Is my car running hot OR WHAT?!?
 

So, I installed my brand-spankin' new PowerFC last week and have started monitoring my water temp on the commander. After driving for about 20 minutes or so, The commander shows a temp of 110 degreees Celcius. If I drive the car hard for a few minutes, the temps creep up to 118-121 C. At that point, the guage in the dash starts creeping up to towards the top, which is obviously when I already have the heat blowing and start driving with no boost.

The car only has about 39,000 miles on it. Everything looks like it's in great condition, but who knows? I'm not losing any coolant and the car pulls nice and hard whenever I want it to.

What could be causing this? Is a simple radiator replacement the solution?

Thanks,

Ian

the fan switch mod will help a great deal. i had a similar thing happen to me when i put in my pfc and commander. i bet it always ran that hot and i just never knew without the gauge.

however i noticed in your mods you have the petit fan switch, so its possible a new radiator is in order. my koyo droped my temps a few degrees celsius. with a setup surprisingly similar to yours my car very rarely goes over 95c. good luck

Are your fans working ?

are you crazy!?? it hit 110C and THEN you drove it HARD!? and you let it get up to 121!!??!!?!?!?! You're lucky if your engine isnt dead. i stop driving at around 94-96 C, and pull over.

At 121C , you are probably boiling coolant, assuming you've got the stock 13psi pressure cap.

I would replace the thermostat and also both pressure caps (the one on the filler neck and the one on the AST). I use new OEM Mazda replacements for the thermostat and filler neck cap (no spring), but a Stant 16psi cap for the AST.


Check this thread out for some more cooling system info:

The Big Fat FD3S Cooling Thread
https://www.rx7club.com/3rd-generation-specific-1993-2002-16/big-fat-fd3s-cooling-thread-571088/

-s-

the PFC can adjust when the fans come on i believe, no real need for the fan mod switch unless your in stop and go traffic alot, I think?

but u seem to have other over heating issues that might be big. you have the radiator underpannel on right? you may be needing a new water pump better have your car checked. if the needle on the stock gauges ever moves above half where it normally sits, you are in big trouble, stop driving.

he has the petit fan switch. plus you need a dataloggit to adjust the temp settings.

To stop driving at 94-96 is a little much I think. When I had the stock radiator my PFC kicked the fans on at 92C I think, and I never saw tempertaures above 98C even when it was 92F outside in traffic. I like to keep my car in the 90s but never go over the 100C mark, but now it never goes a degree above where the fans kick on with the Koyo.

It certainly sounds like a problem in the stock cooling system, I would figure out what the problem is before trying to upgrade to a new radiator. If you get anything above 105C you MUST cool the car down, thats to hot to be driving it hard.

Yeah, your'e running way too hot. While 39k isn't a lot of miles, it's still almost 15 years old. So thermostats, pressure caps, etc can malfunction.

I suggest you take it to a good FD mechanic and have them work things out. While I'm an advocate of doing the research and trying things yourself, I suspect you'd be better served having an expert solve the problem right away. Then you can try other less critical jobs yourself and enjoy the car without overheating it. Plus that mechanic can see if the engine is damaged from that seriously high temperature it's been exposed to.

Dave

depends on the application.
daily driving in normal weather i wud be bothered if it rose above 105degC.
whereas when on the track i often get upto 117degC...and have had no problems.

i think some ppl are a bit obsessive about it.

Damn 121C?????

Holy crap, i freak out when im city driving and i see 190-200F on the gauge LOL.

That seems a bit paranoid but better safe than sorry.

i've never seen my temps go over 88c. my fans are hooked up to the ignition switch so they stay on all the time. i am super paranoid when it comes to my FD

Same with me.

I did the lazy man AC relay mod so whenever i see the gauge at already 160F, i put the fans on, then if im on the highway or freeway, i shut it off. But since i do mostly city driving when i take out the FD, fans basically stay on all the time.

