Just bought a 1999 XK8 ragtop with 60K miles. After getting comfortable with it, I took it up to around 160 m/hr. Shortly after starting having the coolant problems. first noticed a white chalky substance in the coolant, and then noticed the prev owner had added green coolant on top of the orange. Later we determiined the chalk was engine sealer and suspect there had been some undisclosed trouble before they sold it. Saw a spray of white chalky near near the water pump, changed the pump, changed the thermostat housing to aluminum, new thermostat, new thermo sensor, new coolant sensor, new radiator hoses, new pressure cap... Now car runs fine, but continually looses coolant through the overflow. Checked the pressure on the cylinders, 180 on each except for the #5 has 130, figure there is a leak in the head gasket, no water in oil, as I fill the cooling system from the thermostat housing cap, it appears like circulation is good, nbo excessive bubbling, then fill the pressure tank and at idle no bubbles just mild circulation, then if I apply the throttle and watch, small bubbles enough to create a fine foam. Is this normal?? should I apply engine sealer to this problem like the prev owner must have done?? How much would a new head cost?? How much does a new block cost?? Please let me know what you think.
thanks in advance,
Passout Pete

 

I'd seriously consider doing a very thorough flush of the radiator system, maybe even do it twice...with some special cleaner added, if there is such a thing. Bubbles and foam are obviously leftover remnants of the concoction between the green and orange martini mixer. Not sure why it would still exit the overflow of the expansion tank though...how much are you loosing?

 

Sounds like cylinder compression getting into coolant chambers. Had a cracked head in a VW diesel that would pump the coolant out as a stream but never any signs of coolant in the oil. Might wish for just a blown head gasket.

 

thanks alot for you help, I went ahead and sealed the engine with Cargo Liquid Glass and it stopped the leak for now. I flushed the coolant system 6 times with distilled water and then filled with the proper Orange, cleaned the sensor thoroughly and put 500 miles on it with no problem detected. thanks again for all your comments.
Pete