Intermittent Overheating UK TT auto?

[Guest w1ll1ng]

Hello,

First post, first supra. I recently purchased a totally stock UK 1994 TT auto. I have experienced 2 instances of overheating, the needle at red and other at above half at near red. I have been monitoring this since the first overheat. The first time I had the AC on the highest with car idling and went to the ATM for about 3-4 mins, I must say was very that hot day as well. On return, the needle was in the red and I immediately switched off to cool down. I did notice that all the coolant that was in the over flow tank was gone. I eventually filled rad and overflow tank back up with coolant and monitored since. No visual sign of coolant leak in engine bay or under car while car is off and on. I also did thorough driving hard tests and no over heating during between then and now.

 

Everything seemed fine for about a week and more and the rad coolant and overflow tank was more or less at the same level. Then this morning after driving to work (semi hard on one stretch only) and AC off, as I pull up, bang same thing, needle start to raise, didn't reach red but it would have though as the needle was raising quickly. I switched off to cool down. I realized once again all coolant in the overflow tank gone. After it cooled down, logically and was so, the rad coolant was gone or very low. Seems as though something triggers this overheating at once and this happens immediately as as opposed to the coolant being used up gradually.

 

There is no condensation or white stuff (coolant mix with oil) on block head oil cap, no white stuff on dip stick, no oil in coolant and the car runs good. The car starts well 95% of the time, the other 5% I need to tumble twice. The fan speed increases when throttle cables pulled constantly but must admit on idle seems a bit dead. I am going to do a compression test tomorrow as I would like to know if the head gasket may have a leak. I believed it could have been the AC fan not kicking in but the second time I drove with AC off. Note my oil is 15w50 and it's about 32 C or 89.6 F temp outside.

 

I appreciate some advice on possible reasons and solution. I don't want to be taken advantage of by mechanic just met and doing some research (I am hopeful not too bad)

Edited August 20, 2013 by w1ll1ng (see edit history)