probably leave yours off or loose during a test.


Engine will not idle after getting to operational temperatures. Plus the white smoke.The egr valve operation is the big suspect to me. Just pull the vacuum line and stick a golf tee or small bolt in the line as a test. I can be wrong but this is still the first place I would go.


I have to add as another poster mentioned that it could be a lot of water in the fuel as well. Although I still would first do the egr test. Primarily it is just faster than all the work to find and deal with water as well. It is also unlikely the water in the fuel issue would have any dependence or at least less on the engines operational temperature.

great post.

Makes more sense now, thanks.

The car doesn't have an EGR valve. I'm more than willing to take the head off if I need to. What I don't want is to find that there's more to the problem. For instance, having the cracks in the block. With the car starting as easily as it does, I assume there are no problems with the cylinders or pistons.

As for the history of the car, I have had it for 15 years and done a ton of work to it. I was just about to have the steering pump rebuilt and get the car painted, expecting to get a few years without anything breaking.