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Thread: 2.5TDi (and others) Thermostats

  1. #1
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    2.5TDi (and others) Thermostats

    I have had a problem with my thermostat for a while now, and the cam belt is not due for change for a couple of years.
    I know that I can change the 'stat in a weekend, but after reading many posts here and elsewhere about new stats failing early, I looked for a solution

    The best write-up I have found is here Diesel thermostat definative answer , which, although over a hundred pages, is worth reading. Scrag, on the B6 forum has also had a look at this, and used a Renault 5 type 'stat here 2.5tdi changing thermostat - whats involved?

    I have gone for a more expensive, maintenance friendly solution - a remote thermostat.

    I sourced the manufacture of the housing from Classic Mini Parts | Titanium Components | Force Racing. Carl was a great help, and produced a nice bit of kit.

    I decided to fit the housing and 'stat in the top hose, using the coolant return to provide flow past the bulb. Here is the unmodified hose



    The recommended 'stats were from a Suzuki Swift, 1,0 or 1.3 litre, 44mm OD, part no 10/84-02/89 for 82 degrees, part no, 03/89-12/03 for 88 degrees. I bought the 88 degree one.
    I then fitted the stat into the housing



    and screwed the halves together. This took a bit of fiddling, as there is a 'jiggle' pin that aids air removal that you want to keep at the top - it can just be seen here by the 10mm outlet



    There was more pratting about with sealing - I use a green pressure plumbing sealant - and then the unit can be fitted



    I then left it to idle whilst I checked for leaks (and rectified them!) and then the test -



    I have now ran the car about 100 miles, and it stays bang on 90 degrees.
    1999 A4 B5 1.9 TDi FWD Saloon, Green
    2000 A4 B5 2.5 TDi Quattro Avant, Maroon, 'Panzer' Plated (currently sporting wrecked engine)
    2000 A4 B5 2.5 TDi Quattro Saloon, Blue, 'Panzer' Plated, Cruise Control retrofitted, OEM 6 Disc Changer retrofitted

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  3. #2
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    that is a job very well done boss!!!!
    excellent write up too!
    I've stopped counting the miles I've done since my inline thermo,it takes about 3 miles to warm up to 89 degrees but then sits there at tick over or at 80mph.....
    your all set for winter now mate,warm feet and a more fuel efficient car!
    cheers
    PAULF likes this.

  4. #3
    "Stick a V8 in it!"

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    thats awesome!

    My only concern would be the time taken for the heat to make its way along that hose.

    With the stock thermostat, its in the water flow all the time, as it sits in the V right beside the water pump. So as soon as the temp hits 90c (or whatever) the stat will open.

    With the remote stat, the heat has to make its way along a couple feet of hose, with no water flow, before the stat will open... So its possible that if the heat rises quickly (say you boot it down the motorway) it could take a while before the heat conducts along the hose and the stat opens...

    I wonder if the "jiggle pin" lets a small amount of water past all the time, allowing the stat to see the real water temp faster?

    2000 A4 1.8T Sport Quattro Avant, Berry Pearl
    2000 A4 1.8T Sport Quattro Saloon, Black-ish
    1997 S4 - PPC £999 Challenge Track Car Build
    TD5 Land Rover Defender build


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    Quote Originally Posted by aragorn View Post
    thats awesome!

    My only concern would be the time taken for the heat to make its way along that hose.

    With the stock thermostat, its in the water flow all the time, as it sits in the V right beside the water pump. So as soon as the temp hits 90c (or whatever) the stat will open.

    With the remote stat, the heat has to make its way along a couple feet of hose, with no water flow, before the stat will open... So its possible that if the heat rises quickly (say you boot it down the motorway) it could take a while before the heat conducts along the hose and the stat opens...

    I wonder if the "jiggle pin" lets a small amount of water past all the time, allowing the stat to see the real water temp faster?
    The position in the top hose gives a constant flow through the coolant reservoir which, coupled with the 'jiggle pin', allows flow across the bulb. The temp rises steadily to 90 degrees, then stops bang on - and it's been hot outside for the first week!

