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So I'm going through the FD and cleaning out the parts and whatnot the owner left in it and left for me. He mentioned there was an FC thermoswitch. Sure enough, I found it. Its in a clear bag that has "PN41-18 040" written on it in marker (highly faded.) I remember reading about the thermoswitch mod when I had my first FD, so I did some digging. Apparently the thermoswitch is supposed to have the temp engraved onto it?
This one has no writing/engraving on it whatsoever. I was curious as to if anyone knew if aftermarket thermoswitches lacked this engraving. Picture for reference:
Interesting. Probably just an OEM copy made by an aftermarket parts company.
I would test it in boiling water (there should be a test procedure in the shop manual) to verify the temperature that it engages.
Dale
Yeah, definitely going to do that before I throw it in there. One thing that I noticed, though. The factory coolant temp gauge doesn't work, so there is an AEM one wired in. I was driving today, with the AC fan off, temps holding steady around 184. I turned the AC fan off (by pushing the button) and temps rose to 204~. Is it normal for that fan not being on to cause that much of an increase in coolant temps? Possibility of my fans not working?
I haven't been able to get a thorough look at the car since its been raining nonstop since I've gotten it, but I don't believe the undertray is there. I had it running for a solid half an hour tonight, just at a standstill, (put in some radiator flush, so I was letting that circulate) and the temp didn't rise above the 180's until I turned the AC fan off. At that point the heat started becoming actually warm/hot once the temp got up to around 200. What temps should I be looking for at a standstill prolonged idle and steady around town driving without the AC fan on?
Yeah, definitely going to do that before I throw it in there. One thing that I noticed, though. The factory coolant temp gauge doesn't work, so there is an AEM one wired in. I was driving today, with the AC fan off, temps holding steady around 184. I turned the AC fan off (by pushing the button) and temps rose to 204~. Is it normal for that fan not being on to cause that much of an increase in coolant temps? Possibility of my fans not working?
Yes it is normal. Especially in the heat we are having in the SE and once the car is heat soaked and you come to a stop.
I want to say the OEM S5 FC thermoswitch wasn't much more than about $40. Not knowing the origin of that switch pictured and given the small PITA they are to change with the housing in the car, personally I'd just pony up for a new switch and be done.
Reinstall the undertray and see what temps you get.
I want to say the OEM S5 FC thermoswitch wasn't much more than about $40. Not knowing the origin of that switch pictured and given the small PITA they are to change with the housing in the car, personally I'd just pony up for a new switch and be done.
Reinstall the undertray and see what temps you get.
Have to buy one first, lol. But that is my goal. I noticed when I was sitting at an incline today at a stoplight with the front of the car facing up, the temps shot up to 215-220, then dropped back down to 204, I'm thinking there may be a pocket of air in the system, the previous owner did mention he changed the thermostat out before he sold it to me.
If he changed out the thermostat you will want to verify it's a real Mazda thermostat. Aftermarket thermostats fail and stick with SHOCKING frequency, even when new or near new.
The thermoswitch will make the fans come on sooner, but it wont make them work any better. A Band Aid. Ducting and undertray are the most common reason that I've seen for FDs running hot when they're otherwise running fine.
EDIT: A friend of mine has an undertray from LRB that fits great. If you have trouble finding an OEM one or want something different, that's one pretty good choice.
Recently there was a thread which claimed convincingly that the thermoswitch doesn't kick the fans on sooner, just at medium speed when they do come on. @arghx I think you were involved, do you have the thread handy?
If the car is running hot, you can turn the AC and parking lights on and it will kick the fans on. Or set the fan controls to come on lower in a PFC/Datalogit. Thermoswitch is not a bad mod, if you're gonna do it. But, you'll need the alternator off and it's pretty deep in breaky things if you're not careful.
There have been so many cooling threads, I don't remember that exact one. At one point (years ago) I was under the impression that the thermoswitch made the fans kick on earlier, but I was mistaken.
The fan relay that the thermoswitch turns on won't work until the ECU switches on its own relay. The ECU will switch its fan relay on based on A/C load or temperature. That temperature can be lowered with a Power FC. On series 7 they lowered the temperature based enable, but all the USDM cars are series 6.
Conclusion:
If you have stock ECU and you install the lower temperature thermoswitch, the fans won't come on at low speed any sooner. They will come on at medium speed sooner though, and they will run the aftercooling function much more frequently. If you have a Power FC you can make the fans come on at low speed earlier.
If you have a small battery and the after cooling module the thermoswitch will tax your electrical system. If you have a "normal" battery it will be fine.
I’m not certain of fan speed, but I have the S5 FC thermoswitch and fans initiate at a little past 95 C. as indicated on my commander. I have never changed the default fan setting on the PFC. Before the thermoswitch was installed the fans activated at about 105 C. but again, not certain of fan speed.
08-16-19, 08:19 PM
