Difference between revisions of "Thermostat replacement"

Latest revision as of 12:48, 6 November 2013

Overview Guide
Ford Model:	Mondeo MK3
Petrol/Diesel:	Petrol
Estimated Cost:	30-90 GBP
Difficulty?	rather easy
How long does this take?	2-3 hours
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Applies to all Mk3 Mondeo with 1.8 or 2.0L petrol Duratec HE engines. Check Discussion for some additional info.

Symptom: car takes more than a few minutes to produce hot air on a cold winter's day, and even then, it's not as hot as it should be. You can also use the cluster diagnosis tools to view your cylinder head temperature, which should reach 90-105°C after a few minutes driving, then stay there.

Thermostats normally fail in the open position. In the old days it cost 5 quid and took 5 minutes to change. Although a thermostat is a simple mechanical device, on the Mk3 a Ford replacement may cost 90 quid and the garage will quote you at least 60 quid to fit it. A third party version is much cheaper but a problem with these is sometimes that the peripheral rubber sealing ring is not thick enough to give a good seal, so check this and use the ring from the old one if suitable.

It's in a terrible location behind the power steering pump. This is a conceptually pretty simple procedure to do, it's just in a very tight place you have to get to which takes time and skin off your hands (glowes might come in handy!). The hardest bit is removing the hose - if that goes OK, you should have no problems. Otherwise, put it all back together and visit your local friendly mechanic with your parts.

Let's get started - make sure you have all the right parts, these are all the tools needed:

1. New Thermostat (£12-15 from ebay etc., a lot more from Ford)
2. Pliers
3. Magnetic tool (for those dropped screws...)
4. Small ratchet set (only need 10mm/8mm bits)
5. 4 l bottle of engine coolant/antifreeze

You may need a torch too, even in good daylight.

Now out to the car, open up the bonnet and remove the front grill, there are two small plastic clips either end holding it in place, twist these and they will pop out, the whole grill unit will then pop off, just don't force it or you might snap any of the small plastics holding it in place.

Now pop out the driver's side headlamp, in the pic below are two small metal posts which just pull upwards to release the whole headlight, Unplug the electronic connector at the back and the headlight will wiggle free.

Make sure you unplug the connector before you start pulling the headlight out.

Now the headlight is out we have the essential access route to the thermostat.

Below is the view that should greet you when you peer though the empty headlight socket. First remove the large coolant pipe using pliers on the clip. This is likely to be hard work and may take a few goes to move but keep at it and it should eventually move!

And now with the large hose removed...

You will lose quite a bit of coolant when the big pipe is removed. Next undo the 3 nuts that hold the thermostat in place (blue lines in pic). These are all quite hard to get to, you will lose skin, blood and possibly a nail. Be careful not to drop the nuts, or the magnetic tool may have to come out...

You may find it easier to undo the nut holding the power steering hose bracket: this will give you a bit more room.

When all 3 nuts are out you should be able to move the thermostat into an easier position to remove the electrical connector and smaller hose.

Now everything is removed you can take out the thermostat. Below is a picture of my faulty one, you can see that one of the plastic arms had snapped off causing it to stay in only one position.

Both plastic arms were snapped off here:

Here's an image of the new thermostat for comparison (no broken arms):

Now you can install your new thermostat! You should know how to do it now: place the small hose on first, then screw in the three bolts (this may take a while as it is so fiddly) I found that putting a small bit of blu-tac on the end of the ratchet tool kept the nut in place while I lined it up with the hole. Next clip on the electrical connector and finally spend a while swearing at the large coolant pipe as you try and get the clip back on. If it's too hard you could always bin the fiddly clip and put a jubilee clip on instead.

Nearly done, the thermostat is now fitted but we have lost a fair bit of coolant - this needs to be topped up but has to be done with engine running and filler cap off. (There will be air locks in the system which need time to work round the system and reach the filler tank) Run the engine for about 10 mins revving to about 2500 rpm and checking the coolant level every min or so, you will probably hear lots of gurguling sounds as the air works it's way out. keep doing this until the coolant level remains constant and no longer drops.

Done, you should now have a warm car that knows what temperature it's running at and is not wasting fuel!