Radiator fan runs constantly

[SweetwaterJoe]

Hi folks,

Coming home from work two days ago I overheated. Traced it to the cooling fan not coming on. changed the relay and now it runs constantly even if engine not running but key turned on. Hot or cold. Any guesses what I might try next?Maybe the last relay burned out because it was running all the time as well.

Joe

[Petros]

That is classic symptom of the thermal switch failure. this is the electrical connection at the bottom of the radiator next to the lower rad hose connection. The default mode is to be in the "on" position. Not likely you harmed anything with the fan running but you should get the thermal switch replaced.

Overheating it is far more risky, could have damaged the head gasket. Watch your coolant level every day for several weeks (check when it is cold in the morning), if you are loosing coolant, likely the head gasket is damaged. You can still drive it, just keep it topped up. If you do need a new head gasket, follow the procedure I wrote up in the "repair guilds" section and do the mods to improve head gasket durability.

Good luck

[SweetwaterJoe]

Petros,

Many thanks. O.k., I'm on it. I especially like changing things that don't require a contortionist. This seems easy.

I checked Napa since they seem to have things in stock that Auto Zone or Advance doesn't. They show two items when I do a search on 'temperature switch'. One is called a 'Coolant Temp Switch' and the other is called a 'Temp Sender Switch - Gauge'. They look different. The first is two prong and the second looks to be a single prong.

I'll check coolant as advised. Thanks for the quick response. I might be able to take care of this tomorrow due to your help.

Joe

[Petros]

the single prong sender is for the temp gauge, it is located at the front of the head (next to the coolant outlet). The one you want is the temp switch, it is duel prong and locacted next to the lower radiator hose. Access is not too difficult.

You might remove it from the rad and take it with you to the auto parts store and compare it with the new one. You can also test it by putting some wires on the contacts, measure continuity before and after you put in boiling water with a volt-olm meter.