I've had an annoying problem for the last couple of weeks: As the engine warmed up, the water temperature started dropping. Not consistently, but suddently it would drop below the 70 degrees mark. Then back up a bit. Then down to 50!
It was driving me mad.. Is there a air trapped in the system? A leak? Is it boiling? Am I damaging the engine?
I decided, however, that it was an electrical fault. The sensor was new - well only two years old, so I could rule out that and start looking for other problems.
So I cleaned the grey wiring loom connector next to the fuse box. I also carefully checked the wiring measuring resistance from either end. All OK!
Ground connection could be bad... Well not really, because then the oil pressure meter would have shown a similar pattern, which it did not.
Water leaks? Nothing. Check again: Still nothing.
So yesterday I replaced the sensor anyway. I had an old one that had come with a thermostat housing. I think it came off the car that we stripped last year with Waldo. With a busy weekend schedule, I didn't have time to try it out before now, and I have just returned from a test drive. IT WORKS! The engine warms up nicely, then stabilizes around the 70 degree mark, only slowly climing halfway to 90. The completely stable. Impossible to drive up in hard (really hard!) driving, or idling. Just perfect!
I guess the morale is: New parts DO fail. It will be interesting to see how long the new (old) sensor will last!
/Anders