Sporadic running hot, please help!!!

Lee wrote:

To answer your questions... the overflow tank does not return to level, there is a hissing when opening the radiator cap.


 

Head gasket or a cracked head (unlikely)

With the cost of gaskets and the work involved, getting the head faced to be sure that it is flat would be A Very Good Idea.  You might get away without, or the new gasket may let go quickly.

You might as well make a week of it and service the valves, do the tappet clearances etc.

After much trial, research and interviewing several shops, I dropped it off at the local dealer. Very nice guy and mostly very knowledgeable. He basically reiterated everything you folks mentioned thus far. He will go through the engine in detail again to confirm my findings. The head will be removed, taken to a machine shop for a slight polish and reassembled. The head will be checked for any issues and repaired as necessary, although he doubts he will find anything as he's yet to see any head damage on the DOHC engine with chain. 

As for background, I've been living in Greece for 7 years... coming from the USA, I have been involved in the auto manufacturers level as a career. What I've observed here is that almost all makes, models sustain head gasket failures. This must be a "pandemic" of sorts here as I have never seen so many head gasket failures back home. At the dealer, there was a Swift with the same engine as the Jimny, mounted sideways, A Baleno as well as a Vitara with a 2.4. They all had the head removed for gasket failures... Hence my aforementioned description...  As mentioned I bought the car used, first thing I did is go through it thoroughly, I completely drained every fluid and replaced with new. As for the cooling system, it contained a mixture of water and what they call here "PARAFLU", which was explained to me as a coolant of sorts. I replenished with a 50/50 mixture of BLUE fluid, which I brought with me from the US, specifically formulated for all aluminum Japanese engines. 

In the cumulated 155,000 km, I have operated well, no abuse or misuse. It has performed well under in temperatures exceeded 45C under load, climbing steep grades ad all else, the geography here is a mixed bag of everything. I was taken by surprised to experience the sudden head gasket failure...

I await a call from the dealer as to progress and will update herein as necessary.

Thanks you all for your input and guidance, it is much appreciated!