My S1 4.2 OTS runs perfectly but on a long run this week - 80 miles or so - the water temp gauge started fluctuating wildly. Never above 70-75 it started suddenly dropping down to 30o (nothing really) for long periods of time, and then suddenly coming back up to 70o.
Any thoughts? The coolant level is fine and there are no ugly smells or rough running
Thanks
Swap the water (green/blue) connection with the fuel sender (green/black) connection at the gauges and see whether the fault follows the sender and its wiring or the gauge itself. That#'ll tell you where to look to fix the problem as the fault lies with what is common both times.
kind regards
Marek
Does the gas gauge also fluctuate when this happens? If so it’s your 10 V regulator. I would suspect the temperature sending unit or a loose connection at the temperature sending unit. The gauges are very simple devices and are not likely to fail.
It doesn’t - rock steady
My guess is that you have an intermittent faulty connection. The reason the gauge is dropping is because it has no voltage for short periods.
Had this problem on an '87 Toyota Supra with a bad head gasket. (In that era of Supra’s there are only two types - those that have a new gasket and those that ne… you get the drift.) The temp gauge would suddenly go to zero, then a few minutes later it would go back to normal. More bars leaks would fix it for a few months. Not suggesting it’s your problem. I have no understanding of why a leak would cause that.
Now that I think of it an '97 XJR I had 15 years ago would do the same thing. It didn’t have a leaking gasket as far as I know.
It’s possible for the copper rivet on the top of the sender to lose grip. My Mk2 gauge was behaving eratically until I turned the contact (under the rivet) 90 degrees. It’s still on the long list.