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Unexplained Temp rise at 4k RPM

Hi, it's been long time since I've been in here.

I have a 90 miata, with a 92 engine (crankshaft failure) that I just replaced the alternator and belt back in December. The temperature would go up when ever I drove above 4000 rpm for more than a few seconds. I assumed that the belt was slipping, so I tightened it around a week ago. This was after checking the tension about a 1000 miles after original installation and tightening it then. Later that day I'm driving along and the belt snapped. I assumed that it was a defective belt, becuase it seemed to stretch way too much. I limped my baby to Sears (1 mi away?) where I bought a belt and installed it. (Sears wanted way too much to install a belt, and I'm pretty well broke so I couldn't afford to pay them if I thought it was reasonable right now anyway.) When I got home, i checked the tension, cause I did it in their parking lot as fast as I could. Everything seemed fine. So today, I'm driving to work (34 mi one way) and I have the same problem happen again. Any thoughts? This isn't the first time that I've installed a belt, but it is the first time I've had a problem like this. The odd thing is that this only seems to happen at highway speeds, it does not happen if I drive 40 mph in second gear.

Thanks, Karl & Maverik,

90 Red.
Reply to
karl.kittler
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It is unusual for a MX-5 to overheat unless it is a very hot day, and you are running the air conditioning.

Temperature increases at highway speeds can be caused by many different things. The easiest is to change the belt and the thermostat. If a new thermostat doesn't fix it you are looking at more money. You could have bad plugs, wires, or coil pack. Pull the plugs and inspect them to see if any are black or fouled. Maybe your fan is not working properly. If the water pump has been changed you may have one with a plastic impeller. They get damaged and need to be replaced. Are you running a high percentage of antifreeze? If so, your mix should be about 50% water. Your radiator may be plugged and need replacing. Was the head pulled when the replacement motor was installed? The head gasket could be partially blocking the water passages.

Good luck!

Reply to
Larry Gadbois

I can't see where the alternator belt has anything to do with overheating. It broke because you overtightened it.

Assuming you've already ruled out coolant loss, and your car is stock, here are the likely causes of your overheating:

clogged radiator stuck thermostat bad thermosensor bad fan motor

Reply to
Lanny Chambers

My guess was the temp rise was due to the alternator/water pump belt slipping, that's why I tightened it. Coolant is 50/50. The water pump was replaced when the engine was put in, that was in 2002. Clogged radiator/stuck thermostat should give me more trouble, not just when I'm driving at highway speeds right? My fan runs normal as far as I can tell. Thermo sender should be an all the time thing, also right?

How should I go about testing these?

Lanny, glad to see you're still here. Thanks.

Reply to
karl.kittler

As far as mods go:

95 open rear end (blew the old one in Apr. 2003, that was my best option at the time) and 95 mazda bigger brake upgrade Got rid of the stock air box, replaced it with a K&N filter for an RX-7 (planned to switch out the MAS but haven't yet.) Added ammeter this last weekend, after the second alternator inexplicably died, I wanted a little more electrical system scrutiny than the idot light that didn't turn on until I was sitting on a DE highway in the dark. First experience with dead alternator here:
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nothing that would encourage this problem.
Reply to
karl.kittler

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