[Vwdiesel] overheating a2 jetta diesel

[bludodger at att.net]

I have just acquired a '91 jetta gl diesel. The PO said there was a pressure problem with the cool. system but insisted that it did not overheat (what are the chances?). Apparently, the flange coming out of the right side of the head and going to the core was  replaced. In addition,  the flange in the front of the engine was replaced. Eventually,  the heater core went b/c of this problem. Thats the info I had when I bought the car. I am now in the process of diagnosing the situation. I am expecting the worst--cracked head or blown head gasket but would like to check everything before I delve into such work. 

Today I bypassed the core. While filling it up with coolant I noticed that there was a gurgling noise coming from the flange on the front of the head (connected to the top rad. hose and one connection goes to pump). It seemed that the bolts that secure the flange to the head were loose. I gave the two bolts a few cranks. That seemed to stop the leak and the noise. I then started and idled the car. This was the first time I was able to evaluate a "closed" system. Strangely, the rad. fan came on immediately (even though engine was cold) and stayed on.  I did not notice any white smoke coming from tail pipe. Also, I did not notice any overflow coolant coming back to the exp. tank (something that I know is evident in my A1 diesel cars). I am not used to the "new" globe tanks and wonder if I am just not seeing it? The temp guage slowly climbed between 1/2 and 3/4 and seemed to stay there. I let it idle for 10-15 and then took it for a ride. Within 1 mile of my house I saw that the temp gauge kept rising and was aproaching 4/4.  I turned around and parked and let it cool off. It did not seem that there was any coolant lost. I cracked the exp. tank and there was definite pressure and the coolant was very hot. The top rad hose was hot as heck too.

I think my next step will be thermostat and exp. tank cap. Does this make sense? In the meantime, how can I test for HG leak/warped head . I have heard that a compression test can help determine this. Is there any other methods? I am most curious about the rad. fan staying on...could this point to a bad sensor? How about the lack of coolant flowing back to the exp tank? By the way I have not detected any water on dipstick and there does not seem to be any oil in coolant tank. i see no obvious signs of water leaking out of head gasket.


Any other input?

Thank you for your help in advance and look forward to hearing from you soon  

Andrew