How to change a thermostat on V6 engines - A guide - Alfa Romeo Forum
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How to change a thermostat on V6 engines - A guide

The question of engine temperature is often asked on these forums, and more often than not, the first response is to change the thermostat.

For those that have done this job, stop here. If you haven't and would like to know how. Here is my guide.

Tools needed

a 7mm socket or a flat head screwdriver or clic-r pliers for air and coolant hose clips depending on what you have fitted.

A big cross head screwdriver

An 11mm socket on a long extension.

Some coolant.

Some fine sandpaper or a sharp edge tool to remove old gasket/ gunk.

The engine I worked on.

This a 3.2. but any other V6 Busso is of similar orientation.

The thermostat is buried under the intake air pipework. So this needs removing. If you have the original air pipes, a pair of Clic-R pliers is needed. If these have been removed, and replaced with jubilee clips, then a 7mm socket is needed.

With the air pipework out of the way, you will see this (I took this with the new one on, because I forgot beforehand)

The other obstruction is the wiring junction box.

This big black thing here.

To get this off. Pop the top open by pushing in the two plastic tangs with a screwdriver. The top hinges open to reveal this

Ease the wires out, or to one side to reveal two large headed cross head screws. Unscrew these.

Then ease the box up, and rotate it clockwise around the wiring. The box can then be wriggled off of the wires and out of the engine bay. Leaving this

The thermostat is held on by 3 11mm headed bolts. Two short and one long. Before you remove it, unscrew the jubilee clip (or the clic-r clip if still original)
You'll end up with this (and wet feet if you are standing close to the car)

I didn't need to change the coolant temperature sensor, but if you do, its the big black thing screwed into the base of the thermostat housing. If screws out with a 20mm or so spanner.

Next, remove the three bolts and lift off the thermostat.

Take a good while to remove any sealant, remaining gasket, muck and crud. I used a sharp chisel to remove the gasket and some 240 grade wet and dry to remove some stuck on limescale on the sealing face.

I was replacing mine because it was weeping coolant and the temp was sitting lower than it had been recently, a sign of failure. This is why

The stat was all coated in hard water scale. It has been in for a little over 3 years, and although it is in good condition and a good clean would have sorted it, I carried on and replaced it anyway.

In the words of Haynes Manuals, replacement is the reverse of removal.

Fit the new stat and gasket. It only fits properly one way round and in one orientation. If it doesn't appear to line up, then move it a bit until it does.

Here is the difference between old and new.

Bolt it all back together snuggly, and fill up the coolant tank. The change took a shade over 1 litre of coolant in total. I used neat, red, OAT coolant as the winter is coming. I bought a bottle of distilled water to mix the coolant concentrate with, but didn't need it.

The longest part of the job was getting the black wiring box to line up with the screw holes. When you get one, the other is easy, but with all the wires in the way it is a pain in the rump.

When the job is done, run the engine up to temperature and it will burp itself of any air locks. My car radiator has an easily reached bleed valve, so I opened that to let air out of the rad.

Total time was about 30 minutes. Most spent getting the screws lined up in the electrical connections box.

Final step. Go have a beer.
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Great writeup.
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Nice write up Andy.

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How to change a thermostat on V6 engines - A guide

Thank you.

I'm quite pleased with myself.😄
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Great tutorial - if mine fails again I'll definitely DIY it.
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It seems you have a lot of corrosion in your cooling system.
The coolant should have been red or yellow not rust orange as yours are.
Haven't you used anti corrosion coolant?
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The coolant is orange out of the bottle. The stuff on the stat was lime scale from hard water.

The stat appears to be the worse victim, the inside of the pipes and the body of the engine below the stat are all clear. Maybe the stat body is a metal mix the scale likes to stick to.
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Nice, believe it or not I use an old plastic chop stick for lining up the bolt holes with the plastic box - works a treat.

Now can you do a write up for the 20v JTD
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