i would like to know the forums' opinion as to the reason why head gaskets fail.

Because people do not follow the recommended procedure and rate of re torqueing the head bolts on engines. The Mercedes FSM is very specific about it...

Because you have a system that was meant for 15 psi at the most with a smaller turbo and you put a bigger turbo, intercooler where there was none, increase the boost to 22 psi with a boost controller that will only activate the wastegate when the set pressure is reached and not slowly either, port the heads, bigger valves and cam, increas the timing and drive it like you stole it. Also you didn't ring the block or the head nor did you use studs.

Just something I heard. Couldn't be me.

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01 Ford Excursion Powerstroke
99 E300 Turbodiesel
91 Vette with 383 motor
05 Polaris Sportsman 800 EFI
06 Polaris Sportsman 500 EFI
03 SeaDoo GTX SC Red
03 SeaDoo GTX SC Yellow
04 Tailgator 21 ft Toy Hauler
11 Harley Davidson 883 SuperLow

inadequate sealing. could be caused by not enough head bolts, too much movement between the al head and iron block, too much block flex (i'm reaching), or corrosion under the sealing surface. since we have been talking a lot about the 3.5 motors i have come up with three reasons that they might fail more than in the 3.0 motor.
1. larger bore makeingless area to seal the head against the block since both engines use same gasket.
2. the larger bore with same block casting takes some structural integrity from the block perhaps lettting it twist more. while putting more stress from more power.
3. the 350 comes only in the sdl and has a 2.87 gear in the rear, the 300's all seem to have the 2.65 allowing less rpm at a given speed. thereby more stress.

finally got the compression on my 350; 300 1 thru 4, 290 #5, 280 #6. i dont know what i might expect if a rod was bent, but these seem to be good for a place 700 feet above sea level. i am now thinking perhaps my oil rings are stuck accounting for one quart / 500 mile oil consumption. i have added some marvel mystery oil and some lucas oil treatment to the oil. any comments?

oh yeah, i think that the corroded area on the head was #6.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

I have seen new rebuilds fail in a short time due to a head gasket failure, the area between coolant and oil passageways is pretty close at some areas, in this case a 202 with a big V8, an S420 developed an oil leak out of the head.
The replacement used a Reinz gasket instead of OE gasket and it was visibly improved in the area that failed, using some copper cross hatch material that constitutes a sort of crush washer to make a more effective seal.
Using the best head gasket is very important, and there are differences!

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'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!

ok folks,i heed help,step in here.
here is my situation,i am re-assembling my last broken 3.5 diesel from a 1991 350 sdl.i have had the head tested and all is well,my problem is that the head is pitted at the surface where the head gasket blocks the coolant at the top of the cylinder,what is happening is the head gasket is not made of a material that will reject the coolant,coolant soaks thru the gasket to reach the head aluminum surface,now the alum head is the provider of the electron flow and its material gets deposited elsewhere.
at this point if i can stop the current flow from the alum head i have plenty of material left on the head to keep the metal seal ring on the head gasket from leaking the compresed gases,but if the head is allowed to erode away the metal from the seal ring surface(alum metal is undercut) then it will leak compression into the coolant.
http://www.terrific-scientific.co.uk/Topics/Corrosion/Explain/Corrosion-7.htm
sorry i havent figured out how to make this a click on site.
i do think this is one reason why head gaskets fail on the aluminum heads and need help to solve the problem.
thanks larry perkins
72 old cars

I disagree about more stress due to diff ratio.

I suggest you look into the turbo bearings as a source of oil consumption, there is a theory that the burnt oil also makes a carbon cap on pistons that reduces volume and thereby increases compression ratio, that may contribute to bent rods esp if a little water gets into the compression and Blam! I won't say if that is a factor or if some rods are weaker than others but it seems to me that rods would be uniform and that the reason for the failures is related to something other than rods?
If doubt you have a stuck ring. Witches brew lubricant might weaken the oil and you get scored cylinders. Be careful!

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'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!

Coolant is a factor in a big way, it needs to be MB certified and changed frequently! Also the copper gasket improvement I mentioned earlier might be a grounding path for electrons to reduce electrolysis, I dunno!
Take a skim cut on your head if its too deep, hope for the best!

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'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!

i may be over-simplifying, but i have heard that they can blow if you put too much oil in your system.

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1985 300D Turbo "Eunis"

I believe the topic was "why do head gaskets fail", in general.

The comparison of the 3L to the 3.5L seem to indicate that the failure rate on the 3.5L engine is higher than the 3.0L. Any data to support this theory?

Under #1 above, you indicate that the two engines use the same head gasket. Since the seal is provided by the head gasket, the bore diameter of the cylinder is irrelevant. You clamp the head to the block via the head gasket.

Under #3 above, the 300 SDL has a 2.88 rear diff. AFAIK, the 350 SDL has the same diff. Even with a taller diff, you are simply asking the engine for slightly more torque at a given road speed. This torque level remains far less than the maximum torque available from the engine. I don't see how this would relate to head gasket durability?? You are not running either engine close to maximum torque for any extended period of time.

If the engine shows good compression on all cylinders (as this one does), the chances of a bent connecting rod are slim and none.

So, what about looking at turbo seals? I believe that I've got a similar situation with the 3L engine. It consumes about 20 oz. every 1000 miles.

the M104 is known to have a head gasket problem. Even the M103 has a problem, but less so than in an M104.

Notice something about these 2 gas engines and the diesel engines mentioned earlier? They are inline-sixes.

An inline-6 has a very long block, and when the head and block are of different material, the expansion differences between the two are more emphasized, than in one with a shorter block (e.g., V-6 or V-8). And the more the relative movement between head and block, there is a higher probability of gasket failure.

I thought the 103 had head gasket problems and few made it past 100K without a fix? AFAIK, the fix was an improved head gasket that fixed the problems. I heard that 104s have that problem but I hought 103s were notorious for head leaks where you see oil in the coolant tank.

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01 Ford Excursion Powerstroke
99 E300 Turbodiesel
91 Vette with 383 motor
05 Polaris Sportsman 800 EFI
06 Polaris Sportsman 500 EFI
03 SeaDoo GTX SC Red
03 SeaDoo GTX SC Yellow
04 Tailgator 21 ft Toy Hauler
11 Harley Davidson 883 SuperLow

"An inline-6 has a very long block,"

I have seen engines which used several heads instead of one long one to fix that physics problem....

We had some MWM diesels in one of the ferries. V-12's. 12 individual heads.
Actually quite a good design. Cost of parts was a nightmare.

Poor maintainence of the cooling system, if we're talking about long-term non-HP apps.

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I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

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