So, I just overheated the Miata. It hit 240F, I immediately went into procedures to cool it down.

I had no problem whatsoever keeping it cool after that under freeway speeds, and I noticed no boiling coolant in the overflow - although if I took it to freeway speeds, it sure wanted to overheat. There's nothing coming out of the exhaust. However, I have no way of diagnosing anything further or even doing anything on the Miata until I get back to where all my tools are stored, which is a good 2.5-3 hours away.

What do I do guys?

 

This is the age of knowing how to get things done.

 

Use a paperclip to jumper ten and TFA with the ignition on to see if your fans are operating properly. I had a similar situation where the fan would come on, but wasn't spinning fast enough because of a loose connection.

Could also be a waterpump failing or cavitating, but that's harder to diagnose on the road.

 

Verified fan operation, thank you. They do definitely work.

FUUUU... This would be bad. I have enough tools on hand to pull the water pump belt, but I fear that's all I've got. Would it be possible to run it to a parts store without risking severe damage? Any chance of verifying operation/engine health to be able to get back?

 

If this was a fan problem, I'd expect it to be fine on the highway but overheat at lower speed, not the opposite. He should be able to drive non-stop at 80 MPH with no fans at all.


OP- Has the cooling system ever been flushed out in your history of ownership of the car? Have any modifications been made to the cooling system? Anything you can think of that would cause it to not quite be up to par in general?

 

What does it do at idle? does it continue to heat up after the fans have kicked on? And are you absolutely sure it's climbing that high and not a false reading?

Depending on how high it climbs and how fast would be the real test of if you can get it to the parts store or not.

 

Once a year coolant flushes.

Yeah. New rad was just put in, but I just realized that I left the gorramn shroud/ducting to the rad off because the new intercooler didn't fit with it on and I was in a situation of not making class.

I'm thoroughly facepalming at the moment.

It runs hot (210-220F) at ~70mph. It only gets hotter from there at faster than 70mph. It runs completely normally at < 60mph (< 200F), and it idles perfectly. The temperature is verified across two sensors - I seriously doubt they both would be acting up.

 

I had a heater hose blow apart and lost all mo coolant once, leaving me to drive the car home nearly 15 miles. Filled with water, started car, drove until hot, stopped. Rinse, repeat, all the way home.

It is possible to limp home with a compromised cooling system, but it's a real test of patience.

 

That's it.

Even with better than stock ducting, my massive intercooler core just doesn't allow enough cool air to get to the rad.

Turn the heat on full. Limp it back.

 

This being the case, it sounds to me like an air flow/heat exchange issue. Added stress on the engine (over 70mph) may just be enough to push the engine over it's current cooling limits with a missing shroud and intercooler blocking some airflow. The radiator was just replaced, perhaps it has a blockage from the factory? It is possible to have a bum part.


Edit: Erat beat me to the punchline.

 

Thank you. This is going to be a real test of patience.

It is possible, I'll dissect it when I get back. Thank you again Diesel.

Argh - this definitely explains my plight. I think I'll just let the Miata cool down, wait until it cools down outside, then see what I can do from there. It does NOT leak coolant - the coolant system operates normally so long as I don't exceed the capacity of the system to displace heat, I'm not in that situation, it's just a question of engine damage and potential damage caused at this point.

Thank you everyone. I'll wait for it to cool down outside and limp my way back.

 

Since you caught it at 240 and there are no other signs, I think it is unlikely that you have any permanent damage.

 

Thanks Hornet, that is a *huge* relief to hear.

The engine is properly sucking back coolant. I lost no coolant, I have no air in the system, and as far as I can tell I can see no oil in the coolant nor other indications of a compromised head gasket in the system.

I do appreciate the help guys, I think I'm just going to wait until it gets late (And cools down a lot!), then limp it where I need to be.

 

To add to the above: I'm pretty confident the brand new radiator cap is bad now.

Which is seriously aggravating. To anyone that searches this thread: CHECK YOUR RADIATOR CAP, even if it's brand new.

 

The big trouble with a bad rad cap is that the max temp of the coolant goes down. IE with a completely blown cap the highest temp a 50/50 mix can reach is 233, then its boiling and the temperature will not increase until all the coolant is vapor. Which means of course that while the coolant isnt getting any hotter the rest of the engine is. So when you're expecting 240 to be OH **** temp, but the rad cap let go, 230 is your new OH **** temp.

 

Thanks again folks. Everything seems okay, at least as okay as it could be - but I'm definitely making plans for a engine rebuild ASAP with a new head.

Thanks Leafy! Great info! I read during my googling that "percolator noises" were a sign of a bad rad cap, but they ended up coming from my heater core (wtf?) once I had an opportunity to really start tracking them down.

 

Engine rebuild? Pffft It's fine.

Mines tapped 240 before. It still works fine.

In fact, i found out my stock temp gauge doesn't even start to move up until after 230f.

 

I'm having the same problem.. it just seems to get worse.. 1st it was a foul fan switch.. which i replaced.. STILL overheating.. coffee pot / perculating sounds when you turn it off... im going to get a new rad cap and install some hood louvers.. then take it from there

 

Great idea. Take an already compromised cooling system and make it worse.

 

By hood louvers you mean vents right? The cooling system should work just fine without them. Even here in PHX at 120 degrees I don't over heat on the highway or in traffic. And I don't have any hood louvers.