First the background:

Installed a new engine and replaced ALL sensors with new ones and a new thermostat. I also installed the FC thermoswitch.

The car warms up just fine and when the coolant temp hits 82C the fans kick on as they should.

Heres the problem, they never turn off. The PFC commander says the temp is 83C and it never moves off 83C, doesn't matter whether Im driving or at idle.

A couple times after driving then coming to a stop almost immediately the temp dropped to 78-79C but the fans didn't turn off. Once the car is off the temps will shoot to 95-97C. When the temps were being shown as in the mid 90C I was able to grab the rad. hoses w/o a problem making me believe the reading was wrong.

Last night I installed a coolant gauge in the TB to see what was really going on. The car once again warmed up fine but I noticied the gauge was reading 3-5 degrees lower than the Commander. The fans came on when the gauge read 78-79C and after a couple minutes the gauge showed a temp drop of 3 degrees or so but the Commander held steady at 83C as normal.


Any ideas whats wrong here guys? I know most would say don't worry if its running cool and the fans work but there is something wrong here and I wanna know what it is.

 

Try setting the fans to come on at a higher temperature. 83C is too low. Just when the t-stat starts to open, the fans come on. T-stat never opens fully, because fans come on as soon as it starts to open. Engine nevers warms up. Fans should not be set to come on below 93C.

 

My issue isnt really the fans, its the fact Im not getting reliable readings and it seems the PFC isnt getting them either hence its not turning the fans off because it never sees temps lower than 83.

 

How do you know that the gauge that you are using is accurate?

Are you measuring temperatures at the same point in the cooling system?

Why not set the fans to come on at a higher temperature to see what happens?

 

Its a brand new Apexi gauge, if its not accurate what will be?

As stated I'm not measuring from the same place but that doesn't matter. I needed to confirm that the temps showing on the PFC were inaccurate and they are. For whatever the reason the PFC is getting to 83C and never shows a drop in temp until the car is off 98% of the time.

I have set my datalogit to turn on the fans to come on at 84C but they come on at 82C (per PFC) everytime.

Wow was my memory wrong on the FC thermoswitch, I don't know where I got 82C from.

 

Why is it I get the odd problems?

 

Your hose never gets very warm because the t-stat never opens fully. This is because the fans come on too soon.

Two experienced members have advised to you to reset fans to higher temp. You should do it, and see if you still have a problem.

 

Maybe Im not being clear?? This problem is difficult to describe.

It doesnt matter what temp I tell the fans to come on at, they ALWAYS come on at 82C according to the PFC and in the upper 70s according to the gauge. Once they turn on they NEVER turn off and the PFC continues to read 83C while the gauge will show a max temp of 79 and then fall to 76 (it will continue doing this).

I ask again, does anyone have any ideas? Thanks

 

Here is the answer: The PFC uses the stock harness which means that only two things could cause the readings you are seeing.
1. You have a DOA coolant temp sensor.
2. You plugged the wrong connector to the sensor. (check your fuel temp, what does that read) The fuel temp sensor plug and the coolant temp sensor plug are identical.

 

I've heard some people say the fans will stick on with the PFC if the temp is lowered too far. Set the fans to come on at a proper temp (89-92C) and see if it behaves the same way.

There will be a discrepancy between the PFC reading and a sensor mounted in the TB line....the PFC is reading from the hottest part of the motor where the TB is further downstream. Compound that with differences in gauge accuracy and there you go.

 

After tonights drive Im thinking I got a bad brand new sensor . PFC reads 83C (as normal) then went to 85 and never changed till the car was turned of when it went to 94C and then very slowly came down.

I hadn't considered that maybe I have switched the fuel temp and coolant temp since the PFC and aftermarket gauge mirror each other when the car is warming up. I will research where thats at and check it out before speaking to Ray.

My datalogit is telling me the fuel temp is "20" but I have no idea what it should be or how it should change. Once again I will read up and try to keep this thread updated.

 

lol Im not sure how much clearer to state the below statement in response to the above statement



Understood, which is why Im not concerned about the small differences.

 

It might not be the sensors at all it could be the fan relays are faulty.

 

OK, at what temperature have you told the PFC to turn on the fans? Earlier you said you had them set to come on at 83C. You have not indicated at any point that you changed the setting.

 

Ok now that the ice and rain is over finally got back to the car.

I had changed the fans settings to several temps ranging from mid 70s to 100. I had only been changing fan1 and fan2 and saw no difference the fans continued to come on at 82.

Today I changed the AC fan temp for the first time (it was set at 82) to 85. After letting the car idle and warm it reached and stayed at 83 for several minutes (fans HADN'T come on yet, a difference finally) when low and behold the fans switched on at 85. However my independant gauge never showed a temp above 81. The car never showed higher temps than 85 until the car was turned off whenwent to 87 and then went down.

