2nd Generation Specific (1986-1992) 1986-1992 Discussion including performance modifications and technical support sections.

overheating at idle?

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Old Jul 3, 2002 | 05:16 PM
  #2  
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thermostat..
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Old Jul 3, 2002 | 05:25 PM
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If it overheats at idle and cools down once you start moving it’s almost definitely a problem with the fan. You don’t mention any mods so I presume you have the stock clutch fan. When the engine is cold the fan should freewheel quite easily, when it heats up the clutch should progressively lock the fan to the pulley to spin it fast enough to pull more air through the radiator. Check to see it’s doing this; if not replace the clutch with a new one.
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Old Jul 3, 2002 | 06:10 PM
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Fan clutch. If you give it a spin with the car cold, it should rotate once or a little more. Warm up the engine (carefully watching that temp guage) and then try to turn the fan. It should be stiff.

I wouldn't worry about the thermostat unless you replace it with a non-Mazda unit.

Also, good measure would be to replace the rad cap as well.
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Old Jul 3, 2002 | 06:11 PM
  #6  
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Originally posted by dvst8-rx7
hmm ..when should the thermostat be replaced? cuz i replaced it last summer.
NZconvertible....its a stock 86 seven.yeha ill have a look at the fan..is there any procedures in the manual to check this? oh and was wondering how come it causes the coolant to end in the reservoir?
thanks man
3 years out of Mazda thermostat- 3 months out of Stant thermostat--lesson learned.

I would first do a antifreeze/thermostat change.
The fan clutch is like $200. I have seen 16" permacool electric fans for about $100-U.S. and IMO, that is the better way to go.

The FSM says that resistance must be felt when engine is hot. I guess if it chops off your fingers, it is good
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Old Jul 3, 2002 | 06:26 PM
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Originally posted by dvst8-rx7
is there any procedures in the manual to check this?
Yep, but it’s exactly the same as what I said.
...how come it causes the coolant to end in the reservoir?
Coolant expands as it heats up, pressurising the cooling system. When 0.9bar (13psi) is reached the radiator cap bleeds some coolant into the overflow reservoir to maintain that pressure. When it cools and contracts, the cap should let it be sucked back into the radiator. If it’s not, replace the cap.
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Old Jul 3, 2002 | 06:58 PM
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You NEED a fan, period. Those RX-7s "without" fans probably have an electric fan installed that you cannot see.

Leave the shroud, it helps duct the air. Removal means a severe loss in cooling.
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Old Jul 3, 2002 | 07:14 PM
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Here is the deal. After the bimetal strip on the front of the fan clutch see heat the fan pulls hard up to about 4k, and then maintains ~4k as the engine revs higher. Mine was slipping at 2500. You can get the fan clutch to bite better by bending the bimetal strip outward. That should help until you decide to go electric or new clutch.
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Old Jul 4, 2002 | 04:06 PM
  #14  
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Originally posted by dvst8-rx7
...it seemed to spin with some friction when the engine was cold and when the engine was hot the fan spinned but felt the same as if it was cold.
Damn, I should have been more specific about something. To check it hot, leave it idling for a bit to get some heat into the clutch. When you see the temp start to rise, turn it off immediately and then check the fan. Since the temp has risen higher than it should be, the fan clutch should be engaged and the fan will be difficult to turn. It should be noticeably different to when cold.
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Old Jul 4, 2002 | 06:47 PM
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When I said "bites hard up to 4k" what I meant was the fan and engine should speed up together from idle to almost 4k. If the fan speeds up to 2500 but won't go faster, it's worn out. It's a simple test. Check it out.
Bill.
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