121? Way too hot. These are the kind of temperatures you should see from heat soak - not driving the car. Check your thermostat because it sounds like it's stuck partially open (and yes, this does happen - particularly when a car has been sitting for a while, 39k on a car would indicate that).

Same with me.

Allright, so I just cam from my mecahnic's and I just ordered a new thermostat, so hopefully that will solve my issue. If not, then we'll go from there by checking the water pump & radiator.

I'll keep y'all updated.

Thanks for your input,

Ian

Is there any reason to not have the fans running all the time? I would like to just hardwire the fans so they always keep on, can I do this with the PFC?

There is so much BS in this thread it's not even funny.

1. With the stock caps and "normal" coolant/water mix, the coolant will not boil over until over 120C.

2. All you guys worried about hitting 100C are just plain ignorant. The stock ecu/switch doesn't even turn the fans on to LOW until 105C. While it's better for daily use to keep temps REASONABLE, there is nothing wrong with hitting 100-105C in hot weather with the A/C on. When tracking the car, it takes a LOT of modification to keep the car below 105-110C on a hot day.

3. This guy doesn't need a new radiator or fans, he needs a new t-stat. New caps would certainly be good idea as well.

4. Running the fans all of the time is DUMB. It is just pointless wear on the fan motors. Once the t-stat closes, the fans will be doing little but wearing out.

I don't see above 86 on the PFC and solid 190 on Defi D gauge. It's a downside to have your fans on all the time bc it's harder to warm up the car. I have one fan constantly on and a switch to control the 2nd fan.

No real benefit once the car is moving. In addition, and I'm not quite sure how much real effect it would have, one could say that having fans trying to pull in air while air is being forced through the radiator at speed is two systems not totally working with each other at that point.

I've driven with fans on the entire time for 40 miles and then fans in normal mode for the 40 miles back. No significant difference - monitored via a PFC and a DEFI temp gauge - so save your fan life.

Ok, so now the question, where is the best place to buy the new t-stat and caps? I don't see them on the rx7store.net site. Where can I get them all at the same time?

Sounds like you're on the right track. WP is relatively easy to check and if you're not losing coolant than it's probably not excessively weeping.

One subjective way of determing if the t-stat is corroded open is remembering how long it takes for the car to heat up.

If it takes an excessive amount of time to heat up and never fully heats up, then the t-stat is typically stuck wide-open.
If it takes still a long time to heat up and then keeps heating up until it's very hot (sounds like your condition), then the t-stat is typicall stuck partially open - meaning that during cold start there is too much flow (there should be none) and when warm, not enough flow.

I'll put 5$ on it that when your t-stat comes out you can see a small gap between the plunger and the outer flange.

Mazda dealer. You do buy oil filters right?

Listen to rynberg - he knows what he is talking about.

Threads like these are a perfect example of why non-mechanically experienced people should never buy an FD unless they're prepared to pay a bunch of other people to fix it all the time. This doesn't mean one has had to have owned their own shop - but atleast know how to pull an engine, replace a clutch, replace a water pump, replace a timing belt/chain/whatever (on a standard engine), flush coolant, bleed brakes, replace rotors, replace pads, and replace any basic mechanical component on the car. Additionally if one has done head/cam/crank/piston install/replacement/rebuilds before, then they'll be prepared to learn rotary internals relatively easily as well. This is not a "my first performance car" car.

The car is pretty much a track car from the factory that requires semi-constant attention and mechanical knowledge to keep from being overtaken by "voodoo" problems that are really just typical automotive issues in general. Other than the rotary, all the systems used in the car are completely standard among Japanese cars.

Well its summer time so im sure the car will warm up anyway.

I like to be safe. It already became a habit of just switching the fan on when i hit around 170-180F because at least i know when im driving i wont forget.

I remember one time i forgot to switch the fan on and i like 35 min past and i looked at the gauge it was about 210F. I was like damn, time to hit those fans LOL