    When I first tried it, the stat moved in the housing and didn't seat properly, it took forever to heat up, not really making 90. That was purely down to the extra flow past the stat. As long as the temp gauge reads between 80 and 100 degrees, I'm happy, but to see it vertical at 90 is great. Is should be a simple task to replace it when it inevitably goes too.
    1999 A4 B5 1.9 TDi FWD Saloon, Green
    2000 A4 B5 2.5 TDi Quattro Avant, Maroon, 'Panzer' Plated (currently sporting wrecked engine)
    2000 A4 B5 2.5 TDi Quattro Saloon, Blue, 'Panzer' Plated, Cruise Control retrofitted, OEM 6 Disc Changer retrofitted

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    "Stick a V8 in it!"

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    well the guage shows 90 at any temp between 80 and 100c anyway :P

    2000 A4 1.8T Sport Quattro Avant, Berry Pearl
    2000 A4 1.8T Sport Quattro Saloon, Black-ish
    1997 S4 - PPC £999 Challenge Track Car Build
    TD5 Land Rover Defender build


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    Quote Originally Posted by aragorn View Post
    well the guage shows 90 at any temp between 80 and 100c anyway :P


    Interestingly enough, Scrags fix warms up faster than mine. It takes about 10 mins to reach temperature. I suspect this is due to the increased unregulated flow through the coolant reservoir coupled with the designed flow through the 'jiggle pin hole'.
    1999 A4 B5 1.9 TDi FWD Saloon, Green
    2000 A4 B5 2.5 TDi Quattro Avant, Maroon, 'Panzer' Plated (currently sporting wrecked engine)
    2000 A4 B5 2.5 TDi Quattro Saloon, Blue, 'Panzer' Plated, Cruise Control retrofitted, OEM 6 Disc Changer retrofitted

  8. #7
    "Stick a V8 in it!"

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    depends how and where your driving it, more load means more heat etc.

    If your first 10mins involves light throttle down a Basra-esque farm track, and Scrags is streight out onto a dual carridgeway and upto 80mph, yours is obviously going to take a lot longer to warm up!

    2000 A4 1.8T Sport Quattro Avant, Berry Pearl
    2000 A4 1.8T Sport Quattro Saloon, Black-ish
    1997 S4 - PPC £999 Challenge Track Car Build
    TD5 Land Rover Defender build


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    Fair comment,

    (although how do you think I ended up airborne and bent the Panzer Plate?)
    1999 A4 B5 1.9 TDi FWD Saloon, Green
    2000 A4 B5 2.5 TDi Quattro Avant, Maroon, 'Panzer' Plated (currently sporting wrecked engine)
    2000 A4 B5 2.5 TDi Quattro Saloon, Blue, 'Panzer' Plated, Cruise Control retrofitted, OEM 6 Disc Changer retrofitted

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    hi again paul (3 times now i think) what is the I.D. of the tophose??
    2000, A4 2.5Tdi Quattro.
    Tinted, 3600WATTSLoud

  11. #10
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    The top hose ID is about 28mm, and the coolant reservoir hose (the small one) is 10mm. (At least, that was the pipe sizes)

    I had a 1mm lip on the housing to aid the jubilee clip to hold.
    1999 A4 B5 1.9 TDi FWD Saloon, Green
    2000 A4 B5 2.5 TDi Quattro Avant, Maroon, 'Panzer' Plated (currently sporting wrecked engine)
    2000 A4 B5 2.5 TDi Quattro Saloon, Blue, 'Panzer' Plated, Cruise Control retrofitted, OEM 6 Disc Changer retrofitted

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    i'm thinking of the volvo340 'stat as it operates higher than the Ren5.
    2000, A4 2.5Tdi Quattro.
    Tinted, 3600WATTSLoud

  13. #12
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    I think that's what Scrag used in his thread.

    Read what he did - I think he put it in the top hose but at the bottom, by the engine.

