defenderdog · Oct 18, 2015

I am currently prepping my new purchase for its mot on Monday. One of the many problems from my vast list is the electric air con fan which seems to be on all the time. I have pulled the fuse to stop it ready for tomorrow's mot. Is this ok to do or will it cause any damage to the air con.

discool · Oct 18, 2015

Yes but u won't have a/c so turn it off at the dash, but it being on is one indication that your engine has got dangerously hot, thats maybe something to look at after your mot, u still have the Viscous cooling fan fitted don't you?
To turn the fan off and reset back to default u need to plug the system into a dianostic computer unfortunately

defenderdog · Oct 18, 2015

discool said:
Yes but u won't have a/c so turn it off at the dash, but it being on is one indication that your engine has got dangerously hot, thats maybe something to look at after your mot, u still have the Viscous cooling fan fitted don't you?
To turn the fan off and back to default u need to plug the system into a dianostic computer unfortunately.

Thanks Discool. That's a bit worrying that it may have been really hot

this is the problem with buying a car with no MOT and only being able to run it on the drive. The header tank is clean though and I've had the rocker cover off to change the injector harness and it's clean with no milky residue so fingers crossed its ok on the way to the mot station tomorrow

discool · Oct 18, 2015

An other indication is of an over sensitive temp sensor which is not unknown, but first a reset is required,

defenderdog · Oct 18, 2015

discool said:
An other indication is of an over sensitive temp sensor which is not unknown, but first a reset is required,

That would be better. Hopefully if she passes tomorrow I can take her to be reset. Thanks.

sierrafery · Oct 18, 2015

remove the fan relay before the MOT just to make sure... discool is right, there is an overheat fault code logged in the ECM which must be erased

defenderdog · Oct 18, 2015

sierrafery said:
remove the fan relay before the MOT just to make sure... discool is right, there is an overheat fault code logged in the ECM which must be erased

Thanks sierrafery I've removed the 40amp fuse so it's off at the moment. I will leave the air on off until it's been reset. I just hope now the h gasket isn't fooked as I spent hours sorting this motor out ready for tomorrow and that will just about top things off if it boils up as soon as I finally take it down the road. Could a dodgy thermostat cause overheating probs as I've noticed whilst I've been running it on the drive that it runs cold for a long time then suddenly the heater gets nice and warm. But never goes over the halfway mark on the temp gauge.

sierrafery · Oct 18, 2015

you can use the aircon without fear cos i suppose there are less that 28*C in the UK these days and only above that temperature the fan kics in...or if the engine temp rises above 110*C... try to stop the viscous fan with a rolled newspa[er when the engine is hot and if you can that's the root of this problem

defenderdog · Oct 18, 2015

sierrafery said:
you can use the aircon without fear cos i suppose there are less that 28*C in the UK these days and only above that temperature the fan kics in...or if the engine temp rises above 110*C... try to stop the viscous fan with a rolled newspa[er when the engine is hot and if you can that's the root of this problem

Thanks sierrafery I'll try that. Thanks.

discool · Oct 18, 2015

I had an MOT recently and going by the V8 sound coming the garage area

my engine was running for most of the one hour the testing took

So, if that's the same for your disco, than as The Count (sierrafery) said make sure your viscous fan is doing its job.... as in a garage without any forced air the engine temp will be a lot higher.

listerdiesel · Oct 18, 2015

Ours will run at tickover for hours with no problem, there's enough capacity in the cooling system to cool it properly, even with the original radiator.

Peter

sierrafery · Oct 18, 2015

Do you have additional coolant gauge?... cos in UK climate and not driven hard uphill the original gauge might stay at the middle making you think that everything is ok but the coolant temp to be 109*C for ages without even knowing it, at 110 the electric fan(if fitted) kicks in on ECM request to help the cooling system and stops at 105 but if it's above 28*C outside the fan will be on by aircon command so you can drive it for long with the gauge staying nicely at the middle with up to 119*C engine temp cos the gauge goes up from the middle only at 120... also at above 100km/h the fan is disabled completely, the ECM will log an overheat fault code only when 120* was exceeded ... without a locking viscous fan these above 100* engine temp scenarios are very common, electric fans are seized quite often and imo that's not healthy for the engine so my advice for everybody is to check the viscous fan as i said cos it costs nothing and very important.

discool · Oct 18, 2015

listerdiesel said:
Ours will run at tickover for hours with no problem, there's enough capacity in the cooling system to cool it properly, even with the original radiator.

Peter

Okay Peter that's your disco, we wouldn't expect anything less...

but that can be said to be the same with any maintained vehicle can it not? unless the engine has issues which the OPs "may have".
My disco has had it trials and passed with out issue

. In the almighty two hour + motorway traffic jam in 80c + temps and with my AC in full use and moving just at a crawl the V8s engine bay was... hot!... but the viscous fan coped blowing the hat air out under the front wheel arches.
Other vehicles were dropping by the wayside that day, on the M5 when a D2 and caravan both fell over.

defenderdog · Oct 18, 2015

Just checked the vicious fan and its mashed a LRM mag from cold so don't know if that means it's not working right as surely it should be not on as much from cold. But this must also mean it's on full when hot. Or have I got that all wrong.

discool · Oct 18, 2015

That's how it should be, but 50 yards down the road and when the viscous fluid circulates the fan will feather, u should hear the sound of the fan change ad the rad temp changes so will the viscous coupling to suit the temperature. I believe diesels are cool running so u may not hear the fan lockup in traffic on a hot day, which it does with a petrol engine confirmed by the sound of the fan.

defenderdog · Oct 18, 2015

discool said:
That's how it should be, but 50 yards down the road and when the viscous fluid circulates the fan will feather, u should hear the sound of the fan change ad the rad temp changes so will the viscous coupling to suit the temperature. I believe diesels are cool running so u may not hear the fan lockup in traffic on a hot day, which it does with a petrol engine confirmed by the sound of the fan.

Oh right. Thanks for the info.

sierrafery · Oct 18, 2015

That's why i told you to check with HOT engine , actually open thermostat, the fan locks on bimetalic valve action when the heat from the radiator activates it

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