My 300D was manufactured in the fall of 1986, so it probably has the #14 head, unless the PO changed it. Is there any way to visually identify the head?

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Brian
87 300Dturbo 180K #14 head still running R-12 SOLD 12/2017
02 F350 Powerstroke 180K
05 Chevy Express 1 ton w/Royal Utility box 120K
08 Infiniti FX-35 40K
15 Golf Sportwagen TDI 35K
10 Sprinter 3500 chassis with a Class A Winnebago on it. 56K

Yup. The casting number is above the #2 and #3 injectors. It will be 603-016-xx-01 where "xx" is the important part (and in your case, will be 14 unless the head was previously replaced.)

I know this is going to sound crazy, but first, a lower temperature thermostat would very likely effect the performance of the diesel engine in a negative way, as I know this to be true with gas engines, and we all know how rough our diesels run until they reach designed temperature. Second, if you were to install a lower temp TS, I actually believe this could aggravate by adding more of an extreme temperature difference allowing for greater fatigue.

Yes, this could make for a good science project for testing a theory to prove or disprove it, and it could be done but would cost $$$$$$$ to turn theory into fact.

Speaking of facts, I'm not aware any exist with the 603 head cracking as I have not seen any documented analysis published, not that they don't exist somewhere over there in Germany! And "facts" are born from theories, and with a lot of experimenting and testing before theory can become fact.

Before you can solve a problem, you need to understand how the problem originates so you may apply better solutions to correct the problem. I have little doubt that the engineers over in Germany didn't go "back to the drawing board" with the 603 head and try and understand what caused the cracking before embarking on a redesign, without doing that, why it would be like throwing darts in the dark!

There is a reason for everything occuring, just as there is a reason for these costly heads for cracking. So far, it seems to be a mystery and nobody knows for sure why but instead just except only the notion that a one time overheat will do'em in, never really ever knowing why or how it may have been avoided in the first place.

I'm throwing this idea out into this forum (mostly for fun) to see if my theory, idea, could have any merit because there are a lot of intelligent and even brilliant minds here, especially now with all the political activist having nowhere else to hang out!!!

Steve.........

Mr. FP,

Have you had the head replaced? What were the first symptoms? Did it go all at once or did you start blowing white smoke? Did you have an overheating incident?

What was (is) the repair cost?

I have noticed my SDL smoking a bit more. Pretty sure it is not the head, but it had been sort of regularly sending out modest black smoke, even at modest acceleration. I noticed this when I followed my wife driving the car a week or so ago. I know this could be any number of things. Dirty injectors, air cleaner, etc. But I am pretty sure it is the original head as well.

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

Well, count me in on the lead foot test. My '86 300SDL has a #14 head. Looks original and PO's paperwoork indicates same. I drive this car like my previous one (a 560SEL). Only time will tell. It has the cursed green antifreeze and that will be replaced soon. Right now I am more concerned with an overfueling problem that happens just some of the time. That probably keeps the temps down if nothing else. Plays heck with economy and power.

What do you mean by "overfueling" problem?

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

The head on the replacement engine is original to that engine that I bought from Cherry Auto in Toledo, Ohio.

I considered replacing just the head on the original engine in my car (I bought my car with an already cracked head) but after learning that there was an inherent problem with these early heads, buying a used head seemed to risky, and a new replacement head I was quoted was $1900 bare and didn't come with PC's cam, valves, etc. and altogether looked to be 3K. Now I understand a new bare head can be had for $1600.

So I considered buying a another 603 with good head in good running condition and paid $1600 plus ship. Since I've installed the replacement, I've logged approx. 15K miles and have had the head off recently for a new head gasket. A close inspection of the head did not reveal any faults, at least as far as the eye can tell, and since the engine runs great. Also, this engine did have the old trap oxidizer still installed?

Peter is likely correct with this theory. If a heavy foot caused cylinder head cracking, then every head in Germany would certainly be cracked. They don't drive like I do, that is for sure.

One thing that needs to be addressed is the quality of the castings. Casting any metal is a difficult operation that is fraught with risk. The possibility of getting "foreign" material in the casting is quite high. The nature of the auto industry, with cost being the primary driver, ensures that this quality level in castings is probably typical, even today. Aluminum, which is clearly more stressed than its cast iron twin, is therefore less tolerant of these "inclusions" in the casting at critical places. Expansion and contraction of the head will start very small cracking at the site of the inclusion. These cracks are of no great significance until they propogate. When do they propogate? Well, this is something that nobody knows for sure. If the head is overheated, the likelyhood of a crack propogating is much higher. Once the crack grows to a length of 1/4 to 1/2 inch, it is probably going to continue to the nearest casting edge in short order.

If you have doubts about this theory, please allow me to digress to jet engines for a moment. These machines use forged titanium discs in the front (cold) section of the engine. They are under immense loading due to the centrifugal force created by the blades. The fan disc on a large turbofan (GE CF6) must suffer a load of approximately 4 million pounds on every takeoff. This is cyclic loading. Every time the airplane takes off, the load is on and every time it lands, the load is off. The discs are subject to a life limit of 20,000 hours and then they must be thrown away because of the potential for fatigue cracking. The titanium discs are manufactured in the strictest process to attempt to prevent any foreign material from being trapped in the final product. The expense to do this is very high. However, even with all of the controls in place, and all of the expense, the process is not perfect. You all might remember the DC-10 that crashed in Sioux City, IA. This airplane had a failure of the fan disc due to a foreign body in the titanium when it was originally manufactured. The disc operated with this foreign body for 19,000 hours before it finally caused a crack large enough to propogate to the edge of the disc. Of course, the results on an airliner can be catastrophic when this happens. The failure of these discs, while uncommon, does happen periodically, and it is usually traced to a crack that has propogated from a stress point. The point of stress can be as simple as a dent from a hammer or as complicated as an inclusion in the forging when the part was originally manufactured.

