This is a cross-post, also showing on Miata.net.

I’m frustrated beyond description. Have an FMII/Link turbo system, with the M-Tuned coolant reroute kit. Can’t run the AC without overheating. Here in the DC area, it’s hard not to use AC, especially since car is a daily driver.

We’ve tested – and replaced – the thermostat, proper side up. We’ve replaced the radiator. We’ve checked the hoses for blockages. Everything checks out. We’ve replaced the head, and installed an oversized gasket to lower compression and buy a bit more safety.

All this work has been done by an ASE Master Tech – so I have confidence it’s been done properly.

Run the AC on a 80 degree day, and the temp needle marches smartly up to the wrong end.

I’m about to drop a thermite grenade into the gas tank.

Anyone have any ideas of what we may have missed?

Thanks, in advance...

Supremely Frustrated Miata Pilot

 

Fans?

What radiator do you have?

 

Stock under tray installed? What sort of ducting do you have?

 

You cold probably go through this thread and answer your own question.

 

That was my first thought. I've had a miata overheat with AC on when the AC fan was dead. I assume the master tech checked that before everything else he did, but didn't see it mentioned.

 

Sorry...too irritated to think straight.

Fans are good - new, and working. Tested.

Tech is my son. I know where he lives, and he knows what could happen....

Undertray is in place, no custom ducting - just that which came from factory. At the speeds I drive, there's not much "duct effect" to be had most days. DC traffic normally sucks, which causes traffic jams...

Radiator is #4 - last one, all aluminum performance rad, cracked at the neck. IF there is a next one - I'm about to pull the AC off and just forget the whole blasted thing - it will be a FM cross-flow.

This car has been at son's shop for the majority of the summer, and it's still not driveable (to be fair, due to need for new clutch among other things), and I'm irritated beyond measure.

 

The fans might be working, but is the relay?

 

The fans are working, but do they come on when they are supposed to?

Has your son pressure tested the cooling system?

 

1. Does it overheat with a/c on below 25mph?

2. Does it overheat with a/c on at highway speeds?

3. What radiator are you using?

4. What size intercooler are you using?

5. What brand/temp thermostat? Have you tested it?

6. Post pictures of the front end with the heat exchanger stack. If your a/c condenser is 20yrs old and the car has 150k miles on it, it's a pretty safe bet the a/c condenser is blocking a ton of airflow due to its age. Also, ducting is a REQUIREMENT for getting the car to not overheat on the highway with a/c. As in custom ducting, the factory stuff isn't adequate.