I don't understand why changing the AC fan setting had an effect. I will say I not confident in my datalogit software. Maybe the problem lies there?

I feel I can rule out a short in the fans so heres my final question:
Does it sound like my thermostat and/or thermosenser could be bad (both brand new Mazda OEM)?

thanks

 

Are you talking about 'Fan 1 A/C' or the 'Fan 1 no A/C' setting? Also, was your AC on or off when you did the test?

I am really not sure why you keep telling us about the temperature reading from a sensor measuring at a different point in the cooling system.

 

Your stock thermosensor won't turn on the fans until 220F. Unlikely that the t-stat is bad.

I recommend that you change ALL of your fan settings to t least 90 C.

 

AC is off. I changed Fan 1 A/C today (previously I had left it alone since A/C was off) which for a unknown reason had an effect.

I keep saying it as a reference because I don't know whats wrong (if anything). Im just trying to give all I know so someone might be able to help out. If you want me to post like most on here with a problem that leave 90% of the info out I guess next time I will so people will have to ask me for it.


Thanks for the help guys.

 

Normally 'Fan 1 AC', 'Fan 1 no AC' and 'Fan2' are set at successively higher temperatures. Setting 'Fan 1 no AC' to come on before 'Fan 1 AC' would not make much sense because you would want the fans to come on sooner with AC enabled for extra cooling, not later. It is possible that the Datalogit is correcting for what it believes to be an inconsistency, which is not unreasonable.

As Adam said, set everything to 90C and see what happens. The PFC and Datalogit are very robust and well proven at this point so I would be very reluctant to blame them.

 

1. This is your problem, and it's not our responsiblity to solve it. Please don't attack the people who are trying to help you.


2. Start simple. Check your relays first, verify that they're working properly. This thread should help: https://www.rx7club.com/3rd-generation-specific-1993-2002-16/2-trigger-cooling-fans-462760/ It's possible, although unlikely, that you've got a relay that is turning on when it reaches a certain temperature. I'm betting your relays are working OK, but it's still a good idea to check.


3. Also, do the PFC temperature readings seem to make sense when the car is cold? My car's engine is usually within 5-10 degrees of ambient after sitting overnight, and it takes at least 5-10 mins to warm up at idle.


4. If you're able to change the fans' turn-on temps by adjusting settings, that's a good thing. I wouldn't be too surprised if the PFC is activating the fans a few degrees early. Change the settings by 10C, 90-95C won't hurt the car at all. I'd also try to keep all the settings (AC on , AC off) within a few degrees of each other. (edit: looks like moconnor gave good advice here)


5. Is there a fan turn-off temp? If your turn-off temp is lower than the thermostat will allow the car to reach, that could explain everything. The OEM thermostat will try to keep engine temps above 180F (82C). Even with fans on full blast, the thermostat will be bypassing the radiator, and you just won't be able to get the temps much lower because of that. If the PFC doesn't let you adjust the turn-off temperature, it might just automatically run the fans until the temps decrease by 5 or 10 degrees. As Adam C recommended, the fan turn-on temp should be at least 90C, and the turn-off temp should be 85C or greater in my opinion.


6. You might want to ask your same question in the PFC forum. Not everyone here has a PFC, and not everyone who owns a PFC knows how to use it well. Personally, I'm running the stock ECU, so I can't really say "try this, it worked for me."


-s-

 

For starters Im not trying to attack anyone. All Im asking for is help and in what is IMO an unusual problem.

Im simply trying to relay ALL the facts that I know up to this point. In the probably less than 5 "I need help" threads Ive created I have done the same thing. IMO the more info the better.

If Ive hurt or offended anyone in my thread i apologize.

moconnor- I have my fans set as you described. The reason I bring up not trusting the DL is because it has been crashing/freezing/not saving things.

scotty305:
1. Im not expecting others to fix my problems, just asking for help and seeing who else has had this problem

2. The relays have been checked and found to be in good working order.

3. The car warms up normally, my original concern was that it seems to "stick" at the temp of 83 and 85. I was worried I was getting a bad reading and the car was running hot wich lead me to install the aftermarket gauge.

4. The PFC/DL combo is a neat toy, lets you mess with anything you want . As suggested I will raise the fans temps to higher temps.

5. AFAIK the fan off temp is when the temps dip back below the temp you set them to come. What you say makes sense, this is probably the reason it seems to stick at 83C. Maybe the PFC is taking the 82 in to account and Im just to ignorant to know that. I will raise fan temps.

6. The PFC forum doesn't get much traffic and I considered this more of a FD problem than a computer. After reading what has been suggested and tonights experimenting looks like I was (not a first).

Once again thanks for the help and I hope this thread helps someone else in the future.