overheating (1.6 petrol engine)

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image1990
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overheating (1.6 petrol engine)

Post by image1990 »

Hello again everyone.

Well, it's all go this week. After twenty minutes or so crawling along in traffic yesterday evening (with the fan cutting in), I got back up to a faster speed and the STOP and temperature warning lights came on, shortly followed by steam billowing out of the bonnet and a fountain out of the radiator cap when I unscrewed it a while later. Needing to be somewhere in a hurry, I called out the breakdown man, who diagnosed a sticking thermostat - he removed it, made me drive a couple of kilometres and when no warning lights came on, gave me the all clear. Since I'd stopped the engine pretty much as soon as the lights came on, I've apparenty not damaged the head gasket. I must have done about 40 mins varied driving after that and the fan was definitely running, with no overheating.

Clearly, the thermostat needs replacing, but is there anything else you think I ought to get checked out at the same time to avoid future problems? The car has just had a new water pump and new coolant, by the way.

Thanks in advance and vive la BX!
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(CZ)enda
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Post by (CZ)enda »

Well, if you want to be extra-thorough, check that both speeds of the radiator fan work - remove the connector, shorten the first and then the second pin in the socket against the third one and check whether the fan cuts in.
You can also remove the switch from the radiator and boil it in a pan filled with water, use a pickle thermometer and then check the switching temperatures with your multimeter - you will find the exact values of the temperatures required in Haynes Book of Lies.
But I think that this is a bit overkill and once you replace the thermostat and bleed the cooling system properly, your troubles will probably disappear.
image1990
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Post by image1990 »

Thanks a lot (CZ)enda. Just one more thing - is it alright to drive with the thermostat removed for any period of time?
jeremy
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Post by jeremy »

The fans should never run while the car is being driven - there should be enough draft through the radiator core to cool the car and unless there is an enormous following wind at 20 MPH the draft through the radiator should exceed anything the fan can provide.

Your car is a 1.6 and may have a single fan - in which case the speed may be lower - but the fan is really only required at standstill or very low speed.

My guess is that in fact your radiator is blocked. Your car has a crossflow radiator and the water flow is from side to side. On cars with a vertical flow radiator any sludge will collect harmlessly in the bottom tank but in a cross flow radiator it collects in the bottom tubes instead - which is OK until it blocks one tube too many - and the engine overheats.

You may be able to feel this with the engine hot - the bottom of the radiator is cold and the top hot. - You may be able to remove the sludge by vigorous flushing with the radiator out but several members have found a new radiator is the only answer.

Some cooling systems require the resistance of a thermostat to get an efficient and complete circulation. In any event a rapid warm up is desireable on a petrol engine to reduce fuel consumption and emissions as well as for good and efficient running. If it appears to make no difference I'd think the system was not performing properly - which points towards a blocked radiator.
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DLM
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Post by DLM »

And a blocked radiator is nearly always cool to the touch somewhere when everything else isn't, if you need a diagnostic.
Back on two wheels and pedal power for the moment.
image1990
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Post by image1990 »

Thanks for your suggestions everyone. I had the engine running for a good long time while I was doing some Citroen aerobics earlier this evening and then felt the radiator for cool patches, but it turned out to be hot to the touch all over. Could it possibly be that the duff thermostat really was the only problem !?