I recently "blew" my head gasket. I have now removed the head. I find that the coolant paths in both head and block are completely clear, but that the holes in the actual gasket are almost completely blocked. The blockage material appears to the the same material as the gasket. Neither acids, caustics or other solvents touch it. It does support a flame. The material has built up over time.....growth rings are evident.

The gasket failed at one point only. Not a clean break.....just a minor lifting allowing coolant to enter one of the cylinders.

The gasket failed suddenly and without warning. No temp faults....no wonder as the temp sensor seems to be well away from the head.

I have come to the conclusion that, over time, the gasket material has been forced to be extruded into the coolant path/chamber....some result of extremes in compressive forces and high temperature...creating a dangerous/ lethal path towards self destruction/ failure of the head gasket!

1993 XJ6 Sovereign, 4.0L. Original Gasket, 210,000 km, Australia

Good photos and further details are available.

Any thoughts /ideas would be appreciated. It is something of concern.

Peter

 

It's not unheard of, especially if the engine has had periods of extended rest.

The gasket, if original, is 17 years old.

The secret to extended head gasket life on say a Toyota Supra is regular retorquing of the cylinder head to a suitable value. Especially in the immediate months following a head skim and gasket replacement. Thereafter, once a year is good enough. Cylinder head retorquing used to be a regular part of scheduled maintenance. Then owners got cheap and lazy.

The mistake that Toyota made in the 7M/GTE was specifying a factory torque value of 58 ft/pounds. Experienced metallurgists in the community then studied the growing problem and came up with the widely accepted value of 75 ft/pounds given the characteristics of the head bolts and required clamping forces. Most accomplished Supra hobbyists with the correct special tool can accomplish a retorque in about an hour.

 

Thanks Plumsauce, you may be onto something regarding Torque, but I think that increasing torque might well make my problem worse. I always assumed that torque needed to checked as part of running in a car, or after a gasket change, to account for the gasket being somewhat squashed by the first felt effects of high temp and pressure. A re-torque would seem to make sense. However, if this process only means that a gasket is being squashed further and further, and, if the only escape for this squashed gasket material is into the coolant chambers, then it appears that this might not be such a good practice after all! I do wonder how the recommended Torque Settings are arrived at in the first instance.....could well be some guesswork by Engineers here. Do they take into account what the Gasket Manufacturer recommendeds, or do they Specify a Gasket to meet their Torque Rating? I am still worried that there is a serious design problem here.

 

Personally, I wouldn't be worried about a serious design problem on a 17y old orig head and 210,000 km. The years and miles speak for themselves.

Unless you were present when the original head was torqued down and the gasket fitted, you have no way of knowing, what happened.

You might try to hook up with one of our senior members from your city, who has a lifetime with these cars.

 

There is probably not a design problem in the Jaguar six. The increase in torque values was specific to one engine solely for illustrative purposes of the importance of *achieving* and *maintaining* proper clamping values. The first re-torque ofter a new head gasket is the most important. This is because the heating and cooling cycles have an effect on the final shape of the head gasket. For clarity, it is not possible to re-torque without first cracking the fasteners loose.

You have a 17 year old gasket. That is quite a bit different than an engine that regularly blew head gaskets in just a few years.

 

Thanks. I have now received the new gasket. The coolant holes in the new gasket are much smaller then the coolant pathways in either the head or the block....in fact they are much the same the same as what remains in the old gasket. Four holes surround each cylinder. They vary in size from about 4mm to 8mm (roughly) .....in all it's by design I suppose and must be in order to regulate the flow / pressure / pressure drops.

Live and learn !! Problem solved I hope....I hope nothing will foul these small holes and do wonder if their size is critical if they should be surrounded by a metal collar.

Cheers, Peter