I am a wee bit embarrassed to ask ,, still new to the Benz thing. Spent alot of time reading the forums going back through them has saved me costly mistakes , time and money. But I keeping reading a thing called bad heads cracking or blowing head gaskets. I have a 1987 300 SDL 350,000 km on it, and my question is which heads are prone to having problems,, what kind of problems and is there a model / year that a counter measure head was made,,, some have mentioned # 14 head,, and so on ,,,is there a fix?,, My goal is to keep the drive train , basic and original,,no upping the boost,, stock air filter housing etc,,,I have rebuilt 5 Chrysler heads 2.5 turbos,, warpiing cracking the best cure was the mod 1988 head with better water cooling passages,,,I ain't afraid to get my hands dirty, but sure like to know the info before I mess it up How can I tell if I have a bad head ( puns welcomed,,I am old enough to have a bad head,,2 heads are better than one lol ) and or should I plan on getting a back up head ? cheers Dave D.

The original head on that engine was the #14 casting. You can verify that if you look for the raised numbers directly above the #2 cylinder (obscured by the crossover pipe). The second to last group of two numbers will be "14". The last two numbers will likely be "00".

The head can last indefinitely without cracks if it was never overheated.

If it does crack, the symptoms start out very benign and are easily overlooked by the casual observer.

The first sign of an issue is the engine begins to use coolant without any sign of an external leak. Together with this will likely be pressure in the cooling system when the cap is removed the following morning after shutdown the previous night.

Depending on where the crack has occurred, coolant may appear in the oil (verification with an oil analysis) or oil can appear in the coolant (obvious by the condition of the expansion tank).

There is nothing that you can do to prevent it from cracking other than to absolutely be certain that it does not overheat. Maintenance of the serpentine belt and the water pump are critical here.

ahh good,, thank you for info will check the head number at first light Sunday,,I constantly watch the coolant temp and oil pressure ! and never drive her hard,, well perhaps I'll do one 0 - 60 to verify, stats,, thank you ps I'll keep an eye on the coolant level !!!! so far it's been good,,Cheers

You can drive it as hard as you want............you won't crack the head by doing so.

The problem comes when somebody loses a water pump, or develops a severe coolant leak. This engine will go from normal temperatures to well over 120C. in a matter of one minute under such conditions. Very few drivers will be on the gauges to detect this condition before damaging the engine.

Nothing much of a preventative measure can be done anyways. Adding a little water wetter to the coolant may or may not help. I have no opinion on that.

Another thing I have observed. The head casting hardness of the aluminium seems to vary. This has been reported by one member testing various heads at one time from these engines. I cannot comment otherwise either on that.

That said one thing that is never mentioned but should be thought about. A running engine has or develops local hot spots. Before turning the engine off it does not hurt in my opinion to let it idle for a few minutes to equilise the temperature and reduce it slower than otherwise in the hot spot areas. if present.

Also this allows the oil feed to remain on the turbo bearings until the turbo spools down. There will be less potential coking of the oil. Instead sucking heat away from the bearings and bearing seals. As the turbo winds down.

I think if I owned one of these engines I would make a small cool down period a general practice if the trip length was long enough that the engine had really gotten warmed up.

Another factor to consider is that the block being cast iron and the head aluminium may enable a more controlled even contraction of the overall head with a small idle run before shutting down the engine.

Where the cracks appear on these heads is not really random. The location of them might be consistant with too rapid expansion and contraction in relation to other metal in their proximity. Especially if they are a hot spot.

All that would result in my opinion by running these engines a little hotter than they should be is perhaps more stress in that area between the valves during the cool down period especially.

These ports are not far apart either. So a consideration has to be the influx of cool air into the intake and really hot air leaving through the exhaust port. But this is just an item that may add or subtract from things.

If a bubble in the coolant were to form or develop from that overheated area with fast shutdowns or hotter engines at shutdowns . That could do it easily in my opinion. The stresses then could go way beyond what they should or otherwise be.

How this engine has been used may contribute in some way as well. Theretically is a lot of short trips over the years versus a mix of short and long etc. The aluminium in that area just might eventually fatigue out.

Sorry for the long response. Especially since there is no way to really prove this easily. Yet it still will not do any harm, Even if what I think is totally wrong to let the engine idle for a minute or two before shutting it down in my opinion.

Good information I will address these items,, as for hot spots in head it is a valid point,, one the the big ones is trapped air pockets some heads will boil the coolant near the exhaust outlets . bleeding the head is something I do on the motorcycles,, difference in thermal expansion rates of block to head in my turbo Chrysler resulted in premature failure of head gaskets,,, in the 60's we used pure copper head gaskets on turbo bikes,, better heat transfer cooler heads,, and running 10.5 compressions copper gave use better sealing. I forgot about the cool down thing,, very good point,, will do !!!
one thing I ran into on moded bikes with turbos in the 70's,, after the oil leaves the turbo we had to use a large diameter oil return line in to sump,, the bearing and speed of the turbo would froth / whip up the oil and create bubbles.. we added stainless steel wool or wire mesh,,at the end of the return tube to break down the frothing,, net result was good constant oil at pump pick up point,,no cavitation due to bubbles in the oil ,,

I planned for a backup head - got another #14 sitting in my driveway.

I also have an example of a cracked head showing where cracks appear. (You can have this one for free!)

Came across a local seller of a car with the coveted #22 head (MB rebuilt motor!). But the guy was running green coolant and had already replaced the coolant pump, and was making a habit of checking coolant level... with leaks out the front. Hmm... passed on that one. Because the rest of the car was in POOR condition. Obviously not a maintainer.

If you've lurked enough, you know green is the devil color for coolant in these cars.

Dave, what part o' Canada are you in?

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Cheers!
Scott McPhee

1987 300D

Cheers I am in Cambridge Ontario,, noted that your from Edmonton,, was there in 71 to 75 went to NAIT,, drove my 62 MGA in the winter there ,,,and yes it did start every day without block heater,, got to love the manual chokes,,, new batteries are a must there,,do you drive diesel there in winter ?

Personally, I don't think that the green coolant is all that bad. All modern cars have aluminum and plastic in the coolant loop, and enough have aluminum, plastics, and iron that any coolant you can buy today will be compatible with cooling systems containing all three of those things.

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1984 300D
Euro spec, 5 speed
217,000 miles

Heck ya! This car starts at -20C without even plugging it in. Glow and go! The battery is probably a 5 to 6 year old MBenz brand battery... was in there when I bought the car a few years ago. Really impressed with that thing. ' course, now I say this it will go flat tomorrow I should go check the date code on it.

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Cheers!
Scott McPhee

1987 300D

lol and I was worried at the -10 C temps,, and I just bought a timer ,, 20 amp extension cord re block heater, for the Benz !!! oh well good to know yours is a cold stater,,, have you considered welding up the cracked head? Some bikers have done it but not sure if it works long term.. depends on location ? non iron heads too . I tell you how naive I am about diesels for the first week I had no idea what the glow plug light was for but she started up right away anyway.. :} and 6 months later I was told how to turn the fog lights on !!!! who would have thought of pulling the switch out !!!! well I'm learning ,,,

This website will teach you more than you can possibly imagine...........you will get to the point where your knowledge is greater than most any local mechanic...........unless he specializes in these vehicles.

Like any other mechanical device, they require the technician to learn their maintenance, repair, and operational procedures. However, once you get ahead of the curve with them, they provide years of service without excessive attention.