Fan always when engine stops

[timbo6063]

Hello
Every time I stop the fan is on. A few months ago the engine overheated and my garage said get rid. I posted on this site and two members very kindly said get a second opinion (I did not know how to thank them). I did get a second opinion - another garage took it for a blow out run - it passed it's M O T and has gone O K since.
Do you think it is now recurring? I though at the time of the overheating that the thermostat was sticking? What do other members think? Have I got a problem and if so what is the solution.
Tim

[COLVERT]

We need a bit more information.---Are you having to top up the radiator ??

What is the read out on the dash gauge ??--Does the needle run in the 9 o'clock position ??

Normally thermostats fail in the open position so that the engine runs cold.
If it failed shut all the water would boil out of the radiator.

I expect other forum members will post up some more questions.

[SD1too]

Originally Posted by timbo6063

... another garage took it for a blow out run - it ... has gone O K since.

Hi Tim,

It sounds as if you may have an air lock. Has any work been done on the cooling system recently? In any case, an investigation is advisable. Do the "demist test" to check that your radiator fan's low speed is working. Search under that term and you should find it for your 1.8 engine. If not, let me know.

Simon

[timbo6063]

Posted to Rover 75 Club – 20/05/2021
NEW SITUATION
As suspected the engine (1.8 as you knew) overheated today so there is a real problem.
Information –
• I have not topped up the radiator because when I do the temperature control liquid “pours” out forcefully – I am not aware of a radiator leak but perhaps there is one.
• Reading on temperature read out on dash is at 9 o’clock when things are O K. However when it overheated today it went to 12 o’clock and if I pressed the accelerator harder it showed cooler – basically it jumped about between nine and twelve o’clock. Should I gather that the thermostat is stuck open? If so it should presumably be replaced. Is this a big job (what cost should it be?)? I assume the part is peanuts but the access and labour are difficult/time consuming /expensive.
• Re the air lock. Certainly the fan is working as stated – it is on when I turn the engine off and before it stops in the last week. I am not quite clear about the “demist test” but I will go off and look it up – I am not clear how I can tell the speed of the radiator fan but it sounds pretty loud and fierce. Would this tend to indicate that it has to work harder to regulate the radiator temperature and that it is hiding a problem? Would it help if I took it for a blow-out run?

Thank you for your replies. If I can not solve it perhaps my garage can.

[Yorkshire GOC]

tHE DEMIST Test will tell you if your low speed fan is working - this triggers when your engine temp hits 104/105 and brings it down to 90 or so and by doing so will stop overheating . If not working it is generally due to a failed resistor on the fan mounting a low cost fix.

The temp gauge is pretty useless 9 o clock can mean anywhere between 75 and 110 degrees.- you should switch on the onboard diagnostic software which will give you the car running temp as you are driving along . See below you need setting 19/7

https://www.the75andztclub.co.uk/for...ad.php?t=55585

So when the expansion tank is cool are you losing any coolant - do you need to top up ?

[COLVERT]

RE:--My post number two. Your problem seems to be a thermostat failed closed.--- It's forming a large trapped airspace in the engine which is displacing the coolant and giving you that 12 o'clock reading on your temperature gauge.

Forget the---blow out run---that sort of old wives tale is just a waste of petrol.
It also might wreck your engine through overheating if there are areas with no water in.---

[timbo6063]

Thank you everyone.

I intend to refill radiator (50/50) mix and try to get diagnostic test.
If the coolant spurts out (should this be happening?) I will have lost more coolant so will it now take more when it stops discharging? Should the engine be running and the radiator cap on or off?
Then I will get my garage to replace the thermostat and the failed resistor on the fan mounting. I assume these parts are available.
Does this sound like a plan? Should this be a permanent fix?

Tim

[Lee T]

Firstly do the "Demist test" as advised, if fan operates correctly then refill the coolant, and if you have or can borrow a plastic hoover pipe, remove header tank cap and carefully push the hoover pipe into the header tank, making sure it's a tight fit. now fill the hoover pipe with coolant and start the car. Using the OBD temperature display (19_7) watch the temp and the coolant level in the hoover pipe. once you see the temp drop the stat has opened and any air in the system will be expelled via the hoover pipe as it raises the level of the coolant more than enough. Use a syringe to lower the header tank level to the max once engine is cold again, then go for a good drive with OBD temp showing and see how it goes. Good luck. Lee

[COLVERT]

If you run the engine with the rad cap off it will almost certainly over flow.--That applies to most cars.

[Lee T]

Originally Posted by COLVERT

If you run the engine with the rad cap off it will almost certainly over flow.--That applies to most cars.

With the header tank cap off the system cannot fully pressurise, so what would cause an overflow? When I bled mine using the hoover pipe method (credit to Big Russ for that tip) I only lost a little when the air burped out and when I removed the pipe from the header tank.