Hello everyone, my partner's 0.7 has recently had a fair amount of work (new turbo and radiator). She usually only drives around town, but she decided to bite the bullet and take it on the motorway. All fine, temperature fine, until we pulled off and were stationary at the lights. The temperature gauge shot up to the red. While driving on to find somewhere to stop, the needle went back to normal, and so forth. Bonnet popped and we found the coolant in the header-tank boiling furiously. Any ideas?
A Cooling system is pressurized, therefore the boiling point rises. If there is a pressure leak somewhere, the coolant will boil at ~100°C. Maybe the radiator cap is defective, but from afar its hard to tell I would definitely get to the repair shop and make a complaint about it, especially if there was some work done to it recently. Do not drive the car unless you absolutely have to, prolonged overheating can lead to a defective head gasket and warped cylinder head which will set you back hundreds of quid to fix
Thanks for your reply. Well, I had a natter to the garage earlier... they were wondering if it was a thermostat problem. Humour me, but I'm genuinely ignorant on this matter - how does a system stay pressurised when connected to an external tank with a vent?
The external overflow tank isn't pressurised, only everything from the radiator cap back. When the pressure rises in the system, the cap can open a bit to let the excess pressure into the non-pressurised overflow tank, usually by letting hot water into the tank (because there shouldn't be much in the way of air/steam in the system). Later, when the system has cooled, the liquid pushed out will find it's way back into the system again. If the system has got really hot, the pressure might be so great that a lot of the liquid gets pushed out to the extent that tank gets full of boiling hot water. I have seen a faulty thermostat create the symptoms you are describing. But if you have an air-lock in the system, it can do the same. You can get an airlock by refilling without the cabin heater valve open - the empty heater matrix can hold air in the system, where there shouldn't be air, and this can cause all sorts of problems later. I have seen this happen as well. Some cars are really difficult to refill without getting an airlock - I had a Metro some years ago and it took all sorts of stupidity to get it to fill properly. You can test for it by putting the heater on - if it doesn't get hot, then something isn't right there... A leak in the system can create boiling, but generally this would show as a gentle increase in temperature over time until boiling occurs.
Did you check to see if the radiator fan switched on? That would explain the temp rising when going slow after a motorway run
My little car has a hks loader and also a hks bov. If I drive more than 180 km / h I reach also 105 c water temperature and oil when it is outside 30 degrees. It helps a lot turn on the air conditioning when stopping..
Thanks very much for all the replies. I'll print this off when dropping it in at our mechanic next week. Cheers, D
Where do you take yours David ? I'm in Barnsley and looking for a decent mechanic. Snuff Mill used to be good on eccleshall Road but it's been 15+ years since I've had an older car to be fettled.
and i think too, there is a temp sensor at the engine too . if it goes over 115 c (water lost), the engine stops running..
Could be either of the above, temp sensor or thermostat. Never seen a Radiator cap faulty but never know so... Temp sensor will just read funny and if connected (4wires) with the ECU will make the engine run rich etc. Kinda like driving with the choke on most of the time. It will also take a long time to get up to operating Temp, which is the first sign, so keep an eye on the gauge. It will also throw a fault code, not a check light. In that case you need a diagnosis done on it to check for any fault codes? Won't make it over heat though. Just had that happen on my Audi. It will cause other fault codes sometimes and can be misdiagnosed as the MAF sensor. Took me a long time to figure it out as it wasn't over heating. Thermostat, well they can pack up too. Easy check is whip it out, boil the jug & pour the water in a cup or bowl and throw it in there. Pay careful attention and you will see it start to open up. Spring will compress and leave a nice gap. Obviously if it doesn't open or leaves a very small gap its buggered. That will cause it to over heat for sure. If your still unsure, run it without it. If it still overheats then its definitely something else. Also there should be a Temp stamp on the Thermostat, so have a look on the top of it. That will be the opening temperature. Airlock as mentioned above can be a problem on some cars. The Triumph Stag is one that comes to mind. Was the cause of all the over heating problems. Seems it might be related to the work you had done? My car runs around in 30 plus temps in the summer and never over heats. You can also get a D-Sport Thermostat which should be a lower temp than your standard one but that would only be needed if this has been happening regularly and everything else has been checked or the climate is very hot.
A little addendum to marnobs post: Do not run the car without a thermostat for prolonged times, better just replace it should you suspect its faulty. Costs a tenner, maybe 20
Thanks David. I’ll viist next week to see if they can fit my alternator when it arrives and also fettle the squeaky rear brake spring. Did you work in Griffin House at any time ? Name sounds familiar.
