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Hi all ,
I have a fairly standard 1.6 lt 1991 mx5, have only owned it 6 months, basically during the winter months, the temperature hangs around the quarter mark, took the car for a drive today in 33 deg heat, and on a steep climb over about 3km temp rose to about three quarters mark, on hitting level ground and revs back down to about 3500 rpm temp gradually went back to that 1 quarter mark, do you think this maybe a thermostat prob

Yes, maybe jammed slightly open.

Don't just leave it at a thermostat.. You could easily have another problem exacerbated by the engine under load in hot conditions. Cooling system needs to be checked.

Would need to know a little more - like is the coolant level correct (ie in the system not just expansion tank), does it overheat when idle, does fan come on eventually when left to idle etc...

it overheated in the circumstances he already mentioned. An old car and a good chance the radiator is not doing its job. Don't wait for the next hot day to see if it boils and does damage.

Mr M not every loves to run to the mechanics whenever the windscreen needs cleaning! Take it easy, nothing wrong in getting more information about the problem.

radiator is fairly new, coolant levels are normal, fans seem to be working ok, where is the normal position for the temp gauge to sit on an NA? And should the temp gauge move so much, most cars I have had in the past the temp gauge will sit just under the half way mark

My na6 always sits on half way once warmed up.


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rossburns wrote:fairly standard 1.6 lt 1991 mx5 - during the winter months, the temperature hangs around the quarter mark, took the car for a drive today in 33 deg heat, and on a steep climb over about 3km temp rose to about three quarters mark, on hitting level ground and revs back down to about 3500 rpm temp gradually went back to that 1 quarter mark

What kind of revs & gear did you maintain during the climb, given you dropped back to 3.5k RPM when things levelled out?
NA6/8 temp guage tends to sit half way once warmed up, so 1/4 is not typical.

speed wrote:My na6 always sits on half way once warmed up.


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Ditto, and I have a larger capacity aluminium radiator which in my naivete I thought would make if run a little cooler - but then I suspect the guage is not the most accurate instrument in the world.

Tim

could be several things, but things I'd check are 1) thermostat and 2) radiator and rad cap.

thermostat if the engine is running cooler than it should - it should sit at 1/2 way and not drop any lower (thermo is probably letting more through than it should).

radiator and rad cap if it is climbing over 1/2 way as either the radiator is clogged and not cooling effectively and/or pressure is being released via cap and allowing water to boil into steam (which under pressure it would stay as water).

no harm in pulling the thermo cover off (you'll need a new gasket anyway) and replacing thermo with a new item (only a few $$)

id then clean the radiator and let it sit for a day (with a full bottle of flush and clean) but not connected to the engine - just block of the lower hose with something big or clamp it etc (i never like the flush and clean stuff going into the engine for fear of creating leaks in places you don't want). clean out and replace the cap with a new item

refit and see if the problem persists. if it does, then the problem is more serious and should be investigated more thoroughly (maybe a compression test to confirm there isn't a head gasket/ water gallery leak etc).

finally, it is possible (though unlikely) that you have a bad gauge sensor... but I'd be surprised - one sure what to tell is to leave it idle and see if the fans cycle on and off but the gauge reports non-1/2 way reading - which would indicate the temps are fine but the gauge is off (sensor bad) - the fan temp switches are different from the gauge sensor etc

thanks to everyone on your thoughts on my temp probs, will be going through and checking points you brought up, if that doesn't fix the prob will seel professional help