Engine fan comes on at cold start, heaters blowing cold air when idle

[walsie]

2003 1.8t sport.

When started from cold the engine fan kicks in for a couple of minutes then stops.

Also heaters blowing cold air when driving slow or idle. When driven over say 30mph it blows warm/hot air.

At round about the same time i had a coolant level warning light, sure enough i'd lost about a pint, it now loses about a pint every 2 weeks.

I now have an engine management light.

I've read on a few posts that problem one above can be fixed with a new temperature sensor (but where is it?), problem two also fixed by replacing the temperature sensor - or could it be air in the system due to loss of coolant? Problem three i've been told is some kind of flange leaking at the back of the engine.

Any ideas?

[toff3ltr]

Sounds like your fan sensor is on its way out.

Cheap and easy fix.

[walsie]

if anyone's experiencing similar symptoms then here's what my local garage have diagnosed:

Temp switch definitely faulty (computer shows temp sensor reading -40 then +60) this will cause the fans to come on for sure

Small leak from back of engine, flange of some sort? common leak apparently

Water pump failed as no water circulating - this is why the heaters are cold until driven above 3000rpm

They pressure tested the system which revealed the leak. They know it's the water pump because there is no water returning to the filler tank (take the small return pipe off when the car is running, water should come out if the pump is working)

Total cost of repair £400 or there abouts including parts which isn't bad when you consider the whole front end of the car has to come off to replace the water pump and they'll need to do the cam belt at the same time because the pump is driven off the belt. Dealer quoted £600 just to do the pump.

[pippip]

Hi all,

Had my car in for thermostat change yesterday and am having same problem. I got him to change the temp sensors as the engine temp would jump to zero and then back up randomly.

Anyway once i collected the car I started it and temp read zero (both external temp and engine gauge) but the fans came on immediately and blew cold air. made a 10min city drive and realised still no hot air and didn't get any till reached the motorway and then it was perfect. anything below 20mph and the coldish air again.

Is this the temp sensor that would be causing the problem?

Mechanic said there was one in the thermo housing and another seperate which he changed.

[walsie]

I think if you've had the thermostat changed there could be air in the system which is also a cause for the loss of heat, i would take it back and ask them to bleed the system.

My garage said that my water pump was the cause but i'm going to ask them to bleed the system first just in case it's an air lock.

A temperature sensor is only about £20 so it's worth changing it as it can cause the 'fans on when cold' symptom as it may be thinking the car is hot.

[pippip]

I was back onto the mechanic and he said he'll have a look at it in the morning.

His immediate thought was low coolant or air lock so he'll probably tackle that first.

My only thinking is would an airlock cause the climate control to think its hot upon startup and start blowing out cold air immediately? To me that is the computer getting a false reading which i would have thought was a sensor.

He replaced the sensor at the back of the engine (the easy one) when changing the thermo, he mentioned this morning that this is only the engine temp (which is acting okay is it doesn't rise for a few mins) so unfortunately I think it could be the one in the thermo housing.

Coolant level is perfect and only had water pump replaced 30K miles ago.

walsie - is your climate control acting like mine on cold starts? i.e. blowing out cold air immediately

[walsie]

yes mine is blowing cold air when you start from cold but all cars will do that until the car is warmed up anyway, the climate control works the same as standard car heaters using the hot water circulating round the engine, the climate control just regulates the temperature you set it to. When you start it from cold you'll need the engine to be somewhere near normal operating temperature for the heaters to start blowing warm air.


if you've got an airlock it will cause the climate control to blow cold air as there is no hot water getting round the system, by increasing your speed you are forcing the water to circulate and so the heaters get warmer until you slow down again.

i'd put money on it being an air lock.

[pippip]

Sorry the following is what is happening.

I start the car and the climate control on auto immediately puts up the fans to 75%ish power and blowing cold air.

Normally the fans will stay off until the car warms up and gradually increases the fan speed as more hot air is available.

[pippip]

just drove home and the fans didn't start up like yesterday but still no hot air at low speeds.

Fingers crossed an airlock is the problem, will find out tomorrow.