Cooling fan thermoswitch question.
 

Until recently I've been pleased with the Summit thermoswitch I put on the Miata a couple years ago. However recently it started not shutting the cooling fan off once turned on. Research indicates this is a common problem with Summits 200 deg-on, 185 deg-off switch.

In my search for a more robust switch I found the SW510 switch, an original equipment switch for 80s model 4 cyl. Mustangs. The problem is with it installed the fan runs all the time. It appears this is a normal closed switch where the Summit was a normal open switch.

If the above is correct, can I fix the problem with a change in wiring? I'm currently running a four post, 50 amp relay with a 180 degree thermostat.

Thanks in advance. RR

Currently I am using the Mazda fan switch to trigger my Ford fan relay. I also have a dash-mounted toggle switch that can activate the fans as well. I have found that turning the fans on BEFORE the coolant temps rise in traffic to be a good thing.

I've used a Hayden thermocoupler kit on a few builds. The entire kit is around $25 and includes a relay and fuse. If the fixed on/off on that kit is not what you want they also have a whole range of adjustable ones that all cost less than a new Miata thermoswitch.

http://www.summitracing.com/search/b...n%20Automotive

I have mine triggered using my MS2 to come on at 210 and off at 195 which keeps street temps right around 190-195 and track temps around 200-210. If I was not using Evan's waterless coolant (higher boiling point than water) I'd set it about 10 degrees lower.

-Jason

Tom and Jason, thanks for the comments. I'll likely use the Summit kit Jason linked if I can't make the newly installed replacement switch work. I do like the idea of factory switches since I'd expect longer life than typically found in cheap devices designed for and sold to the hot rod market.

Like tbone, I have a manual switch so the car isn't grounded. I just turn the fan on in low speed situations and when stopped, off if above 30 mph.