Have been discussing the root cause of failure of head gaskets on TD5's
One suggestion was that some sort of heat cycling causes the heads to lose tension and allow a loss of tension. (Okay . if this was plausible.then how would it manifest itself , what would you expect to see ?)
MMM ,interesting Failure mode , Head bolts lose tension (?)due to alloy head heat cycling loosing overall height (?) Expansion rates of Alloy (silicon content ?) versus carbon steels . Therefore one could ASSUME that all engines with alloy heads held down with Steel bolts/studs would suffer this problem ? Interesting !!!
Would love to see from all those that actually had a failed head gasket , what the observable symtoms were .(from careful examinaion of the head gasket and mating faces )was it in the same place or in the same areas ? Not interested in what was bubbling or leaking or overheating , just interested in the actual gasket failure , that being a likely consequence of many and varied reasons of water loss or coolant breakdown , incorrect tensioning , operator abuse , bad fuel , etc etc.
So all you TD5 , owners , are you indeed resigned to the fact the your head gasket will fail and the only way to prevent the unwanted consequences is to replace it , if so at what interval ?

The main cause for head gasket failures on TD5s is overheating, you really only need to overheat it once or twice and that will do it, just like any alloy head motor, motors with alloy heads seem more sensitive to high temps.

Could have something to do with the different heating and cooling temp rates between the cast block and alloy head

Baz.

__________________
2011 Discovery 4
Redback Country Camper Trailer.
1973 Kawasaki H2 750
2009 CRF230L
2002 TTR250R
2001 XT225 Sero

We swear by the Southern Cross to stand truly by each other and fight to defend our rights and liberties.

From my engineering days the expansion rate of aluminium alloy is 2.5 times that of cast iron, steel is similar to C.I. I imagine that is why modern head bolts are so critical, they are effectively spring steel. Horizontal movement of head gasket fire rings is what I have observed in older alloy head petrol engines that have no signs of overheating. In V8's with blocked bypass water flow the thermostat can swing wildly over 15C twice a minute, and can wreck head gaskets in as little as 3 months.

Without knowing the usage of an engine, a city based short run commuter's head gasket would fail way before a long distance country car because of more heating/cooling cycles.

MY TD5 head gasket failed between # 5 and the water jacket.
IMO caused by the plastic dowels. Allowing the head to creep pressurising the cooling system. This engine had never been overheated.
The arguement that dowels are only to locate when assembly takes place is all well and good, but.... every other motor I have worked on has had nice big steel dowels which aid in keeping the head located.
Secondary cause, again, IMO those long head bolts were not properly torqued at the factory. No proof of this just a theory based on the other bolts ie. oil pump not being correctly fitted.

cheers.

You are correct about the overheating being the main cause. TD5's are actually better designed than most alloy head engines, as the bolts go right through to the bottom of the engine, and the bolts are placed adjacent to oil ways, so that the temperature of the bolts reflects closely that of the engine as a whole, thus reducing differential expansion and reduced bolt tension.

Cheers,

Lionel

Ah ha , someone actually has an example of a "Blown: headgasket , as per Mr Strangy .So did it blow out the fire ring , or blow under or over the gasket and into a water gallery ? Is number 5 cylinder the rear cylinder ? (Wont make any basics assumptions yet) When looking at the heads clamping design , would there be any reason why the gasket would blow in that area ?
Im not to sure about this alloy gets heat cycled theory , its not very scientific to say the least.
Ive built many 400 to 700 HP engines nearly all with Alloy heads , with BMEP's up to 5 times greater than a little diesel and have never seen or experienced this Phenomena .(unless as Redback has said , there was a significant temperature excursion .Head gaskets were always seen as the safety valve , and were vitually sacrificial .Them steel dowels or any dowels are only for correct alignment , they have no effect on the Clamping ability .

No 5 at the back of the motor.The passage of gas was between the top of gasket and the head, about 10 oclock when looking from the front of the engine (towards the firewall) Into the water gallery. IMO there is no more or less clamping force available here than anywhere else. As in the previous post, sure dowels have no impact whatsoever on clamping, but in the case of mine I could see the sealing area associated with all the fire rings had suffered some fretting from movement from the head. Had there been positive location, I truly dont believe it would have failed.
It was a matter of "when" rather than "if", a total failure occurred. The remaining 4 cylinders were ready to fail in the same way with the passage of time. Horizontal movement was obvious.
Why did # 5 go first?
Who knows. Maybe the rear dowel failed first allowing a little bit more movement at that end. Incidententally my chip went in after the head gasket change, so has no bearing in this case.
In my case I cant find any reason other than a dowel or bolt combo.

Interesting this thread came up now because I am finishing off the head rebuild on my Mitsi VR4
I dont see it designed or built any better or worse than the TD5 but I can assure you it gets hotter than the TD5, but there was no evidence of head moving longitudinal to the block like the TD5. The TD5 is the only head I have seen display this.(doesnt mean Im right)'. They have a 15mm hollow steel dowel. The bolts are 1/3 of the TD5 length.
Maybe LR knew something by changing to the steel dowels in later motors.
Now I can only speak for an earlier motor 9/00 build. perhaps some data on year etc is also important.

So make of that what you will.

Cheers.

of all the cooked td5's ive seen about half of them have overheated for an external reason, (blocked radiator, stuffed pump, thermostat, cracked tank, blown hose) and then taken out the head and the gasket.

the other half leave it as the age old chicken and the egg situation. Did the cooling system do something to let it over heat and then it took out the head gasket OR did the headgasket let go and take out the cooling system?

my personal feeling on the head gasket failure method is loss of clamping pressure after a short shutdown when the head gets a quick cooling(relatively by the coolant thats blown of temp in the radiator cools the head and allows the fire ring to be attacked at the edge by the combustion process. Over an extended period of time this gives you your weak point in the fire ring seal and then the gasket or head (more often both) gets scoured out along the line of least resitance.

__________________
Dave

"In a Landrover the other vehicle is your crumple zone."

Fozzy, 2.25D SIII Ex DCA Ute
The midlife crisis car
Some D1

For spelling call Rogets, for mechanicing call me.

Where is JC

WEll it seems that there is no real defintive root cause for head gasket failure , that arent a result of some sudden temperature excursion from what I can understand .
So is there a range in Kilometers hours , use that would be deemed acceptable ? Say 200000 Ks plus is an expected life , 300000 is lucky and 400000 is impossible ?
Its a Pity we cant get more examples of truely blown head gaskets , just to make sure there isnt some inherent design issue /
HAs anybody heat gunned the engine carefully front to back to see if there are no hotspots or areas with sustantially more heat than others . ?