Cooling Fans Not Turning On at Temperature

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10-18-2026, 04:51 PM
JRNY13

Cooling Fans Not Turning On at Temperature

Out for a drive today and the car worked fine. I idled for a few minutes to talk to a neighbor and I noticed my engine temp rising. This didn't concern me, however at least once a year I let the car idle so I can verify my radiator fans are turning on and working as they should, so I got back into my driveway and got down in front of the car to listen/feel the fans working. They didn't come on and I got uncomfortable with the engine temp so I turned the AC on. The fans immediately came on so I know they have power and work.

I'm thinking my otterstat is bad or I have air in my cooling system. This summer my mechanic worked on my AC system and replaced my low pressure switch. Could this have introduced air into the cooling system?

I attempted to jumper the otterstat but I realized I don't have a jumper wire. I can't seem to buy one anywhere, is this something I have to make myself? What could I be missing or am I on the right track? Thanks.
10-18-2026, 05:29 PM
Bitsyncmaster

A little stranded wire can work as a jumper. There is very little current at the otterstat. Don't force anything in the pins or else you may damage the pins. Otterstat or diode near the fan relay is probably your problem.
10-19-2026, 09:47 AM
David T

Quote:

Originally Posted by Bitsyncmaster

A little stranded wire can work as a jumper. There is very little current at the otterstat. Don't force anything in the pins or else you may damage the pins. Otterstat or diode near the fan relay is probably your problem.

Also check if your Otterstadt switch is on top of the pipe or underneath. The "older style" where the "O" switch is on top can have get a bubble of air trapped in it. The "newer style" has the "O" switch in the bottom of the pipe and won't trap a bubble. Easy to convert if you have to. Make sure both wires are securely connected to the switch. If you replace the switch get a new silicone gasket and if you don't have the clip to hold it in you can use a strap tie. Only use coolant to lubricate the gasket to install, NEVER use silicone on it.
10-19-2026, 12:30 PM
JRNY13

Switch is definitely underneath, facing the ground.
10-19-2026, 06:38 PM
Gregadeth

Quote:

Originally Posted by JRNY13

I'm thinking my otterstat is bad or I have air in my cooling system.

I attempted to jumper the otterstat but I realized I don't have a jumper wire. I can't seem to buy one anywhere, is this something I have to make myself? What could I be missing or am I on the right track? Thanks.

I would bleed the cooling system first--at the pump and at the radiator. Reconnect the otterstat and get up to operating temp. If the fans still don't turn on, then try jumping the connectors. It's pretty easy to make a jumper (google/youtube it). If the latter works, then the otterstat could just be bad. After replacing the otterstat, you'll have to re-bleed the system.
10-19-2026, 08:42 PM
David T

Quote:

Originally Posted by Gregadeth

I would bleed the cooling system first--at the pump and at the radiator. Reconnect the otterstat and get up to operating temp. If the fans still don't turn on, then try jumping the connectors. It's pretty easy to make a jumper (google/youtube it). If the latter works, then the otterstat could just be bad. After replacing the otterstat, you'll have to re-bleed the system.

If you are quick about it and use your fingers to hold back the coolant while you remove and replace the "O" switch and gasket, you will lose minimal coolant and should not have to bleed the cooling system. Just don't do it while the system is hot! I agree, testing before replacing the switch. Use a non-contact infra red temperature gun to see how hot it gets. The fans should start when the thermostat housing is about 180 degrees.
10-19-2026, 09:19 PM
Jonathan

Quote:

Originally Posted by JRNY13

Out for a drive today and the car worked fine. I idled for a few minutes to talk to a neighbor and I noticed my engine temp rising. This didn't concern me, however at least once a year I let the car idle so I can verify my radiator fans are turning on and working as they should, so I got back into my driveway and got down in front of the car to listen/feel the fans working. They didn't come on and I got uncomfortable with the engine temp so I turned the AC on. The fans immediately came on so I know they have power and work.

I'm thinking my otterstat is bad or I have air in my cooling system. This summer my mechanic worked on my AC system and replaced my low pressure switch. Could this have introduced air into the cooling system?

I attempted to jumper the otterstat but I realized I don't have a jumper wire. I can't seem to buy one anywhere, is this something I have to make myself? What could I be missing or am I on the right track? Thanks.

Here you go...

https://dmctalk.org/showthread.php?1...l=1#post166051