How To: MK3 (NC) Thermostat swap

[Horney]

Own and NC and find the heaters aren't as good as they used to be? Do you find the temp dropping on long runs of clear road in the cold?

You my friend need a replacement thermostat! The pic below shows my car after it had got up to temp. It dropped right down once on the motorway.

Untitled by Nicholas Horne, on Flickr

So order the bit from your preferred supplier. There's two different types with a long or short wide pipe. If you just get the long one you'll have no problems. The image below shows the difference between the original version (right) and the uprated fully metal assembly of the new stat (left).

Untitled by Nicholas Horne, on Flickr

So you'll need some tools to do the job. A selection of small sockets, some extensions for your ratchet, a cross head screwdriver and some long nose pliers for the coolant pipe clamps.

1) Drain the coolant.
You'll find the drain hole for the rad on the passenger side of the car in a hole in the under tray.

Untitled by Nicholas Horne, on Flickr

Untitled by Nicholas Horne, on Flickr

Pop that little across head out and your coolant will drop out. Undo the filler cap to drain it faster.

2) Remove the airbox.
I couldn't really document this to well as I have an induction kit on mine. Your aim here is to get all the inlet pipework off the throttle body. You need to disconnect the breather and loom plug illustrated below.

Untitled by Nicholas Horne, on Flickr

Should then look a bit like this:
Untitled by Nicholas Horne, on Flickr

3) Remove Throttle Body and Thermostat hoses
Pretty simple, undo the 4 8mm bolts holding it on. You'll need to remove two little water hoses which I forgot to photo but it's very obvious.

Untitled by Nicholas Horne, on Flickr

Once off it looks like this and you can easily get to the two Thermostat hoses that need removing:

Untitled by Nicholas Horne, on Flickr

4) Remove Thermostat
This is a little tricky. It's held on by three 8mm bolts (vaguely indicated on pic below). You can see two of them but the other has to be done by feel.

Untitled by Nicholas Horne, on Flickr

With it removed you can see the bolt locations

Untitled by Nicholas Horne, on Flickr

5) Fit New Thermostat
Refit is the same as removel as Haynes love to say. It's not. That hidden bolt is a real pain to get back in. I suggest a blob of grease or blue tac in your socket to hold the bolt in while you faff about trying to get it in the hole.

Untitled by Nicholas Horne, on Flickr

Untitled by Nicholas Horne, on Flickr

Everything else is fairly straight forward to put back together.

6) Refill with Coolant
Now this is the bit that gave me the most grief. The MK3 seems to be a real pain to bleed the coolant. I had a huge airlock in the Heater Matrix that took me several hours and a lot of swearing to clear. If you can fill the car with the nose up high on stands.


Hope this helps out a few people. I have another one to do next weekend on MrsHorney's MK3 so I'll update with photos for an airbox equipped car.

[Clem]

Now you mention it ... mine does that on motorways.

How much were the stats? Also ... when you do the Lady Hornes ... please to update with better bleeding technique?

[Horney]

Thermostat was £28 from Euro Car Parts. Bleeding part 2 will commence tomorrow. Hopefully faster and with less swearing this time!

[Clem]

Im happy if the technique requires more swearing in order to reduce the time ...

[sandys]

Useful guide but if you are a heavy handed muppet like me you should add to this the following

bolt torque is 8-11.5 nm for both throttle body and thermostat, yes I did spend this week getting sheared bolt out of car.

[Horney]

Doh!

THis is such a common problem on these it seems, I'm having to do the one on the black track car. That's all 3 NC's we own having needed to be done.

[sandys]

Nick mentioned it to me I never really pad it much attention just assumed it was a characteristic but as I was doing the rad and dropping coolant may as well do that.

[Horney]

My black on is so bad it runs on cold start enrichment pretty much all the time. I'm getting about 15mpg!

[sandys]

Is that more likely to be a dodgy lambda sensor making it run rich more so than water temp? You can monitor water temp by OBD,

[Horney]

It's deffo the water temp. At 80mph the garage sits at 2 blips, on the grey one it's bang in the middle. When you progress through the revs you really feel the VVT transition. If you sit in traffic for ages and it actually gets warm then the VVC transition is the same as my grey one.

I think they get stuck at varying degrees of openness and this one seem stuck wide open. I can drive it 28 miles to work, 90% of which is motorway, and it never gets warm.

[sandys]

I'm hoping it might be why my car has always been variable performance wise.

[sandys]

Would the air lock manifest itself with poor heat out the heater, I have done a couple of drains and refills, starting to suspect the thermostat is just working at the wrong temp, stays rocksolid in the middle and the engine seems hotter, judged by oil pressure gauge, not been as low as it is now when warm unless I have been soloing all day.

[Horney]

Mar 24, 2017 19:51:48 GMT sandys said:

Would the air lock manifest itself with poor heat out the heater, I have done a couple of drains and refills, starting to suspect the thermostat is just working at the wrong temp, stays rocksolid in the middle and the engine seems hotter, judged by oil pressure gauge, not been as low as it is now when warm unless I have been soloing all day.

Yup. The air lock always seems to be the heaters.

I believe the oil pressure gauge is fake and makes up a reading based water temp and revs.

The temp gauge is a proper one and can be trusted to give real data.

[sandys]

So how do you sort an air lock?

[Horney]

Mar 24, 2017 20:38:29 GMT sandys said:

So how do you sort an air lock?

The heater matrix is almost the high point in the system. Try bleeding it up with the nose elevated. I found that helped but ultimately a good thrash around seemed to clear it. There doesn't seem to be a sure fire way of doing it.

When I had the air locks in both mine and Lizzie's I could leave them running and take the heater matrix pipes off from the bulkhead and no water would be flowing out of them. It's a right pain in the ass.