Hey, I'm a Mazda master at a small dealership in Va, I'm not old enough to have much experiance with the FDs, mostly an RX8 guy buy force not choice. Anyway, the question is, do the FD water pumps have any problems breaking their impellers. Or is there anyother reason they wouldn't over heat while at idle but over heat at speed. (the radiator is ok, the cap is ok, the t-stat is ok,)

Thanks.

 

No the impeller on the 3rd gen is not known to break off like the plastic impeller on the 92-95 929. Have you pressure tested the cooling system to assess whether it is losing coolant into the combustion chamber? The FD "IS" however is known for its difficulty in removing air pockets while filling the cooling system. It is easy to think that the system is completely bled when it is not.

 

I would suggest checking the coolant seals. It doesn't matter if you work with a FB, RX5, FC, FD, FE's... There all the same engine rotary. Do as mazmart suggested get a pressure tester, or another way to check is fill the coolant to brim pull the ecu fuse and have someone crank the car over. If the coolant level doesn't over flow or pour out of the filler neck then the seals are fine. (Leave the radiator cap off also) That is another way I check to see if the coolant seals are still good if you do not have a pressure tester around.