I made the move to the FC Thermoswitch when I had my engine rebuilt two years ago. Since that time, I've gone through two (standard size) batteries and the current one is beginning to show signs of being tired. It seems possible that the additional run time of the fans could be prematurely aging the battery. Has anyone else encountered this problem? Is there a workaround?

 

Doubtful that the FC thermoswitch has any effect on your battery...however, what is your driving like? In other words, do you drive long enough to FULLY charge the battery? Also, your fans could be pulling too many amps if there is something wrong with them. I believe the FSM has the required information.
Realistically a decent battery ought to last 2 - 3 years, so if you are experiencing higher replacement intervals, you need to find out if there is a parasitic loss somewhere or maybe the alternator isn't working properly, etc.

 

Read my posts on the fan recall. Fans running after the car shuts off isn't doing you any favors, it's just running your battery down.

Dale

 

Have you considered using a battery tender? There are several available however, a popular model is the Deltran Battery Tender line. It (tenders in general) significantly prolongs the life of a battery.

If you have a gel type battery then make sure the battery tender is compatible with it. There are no known issues with any (sealed) lead-acid batteries.

The lead-acid battery on my FD is going strong after 10+yrs because of the battery tender. It is also important to keep up on battery maintenance - check fluid levels unless it is sealed, keep terminals clean, and use the green & red terminal pads to reduce corrosive build-ups.

High end cars like Ferrari and Lamborghini, to motorcycles, ATVs, etc... use them with great success. Even classic "Gold Level" certified cars use them to keep their vintage batteries charged up.

Cheers,
George

 

The fans draw a lot of current. But, I'd be surprised if it's eating batteries. I've run the FC thermoswitch and two 51r small batteries with success. I did eat an alternator, but the new one is doing fine so far. After 25years it's hard to chalk the alternator up the the fan switch specifically.

 

The thermoswitch is part of the triggering logic for the after cooling mode on shutdown. We can debate the merits of after cooling; I think it's worthwhile, Dale doesn't, make your own decision.

With the FC thermoswitch, you will run the fans on shutdown more, but especially if you have been running the A/C. A lot of you guys don't have working A/C so you may not have noticed as much difference.

If you have a standard lead acid battery, look at the cold cranking amps. Johnson Controls is the main supplier of batteries under various brand names, and they sell in 3 flavors: standard (1 year warranty), silver (2 year warranty), gold (3 year warranty). The longer warranty batteries have more cranking amps. Basically, they're stronger batteries.

I would use a minimum of a standard sized (as in, original size when the car was new), silver battery (2 year warranty). If you are using a 1 year warranty standard sized battery the thermoswitch is probably stressing your battery. If you have a battery relocation, it is probably stressing your battery. If you have a smaller than stock battery (Miata battery, some kind of racing-intended battery), it is probably stressing your battery.

So you can take the thermoswitch out or delete the fan control module. Or replace batteries more frequently.

 

I too have run the FC thermoswitch for years and can't believe it is the issue. Yes, the fans DO run longer, and that is not a BAD thing to help rid the engine bay of some heat, but we're talking a couple of minutes or so...it's not like they run forever unless of course there is another issue like Dale noted.


Arghx hits the nail on the head...get the best battery you can. Heck, I saw this Exide battery at Academy sports the other day:
Exide Edge Flat-Plate AGM Marine and RV Starting Battery | Academy


and it would be perfect for an FD.