I have a 1989 Civic DX Hatchback. When I turn the ignition key on the coolant temperature gauge immediately gets pegged to "hot", although the engine is cold.

I grounded the temperature sending unit with an ohmmeter. I got the resistence down to 172 ohms, but I don't have a thermometer so I don't know at what temp that reading was. The manual calls for 134-176 ohms @ 122 F. The sending unit looks as though it's okay though. If I'm wrong about this, let me know!

Does anyone have any ideas as to what to look for next?
Thanks in advance for any input!

Kronos

 

is your car overheating? or is the gauge off?

 

Thanks for replying, polo708.

I have zero overheating problems. The gauge will race to "hot" and stay there even with a cold engine.

 

wow... all I can think is maybe a wire is crossed somewhere.

 

When did the problem start? Can you correlate this with other work/repairs where a wire may have got snagged?

What happened to the gauge when you disconnect (open circuit) the sender?

Other test here is to put the 130 ohm resistance in in lieu of the sender - see what the gauge does then.

You can get a resistor from a TV repair shop or similar. Or any ham will have one if you know any.

 

I have been out of town and just back to checking out my car. It turns out that the temperature sending unit had been the problem all along. Found a thermometer and took a resistence reading again and it was out of spec. Installed a new sending unit and the gauge works fine now.
Thanks to polo708 and malcom for their input!

Kronos