Thermostat replacement

Pinkythelabrat

A2OC Donor
Thanks Steve. :) I thought I was going mad that I couldn’t make out the screw. The top one matched a bleeder screw and I did let that out and have run it to temp as recommended. All looks fine. I’ll keep a nervous eye on it for a few days.


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Robin_Cox

Member
I'm also in the boat of needing to refill the cooling circuit after a thermostat change.

After an easy 550 mile / 9 hour drive from Dundee to Plymouth yesterday morning I decided after lunch that the time had come to replace the stat as even on major hills en route the temp gauge never exceeded 80˚, and usually back to <60˚ when cruising. I'm only getting around 55mpg over distance and low 40s for commuting and the temp gauge never moves normally unless I'm in a rush so it is clearly over-cooling normally. I'd bought a Circoli one from ECP a while back but the weather has been so ropey I've not got round to it.

Undid the jubilee clips on the boost pipe from intercooler to engine and was able to rotate the boost pipe vertically to make access easier. Couldn't get the spring clip on the coolant pipe undone with the bowden cable thing because it fouled on the Alternator casing and dipstick tube respectively, so instead I undid the thermostat housing bolts with the ratchet spanner / 10mm combination. Housing and pipe came off with one plastic finger broken, but the stat and O-ring stayed in the block.

Eventually worked out the o-ring could be released using a fine screwdriver, and then after a pull the original stat (Audi / VW branded) came out, followed to my surprise by several glugs (I'm guessing a couple of litres) of very clean pink coolant, some of which splashed on the alternator. The expansion tank that I'd loosened off before then drained completely. Assume I should have sealed this up to minimise loss - learning curve is particularly steep at the moment!

Followed diagram to insert and rotate the new stat with O-ring in front to the housing. Bit loose owing to one missing finger but enough to hold them in place while re-locating the housing back onto the block and inserting the screws. Much cursing later the screws were in place and tightened down, so I'm at the point where I need to refill and check for leaks once the local motor factor reopens tomorrow to get more coolant concentrate & distilled water.

Am I right in thinking this is a case of undoing the airlock valve by the radiator, then filling suitably diluted coolant into the expansion tank until bubbles come out of the former, tighten this up and continue filling up to the expansion tank? Then run engine for a few minutes to shift further bubbles, top up and put lid on (with another check after 24 hours)? Assuming the system has drained down to the level of the stat in the engine block, what sort of volume should I expect to need to fill it back up?

>>Found the answer here in A2OC - 5 litres of 40% G12+, and the above appears to be the procedure. Thanks again to all who contributed to previous threads with information and advice.

I'm praying I've got the stat and o-ring seated again without leaks, otherwise it's going to be a fun 550 mile journey back up on Friday. As usual, any comments gratefully accepted.
 
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Robin_Cox

Member
Final report .. topped up with 2.5L of 40% G12+ coolant earlier ; radiator bubble release valve started dribbling after 1.5L ; tightened this up and filled the expansion tank up to min ; then ran the engine for 2 minutes at 2000rpm per the instructions. Watched lots of bubbles flow out of the coolant return pipe next to the lid of the expansion tank as the coolant circulated. Finally, after topping the tank up to 'max', put the screwcap fully on and went for a 5 minute drive. After half a mile the coolant temp gauge shifted and ran smoothly up to 90 for the first time ever since I've had the car and stayed there. No visible leaks around the thermostat. Hoping this has fixed it for the time being - all the info I needed was here at A2OC. Confident to do this again now as and when necessary.
 

Robin_Cox

Member
In a nutshell, yes - more obviously so recently now that the summer heatwave has dissipated, commuting miles while the engine is trying to warm itself up has been markedly better with a working thermostat keeping the radiator shut off until the temp gets up a bit in the block. Obviously we'll see how things go during winter, but even now non-warmed up commuting gives low to mid 50s mpg (i.e., 10-15mpg better than when it wasn't fixed and never warmed up properly), and if I'm careful on a long run I get >65mpg (55-60mph for an hour) ; on the Plymouth run I try to average 60mph over the 550 miles so the economy takes a dip down to 54-55 or so but that is pushing pretty hard for 9 hours.

