Make sure the new one can handle at least 20 amps. More is fine, less is not.
Sounds to me like your otter switch is faulty. I would recommend you replace it with a switch from CoolCat. Excellent switch and reasonable. Much more accurate than the conventional otter switch.
Mike I just sent you a email. Dick
Hi All,
Removed the new relay and installed a very old Lucas relay from a British car club member friend of mine. A very old relay from his parts box…
Fans fired right up, as they should, when the engine temp reached slightly above normal, gauge at 90 degrees!.
Sometimes old is better than new!
Thanks, Bob