'99 Overheating

I'm starting to see some problems with overheating. My temp guage hasn't reached the 'H' yet, but its gotten about 3/4 of the way over there, as opposed to being locked dead center the way it has been for the past 4 years.

Scangauge is reporting 235 at its worst so far, cruising @ 65-70 yesterday through Dallas it was reporting 220, remember it was about 105 yesterday.

Worse overheating happens @ idle with the A/C on, if I turn the A/C off, engine cools off fairly quickly. Also, the A/C isn't cooling as well as it used to, I'm assuming this is due to the buildup of heat, so the outside coils are able to cool down effectively.

It's got >207,000 miles on it, this past weekend I replaced the thermostat, flushed the radiator & put in a fresh 60% water/30% antifreeze mixture, replaced the top radiator hose, weather stripped the aux fan shroud to better baffle the air, and the radiator is less than 2 years old. Still over heating, and did so this morning idling in the parking lot @ 85 degrees. I'm thinking I should try to replace one or both fans, but I'm trying to avoid the $400-$500 for both. I'm wondering if anyone has tried the $49.99 Aux and/or the 59.99 Main, Hayden (3670&3680) universal fit fans that Oreilly sells as a replacement.

Also, this miata tends to 'eat' catalytic converters, I've had 3 different cats put in, and each time, within a month, the cat fails. The car is performing well otherwise, has plenty of power, and is getting relatively good gas mileage - 27-28mpg with A/C on full time driving @ 60-80 mph. Just replaced the plugs, and there was no indication of burning oil, and the car doesn't smoke. I mention this because I've heard people report that a plugged cat can cause overheating, but wouldn't other issues like performance or gas mileage also appear? I'm thinking about having a straight through pipe welded in as a test.

Any other opinions on this issue are welcome.

Thanks,

-Tim

With that many miles, a compression check would be on my to do list.

Does the 2nd fan come on with the AC? How old is the radiator?

As far as cat killing, you may have a coil-pack issue and it's randomly mis-firing. Common on '99's.

Both fans do come on, and seem to at the appropriate times. Radiator is about 2 years old. Only trouble code I get out of it is the catalyst inefficiency PO420. Wouldn't too many misfires kick off another trouble code?

-Tim

water pump?

Sorry, forgot about that one. New water pump & timing belt about a year ago. I'm not loosing antifreeze either.

Have you checked the amperage on the fans to see if they are out of spec before ya go an replace them??

'99 Service manual shows the need to be at 4.50 to 6.49 amps @ 12V

Also what is the condition of your A/C condenser is it plugged up or does it have a bunch of folded fins??

Ya got the underbelly tray in place??

+1 on what POS said. Both fans may be coming on, but one may be weak/slow - I've seen this on other cars before.

Radiator cap? Can you hear a boiling when you stop and tun off the engine?

The '94 had a weak fan that caused it to run warm. Replaced it and worked great.

I'll check compression & fan current draw tonight. There are bent fins on the condenser, but certainly not a majority of them. Doesn't appear plugged from what I can tell, but tonight I'll spend some time cleaning and attempting to straighten them some.

This problem came on fairly sudden, and until last night I had one of the Moss radiator screens installed for that very reason. I took it off last night thinking it might be contributing to the overheating.

Hopefully you got a new cap when you replaced the radiator. I'm wondering why you're going through cats so much. Something ain't right there and I'll bet your heating issue is tied to it. Could the timing belt be off and cause a cat to fail?

When I replaced the plugs, they had about 100,000 miles on them, so I wonder if its possible that the worn plugs caused the cats to fail, now I have new plugs, but haven't replaced the cat.

Quote:

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Originally Posted by POS Racing

Have you checked the amperage on the fans to see if they are out of spec before ya go an replace them??

'99 Service manual shows the need to be at 4.50 to 6.49 amps @ 12V

Also what is the condition of your A/C condenser is it plugged up or does it have a bunch of folded fins??

Ya got the underbelly tray in place??

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So what would you do if your AMP's and or Voltage was low?

I did check the voltage at the aux fan, and it was at about 13.8 V. Haven't checked the current yet, I don't have the clamps & wires to assemble that setup right now.

Quote:

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Originally Posted by scorn001

When I replaced the plugs, they had about 100,000 miles on them, so I wonder if its possible that the worn plugs caused the cats to fail, now I have new plugs, but haven't replaced the cat.

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How did they look when you took them out? I'd think it's possible if you ran rich for a long time that could kill a cat.

A buddy that works for Mazda did it for me, and I quizzed him on that, he said they were extremely worn, but no indication that the engine was having any real problems. No discoloration, and not white or anything. Just looked worn out. Insulation on the wires was starting to go bad, that is about it. He indicated that in general, everything looked very well, especially when you take into account the mileage.

Quote:

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Originally Posted by MiataMike

So what would you do if your AMP's and or Voltage was low?

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I'm not sure I get your question.

You could always break out a little ohms law action! V=I/R

Or put a charger on the battery and see if you can get the battery output back to 12V. ;)

Quote:

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Originally Posted by POS Racing

I'm not sure I get your question.

You could always break out a little ohms law action! V=I/R

Or put a charger on the battery and see if you can get the battery output back to 12V. ;)

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All i was asking is that if hypothetically you were having a low amperage or voltage issue. What course of action would you take to rectify cause.

Key thing you want is the amperage in the acceptable range (4.50 to 6.49 amps @ 12V) if it over or under then ya may want to pull some fan motors. ;)

scorn do ya got the underbelly tray in place?

I know my '94 was not happy to sit still in traffic yesterday the A/C would start loosing the battle but once it was moving it seemed a bit happier. I need an underbelly tray from mine! (Not saying that is the cure all but it can't hurt!)

Tray is in place, has a pretty big crack in it, but no missing pieces. The condition of the tray hasn't changed since I bought it 4 years ago though, and this is the first occurrence of overheating.