--------------------------------------------------------------------------------

So, go for a spin - about 400 miles, driving gently enough to average 24mpg.
Gauge shows 190 for a few miles, then 230, then as I slow down in a town, 250, than a little later 295!!!!!!!!! Red light comes on. No fans have cut in, so I stop and hotwire the AC helper fan, this gets me home OK.

Ordered 2 new relays, engine temp sender and coolant switch thats located just at the front below the thermostat housing. Just fitted all 4 items.
Have not run the car yet - its a bit too late at night here, but with the engine totally cold - 74 degrees, the dash gauge is showing 174 !!

What is going on ????????

The good news is your temp sender or harness is probably to blame. Unless there's a family of chinchillas having a bonfire in your bottom end.

If the new guage sender has the same issue then you need to check for proper ohms on the harness end. All the way back to the connection at the computer if necessary. I can say what ohms equals what temp because I don't have the helms handy.

The computer is controlled by a different sensor than the guage. Which is probably working so it didn't trip the fans. Its impossible to get to 295 without boiling off lots of coolant first so don't worry about the motor.

Drove home about 180 miles, with the hotwired AC fan going and the heater on full, doing about 50 - 60 mph, just to put as little heat as possible into the engine. On the open road, will good cool air going through the rad, plus the above help, the guage was still showing 220 - 250 degrees.

I tested my stock harness on that by buying a pack of resistors at the store and sticking those into the harness and seeing if the guages matched the resistance. Resistors in parallel add like so...

500ohm + 1000ohm = 1/(1/500+1/1000) = 330 ohm

Here's info on the 1984 coolant guage sender. Looks like it changed in 90 but I think it was just to change the connector type.

1320 ohm = 100F
115 ohm = 230F


And here are the resistances on the sending unit to the computer, which is the two-prong one on the front of the intake. I'm guessing this one is accurate otherwise it wouldve brought the fans on.


7500 ohm at 40F
3400 ohm at 70F
1600 ohm at 100F
450 ohm at 160F
185 ohm at 210F
70 ohm at 266F

Many thanks.