How to: Change a thermostat on a twinspark.

This is by no means the definitive guide to changing a thermostat but is how I did it (with inspiration from Andymac). Its meant as a rough guide and I take no responsibility for you damaging your own car whilst using this info.

Click on pictures to enlarge.

You will need a new thermostat, thermostat gasket (mine came with the stat), 1x 29-41mm hose clip, 1x 10-13mm hose clip and 2x 13-19mm hose clips as well as an assortment of tools.

1. Open bonnet and remove air intake pipe that goes from the airbox to the throttle with 7mm hex socket.
Stat1.jpg

CAUTION: do not turn the ignition on with the temp sender disconnected.

2.Remove big hose at the front of the thermostat (lots of coolant will come out), the small hose at the top, the hidden hose underneath at the front and disconnect the temp sender(the bit with the wires at the top). Note there is still one hose connected at the back. Unless you have the special pliers that takes the clips off you may have to cut them.
Stat2.jpg

3.Using a 13mm socket remove the two bolts that hold the thermostat onto the side of the engine. Prise the thermostat away from the engine with you hands and disconnect the last hose on the back.
Stat3.jpg

4. Take time to clean the mating surface of the engine being careful not to scratch it or get debris into the engine. Wash the drained coolant out of the engine bay as well.
Stat4.jpg

5.Using an appropriate spanner, transfer the temp sender to the new thermostat giving it a good clean with solvent as well. You can buy new ones for about £15 but I am too mean.
For added support you can remove the temp sender wile the thermostat is still attached to the engine.
Stat5.jpg

6.Refit in reverse order using the two 13-19mm clips on the lower hoses, one 10-13mm clip on the top hose and the big 29-41mm clip on the front hose.
Stat6.jpg

7.Refill the coolant (50% mix) upto the max line and squeeze several times on some of the big hoses to bleed slightly. Then refil back to max and replace cap.

8. Re-install air intake pipework.

9. Start the engine and look closely for any leaks. Let the engine run up to normal temp while keeping an eye on the coolant level and for leaks.

10. let cool down for a couple of hours and refill the coolant to max, as the system will have bled itself.

11. The next few times you use the car check the coolant level before you start and top up if neccesary. Make sure to check the coolant level with the cap removed.

12. Enjoy

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The only thing I would add to that is remove the temp sensor from the old stat while it is still attached to the engine.

Also, when checking the coolant level after a few days, remove the cap. Sometimes the level will only drop when the cap is removed.

Nice clear pictures.:

Originally Posted by David C

The only thing I would add to that is remove the temp sensor from the old stat while it is still attached to the engine.

Also, when checking the coolant level after a few days, remove the cap. Sometimes the level will only drop when the cap is removed.

Thank you, will amend accordingly.

Originally Posted by zulu ferret

Nice clear pictures.:

Taken on a Nokia N95 mobile phone!
Only set on 2 megapixels as apposed to the full five to help keep the file size down.
Helps it was sunny too

Well done, even came up in Google Great idea, thanks for adding

I always thought the stat was meant to be an akward thing to do doesn't look too bad there.

I have sausage fingers and managed ok!

It just looks complicated with all the different pipes. Chance of cross connecting is virtually zero.

Job might have a bang off that then so.

Just wanted to thank MPH for this guide.

I changed my stat last night as temps were dropping to 70ºC or below on the motorway. I only had a little run but it seems much better. Temp dropped lower than I would have hoped at 60-70mph though. Had been led to believe that it would glue to 90ºC with the new stat but it seems to drop down to maybe 3/4 or 4/5 of the way between the 50 and 90 marks, which are really non-linear so no idea what that means. 80ºC? 85ºC? I think the system is still bleeding though as I was able to put in 400ml more coolant this morning. Where is it all going? Hope not out the bottom!

Doing 500miles this weekend so should get a proper feel for how quickly it warms up which was a major problem before and what the high speed temperatures are doing. I hope it solves the problem!

P.S. my top tip for removing the Alfa jubilee clips which are a right pain in the ass without the right tools would be to get a screwdriver and a hammer and chisel them off. Wish I had thought of that earlier would have saved me faffing around with hopelessly inadequate plier/cutter things and numerous minor injuries. Italians must have tiny hands!

Also I have a CF2 engine and the air hoses were much further to the right of the engine bay compared to the guide so I was able to (just about) get away without disconnecting them.

Cheers! Dave

Update: It took a couple of runs for the level to settle nicely and I guess bleed out all the air. Now it sits on the max, the temp dial starts to move up the gauge towards 50 within a mile or so from cold and will mostly sit a couple of degrees below 90 whatever I am up to apart from sitting in traffic.

As a bonus it looks like my mpg has gained 2-3 too which is quite a nice added extra. I would definitely recommend doing this if you see your temps drop below 80 at speed!

The only thing that I would add, is that the pictures are from a plastic cover topped engine (cf2 ?).
I have to change my thermo on the 155 (cf1), and there are 6 pipes going to the housing.

Ok, managed to change the thermo today.
Doesn't take long - about an hour.

As I said above there are 2 additional pipes on the earlier engines.
They connect to E + F in the picture, and I had to remove them after I had taken the thermostat off the engine.
I managed to get to both the bolts holding the housing on to the engine using a long reach 13mm socket

Nice one Celadon.

Thanks for adding the pics

What perfect timing i was just searching for 'how to' as i'm doing mine this weekend!

Thanks MPH

No probs

Good luck and use lots of patience.

Has anyone made photos of this work in a 1.9 JTD 16V, it would be very useful!