So, if the process to manufacture titanium discs for jet engines cannot be completely insured against a foreign inclusion, what do you thing the process is for an aluminum head that costs the auto manufacturer less than $200 to manufacture?

Whether a #14 head cracks or whether it does not crack is going to be based largely on the quality of the original casting. If, by pure chance, the original casting has no foreign inclusions or air spaces at the highly stressed areas of the head then it will not crack. If it does have any inclusions in a highly stressed area, then it will crack. However, when it will crack is unknown. It might go 10,000 cycles before it will crack. On the other hand, if you help the crack along by overheating the engine, then the head might go 1,000 cycles before it cracks.

In the case of the DC-10, the disc was at the end of its life. If it had made it another 500 hours, it would have been taken out of service and nobody would have been the wiser. And, 150 people would still be alive today.

The redesign of the heads will add more material in the critical areas, thereby allowing any small cracks to stay small. It is likely that the small cracks still exist, however, the head will probably go the life of the vehicle without a crack propogating. There is no magic to a #22 head. The stress in the critical areas is reduced and it is likely that small cracking at the inclusion sites will not propogate for many more cycles than they would otherwise propogate in a #14 head. We categorically state that a #22 head will never crack. This is simply because we have not cycled a #22 head long enough to witness the cracking. If you ran a #22 head for a sufficient number of cycles, I'm quite sure that it too, will crack. However, it is possible that the number of cycles required for crack propogation is so long that it won't happen in our lifetimes.

So is all of your research based on analysis of the original cracked head that was in your car?

FWIW, my local Indy told me that he hates the 603 bacause they have replaced heads on some engines 2 or 3 times. Apparently something to do with the quality of the new heads or how they match up with the block.

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

I think it's closer to Doc Booth's theory about the trap oxidizer, and city-driven 603's, with excessive heat load very close to the exhaust port area.

Alan - could you get more info from your indy? Is he claiming they installed new #22 heads and had to replace them again? Because I don't buy that. Maybe they're not doing something right, because so far, everyone who's installed the new/improved head hasn't had any problems. Now if he's talking about a GASKET issue, that's a different story (i.e., pulling the new head to replace the gasket).

Next time I see him I will ask for more details. He was just moaning about the alum heads and mentioned that they had a recent car come back a bunch of times and they were losing their shirts because of the head replacement issue. And it had happened before. They specialize in these cars so I kind of listen when he talks.

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

If the excessive heat load created by the trap-ox was solely responsible for the cracking, then removing the trap-ox would eliminate the cracking problem.
Clearly with the recent rash of cracked heads, well after the trap-ox was removed, this is not the case.

There must be some fundamental casting flaws that result in the start of minute cracking around those flaws. The excessive heat generated by the trap-ox, or by running at very high power levels will cause those cracks to propogate, however, they are not the fundamental source of the cracks.

Since most of the existing #14 heads had the trap-ox at one time, they should all be cracking by now. Many are fine, even with mileage over 200K.

The trap-ox, in and of itself, cannot be the source of the problem.

The idea was the source problem was cumulative. So if the cars had the TO for 10+ years, it could still crack later because of thermal stresses 'adding up' during the first 10 years or so. Also, the TO was to be replaced every 30kmi. Some owners did not do this. There was also a procedure for "cleaning" the TO, and again, many owners had no clue and did not do this. Perhaps the long-lasting heads were from cars that had proper TO maintenance? Or they spent most of their time on the freeway, with some WOT to keep things clean? Nobody knows for sure.

It seems the fundamental problem was the original casting was simply TOO THIN. That, COMBINED with the TO, is the most likely cause. The Euro models had the thin heads too but no TO! There are also a lot of (USA) 603's out there running great with cracked heads because the owners don't know how to test them, and don't see any symptoms (yet). Check out that near-mint, low-miles 1987 300D on eBay right now in FL, and take a peek at the plastic coolant tank (note the color inside).

Alan, by all means, see what else you can find out! I bet the problem is gasket issues with a newer head. But I'm curious to hear more details.

Thermal stresses do not "add up" over 10 years. Thermal stresses that cycle, which these heads suffer from, cause fatigue in the casting over a certain number cycles. However, if it were just fatigue that fails the #14 head, over time, then it would be highly unlikely that Plantman could go 330,000 miles and Hatterasguy can go 235,000 miles with them when we have seen failures at 130,000 miles. Not impossible, but unlikely. Now, if Plantman has only 1000 cycles in 330,000 miles, that is a different story. But, how likely is that?

A much more likely scenario is that the casting flaws are an additional variable that cause some heads to crack and others to run, effectively, forever.

You ask this question as though I have zero bases, therefore I have no business questioning or theorizing possibilities! While having read the many posts here about 603 head cracking, and having taken apart and examined the failed 603 head I have, I wanted to understand how I could prevent a reocurrence with the replacement I got. As I mentioned earlier in this thread, I am not a professional mechanic, nor versed in vast amounts of data, I have not proclaimed to even be qualified, but I do have a brain! It seems logical to me that some of what Brian Carlton mentioned above is what I have been saying throughout this thread with respect to cyling, heat and fatigue. As for the rest of what he says, I hadn't considered casting imperfections, occlusions, and I have no doubts his story has merit.

It is why I opened this thread, expressing my idea, or theory, and to see what it would generate.