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Car Forum / Mazda / Mazda Miata / July 2005overheating at speed
I have a 97 1.8 standard mx5. Today was hot in the UK (probably about 85F). On a long motorway journey the temperature gauge was creeping up. This was at a steady 75-80mph. Slowing to 65mph lead to the temperature returning to normal. Coolant levels normal. What's the most likely cause of this? My ideas so far: Clogged system Failing water pump Bad thermostat Any opinions most welcome > Clogged system > Failing water pump > Bad thermostat Probably not the water pump. Assuming you have no coolant loss, check the fan(s) as well. My similar symptoms were caused by an intermittant fan motor, which had a dead spot on its commutator. --- Lanny Chambers '94C, St. Louis http://www.hummingbirds.net/alignment.html >My similar symptoms were caused by an intermittant >fan motor, which had a dead spot on its commutator. Mine were due to a failed thermostat - resulting in the fan not turning. Jim  SignatureJim Hayter home: jhayter AT alum.mit DOT edu Columbus, OH work: jhayter AT ecnext DOT com Red '93 B Miata Garnet '05 Legacy 2.5 GT Ltd Thanks for the ideas. I'm surprised the fan is mentioned - should it ever turn on at 70mph? A friend suggested I check the air flow. Though there's a good number of dead flies and a few bent vanes, the rad is pretty see-through. My next idea is to change the thermostatic valve - it might not be opening fully > I'm surprised the fan is mentioned - should it ever turn on at 70mph? Yep, if the ambient temperature and engine load are high enough, and especially if the A/C is on (because the condenser throws hot air at the radiator). The Miata does not have a huge reserve cooling capacity even when everything is working properly; if it's not, it tends to overheat. When my fan motor went bad, I saw the needle creep upward on 95-degree days if I went over 80, or over 75 uphill, or over 60 with the A/C on. Around town, the A/C condenser fan, which still worked fine, was sufficient to keep everything cool. On a 1.8, the ECU switches the condenser fan on at 106C even if the A/C is not in use, just in case the main coolant fan is fritzed. Handy safety feature, but it sure made diagnosis difficult. By the time I discovered the bad fan motor, I'd already replaced the thermostat and radiator, removed the front plate, and sacrificed two chickens and a goat. --- Lanny Chambers '94C, St. Louis http://www.hummingbirds.net/alignment.html > Yep, if the ambient temperature and engine load are high enough, and > especially if the A/C is on (because the condenser throws hot air at the [quoted text clipped - 15 lines] > '94C, St. Louis > http://www.hummingbirds.net/alignment.html No ox? No wonder it took so long. Even without reading the miata enthusiast's manual I knew that sacrificing an ox, in addition to 2 chickens and a goat, is required for problems that can not be diagnosed on a miata. Sheesh, everyone knows that. It sounds to me like you cheaped out on buying the ox. pat > It sounds to me like you cheaped out on buying the ox. In my defense: after my earlier livestock purchases, the car maintenance budget was somewhat depleted for the quarter. Still, I kept scanning farmanimals.ebay.com for oxen, but I kept getting outbid by a cult of fundamentalist Babylonian sodbusters from Kansas. *sigh* --- Lanny Chambers '94C, St. Louis http://www.hummingbirds.net/alignment.html > In my defense: after my earlier livestock purchases, the car maintenance > budget was somewhat depleted for the quarter. Still, I kept scanning [quoted text clipped - 5 lines] > '94C, St. Louis > http://www.hummingbirds.net/alignment.html Damn you Lanny, now I have to clean coffee off of my keyboard! That was rather good, I concede defeat and will continue to plod along with my day job rather than attempt the comedy circuit. :-) Pat >> It sounds to me like you cheaped out on buying the ox. > > In my defense: after my earlier livestock purchases, the car maintenance > budget was somewhat depleted for the quarter. Still, I kept scanning > farmanimals.ebay.com for oxen, but I kept getting outbid by a cult of > fundamentalist Babylonian sodbusters from Kansas. *sigh* This reminds me of a hilarious episode that happened to me about a year ago. I was on holiday on a small Greek island. One day a whole bunch of people in white descended on the island, all Americans (myself and my friends with whom I was there are from the UK). It transpired that they were members of some cult or other who were convinced that Armageddon was to take place on one of the days we were there, and the only place in the whole world that would survive was this particular island. They holed themselves up in a hotel they'd group-booked, then reappeared the night before the Big Day and went wandering around the town. Needless to say, Armageddon didn't actually take place. What we wanted to know was: - How did they get back home? One would assume they got one-way tickets. - Once they got home (if indeed they did), did they have anything left to go back to? Or had they told their bosses to shove it, sold the house and spent all the money on one hell of a party? - What DID they get up to in that hotel in the few days they disappeared from view??!! All I can say is keep scanning farmanimals.ebay.com, Lanny, something's bound to turn up sooner or later. Eric > Needless to say, Armageddon didn't actually > take place. What we wanted to know was: [quoted text clipped - 3 lines] > back to? Or had they told their bosses to shove it, sold the house and spent > all the money on one hell of a party? Here's a website about a book I read for a college psychology course: http://www.whenprophecyfails.org/ It's the classic study of exactly the same phenomenon. The cult in question believed it would be rescued by an alien spaceship just before the Earth exploded. The authors infiltrated the cult to gather data. When the date passed and the Earth didn't go boom, the cult attributed the planet's survival to the power of their prayers. The book is out of print, but widely available used. It's a fairly depressing read for anyone who imagines the ignorant can be persuaded using reason and logic. --- Lanny Chambers '94C, St. Louis http://www.hummingbirds.net/alignment.html > This reminds me of a hilarious episode that happened to me about a year > ago. I was on holiday on a small Greek island. One day a whole bunch of [quoted text clipped - 11 lines] > go back to? Or had they told their bosses to shove it, sold the house and > spent all the money on one hell of a party? In my limited experience, it's cheaper to buy a round-trip ticket to someplace than a one-way. I have taken a few one-way trips by buying round-trip tickets and not using the return tickets. Of course, if the end was near, what difference would it make on how much to spend on the trip? The bills would show up after the end... > Of course, if the end was near, what difference would it make on how much to > spend on the trip? The bills would show up after the end... Next time the world ends, please give me a couple days' notice. I'll put a Ford GT on my MasterCard. --- Lanny Chambers '94C, St. Louis http://www.hummingbirds.net/alignment.html >>> It sounds to me like you cheaped out on buying the ox. >> [quoted text clipped - 25 lines] > > Eric I'm guessing that the world as they knew it, did, infact, end for them. Not having any livestock to hand, I replaced the thermostat. When testing the engine at idle I noticed there's a cold area on the rad I hadn't noticed before. Fan turned on fine - but the cold area is exactly where the fan is! Is it worth trying to flush the rad or is that a waste of time? Any time spent on bonding with your car is time well spent!=) > Not having any livestock to hand, I replaced the thermostat. When > testing the engine at idle I noticed there's a cold area on the rad I > hadn't noticed before. Fan turned on fine - but the cold area is > exactly where the fan is! > > Is it worth trying to flush the rad or is that a waste of time? > Any time spent on bonding with your car is time well spent!=) LOL! Very true - I need to repair the relationship as well as the radiator! I might give it a go. As half the rad is hot and half cold I can only guess the blockage is not in the individual tiny tubes. Final update on this... Attempted to flush rad, all directions, used descaler. Complete waste of time (apart from the bonding!). New rad bought, works great |
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