I have a 1988 Vanagon and I have had a problem with the engine coolant temperature. The temperature gauge goes up about 1/4 of the gauge below the top line and often the warning light starts to flash. I had the gaskets replaced, a hole in the line repaired and replaced the thermostat, but the temperature gauge still goes up to about 1/4 from the top line?
Has anyone actually measured the temperature? I would like to know if it was overheating or just indicating it was overheating. It could be nothing more than the sensor, which would be my first guess. I don’t know the cost of that sensor or how difficult it may be to get to, but I would consider just replacing it if it is not expensive.
When the heads were off did you have them checked for cracks, and straightness? Also you mention nothing about the water pump. Has that been checked/replaced?
With a twentyone year old radiator, it could very well be partially restricted to the point where the engine is beginning to run hotter.
Tester
That isn’t an indication of temp, it is an indication of low coolant level. You either have a bad coolant level sensor in the expansion tank (not the overflow tank you can see behing the license plate) or need to bleed the system. If air gets in it can do strange things to the level of coolant as the van heats up. You may also have a bad pressure cap on the expansion tank. These go bad frequently. Replace that and the sensor. About $30 total and 10 minutes. Check TheSamba.com. Hundreds of posts on problems like yours. I’d recommend bleeding it. If you build a “Libby Bong” it will make bleeding the system very easy.