I have a 1996 Turbo Miata and I'm running into overheating problems. I'm running a mega squirt and am able to read the coolant temp off the laptop. I've noticed that when driving on the highway for a long time, temperatures will start to creep up. While driving at around 70 mph for around 20 minutes, I noticed that the dash temp gauge was starting to move past 12 o clock. I immediately looked over to my laptop and saw the temps were at 228 F. After letting it cool down on the side of the road, I kept going, with the heat on full blast, which allowed me to keep driving at 64 mph and have temps around 215 F. There is something wrong but I need helping to figure out what it is. The car never ran this hot in a while. *Note* I am running a stock cooling system, besides a 50mm Aluminum radiator, and have replaced the thermostat about a month ago. I replaced the thermostat because I was overheating, a very similar but worse situation to what I'm experiencing now. It is strange because I remember I used to be around 185 F while cruising on the highway. Now I'm thinking it's either the thermostat again(just replaced), or a water pump. But idk, do water pumps go bad besides just leaking?; they usually still work just leak right?.

Main Points:

• overheating on highway
• cruising temps around 214 F(with heater on full), use to be 185 F
• can regulate itself decently to around 200 F at idle
• Fans do work
• Turbo 1.8 engine, running 10 psi.
• stock cooling, for the most part, NO REROUTE
• amazon 50mm aluminum radiator
• just replaced thermostat
• just did coolant flush, it held a vacuum with coolant machine
• no air in the system, I used a vacuum filler
• not losing coolant.

Predictions:

• bad thermostat again?
• water pump?
• clogged radiator?
• head gasket? :(?

anything would help, thank you.

 

My guess is just not enough airflow is getting through your radiator. Seems to be a common issue. Try and make sure all of the air is ducted through the radiator, and seal off any areas that could allow air to bypass.

 

1. Use under-tray
2. Usually some ducting is needed.
3. Make sure that all of the air does not have to go through the FMIC to get to the radiator. Some air should by-pass the FMIC; typically above or below it.

DNM

 

You do have a good point, There is a possibility the radiator is partially clogged. I will try to flush it out and see if it makes a difference.

 

I'd guess probably not clogged, more likely not ducted very well and/or partially blocked by your intercooler.

 

I just fixed this issue with my fab 9 intercooler. It has been 90+ here and even without ac I was cruising around town at 210. With ac on if see a slow creep up to 230 if I’d let it.

my intercooler covered most of the bumper mouth. I made some brackets and tilted the intercooler back and down a bit. 100% fixed my issues. AC on full time today at 93 degrees and it barely ever goes over 200. IACs are barely changed. I have some ducting but honestly it barely made a difference prior to the repositioning the intercooler.

 

I have the Fab9 core too, it pretty much blocks the whole mouth, which makes ducting even more important. Do you have any pictures of mounting brackets you made?

 

After thinking about this some more I decided to go some more tests. I took the thermostat out and drove the car, It still was getting hot on the highway. Additionally, I used a pressure tester set to 14 psi. I found that the heater core hoses were leaking at 3 places, enough for it to leak down under the car. After tightening the worm clamps, It set it to 14 psi again and it went down to 13.5 after 1.5 hours sitting. It seems like those leaks could have caused my system to not perform as it should but IDK how big of a leak it would need to be to cause a problem. Tomorrow I will try to bleed the car, with the front jacked up, and see if the problem was those leaking hoses. Aswell I performed a compression test to see if there was any sign of a bad head gasket. The numbers were lower than the last time I checked but the variance is within spec.

 

Leaking hoses won't effect cooling ability unless you've lost a significant amount of coolant. The worst that will happen is it won't hold pressure which will lower the boiling point.
If you're cooling at idle but overheating at steady highway cruising speed, its an airflow issue. Is the undertray on? Running without it will cause overheating when moving due to stalled air.
You said you replaced the radiator, did you replace the fans as well? Are they maybe wired backwards which will make it push air forward? This will cool the radiator when stationary but will stall the air at speed and cause overheating.
Check both these things.

 

I thought I had an airflow problem but it was air in the system. Turbo, reroute, hard lines, big radiator, etc. bled the bypass in the back, then jacked it up way high, kept pumping the hoses and heater core hoses, etc trying to get every last bit of air out. took several tries of that and now it seems to run at the right temp all the time.

 

You need to get the yellow Lisle magic funnel. It sits in your radiator opening and allows you to keep water as the highest part of the system. I use that along with putting the front as high as possible in the air. Then run the car and let the fans cycle on for 3 or 4 times. Then let it cool down and make sure funnel stays full. Then cap it and run the car for a few fan cycles to verify everything is good.

 

Yes, this is exactly what i do and it gets pretty much all the air out of the system.

 

UPDATE: I ran the car with a cooling system cleaner and distilled water, drained refilled with coolant, and bled. For the bleeding, I had the front jacked up and I used a tall no-spill funnel. Additionally, I changed the angle of the FMIC so that it leans back and has a gap on top that air can flow into through the radiator. After bleeding the car for about two fan cycles. I drove it for about an hour and a half and it still seems to be running hot. If it drove too fast for too long on the highway, it would start to creep up. Though this sounds normal for any car, I can't remember it doing this. It used to be able to take a beating. At this point, it drives fine and takes a lot of ripping to get it too hot. I'm satisfied enough right now with how it is. I don't know if this is just how my cooling system is, without a reroute, But ill look into getting a reroute in the future.