Mazda Miata (1991) overheating problems

[Escoda]

Recently experiencing overheating problems, my fan seems to be turning on just fine, radiator is filled an working and so is the waterpump yet it still overheats? If anyone could help me with a solution or direction to look for my issue I'd be eternally grateful. 

 

For extra information:

The car doesn't overheat while idling, only on the highway after driving for about 30 minutes. 

 

I'm almost sure there's something electrical going completely haywire. 

Edited May 13, 2015 by Escoda

[loki]

How hard would it be to check that the thermostat hasn't failed?

[Escoda]

Already checked that, thermostat seems to be working just fine. I've dropped it in a cup with hot water and it opens up just fine.

 

Please keep in mind that I am not the most knowledgeable person when it comes to working on cars, that's sort of why I choose a Miata because there's more than enough material online to read and try to work things out yourself before bringing it to a garage. It's the first car that I am actually working on.

[loki]

just thinking about for a little longer, only thing i can think of is something is restricting your flow of cool coolant into/out of the engine.

[Drew Dowdell]

Could you have or be developing an air bubble in the cooling system?  Do you ever see foam in the radiator after a run (and after it has cooled enough to open)?

 

I also wonder if it is possible that something is up with the water pump.  

 

What ever it is, you're looking for something that could be restricting the flow of coolant.  At idle, the coolant is flowing enough to prevent overheating, but at speed, there isn't enough flow to cool the engine sufficiently. 

 

At highway speeds, the fans would do little if any cooling, the radiator gets all of its airflow from the movement of the car.

[G. David Felt]

Interseting, found that at 100K miles these autos tend to have over heating issues and it boils down to clogged radiators, clogged hoses and dead spot on the electric cooling fans so that the fans do not always work when you thing they will.

 

How many miles on your auto?

[Thed]

Water pump, clogged head gasket, clogged radiator, and a faulty thermostat all came to mind. Usually I'll just throw a new thermostat in there, just because they're so cheap and it can never hurt. Then a coolant flush would probably be in order. If it still overheats, your water pump is more than likely going out.