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Noticed the temp nearly maxed-out this arvo coming back through the traffic. Wasn't for long as I was rarely stationary, and the needle didn't go beyond the upper 'normal' limit mark. Checked the coolant when I got back and all ok. Got a feeling the fan isn't kicking in. After I'd unpacked, I checked the bible and bridged the appropriate terminals in the debug block and the fan ran up ok, but it was then dark and too late to do anything else. I need to run it up to temp again and see if the fan starts by itself.

If not, looks like the next thing to check is the temp sender. Are these known to be unreliable? Expensive? Easier to just replace the thing as I'll have to take the old one out to test it anyways?

davamb wrote: I need to run it up to temp again and see if the fan starts by itself.

Try that first. If the fan doesn't start, it's most likely the sender on the thermostat housing causing the problem.

And they are NOT cheap.


Jules

Thanks for the input guys.

Ran hot on the way home again last night and I pulled over to check the fan was running and all seemed ok there. By the time I got home (around 7:30) it was really cooking, but I had lost no coolant.

I did a reverse flush late last night after it had cooled down, both radiator and engine. I removed the thermostat and boiled it up in a pot. I couldn't find my immersion thermometer, but bubbles were forming just when it started to open. It's stamped 82C open, so I guess this is about right. It didn't seem to open very far though, maybe a clearance from outer ring to seat of 2mm. Thought it would open further than this???
Do these beasties fail open or closed? My guess with that humongous spring that it would be closed.
Seemed a bit better on the way in this morning and I was stuck in the Bracks Block at Springy and Whitehorse Rd for 15 minutes and temp never moved above 50%. Later on in slow moving traffic, it got up to 60%.
I then ran the aircon for the rest of the way and it was steady at around 50%.

I was pretty low on my ethylene glycol reserves at home so she's running only about 20% coolant, but I figure I'm not going to rot the engine between now and the weekend when I can do a full coolant change.

Any ideas as to what's cookin'?

I'd be replacing the thermostat, cheapest option first!

Or just leave the thermostat out for a few days to see what happens.

Burson have one with gasket for $27.40. Will go grab it at lunchtime. Let ya know how I go, might even fit it before driving home tonight, only a 5 minute job to swap it out.

Sounds like thermostat to me. The Mazda genuine one is regarded as a better option to aftermarket though.

Jules

Thanks Jules and Reddie,
the thermostat seems to have done the trick, got nothing higher than about 55% on the trip home tonight. Agree on the genuine article when it comes to spare parts, but no Maz dealers within cooee of work, so the Burson part was pressed into service. The number plate doesn't block the airflow into the intake, so should be pretty right there. It sits up quite high on the (daft) mounting brackets. Will just have to keep an eye on temps for the rest of the week and get some proper coolant/water mix in there first thing Saturday morning.

Hmmmm. Temp gauge ideally should be resting at 45% at all times.
I had plenty of issues with the car getting hot before finally tracking down the problem to rusting of one of the thermo housing pipes with several pin holes that wept.

That and the number plate jammed in the mouth.
I'd keep an eye on it if it's resting at 55% heat range.

Jules

Well, still not sorted. Had been sitting just below 50% the last half of the week and I thought I'd got it sorted with the new thermostat.

Ran hot again this arvo in Springy Rd stop/start traffic. I ran it up again just after getting home and the thermo fan kicked-in at just on 50% and the temp dropped to around 45 and stayed there. I had a good look at the radiators to make sure the aircon wasn't blocked up with crap, reducing airflow to the radiator. Seemed ok, but got the hose out and gave it a good blast through to remove miscellaneous bug bodies and stuff. Now it's a bit darker I've put a torch in behind and can see clearly through to the radiator through the aircon vanes.

So it's fine when I'm moving at above 20 or so kph, and seems fine when parked and the thermo fan's running. There's no problems with the number plate - it doesn't interfere with air to intake at all.

Air not exhausting from the engine bay? Tempted to take the plastic undertray off and see if that makes a difference.

Any ideas chaps? I'm really at a loss on this. Might have to go seek 'professional' help and I can't see that as being cheap. Groan...

sounds to me like a blockage in the radiator itself mate

Try again in conditions similar to those when it started to overheat.

See if the temp comes back under control when you turn the A/C on. If it does, it's possible that the thermoswitch is not closing until the temp is too high or that the radiator is a bit blocked. The thermoswitch should start the fan below 50% (should be about 45%) and the temp should stay there. The actual operating temp for the thermoswitch is 97 degrees C.

Try replacing the radiator cap. It fixed a cooling issue that I had with similar symptoms.

$10.... no brainer.

Start with the cap and then move on to get the radiator checked and potentially cleaned. If the car is overheating while moving in stop start then it's not going to be your fan. I'm inclined to think it's a flow problem, so either the water pump - or more likely, the radiator is clogged.