Bottom line - whether remapped or not on a Tdi, make sure the thermostat and coolant temp sensor are in good health - for the sake of what I now know to be 20-30 minutes work with the right tools, and £12-15 worth of bits from Circoli / Febi and some clean coolant it makes sense. A final thought - I also realised later in the summer that a new coolant tank lid also is a good idea because the O-ring inside this is critical for proper sealing and pressurising of the system as it warms - and if it has perished due to 15 years of exposure to boiling-temperature coolant it won't be as effective. Again, fitted a suitable Febi part and haven't looked back.
 

TFG

A2OC Donor
Febi list 2 'stats for the TDi:
P/N 17888 which has an opening temperature of 87C and has no application limitations
P/N 17908 which has an opening temperature of 80C and is only for the AMF engine, "for warm countries".

Any recommendations as to which is better for the A2? Are the Febi ones OK?
 

Robin_Cox

Member
Febi are generally pretty good for most things and I got my coolant sensor & expansion lid from them ; got the Circoli stat from Eurocarparts for around 4 quid and as others here have commented, it seems fine.

Arguably, if you don't live somewhere hot, you will need a stat that opens as close to 90 as possible, otherwise the legendarily "cold" Tdi will simply not get there once the radiator is in play if you're not driving hard, particularly as the average daily temperature drops off. This would result in the engine being one or two map steps off the most efficient fuelling level as well, so your economy would suffer as if you were running 'with the choke on'.
 

Reubenah

Member
When putting in the new thermostat it seems that the part to tighten it up sits a few MM away from the thermostat and the mating face, is this normal? And does it sit against the mating face once tightened
 

Robin_Cox

Member
Hi Reubenah,

when the thermostat has been fully pushed into the block, the o-ring should then be located in front of it before the plastic housing is bolted onto the block. The way you've described it the o-ring isn't there - which way round have you put the parts in?

https://workshop-manuals.com/audi/a2/power_unit/3-cylinder_tdi_unit_injector_engine_(1.4_ltr._2-valve)_mechanics/engine_cooling/cooling_system/removing_and_installing_thermostat/

See diagram A19-0549. Obviously, the intended assembly order in the instructions doing it properly is to insert the o-ring and thermostat into the plastic housing, rotate into the correct angle behind the retaining fingers, then insert the whole assembly into the block.

What I found doing it myself was that the broken off fingers didn't hold the thermostat properly in place, meaning that putting the stat followed by the o-ring into the block and then bolting the housing onto the outside was the best way to do it.

If you've got any more questions, please by all means ask further - I can't guarantee more than my experience doing it myself though - am not an expert by any means.
 

Reubenah

Member
Found the problem... I was sent a thermostat that doesn’t fit and is not for an A2 quick trip to the local car shop and he had one in stock and it fitted perfectly, car all back up and running.

Thank you for your help
Reuben


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LordTJC

Member
I'd had a consistant low reading on my coolant temperature gauge It was just under 80 deg C. A visit from Tom (Timmus) established that it was a faulty thermostat. I've surprised myself, today! I completed this task (A2 Diesel) in under 30 minutes. Here's how :-



View attachment 25720 Where the thermostat is located

It's between the alternator and the oil-filter housing. There is a difficult to access 10mm bolt below the housing. You need a shallow socket.



View attachment 25721 I used this tool (Source: Halfords)



View attachment 25722 The faulty thermostat (corroded)

A few tips ..... When unscrewing the lower bolt, have a magnetic grab tool adjacent, so that the bolt won't drop! No need to drain the system down. After removing the thermostat housing, pull out the rubber ring seal. Make sure that you have the replacement thermostat to hand. Quickly pull out the faulty thermostat and then insert the new thermostat. The result? Very little loss of any coolant!. After a run and checking for leaks, the job is done. The displayed temperature was a rock-steady 90 deg. C and the warm-up was quite rapid.

David
Where did you get that adapter to put the ratchet spanner onto the socket? I’ve just pulled mine apart and realised I don’t have any tools that fit!

Tim
 

TFG

A2OC Donor
In case you are doing this and need a cheaper tool, this worked great for me with halfords spanners

Can you clarify something on that Wera socket? The description says it's 1/4" square drive, but the picture of it seems to show a socket with a male 1/4"(?) hex sprouting off of the back of it (which would be great for me). Which is correct? Have you got a picture of the Real Thing that you can post?
 

TFG

A2OC Donor
Ah. Just found this picture on the web and it makes more sense now. What's the AF of the outer hex?

1580219683879.png
 
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