I have a 1986 Ciera with GM's 4tech engine. Recently, I noticed that the temp gauge (which is part of the digital instrument cluster) will sparratically, and under no particular driving conditions, jump way up to hot, then after a moment, go back down to normal. This happens VERY rarely, and I know that either the fan or fan relay is bad, and have yet to replace it. The radiator fan does not kick on at all, but normally, the car runs so cool that it probably wouldn't kick on, even if it could. I've checked the coolant temp manually immediately after this happened the last time, and it was at 180 degrees, so it wasn't running hot.
I'm wondering if there is a sending unit in the fan relay that may be telling the computer to kick up the temp gauge in response to the fan not kicking on, regardless of the coolant temp. I'm planning on replacing the fan relay and if that doesn't work, obviously the fan, itself, but in the meantime, I'm curious as to if this issue can be attributed to the fan problem, or if there is another problem in the works. The head gaskets seem fine, no oil in the coolant or vice versa. Water pump is new, thermo is new, rad cap is new.
Anyone?