Keith Park

Early 93, 34Kmi, nearly bone stock, fine around town on a 90+ day, Ok, maybe a bit warm but if you turn on the AC, moving or not the temp on my digital gauge

Will head up and I turn off the AC as it approaches 240, the stock gauge naturally never moves.



This is with all fans forced on, so its not a fan relay…. Put a new radiator in it last year that was supposed to be for a later model with an extra row of cooling

But to be honest, it looked identical to the original radiator, so weather its bigger or not I don’t know but it was new. Radiator fluid flushed and changed every 5 years, always comes out looking clean, so I think the radiator is OK, nothing blocking it.



Temp goes up fast when AC is switched on, I had the AC recharged for the first time last summer so it works great but… when I switch it off temps don’t really start to go down till I turn off the interior fan, THEN it cools rapidly. It has had issues with trying to run too hot with the AC on on a hot day in the past, its why I put the radiator in it last year but this is the first time its been hot since I did that and got the system has been re-charged so it can work. Its definitely worse now though. Everything in the cooling system seems to be working, but..

it also has the new aluminum expansion tank, I put that on when I got it.



Ideas?



Thanks



Keith

arghx

iTrader: (3)

Where are you measuring the temperature?

DaleClark

iTrader: (55)

May also be worth putting a new Mazda thermostat in. Old or flaky thermostats will do all sorts of weird stuff.

When you turn on your AC does it cool the cabin down well? Are the fans on when the AC is on?

Do you have the precat or a downpipe?

Dale

Sgtblue

iTrader: (16)

+ 1 on replacing the T-stat. Personally I’d go OEM and make sure the jiggle-pin is at 12:00 o’clock.

Other things that might help…
* Use as much distilled water to coolant as possible, but not less than about 20% (coolant).
* S5 FC fan thermoswitch
* Bite the bullet and get a larger capacity aftermarket radiator.
* check the hidden back face of the A/C condenser for debris
* look thru the nose and stuff upholstery foam in any gaps around the radiator face and duct that you see.
* Check the face of the oil cooler(s) for debris and straighten any bent fins
* check hoses for anything that may have accidentally gotten kinked or pinched with the radiator replacement.

Keith Park

I did put a new mazda thermostat in with the new radiator, records are showing 2017 but its only been driven 6Kmi since then.
AC works great, had it charged for the first time last year and its ice cold
It has a racing beat Catback, rest is original and stock.
fans are all on.
Temperature is measured on the filler neck, above the radiator hose and below the cap, about halfway down.

I do have the FC fan thermoswitch in it.

Everything looks pristine clean in there, car is never drivin in dirty conditions...Ill have to check the hoses more carefully tomorrow. When I did the radiator I did want
to put a nice aluminum one in there like I had in my old FC, but at the time they all needed mod's to fit and I didnt want to modify the near bone stock car so I
didnt go that route. Besides, this care used to be fine running the AC on a hot day, as I recall the temps would go up then the fans kicked on and down they came again, never
anything approaching overheating so while not the best, the stock radiator should at least let me drive it normally on a hot day with the AC on.

Thanks,

Keith

arghx

iTrader: (3)

In the past you report it did not overheat, but were you measuring the same way?

Keith Park

correct. I put the digital gauge on it when I got it in 05, and it used to be OK with the AC On despite the heat. starting having issues before I put the new radiator
in and now afterward. I didnt really use it much in the heat past couple of years but temps have always been measured the same way with the same sensor in the same location.

Keith

DaveW

Just a guess, but check the wiring/grounding related to the digital gauge for issues. Also the gauge display itself or its sensor could have a problem. It could just be a faulty reading since your stock gauge is not showing any problems, not that it's that useful....

Any chance the voltage source for the display or sensor is the same as the power source for the AC compressor clutch?

Keith Park

Those are good points, the voltage source for the gauge was from the fuse box if I recall right, that was 15+ years ago when I wired it up though,
this is something that used to be fine though, and the wiring hasnt changed so I suspect Im getting the right readings but putting a thermocouple on the
filler neck to verify isnt a bad idea. Ive always gotten quick and distinct temp changes there in that location, from 180 to 230 depending on outside temp, how im driving, and using AC or not while the "Painted needle gauge" has never moved except up to park the needle when it warms up.

I think Ill try changing out the thermostat first.

on additional note, the heat in the car has become poorer over the years, I suspect the heater core is getting plugged... its the original, but this wouldnt affect the
coolant flow thru the radiator when the heat is off would it?

Thanks

Keith

Axton

If I'm remembering right, the FD cooling system is open loop, meaning that it still circulates through the heater core even when the heat is off. It's not fun removing the dash and taking the core out, but removing the upper and lower hoses and trying to flush it from the engine bay side with a hose might be worth a shot?

Sadly, new heater cores are NLA from Mazda.

Keith Park

this leads me to ask a question, suppose the core is plugged solid, would that disrupt the flow of coolant enough that it would
lead to a cooling issue with the AC on like I have?

are there any alternatives for the heater core in the aftermarket? or is my driving season going to get shorter and shorter as I get
less and less heat...

Thanks

Keith

Axton

If the heater core is plugged solid, it will begin to over heat whether the AC is on or not, then you might experience a foot well full of coolant (ask me how I know 😞 ). The end tanks of the heat core is plastic and the radiator shops I took it to didn't want to touch it.

