I have been having some troubles with the heat rising while driving on the highway on really hot muggy days. Hot dry days there was no temp rise. It is 95 + in indiana.

Did the fan switch mod.

Did a temp gage mod. Moves up at about 210.

Did the FD to FC thermoswitch mod. The new switch was an FC at 97 C. I think the older ones were 95C. Anyway, got it from Malloy.

After searching and reading, felt it was a good idea to change the thermostat. Ordered it from Malloy. Fast shipping right away...

Changed it out with no trouble, and the old one seemed to be messed up. It was obviously working, but not well. The rubber around the center seal had enlarged from use and was a bit swollen, thus reducing flow through the orifice. It wouldn't take much to reduce the flow significantly I think.

I have not seen the temp gauge move off of normal since the service.

IMO, I don't think these thermostats are well made. The rubber center seal doesn't appear to be made for longevity. Would anyone agree?

 

What temps do you usually run at now? I have had the fan mod, and just installed the FC thermoswitch from Ray today, car should be together in the next couple of days after I install my new fuel injectors. My Power FC always reads low normal temps, but my digital water temp gauge ranges from 195-230 sometimes(changes up and down fairly quickly, t-stat housing location). I hope to see an improvement with the FC thermoswitch, which also has a 97 number on it.

 

When temps break above 90, you should turn on your a/c to drop the temps down. I usually cut the fans in once I'm off the freeway. I usually see temps of 85-88C as read by the PFC

 

I also usually I usually see temps of 85-88C as read by the PFC when the fans are on at least the low setting.

Before I took my car apart, with the FD thermoswitch, my fans would always come on at 94C everytime, they would come on when I was doing the self learning idle process for my power fc I had just installed. This was with the ac off and my fan mod switch off. I always thought this was strange because shouldn't the fans not kick until much higher temps without the FC thermoswitch. So I actually thought maybe my car already had the FC thermoswitch, but I just found out it didn't after looking at it. Now I am wondering when they will turn on after I put my car back together with the FC thermoswitch, I've read 95C or 97C, but then that would be higher than before. Anyone know how this could be?

 

That is kind of weird. The FD switch is supposed to come on at 221 F low speed. The FC switch should bring it down to 206 F or there abouts. I am converting in my head...Since it is a switch and not a temp sending unit, it all depends on what ECU you have and what the system is programmed to do. For the record, all my stuff is stock.

I have noticed two things so far.. The fans come on more, which is to be expected. Second, they will stay on for more than 2 minutes sometimes, which causes the fan timer to kick into the 10 minute hold mode. That never happened with the FD switch. Now that tells me that in some cases, the temp was higher than 206 for greater than 2 minutes. It has happened only on the highway at 80 mph. This is why I suspected the thermostat.....If it was partially blocking the passage, then it is conceivable that the coolant was being retained in the block.

The thermostat was in tough shape when I took it out. The outer seal was also misaligned (previous service idiot). There is a weep hole that should be lined up with the seal relief area. It is a small detail, BUT the little metal plug had been interferring with the seal. What does it mean? I don't know. I drove the car a bit afterward in town with the new thermostat. Very hot out, and the temp stayed lower on the gauge. I don't recall the fans coming on, which makes me think that the thermostat was bunk. That inner rubber seal is a bunch of crap.

Also, I noticed a small amount of brown deposit in the inner thermostat housing. Time for a flush for sure. I suspect the design margin on this system is poor, meaning that if everything is not completely A1 shape, you will always have problems. De-I water and good coolant, flushed system, unblocked radiator, and all the ducting in good repair. Otherwise, it is a bust....Might want have an extra thermostat laying around....what a joke......but I guess that space was a premium when they designed it....

 

i would use a miata fan switch with an RE-Amemeyia 80 degree (C) thermostat. The miata switch kicks in about 20-25 degrees earlier than the stock FD one.

 

The FC is a direct plug in install. That's why it's gaining in popularity. Dale Clark enlighted us to it. I changed my T-stat at 50K miles. I think everyone should do it at least that often. They're so damn cheap, why not?

 

I put my car all back together today with the new FC thermoswitch. Well I am 99% sure the fans kick on at the same exact temp as they previously did with the FD thermoswitch I took out (which has a number 108 on it). I'll check again more closely tomorrow, but I am pretty sure the fans turned on at 94C as read on my PFC commander, just like they did before I took out the FD ts. Strange. I know you can change the temp when the fans will kick on with the datalogit (I don't have) for the PFC, but maybe the PFC is preprogrammed to turn on the fans at the same temps as the FC thermoswitch even if you have the FD thermoswitch??, that seems possible to me maybe. I don't know what temps my fans kicked on before I installed the PFC because I didn't have the commander to tell me, I did have the digital water temp gauge but I never figured out what temps the fans would kick on before the PFC.

I also relocated my water temp gauge to the coolant hose that goes from the throttle body to a metal pipe under the UIM that goes to the back of the thermostat housing, not the coolant line from the block. The coolant hose I used was very long (previous owner) so I just used that hose since it was long and easy to do. I am mentioning this because my digital water temp gauge reads considerably lower temps than it did when it was in the thermostat housing. Today I don't think it went above 200F, before I would regularly see up to 235, but it would go up and come down fairly quick with the fans on medium or high. Maybe my ground wire is causing it to read a little lower than it should, or the temps are just normally higher in the thermostat housing.