Overheating Problem

[alanyboy]

My MX-5 has suddenly developed an overheating problem which is most annoying. The gauge will go up to around the 3/4 mark when sat at about 50-70mph or 4000rpm. So far I have replaced the radiator and dug the water pump out to check for missing impellers but all is fine.

Any ideas on what it could be ?

[_Batty_]

rad cap and stat next.
make sure you purchase OEM equipment from someone like MX5parts.

[alanyboy]

Interesting you say rad cap ? How would changing this help ?

[snotrag]

alanyboy said:

Interesting you say rad cap ? How would changing this help ?

The coolant system works under pressure - this pressure stops the water boiling and increases its capacity to deal with the heat.

The radiator cap is the seal in this sytem, and once it no longer seals the coolant cant cope with the heat so much and the system is not under pressure.

Dirt cheap, and easy to change - make sure you get a genuine mazda one though as pattern parts are not very reliable.

[alanyboy]

Thanks for the help so far. I replaced the radiator, but this seems to have had no effect. Would a blocked heater matrix produce a similar problem ?