Miata overheating

Hi all, my son's girlfriend recently bought a 97 Miata and has been chasing issues since day one.

The timing belt and water pump were replaced, the thermostat was replaced, all kinds of oil leaks so all seals and the valve cover gasket were replaced. On a drive from West Palm to Lakeland (around 150 to 200 miles), the transmission went out (automatic). Got that fixed for a steep price. The tranny shop basically said something melted inside and shot the whole thing.

The car still overheats while driving on the freeway after about 50 miles. Have to stop and wait 10 minutes or so to cool down and resume driving. It is not leaking water, seems to be an internal issue.

I love cars, but don't know squat about working on them, generally I just go to a shop. But the ones around here apparently cannot figure it out.

Any suggestions for what to look for ? Or does anyone know a shop that is good with Miatas in the West Palm Beach area ?

Thanks, Bill

Maybe the Miata is expressing its disdain at having been fitted with an automatic transmission .

Not just a radiator blockage is it?

I'd bet it's radiator related. New ones are pretty cheapish at $100 or so. I'd swap that bad boy out and see how it goes. First I'd check to make sure nothing is blocking the rad. I'm sure any shop you've taken it to has done this but why not check it yourself?

Might be a silly question...does the car have good heat? If the heat is weak you could have a blocked heater core. Miata's send some water through the core. I'm just guessing that a blocked heater core might cause some flow issues. If heat is never heat you're not getting decent flow through the core.

Another thing...GREAT TON of information at www.miata.net. Tons of overheat threads on there.

Check the head gasket. I've got an overheating Miata right now, and after replacing everything including the water pump, radiator, thermostat, hoses, and so on, the head gasket finished dying and let me know what is the real problem.

As an aside, when I bought the car, the PO had put on a new cam belt. He mis-timed the cams (both were advanced one tooth) which made the car sluggish and prone to overheating at highway speeds.

Thanks for the tips. I'll see if she has heat or not to check the heater core. I'll check with her on the head gasket as well, not sure if she had that replaced.

If the radiator is blocked, how would I check that ? I'll hop over to the Miata.net site as well and glean some stuff there.

As far as the car having disdain on being an autotomatic.. I offered to teach her how to drive a stick with my Miata, but did not want to. Kids these days

Thanks ! Bill

Check to see if the fans come on too.

Keith beat me. Especially with the long list of work that has recently been done, it wouldnt surprise me at all to find that someone has broken the temp sensor that drives the fans(got the t-shirt). It can look solid and still be broken internally. If the fans work, I would then make sure that the radiator flows properly. An infared pyrometer works great here.

I ran across an oddball problem on a Miata a while back, the fans came on but no airflow. Whaa? Turns out the 5mm nuts that hold the blades to the motors were MIA, the fans just fell off the shafts. Pulled the motors, reinstalled the blades with nuts I scrounged out of my junk box (and a dab of Loctite), no more problems.

But if the car overheats at highway speeds, the fans aren't the issue. Inoperative fans will only cause overheating if the car is idling at a stop or at very low speeds. Since it takes a while (50 miles) to manifest itself, that sorta rules out coolant flow in the radiator issues, that generally happens pretty quickly as in: the car will do fine around town and as soon as you get on the highway the temp will rise, it will go back down as you slow down but it takes a while.

So I lean towads a bad HG as well. Sorry about that.

You could get the cooling system back flushed or do it yourself. Heater core,easy check, one pipe would be hot the other not so. Will not cause overheating.

I disagree on the radiator flow issue. When we built the EGT ITA car the thing could be driven around the back roads and subdivision with no issues on overheating but two or more laps at the track at full throttle would cause overheating. David Green allowed us to go to his dealership and remove a radiator from a used car on the lot and those radiators would work just great. We could never get that OEM radiator to work so we eventually threw it away and replaced it with a new one. YMMV

Jensenman wrote: But if the car overheats at highway speeds, the fans aren't the issue. Inoperative fans will only cause overheating if the car is idling at a stop or at very low speeds.

I disagree with this - fans have a considerable effect at highway speed. I actually own a Miata that would overheat on the highway and only the highway. It's modified, of course. A set of upgraded fans solved the problem where various radiators and other "solutions" didn't.

And hey, it's easy to check fan function. Miata head gaskets are pretty tough to kill, you usually have to overheat the car using some other method before it'll let get.

Hmmm. If the fans help at highway speed, then the problem is insufficient airflow. That's a well known problem with Jensen Healeys, the snout is designed in such a way that it's difficult to get good airflow at highway speed. That's why you will see a myraid of different chin spoilers etc which do nothing more than channel extra air through the radiator. Mine used to run constantly at ~210-215 degrees even with a 3 core radiator and a fan shroud, I made a (rather chintzy looking) sheet aluminum 'scoop' which channeled more air into the radiator, voila: ~180-185 degree temps with a 180 t-stat.

Had a similiar problem when I bought my 99 Miata. Went through the whole cooling system. Thermistat (2 of them), water pump and checked the fans. Even back flushed the radiator. Replacing the radiator fixed the issue. Mine would overheat at highway speeds but stay around the normal range at in town speeds all day. Had flow through the radiator, just not enough to handle higher speeds.

Then the AZ water pump went out on the highway about 20 miles from anything and toasted the engine getting to the next exit. No issues with the low mileage 2000 engine and new radiator. Nothing but Mazda, Mazdaspeed or quality better than stock aftermarket now for the car.

In reply to Jensenman:

11 years ago while living in Arizona i could drive this car on a 110 degree day one mile per hour per degree and the needle never got past halfway. Now, when I get it up to 80 it almost pins to extreme hot. I have changed everything - head gasket, radiator, hoses, thermostats, what-have-you, to no avail. Now it occurs to me that in Arizona there was no front license plate - but here in New York there is. Is this logical? could it be that simple to fix? (I'm gonna try it anyway! - but would appreciate some conjecture or experience on this. thanks!

dukerino, I guess it's possible. A J-H owning buddy here in Charleston cut a hole in his front bumper to fix a highway speed overheating problem. What kind of car are you working with? If it's a Jensen Healey, then yeah ANYTHING that interferes with airflow can definitely cause highway speed overheating. I also once had a Courier pickup which ran nice and cool around town, on the highway bam! peg the gauge. Sent the radiator out, someone had used block sealer and abouth half the tubes were clogged. Stuck in a boneyard radiator, it then ran at normal temps no matter what.

Once when changing Miata hoses, I discovered that the small aluminum elbow was full of corrosion and creating a restriction. It might be worth checking out. It's pretty easy.