Mazda Miata (MX-5) This compact RWD model, offered with many engines options for those are who want to cruise with the top down in a base model, or hit the track in one of the high performance models, has been a popular model since its introduction.

Everything New but 99 Miata still overheats

Old 06-12-2013, 06:00 PM
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Join Date: Jun 2013
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Default Everything New but 99 Miata still overheats

Help please. Here is my complete story.

*2 years ago had the radiator replaced.

My daily scenario I leave work get on the turnpike for 15 minutes and when I get off I sit at the light and the temp guage climbs to H.

Here is when it started:
*1+ months ago my 99 Miata had a major oil leak and my car temp guage was going to H.
Shop checked and put new valve cover gaskets and a new timing belt because the old one had oil all over it.
Left the shop and car was still going to H.
*They took it back and checked it again and said it was the water pump and replaced it.
Left the shop and car was still going to H. UGGHH
*They took it back and they said it was probably wire to the fan. They replaced it.
Left the shop and car was still going to H.
*I didn't want to take it back to them but they said they thought the fan needed to be replaced but wanted to try just changing the wire to see if that would fix the issue and they offered to install the fan for free. I let them do it.
Left the shop and car was still going to H.
*Took it to another shop and asked them to check it. After running the car with the air on for an hour the car would not go to H. They couldn't find the problem.
Left that shop and car was still going to H.
*A friend advised to change the radiator cap. Did that last night.
Car is still going to H.

I really am at my witts end trying to figure out what it could be. The car is almost brand new now with radiator, radiator cap, fan, fan wire, water pump all being replaced.

Please help!
Old 06-12-2013, 06:09 PM
Join Date: Dec 2011
Location: Canada
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Old 11-27-2013, 01:57 PM
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Join Date: Aug 2007
Posts: 1,324

There is a known issue with the small bypass hose at the front of the engine collecting slag and stopping up. Remove the hose and blow through it to remove any slag. The hose is maybe 5 inch's long.
Old 11-28-2013, 04:50 AM
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Location: Queensland Australia
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Definately give the whole cooling system a huge flush and replace the thermostat.
Old 12-22-2013, 10:23 PM
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Join Date: Dec 2013
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Had similar overheating problems. New thermostat, waterpump, radiator, flush......It was a pinhole leak in a head gasket. Might be the same problem for you.
Old 12-23-2013, 10:02 AM
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Join Date: Nov 2013
Posts: 216

if the car has the tendency to go to H, more than once you might have a bad head gasket. do you see bubbles in the radiator ( car cool, remove radiator cap, start engine and watch.) a few bubbles might be a bad gasket. do a compression test. if compressio is low in 2 adjacent cylinders, the head gasket might be bad. if you have a check engine light, misfires, rich condition, white smoke coming out of the tail pipe and the car consumes water/coolant, you might have a bad head gasket. first make sure there are no leaks in the cooling system or a bad heater core. i recently went trough all that. if the head gasket needs replacement, take the cylinder head to a machine shop to make sure is not warped or cracked. get it rebuilt. and buy a fel-pro head gasket. the car will stay pretty much on its temperature range if left on idle. but take it out and after driving about 10 miles, that needle starts climbing really fast. that was my case. bad head gasket, had a crack between cylinders 3 and 4. it all atarted because my son did not stop the car when it broke a hose and ... well, things got complicated.

Last edited by Juanky; 12-23-2013 at 06:51 PM.
Old 03-26-2014, 07:30 PM
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Join Date: Dec 2013
Location: Vancouver, WA
Posts: 19

get a temp gun and measure the actual coolant temp at the thermostat housing and compare to what the ect is reading.

also may want to check for hydrocarbons in the cooling system (possible blown head gasket)

do the cooling fans cycle properly?

I would check those first and see what you come up with
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