howzit does anyone know if its common for the 4.0 to develop head gasket leaks in heat of the summer? last 2 summers it uses water but during the other seasons ,non lost .

 

I suppose that anything is possible.

But I would check the expansion tank cap and move on to the thermostat, before jumping to a head gasket.

Any oil in the coolant/coolant in the oil?

And don't jump to conclusions if you see some mayonnaise in the filler tube in cold weather, condensation happens.

 

An indication of a blown head gasket is pressure building up, so to check this take the cap off the expansion tank and start the engine, if there is anything from bubbles to coolant pouring out the head gasket is probably the culprit.
This may not be the problem though, the car will run hotter in hot weather thus more pressure so coolant may be escaping due to this. As translator said check the expansion tank cap to see if it's holding pressure or you may have a hose about to let go (just seeping at the moment). Check to see where it is leaking (will be a patch of coolant on the ground) after you pull up to give you an idea where it's coming from. Mine was seeping from the water pump - problem fixed by replacing that (though that would be leaking regardless of the temperature).

 

thanx very much!
greatest forum ,problems are many w/these old jags but I would not take for mine .no way.
look under a true jag and then under a true american or otherwise car to see the differences aplenty.
Great example is the gas tank ,connecting lines etc ...quality abounds everywhere .
back to this issue w/losing h2o in hot months here in dallas texas 118 last summer.
will check these things listed in order starting w/the overflow and go from there.
hope its NOT head gasket even though have a good friend ,a former jag dealer tech who is amazingly correct everytime out .He can do the head gasket w/out removing the head completely . He is able to lift enough to get the new one in and not pinch it or align it badly as he has done tons of them on the xj40's.
He too suspects hoses back to overflow and I see a bit of dry coolant actually and will check the pressure to see if thermo is sticking causing the build up of pressure[pressure anywhere is not good when talking about coolant ,hoses etc i guess] and have a feeling a hose may be the offender. thanx again!
will advise .