I couldn't find an alternative a year ago, unless you provide the original one to someone who's willing to build a replacement. I ended up getting lucky and found a removed HVAC with a good core still in it online and used it as a replacement.

I was able to drive the car with the bad core in it temporarily by bypassing the heater core. (Remove the line coming from the engine to the core and connecting it where the other ran to) but it was terrible in winter.

Come to think of it, you really have brought up a good point on this. I worked with PWR here in Australia and have their Radiator and AST in my car. Maybe if I reach out to them and send my old heater core to them, they might decide to start manufacturing replacements 🤔

arghx

iTrader: (3)

Unfortunately heater core failure does happen on these cars and it's an ordeal to fix.

Keith Park

Well my heater core does pass enough coolant to give me SOME heat for the late fall and early spring I drive it when the salt is off the roads,
but I suppose I could put a bypass valve in it for the summer use... IF thats the problem. cant think of much else, but Ill try a thermostat.

Keith

Axton

If you're going to dig in and replace the thermostat, it might be worth considering doing the water pump at the same time while you're in there. It's not that much extra to do and might help with the cooling. The pump fins can corrode out when left sitting for some time with coolant still in the motor.

mecman

iTrader: (11)

I can vouch for the Thermostat replacement. Before you put the new one in, you can test it by putting it into boiling water to see if it opens. And down the line I would definitely replace your radiator with a Fluidyne or Koyo all aluminum one.

gdub29e

iTrader: (16)

An easy way to see if your heater core is getting plugged up or not is to warm the car up to operating temp and feel the differences between the heater core hoses running into and out of the firewall. They should be the same temp. If one is hot and the other luke warm, it’s a pretty good indicator. You can use a infrared thermometer to make it a lot easier. Turning the fan all the way up and turning the temp to max warm won’t make a difference for this because the fd does not have A heater core shut off valve. The heater core circuit is a separate loop from the main cooling path that runs through the short block. Even if the heater core was completely plugged, it shouldn’t affect what you are seeing. A faulty thermostat will definitely give you those symptoms. It’s easy to test one and it’s in the shop manual how. I agree with a good koyo radiator. Also as a side note I would make sure your cooling fans are both operating correctly ( bumping up speed when the ac is on ). If only one fan was working, it could exhibit the same symptoms.

These threads will help you>
https://www.rx7club.com/3rd-generati...-876767/page2/

https://www.rx7club.com/3rd-generati...thread-571088/

This is for a koyo on a bone stock car without any modifications.

https://www.rx7club.com/3rd-generati...-tips-1107155/

~ GW

Keith Park

Ok, since were talking about it, tell me about the Koyo and Fluidine... I put a Koyo in my 10th years ago and it was an excellent improvement. As I recall
there were mods to make to make them fit, this car is close to bone stock and I really dont want to hack up anything but if your familiar with how to make them fit
please let me know, Ive never felt I had enough radiator, or enough flow thru it... even when I first got the car when I hillclimbed it and ran heavy throttle Id have 2-3 minutes before I had to stop and let it cool on the steep parts, and that was with it doing nearly 100mph at the time on a cool day.

Thanks

Keith

gdub29e

iTrader: (16)

Keith - Check out the third link I posted from Banzai. It has a step by step for the Koyo with minimal adjustments that you won’t even notice for a bone stock car.

I run the standard koyo “ R Series (93+ RX-7) HH060644 “ it’s a quality unit and pretty much drop in. I do run a standard temp thermostat as well. Never had an issue with excessive temps. The koyo N-flow is dual pass that I feel is overkill for a street car, but I’m sure some will disagree.

Keith Park

Thanks, this is helpful, Koyo install doesnt look bad at all!
Today I drove it home, only 75 degree's out, not 92 this time but I ran the AC cause you dont drive these cars in the rain with the windows cracked
and it did NOT run hot, 202... heck it runs hotter than that sometimes without the AC on. So thermostat is now looking more likely, will change that next and
try it on a hot day. I didnt expect it to run as hot as on a hot day but it didnt even approach that.

Keith

Oppai

I actually had the exact same problem driving my car at 7's day.
In HEAVY (times square) traffic, water temps creep beyond 220, peaked at 240 with AC on.
Oil temps I saw go as high as 260.
Will be replacing my tstat and possibly looking at a rad upgrade too while I'm at it.
My temps would both drop very rapidly once the car got moving at all, so it makes me think it's probably not a stuck tstat.
I'm also wondering if it's possible my cheap glowshift gauges are just reading high.

DaveW

That makes me think the fans are either not working properly or not sealed enough to draw only cool air through the radiator.

Oppai

The fans definitely run full blast when the ignition is on and engine off. When engine is on it's difficult to hear. I can hear them on but can't really tell what speed they're running at.
I have a factory undertray on the car with stock fans and stock fan shroud so I don't see why it wouldn't seal.
If it's an issue with the fans running weak then turning the AC on shouldn't make the temps creep higher since the AC should make fans turn full blast no?
I'll take some stuff out and check if I'm down to one fan or something.
Any place you would recommend to start troubleshooting the fans electrically?

gdub29e

iTrader: (16)

Read post #17. First link is what you need.


~ GW

DaveW

That was my point - if the fans work correctly, at low engine load at low speed or standing still, the fans come on when AC is on and should be able to keep the coolant temperature down close to the T-stat opening temperature. If they don't, then you'd see exactly what you describe: with AC on, coolant temperature rises at a standstill but drops as soon as you get moving and there is ambient airflow through the radiator.