Help My 1990 Miata Keeps over heating!

[spikedchez]

Last year I replaced the engine in my 1990 Mazda Miata. I replaced the engine not because it's performance was off, The little car ran like a top and averaged 32 to 35 mpg however it would not pass the California Smog Certification. With 233,000 miles on the engine I felt rebuilding the original engine didn't make sence and bought a used engine with 30,000 miles on it. However the company sent my mechanic an engine for an automatic Transmission Miata not the 5 speed. Rather than send it back he installed the "Auto Trans Engine". It runs fine although it's MPG's are not as good but in traffic it overheats forcing me to pull to the side of the road and let the engine cool down. The Fans do not seem to activate I have replaced the radiator witha Misimoto 3 core aluminium raditor and high performance double fan shroud but the problem continues What can I do?

[ibid]

Is it safe to assume there is no air in the system?

What about installing a 180degree thermostat so the cooling starts sooner? ...or even remove the thermostat completely for free flow all the time (better flow too as this is typical for spec miata racers to just remove the thermostat entirely)

Have you or your mechanic checked to make sure everything flows freely?

[atank]

Are the cooling fans now working? Does your Miata leak coolant? When you check the oil is it an off white color?

[kung fu jesus]

Is there coolant in the reservoir (behind the the passenger side headlight)?

If the fans aren't kicking on, you have your issue.

First check to see if the connector on the fan thermosensor is connected. If it is, gently remove the electrical connector and check for corrosion. These often corrode with age and no longer register a signal needed to turn on the fans. It is the piece circled in red:

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After that, check the wiring connectors for the fans themselves. See if they are corroded or not connected. They run along the top of the fans/radiator.

Next, if you have AC, with the car running, turn on the AC and see if the fan on the passenger side turns on.

If the fan doesn't turn on and the connections mentioned above all seem fine, try going to the diagnostics port (the little port you would do the "TEN/GND" jumper at) and put a wire jumper of paperclip in "TFA" and "GND", the fan should activate if the ignition switch is on. This is a good test to determine that the relay and fan motor are working. (This test will not activate the A/C Condenser Fan.) Here is the diagnostic port I am referring to, in the engine bay, driver's side (left):

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Open it up (it is hinged) and place each end of the jumper in these holes, as highlighted:

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If the test above fails to activate the Radiator Cooling fan, then the 30 amp Cooling Fan fuse in the Main Relay and Fuse Box is blown, or the Cooling Fan Relay or Main Relay has failed open, or the fan motor is bad.

The fan relay is here:
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The fuse block is in the car, on the driver's side (left) near the knee. The cooling fan fuse is number 6 (highlighted in red), it is a 30 amp fuse:
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If everything works fine after that, the car still overheats, the system may need to be burped.

[kung fu jesus]

If none of what I said above makes sense. STOP. Go to a trusted mechanic and describe your issues. There are a good number of Miata specialists between Orange County and San Diego you should be able to take it to.

[Phatmiata]

Like KFJ stated, if your fans are not coming on that is your problem right there!! Check the fuses!

[cabbageroll]

Check Fan, Temp Sensor, and Radiator cap. My 90 NA overheated and issue was bad sensor with bad cap. After buying a rad cap and made sure my fan actually works,it was fixed. I assume the pressure wasn't enough and the fan which didn't start probably messed it up too.