FYI my #14 head is running just fine at 258K (knock on wood!)
I drive lead footed (continuous Italian Tune Up). The PO put most of the miles on the freeway. I did have the head off to replace a leaking head gasket and had it skim cut, there were no cracks and corrosion was a small amount. I was more concerned with corrosion because a friend who is a mechanic at the local dealership warned me that they see frequent head gaskets failing because of the corrosion problem, also in gassers. The aluminum gets attacked by chemicals resulting from old radiator coolant, the byproduct of the breakdown process that occurs after the fluid is a few years old appears to be the cause.
I believe that is part of the problem with failure in these heads. The other problem is graual loss of cooling system efficiency, I recall seeing gsxr's picture of water pump impeller that was half rusted and missing the blades, probably a dissimilar metals problem, swimming in corrosive fluids it gets attacked too.
Add to that a bad visco-fan clutch, lots of stop and go driving with heat load from an AC and that is a recipe for aluminum head failure.
Dieseldiehard
1971 220 (gas) 4-spd manual 106441
1979 300TD w/ ’85 turbo engine 295530
1983 300D 243280
1985 300TD 217300
1987 300D 258230

__________________
'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

Maybe I haven't made myself clear enough because you are advocating very nearly what I'm trying to convey but with one exception you have not mentioned. The accumulation of stresses, fatigue, and cycling towards the end of the road with these heads (higher mileage as opposed to say under 50K) need only to be overheated to finalize propagation of a crack. Overheating is more likely with an older cars as radiators, thermostats, pumps etc. are more likely to fail thus overheating.

All I've heard anyone say is the cause is due to overheating, and I've thought there must be more to it than that? Hense my theory!

Ouch, boy did you take that wrong! I'm sorry. From your description of the process of "just replacing the engine and not the head, I was just trying to figure out of you were going ahead and repairing the old engine as a backup. Sounds like you went ahead and tore it apart which I find admirable. To do that and spend the time you have trying to figure out Why and How is amazing.

In no way way I questioning your basis or you analytical skills or processes. Again, sorry if you felt that way. I am glad you started the thread and discussion. Especially since I own a 603 while a bunch of miles and probably a "014" head.

__________________
Alan Hamm
'87 300SDL 277K Miles
'89 560 SL 68K Miles

Side note - engines with low miles could be city driven, have lots of heat cycles, and fail at "low" miles. Conversely a high-miles engine could have spent a lot of time on the freeway to rack up the 300kmi+, have much fewer heat cycles, and still have a good head. (Right?) So mileage may not be a useful factor in estimating future crack probability.

No offenses taken! I shouldn't be so sensitive as I tend to be sometimes. I am also too much of a perfectionist and also a bit paranoid as you can see!

I have fostered a new hobby with this car and am getting a lot of satisfaction working on it, trying to understand it's falts and trying to understand ways to prevent failures. The head is a challange! If there is a way to prevent what may be inevitable, it now seems to boil down to just that, never ever overheat a 603 head!

But now I wonder, has anyone ever overheated one of these heads and never suffered any problems such as cracks?

I have never seen a temp gauge in the red, but was told it only happens once with aluminum heads, they warp, not withstanding the cracking issues that seem specific to the 603 head.
Mr. Fancy Pants said: "I have fostered a new hobby with this car and am getting a lot of satisfaction working on it" . . . . . .
Just wait till its fixed and I hope you enjoy driving yours as much as do mine!
I love the W124 diesel Turbo! That said, I do watch the temp gauge a lot, especially in hot weather while I have the AC running, on long uphill grades, etc.

__________________
'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

An interesting modification might be to add an overtemp idiot light. The 105/128C blue coolant temp switch (on 124's) can be replaced with the 105/120C gray switch (from the 126), and use the 120C portion to trigger a light on the dash. On the 124, there is one unused bulb position in the instrument cluster (left of the glow light?) that could probably work. Or we could drill a hole in the temp gauge cluster and add a nice red LED. I mean, it would be nice to have SOMETHING other than a needle moving 1/2-inch too high as a warning!

(Ditto for low oil temp, but that's more involved because you have to tee into the oil pressure sender & add an aftermarket switch.)

This is a very necessary modification, IMHO. If you are not in the habit of looking at the gauges every three minutes or so, you will seriously overheat the engine if a problem develops that you do not immediately hear.

At 3000 rpm, you have precious little time to come off the power and get to the side of the road

Every three minutes??? I often think I spend more time watching the gauges than watching the road. That was part of the fun of doing the veggie conversion-it gave me three more gauges to watch.

__________________
Keep everything as simple as possible-but no simpler--Albert Einstein

At least in our diesels, we *can* watch the gauges more than the road. In my E500, well, it's best to watch the road more than 50% of the time. And on my sportbike, ummm, let's just say you can't really look at the gauges much at all when you're going Warp 9-point-something...! That's a good way to become a large, permanently-embedded trunk ornament in a 240D, Festiva, Neon, etc. (I've learned to shift by ear and largely ignore the tach anyway.)

You're probably hosed once the engine is at 115C and climbing. If you shut off the engine it WILL go over 120C or at least the gauge will indicate such when coolant stops circulating. Dave's trick of leaving the ACC circulation pump running is about all you can do.

If you're going to add a warning light, hook it up to a strobe and smoke detector piezo speaker so it really gets your attention For that matter, hook it up to the overboost switchover valve to reduce the load on the combustion chambers. You should be able to coast to safety without boost.

Sixto
95 S420
87 300SDL

I have wanted recently to install a low oil pressure alarm system after having read where a few members here had oil pump failures and thought it should not be to hard to find a way to incorporate a pressure switch set to sound a buzzer at a pressure slightly lower than the lowest idol pressure.

Aside from a nice audible alarm for the oil, the only other critical warning device would be temperature as Dave mentions.

I cant think right off hand of any other systems so close to critical that would require an audible or Light alarm, and I dont think it's over-kill to have such an early warning system. The buzzer goes on, and you look for a place to pull over while at the same time switching the key off and saving your engine!

I think sixto has the best idea I've heard of (why didn't I think of that!?)
Easily done too. I wonder why the factory didn't add some fail-safe stuff like that? It wouldnt add much to the cost.

__________________
'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

It doesn't fit with the German philosophy of driving. They expect you to be responsible, watch the gauges, and know what is going on with the car. If you're in a situation where you need power for 3 more seconds even if it will toast the head, then they let you make that decision instead of having the car make it for you.

Giant idiot lights for low oil pressure and high temperature would be nice. But, then again, Mercedes-Benz didn't expect idiots to be driving their cars. (kidding!)

__________________
Rick Miley
2014 Tesla Model S
2018 Tesla Model 3
2017 Nissan LEAF
Former MB: 99 E300, 86 190E 2.3, 87 300E, 80 240D, 82 204D Euro
Chain Elongation References

Ya, I thought that niffty little trick with that little pump down on the firewall is great if you think to leave the key on acc.

I guess with the overheat situation you would need to have a warning come on slightly higher than the highest normal reading you would get and I wonder where the best place to install a sender would be located in the cooling system.

Whether or not a warning system such has been described would actually save your head, or from toasting your engine from low oil pressure, in time, who knows but I think it's better than having no warning system at all for idiot's like me!