Early Activation of Cooling Failsafe?

[Dr Jekkyl]

Strange issue.

When under load the temp guage is rising (to R or M of NORMAL) and then the engine starts 'chugging'.

I presume this is the coolant failsafe kicking in but this seems WAY too early.

I am thinking it's a sensor problem but would love to hear your opinions.

[smally289]

Need more info. Is the engine actually misfiring? If it is due to high coolant temp then it will miss at idle and not just under load. Also the miss will not be spark related as the system shuts off the injectors in a set sequence.
If your miss is under load then I suspect it is just a lead (very common) or maybe a coil pack. Sometimes these are only felt when hot.
If it is more of a surge on light acceleration then maybe it is being caused by the early lock up of the torque convertor due to the increased coolant temp. The PCM does this to try and cool it down when it gets too hot.

[mik]

maybe the gauge is wrong , perhaps it`s actually hotter than that? got coolant?

[Bushbasher]

Further to what Mik said, if your gauge is wrong it may be that your temp sensor in the back of the head is faulty. I had a similar issue except at the other end of the scale, my gauge was struggling to get up into the normal zone which seemed to be affecting my mixtures on gas, causing my converter to start to freeze up after start up for the first few minutes. A change of temp sensor fixed it. If you do have a faulty temp sensor then you still have an overheating issue to deal with. How old is your radiator and when was the last time it was flushed?

Bushbasher

[auIILTD]

Hi Jekkyl. The gauge is not really an accurate guide, but from what I have read and discovered from the tuning side of things, most gauges on the AUs are very similar. To give you a guide, when I first started tuning my car, (one of the logged fields is Engine Coolant Temp), my gauge was sitting around the 'O' of normal which when looking at the actual ECTs, was from 200 to 210 degF, which is around 93 to 99 degC. Way too hot and close to boiling.

With your gauge showing so high, my guess would be that you are above boiling and the only thing stopping it boiling will be the pressure in the system and the anti-boil. As for the behaviour of the car when it is hot, I do know that the tune will start retarding the timing when ECTs get too hot, so maybe that is what is happening.

Either way, I suggest you get it checked out before any more damage is done. Most radiator places will do a free assesment for you.

Hope that helps.

Stu

[rowan194]

Originally Posted by smally351

If it is more of a surge on light acceleration then maybe it is being caused by the early lock up of the torque convertor due to the increased coolant temp. The PCM does this to try and cool it down when it gets too hot.

Interesting. I've experienced shuddering on acceleration (then surge when I back off) when my coolant was low. At the time I was told it was because the oil was overheating, which was making it too thin inside the torque converter.

Failsafe cooling seems to be almost totally useless if your trans overheats while the engine keeps going?