mx5cartalk.com

Hi all,
Had a crack'in day at the Winton track day last Sunday, drove home to Melb. never missed a beat, i drove the car to work on Thursday, after a 40 min. drive (in some traffic) or the first time ever i noticed my thermo fan come on and stay on after i turned the car off. I came back to it 30mins mins later and the fans were still on...the gauge was still only on half which is what it normally on.
I felt the top hose and it was HOT, top of the radiator was HOT, but the bottom hose was cold.
May be a dumb question but is this a stuck thermostat, or some thing more serious!!
TSM

To me it sounds like a stuck thermostat (that is letting some heat past into the top hose) or a dead water pump.

What's the easiet way to diagnose thermostat versus water pump? I think i will take the opportunity to flush the coolant etc.
TSM

The coolant fan was on even though the ignition was turned off? Sounds like a stuck relay of some sort.

Yeh, i thought that was also weird....

It stayed on for a good 30-40 minutes after i got home, i eventually un-plugged it to stop the battery going flat.

So diognosis so far, is potential stuck thermostat, or busted water pump (or both) , and dodgey thermo fan relay????

Is the the relay a Mazda spare part?

TSM

Fan switches off with ignition regardless of temp. Busted relay is my guess. If the engine was hot the gauge would have moved, so no drama there, just the relay.

You sure about that Bigdog? The fan on my NA6 will occasionally stay on for a minute or so after the ignition has been switched off, after a quick but spirited track session. Most commonly occurs after a single lap event like a hillclimb.

On my NB it switches off - I was looking at rewiring mine to stay on till the temp drops to save popping the bonnet up after runs. I stand corrected if the NA has more sensible wiring Nevertheless I think the OP's relay is toast.

My NA (and other NA's I've used) have never kept the fan on with the ignition off.

OK, so as a process of elimination, should i remove / replace, thermostat? and replace thermo fan relay, then see if problem solved? if not repalce water pump??

TSM

Well is there any other signs of overheating or is it just that the fans are staying on? Have the fans ever gone off since?

Thermostat is pretty easy to replace in a stock MX5 (mine is now at the back of the head) I find it very unusal that the fans stay on with the ignition off.

http://www.miata.net/garage/CoolingSystemProblems.html

the fan should activate if the ignition switch is on

http://forum.miata.net/vb/archive/index.php/t-249000.html

Should the fan run with the ignition off ?

Nope. If that happens, the fan relay got stuck closed, and it has happened to some owners here.

Temp gauge was at normal pos., no other signs, i did notice it getting hot through the Gearbox tunnel in the cockpit, my car is a track car so no carpet etc.!

Did start idleing a littler higher than normal...

After i unplugged the fans after they were running for 40mins at home, i have not dríven it again until i sort it out...

TSM

OK, so just priced the Thermo fan relay from Mazda ($50) and to buy the thermostat gaskets require you to buy it with one of the hoses that attached to the thermostat housing ($140 ex-Japan), oh and priced a Water pump just in case ($239).

Hoping for a weekend job, does anyone know if the relay needs to be OEM, Mazda can't get one for 4 days...

TSM

Sorry if my comment led you astray, I got the impression your car was running hotter than standard just try a relay first.

Sounds like nothing's wrong with the thermostat. Hot water exits the head, passes through the thermostat into the top of the radiator. It cools on the way down and emerges just warm at the bottom before going through the pump and engine again. No problems.

The fan relay is probably toast though.