AboutMp2 Expertise I prefer to answer questions relating to the Miata since this has been my area of specific
expertise since 1991. I can answer questions relating to the other Mazda models however
some limitation of expertise may reduce my accuracy.
Experience Mazda technician since 1987, shop owner and specialty are regarding the Miata since 1991 covering mechanical, electrical, trim and body. Specializing specifically in drivability concerns.GKHS 1985, BVC 1987, MNA 1989, ASE Master Technician Mechanical 1995, ASE Master Body/Paint/Collision 1996
Education/Credentials GKHS 1985, BVC 1987, MNA 1989, ASE Master Technician Mechanical 1995, ASE Master Body/Paint/Collision 1996
Question Hi, I read on your forum about another person with a similar problem - my 1990 Miata overheats. I replaced with a new Miata thermostat, radiator cap, hoses seems to be fine (not collapsed), bypass hose to waterpump is not clogged, radiator flows nicely when thermostat open, fan comes on fine, waterpump was replaced about 4,000 miles ago when timing belt replaced (orig owner, low mileage - only got 91,000 on it now) . But about 5 minutes after running it, temp creeps up. Also ran it with radiator cap at first notch (not fully closed) - same overheat symptom. In all cases, turning heater on full blast seems to bring it back down to normal temperature temporarily.
Any other ideas? Could a partially clogged radiator give this symptom?
Answer Most cooling issues have to do with air flow. Check that both fans are on (AC on) and that they are pulling air, a bad motor can spin the fan but not have power enough to pull air sufficient to cool. A weak one is noticeably slower and has less force. TIP: you can unplug and re-plug each while they are running to see the startup force of the motor.
Condenser air restriction, clean the air coils.
If you see noticeable flow of coolant then circulation is not likely an issue, though condition of old coolant could give you some insight, either having it boiled out or better yet replacing it with an OEM style new one is even better. (plastic top and bottom tank, aluminum core - avoid the cheap all metal ones they are trouble)
If your able to cool it down using the heater then air flow and fluid flow are where you need to look.
