cooling fans,header tank overflowing?

[lostu]

Hi ,can anyone help yesterday i started up the lotus after a couple of weeks from the last start up.at present i have not had any problems with the fans coming on etc and the temp gauge sits at under 90.as i left it idling for about 40-45 mins normally the fans kick in after 30 mins but as i was outside the garage was not sure if they kicked in so hence i gave it longer which lead too boiling overflow.

Today i topped up coolant and started for 30 mins the temp gauge sat at just under 90 and all was fine.My question is DO THE FANS NEED TOO WORK SOONER or is it because the cold conditions at the moment as its only idling and not summer tempertures or as i`m lead too believe the fans only kick in after 90 degrees and when driving the cold air intake keeps the temp steady.please advise me and thank you for your help

cheers stu.

[molemot]

The otter switch turns the fans on significantly past 90 deg C. If you sit in the thing and watch it you see the gauge go up, past the normal reading, then the thermostat opens and the reading drops...if you check the hose temperature where the otter switch is, you can feel when the thermostat opens as the hose gets hot. When driving, the fans don't come on because the cooling system (if it's in good order!) gets enough cooling from the airflow through the radiator to stay under control. In really cold weather, you might never get the fans running as it never gets hot enough!

Having said all that, it definitely shouldn't boil; if you have filled the system right up, it will lose some coolant until it gets to it's natural level...this applies to the cars with just the cylindrical header tank with the pressure relief cap on top. Mine has the modified system which replaces this header tank with a similar one having a plain cap, and takes the overflow from this tank to a plastic expansion tank on the RH wheelarch....also some mods to the pipe runs. With this system, the cooling mixture expands into the expansion tank (which has the pressure relief cap fitted) and gets sucked back into the system when the engine cools. The original system always ended up with the level in the expansion tank 2 or 3 inches below the top...this was normal.

All sorts of fun can be had bleeding the system, there is a bleed screw at the top LH corner of the radiator under a rubber cover in the front boot...you need to get the engine proper hot, then loosen this screw until only water comes out...it'll hiss and pop as the trapped air comes out of the system, and be VERY CAREFUL as getting scalded is almost a certainty otherwise!! I have heard of people parking on a hill to get the trapped air to one end or other of the system...but the flat has always worked for me!

[Wilf]

My fans do not come on at all in this weather sits at 82 degrees the whole time. Think I should really have an 88 thermostat as would give a hotter heater too.

[lostu]

Hi john,ye that makes sence my level in the header tank was near the top and as the lotus was idling for about 45 to 50 mins i think it expanded a little hence the overflow,ye i will drop the level too about 2 inches from the top as before after a run if level too high i`ve had the over flow a little when i park it up,likewise charles the fans will not come on as its very cold air at the moment,i watched the gauge today when idling and it creeped up slowly and just sat under the 90 degrees no issues i was just abit concerned as this has never before been a problem ,thanks again for great advice

cheers stu.