I pulled into a drive thru to get some coffee after work tonight and steam was coming out from all around the car. I had been driving about 40 minutes and the temp gauge was in the middle where it always is so I know I didnt overheat. I pulled under a streetlight and all around the expansion tank cap was wet and the top front of the engine right behind the cap was wet. I couldnt find any leaks or dripping at any hoses. Could the expansion cap be bad and is not holding pressure causing antifreeze to leak and spray back and make all the steam? I slowly opened the cap and there was no hiss or pressure release so I know the system isnt pressurized. I have never had one of these go bad before. Do these caps fail like this? I will change the cap and if it continues to do this get the system pressure tested. I'm hoping it is the cap, has anyone ever had this happen?

 

There is a small hose that leads to the top of the expansion tank. The nozzle where the hose connects to the expansion tank breaks and leaks sometimes. Could explain your symptoms.

 

+1 for the crappy plastic expansion tank breaking/cracking at the vent hose.

I was really hoping someone would have come up with a nice improved design retrofit, but so far seems not. I had to buy and fit another crappy plastic tank, which I'm sure will break again.

By the way, the temperature gauge, if its the same as the previous cars does NOT show the actual engine temp....... it is pegged to the middle spot and once it starts to move upwards, it's usually a really bad sign (like the engine is already overheated)

If you look up "realgauge" on the XK sub-forum you will see a nice mod one of the members came up with for the older cars

 

Thanks guys! Expansion tank is fine, hoses are fine too. This morning with everything cold I noticed the RH front upper hose( I think it is the intercooler return hose 2" OD )was collapsed when I opened the cap There was vacuum and the hose popped out to normal. Isnt the cap designed to work the opposite way? Let air in when cooling and hold air to approx 16psi when heating? I looks like the cap is sealed when cooling and was spurting antifreeze when hot. I am going to install a new cap just wondering if any of the members have had this experience before.