Hello all, my 3rd gen has overheating issues and through a process of elimination as it turns out it is a bad ground feeding the fans but I am unsure where to go from here.

Here is what I have determined,
- When connecting the fans directly to power, they come on.
- When I manually ground the fan to the battery and turn on the AC, they come on. They will not engage on their own though even at 230F.

So it appears that there is a grounding issue further upstream. I was told to check the ground on the coolant temperature module or to the temperature switch. Unfortunately those all seem pretty buried in the engine so I am unaware where to trace this back to.

Can anyone suggest where to go from here or if there is a way to just bypass and have the fans come on (preferably at a lower temp than stock) automatically based temperature without having to trace all this back through the relays? I also want to avoid having to manually turn the fans on based on running temp. Could this be caused by a relay? I was only able to pinpoint one relay for the fans as clearly marked on the box but I hear there are a total of three? If there are any images anyone can point me to where to look for these it would also be appreciated.

Thanks in advance for any help.

 

check the relay under the hood

 

After scouring these forums for every cooling fan issue/suggestions I could find, I went through everything looking for a bad ground. Pulled the intercooler out, got to the wire harnesses and checked for any broken wires, which I could find none. I pulled all 4 relays out and tested them all on a volt tester and they all passed.

As I was putting everything back together, I noticed a blue plug that was dangling tucked down behind the water pump. I was not able to find anything that it plugs into, in the off chance it was related to my fans not engaging I was hoping someone could tell me where to plug it in.

I also found some posts suggesting jumpering a couple points in the diag box as well as a few other places as a process of elimination. If I cannot find the break, is there any way to rig this so it still comes on at temp or is my only other option a manual switch?

Thanks for any suggestions anyone may have.

 

Behind the waterpump housing there are TWO sensors. The TOP sensor is the ECU's temperature sensor and also provides input to the worthless stock temperature gauge. Just below that and of particular interest to you is the Fan Thermoswitch. IIRC, a single wire connector. It serves to activate the fans at a (stock) threshold temperature of 108 C. That wire and connector can get brittle with age and heat. If your fans are not turning on by themselves, that would be my first suspect.
It's a small PITA to get to. You can access it two basic ways. (1) By removing the crossover tube and support bracket going to the intercooler, along with the alternator and tensioner and a few other things. Doing it this way is a little quicker but doesn't give you much room to work. The other way (2) is to just drain the coolant, spring for the cost of a gasket and remove the waterpump housing.
I highly recommend going to the 3rd Gen. Section stickys and (if you haven't already) downloading the Factory Service Manual. Go to the cooling section and you should also find some trouble-shooting hints and more information on how to do the above.
IF you get in as far as the thermoswitch, I also STRONGLY recommend replacing the stock sensor with a S5 (FC) thermoswitch. Doing so will activate the fans at a threshold temp of 95 C....much lower and safer for the car. It is a VERY common mod for the FD. Completely plug and play, it installs just like the original.
A quick search in the 3rd Gen. section for MALLOY MAZDA will get you a toll free number. Ray in the parts department will know exactly what you need and is a trusted source to forum members for OEM. He's also typically cheaper than anyone else, even with shipping. My guess is the sensor will be about $45.

BTW, 230 F. is VERY hot. I've read where some believe the coolant seals start to degrade at about 240 F. So I wouldn't let it get that hot again.

 

Wow thank you so much for taking the time to detail your suggestions! I haven't pulled anything as of yet but looking at it, I see there is a white/green plug going into the back of the water pump which I am assuming is the ECU's temperature sensor. Unfortunately I cannot see below to see the thermoswitch.

I really wanted to mod it as you suggested for the S5 (FC) thermoswitch (which is for a miata if I understand correctly), so regardless I need to get to the thermoswitch to make this change.

Since you did not mention it, I am guessing the picture of the unknown plug I linked pictures for may not likely be part of this issue?

Once again, thank you so much for your help. This car over that past 12 years has been nothing but learn as I go since there is no specialists anymore in the Sacramento area to take it to.

 

The Miata thermoswitch is not the same. Its threshold temp is also 95 C. and we used to use it years ago but it takes a different connector. It was then discovered that the FC (S5) switch has the lower temp and uses the same connector as our cars.

I'm not sure offhand what that plug is for. Ill look again at my car and your pics when I can.

 

Cool thanks for clarifying, I am sure that was a way old thread.

I did want to add one reminder, the only way I can get the fans to turn on is connecting them directly to power. Turning on the A/C does not engage them so it is more than just not coming on at temp. Wasn't sure if that could signify more of an issue than the thermoswitch.

I would be totally sunk without the rx7club, thanks so much for the suggestions!

 

/bump in hopes to get my additional comments answered.

"I did want to add one reminder, the only way I can get the fans to turn on is connecting them directly to power. Turning on the A/C does not engage them so it is more than just not coming on at temp. Wasn't sure if that could signify more of an issue than the thermoswitch."

Also, if anyone can tell me where the plug I displayed in my attached images, it would be a huge help.

 

egr

https://www.rx7club.com/3rd-generation-specific-1993-2002-16/engine-wire-harness-picture-w-connectors-labled-667600/