Car says it's overheating but I think it's telling lies

[monkeys437]

Hi all, I'm going over to my missus place after work to hopefully fix a sporadic overheating issue she's been having and I'm hoping to get some Ideas if anyone's come across a similar issue. The Temp gauge says its overheating but it sounds like it could be getting a false reading or something

Its a VT S2 exec V6 in A1 mechanical condition

Twice in the last few weeks the car has gone from running at normal operating temp to instantly full hot with the temperature alert going off. The first time it happened she pulled over, but before she had a chance to turn it off, the gauge went to normal operating temp again. She turned it off, checked the coolant (all sweet) and kept driving at normal temperature. Around the corner from home same thing again, the temp gauge sprung up instantly to full hot and the warning alarm came on.

Never had an issue after that in about 4 weeks and 1500km, but the same thing happened today, and went from overheat to normal temp about 3-4 times. Now there's plenty of coolant and apparently when its overheating it doesn't feel hot when shes popped the bonnet. I know when a car cooks itself you usually can feel the heat when you pop the bonnet

My thoughts are this:

1.) Possible false overheat i.e a faulty coolant temp sensor. Anyone know how I can check or confirm this?

2.) Epic Air bubble in the system (might need to bleed it). I'm hoping this one is the issue since its an easy fix, my only thing is Shes had the car for 12 months, never lost a drop of coolant, never had to add coolant so I don't know how it could get any air stuck inside?


Any other suggestions are appreciated. Shes says the fans came on and there is no consistency as to when this happens (traffic, cruising etc)

[acarmody]

I'd say you ware on the write track with those two suggestions. Try bleeding the system first as that takes very little effort and time. If that doesn't work, maybe look into changing the sensor and maybe the thermostat.

Also make sure the car heater is turned on while bleeding the system, just in case you didn't know.

[monkeys437]

Replacing the thermo might be an option if bleeding doesn't work.

[Killr6]

i had this problem mate and i had a blocked radiator, my car is in perfect A1 running order.

i changed everything to temp sensor, thermostat, radiator cap, and bleed the system, until i found out it had a blocked radiator.

Dan.

[monkeys437]

Thanks dan ill check for that. Did you just run a garden hose through it to unblock it or did it need replacing?

Well I had a look last night and there was a bit of air in the system and it is leaking a bit from the heater switch (think thats what its called, beside the engine with a few heater hose going to it). So I managed to get 2.5L in despite her old man telling me there was plenty of coolant in there.

First step is to replace that, then Ill flush out the coolant (which should see if the rads blocked hopefully) and see how its looking after that

[Killr6]

your heater tap valve was leaking a bit?

and nah i got my radiator professionally cleaned.

[monkeys437]

http://forums.justcommodores.com.au/...heater-tap.png

This thing is leaking a bit. Looks dead easy to change so Ill do that first, run a radiator flush and see how we go. It still doesn't really explain the erratic behaviour of the temp gauge but its a start

[johnno010684]

hey mate, if you added 2.5 lt of coolant id say it was low! im guessing from a similar experience when i didnt have much coolant in a car that the fans kicked in when it was up the top of the gauge and that brought the temp down. and good spotting with the heater tap ive had to replace a couple, thats where your leak is.

[Killr6]

yeah you always want to fix leaks strait away, but yeah a heater tap is easy to change, just drop your coolant and do it again.

but yeah 2.5L of coolant is not much id say add about 5L

[gw0071]

Considering the heater tap valve's function and location, the material it is manufactured from is of very poor design. They are readily available on ebay for approx $20 and are quite simple to replace allowing you to keep your hard earned in your sky rocket! Good luck

[SweetWagon]

When it does it, feel the top radiator hose, it should be fairly hard to squeeze, but if its still soft and squishy its due to the cooling system not pressurising properly likely due to an air lock