MX5 Overheating? Temp gauge high

[sabretooth]

That seems a bit high to me. Does the temperature go down if you turn on the heater to full?

The easy thing to check is that the coolant levels are OK.
Next I'd be wanting to check if thet op radiator hose gets hot when the temperature hits the halfway mark.

Then the thermostat - I'd do the boiling water test on it to make sure it's opening up.

FWIW mine sits a smidge below the halfway mark.

[Matty]

yeah, something's not right. Get it looked at, but possibilities include thermostat, head gasket, radiator core, and probably others.

As sabre said, a smidge below half is normal for a 1.6 (there's a big deadband in the gauge there)

[Miata Bart]

if the number plate is in mouth restricting air flow through the radiator, relocate it.

[Mr Morlock]

li21 I doubt the number plate is the culprit. If you cook your engine which can happen in a blink then the cost can be high. Better to get it checked and cleaned. People often scoff at preventative maintenance but it has much to recommend it. Not so long ago I ignored very minor leak around a water pump and it subsequently seized and broke a timing belt - silly boy!

[rossint]

My car did the same thing when I bought it. I changed the thermostat which helped a little but didn't fix the problem. My mechanic pulled the radiator out and got it checked, the cooling system was over 70% blocked so he cleaned it all out and now my car no longer overheats.

[Miata Bart]

If you dont know the service history of a car it always pays to drop the contents of the radiator/cooling system/heater & replace with the correct coolant.

But hey, why not take the plate off & give it a run.

My first NA ran hot because of the plate in the mouth. Only in Summer though when the weather was hot. It was just enough to cause a problem.

So also was the aftermarket grill. Great for winter, no good for summer.

Other simple causes can be bugs caught in the cooling fins, bent fins & any other external stuff that can reduce the efficiency of the radiator.


Relative to thermostats - easiest check is to take it out & drive the car until it reaches operating temperature. If it is running lower than before, it may be the problem.

I did have a heating issue with both mine & on both occasions a cooler high flow thermostat did the fix. If the thermo is part of the problem buy this part. TRIDON TT240-160. They run a fair bit cooler than standard & are the duck's guts.


Radiator caps can be a problem too. They are made to flow both ways - to & from the expansion tank.

All these fixes are cheap & easy, but if there are bubbles in the coolant when the cap is off you may have major dramas (but I know you would have checked for that before you bought it).

Work through all of the problems as ypu say, cheapest to the more expensive and only one at a time so you identify the cause. It can also be a cumulative effect of a few minor problems.


I had an overheating problem on one occasion where the bottom radiator hose was too soft. When under heat & the revs were up the rubber pipe would vacuum somewhat thus reducing the flow & causing problems.

All part of the fun.

[Miata Bart]

yep.

it will also be higher as the engine is warming up.

[john!]

From experience, if you have a car with an uncertain service history, replacing items like thermostats is just preventative maintenance. Almost found this out the hard way with a second hand engine where the thermostat stuck and most of my coolant was subsequently pumped out the overflow tank. It is worthwhile if you haven't already done so to throw a few dollars at getting the radiator reconditioned as well, especially if the top tank is looking a bit brown and faded, they do tend to crack with age. Might cost a few hundred to get it all done, but that is still cheaper than a new engine.

john