overheating at idle?
 

hey guys, im faced with another problem with my car. Its overheating for some reason. today i left my car warming up outside for 10 minutes. then when i came back the meter was up 4/6 up on the temp guage. but when i step on the gas the temp gauge goes back down to normal operating temp. so i popped the hood n looked at the coolant reservoir and it was freaking full of boiling coolant spraying out out the reservoir!! its not suppose to be full !! so has anyone have a clue on what could be the problem? could it be the temp sensor? on the radiator?

thanks guys

thermostat..

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.

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

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.

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:D

Yep, but it’s exactly the same as what I said. 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.

ok thanks guys ill have to do the tests on the fan tomorrow n ill let you guys know what i found thanks

hmm...say it was the fan clutch that was screwed...do i really need this to cool the radiator? cuz ive seen pictures of rx7's that dont have the fan and just cools by the air while driving. i was thinking of taking the fan n whole shroud off so i can get more room....any comments?

jack

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.

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.

hmm ok forget what i just said .. so ill go test out the fan tomorrow n see what happens ...ill let yeah know. thanks guys

hey guys..
so i tested out the fan, 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. what do u guy mean by freely? cuz when i rotated it it only turned 3/4 way n stopped.

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.

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.