    Also have a good read of the Rover thread it's quite interesting!
    1999 A4 B5 1.9 TDi FWD Saloon, Green
    2000 A4 B5 2.5 TDi Quattro Avant, Maroon, 'Panzer' Plated (currently sporting wrecked engine)
    2000 A4 B5 2.5 TDi Quattro Saloon, Blue, 'Panzer' Plated, Cruise Control retrofitted, OEM 6 Disc Changer retrofitted

  14. #13
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    i have done.... well most of the rover one, the scrag one i think is brill, i may "upgrade" to your method in the summer,
    2000, A4 2.5Tdi Quattro.
    Tinted, 3600WATTSLoud

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    So how do i go about buying the necessary bits to do my car which is a v6 petrol a4 the top hose looks the same as in the picture

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    Quote Originally Posted by Ian2012 View Post
    So how do i go about buying the necessary bits to do my car which is a v6 petrol a4 the top hose looks the same as in the picture
    pm sent...
    FOR SALE:
    -Golf mk 5/audi a3 1.6 FSI fuel pump, brand new genuine part boxed + seals
    -audi a3 (1998 to 2003) genuine clutch slave cylinder to fit 1.6 engines BRAND NEW
    -Rear bush press tool to fit new rear axle bushes on Golf Mk3/4, Audi a3/S3, Seat Leon/Toledo, Skoda Octavia mk 1/2 used once

  17. #16
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    adamss24.... got any hints for me too plsssss :P
    2000, A4 2.5Tdi Quattro.
    Tinted, 3600WATTSLoud

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    Quote Originally Posted by Mackers View Post
    adamss24.... got any hints for me too plsssss :P
    Yes mate, do it properly for 130 quid supply and fit genuine thermostat and seal...just like the factory intended !
    FOR SALE:
    -Golf mk 5/audi a3 1.6 FSI fuel pump, brand new genuine part boxed + seals
    -audi a3 (1998 to 2003) genuine clutch slave cylinder to fit 1.6 engines BRAND NEW
    -Rear bush press tool to fit new rear axle bushes on Golf Mk3/4, Audi a3/S3, Seat Leon/Toledo, Skoda Octavia mk 1/2 used once

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    Noticed mine wasn't going above 70 degrees, plumbed this in today with an 88 degree stat and it's maxing out at 95, dropping to 85 at idle.

    Rover K-Series | QED Remote Thermostat Housing | QED Motorsport | Ther

    NB - it's made to take 32mm ID hose and an 8mm return. The 2.5 hoses just squeezed on and I replaced the return fitting with a 10mm. Cost me nothing and works a treat
    PAULF likes this.
    2.5 TDi (AKE) Allroad

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    nedge, do you have some picture please? i am looking to do it this way, also were your hoses 28mm ID?

    many thanks

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    Didn't measure my hoses, just went on what Paul said and figured I'd be able to squeeze them on. 28-30mm is about right.

    My 10mm return fitting went in nice and snugly.

    The most i've seem my temp climb to so far (with the 88° stat) is 99° under hard load - but a 50/50 G12 mix shouldn't boil until 107°. I'm happy

    IMAG0677.jpg
    Last edited by nedge2k; 11th November 2013 at 18:06.
    2.5 TDi (AKE) Allroad

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    many thanks, looks like you have an extra return hose than me, i dont think i would need the t piece

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    I just used the QED housing, that t-piece is factory.
    2.5 TDi (AKE) Allroad

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    mine doesnt have the t piece in at all so would just be the housing, thanks for your help

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    Nice job Nedge, mine is still going strong after 18 months and 20-30'000 miles.

    I'm in the process of doing my belts, so I am changing the stat too. I will still keep my inline one as a backup though.

    One thing I will say is the one I had made was about £80 IIRC, so a bit cheaper than the Elise one. The Rover site has links to a few housing manufacturers, but I went with the cheapest!

    Be careful Trawaki, without the Tee giving an constant flow past the stat bulb via the coolant expansion tank you may find the stat doesn't heat up enough to open. If the stat you use has a jiggle pin or hole you may be ok. Alternatively drill a small hole in the stat flange to give a small flow. See the Rover thread for more info.
    Last edited by PAULF; 11th November 2013 at 20:10.
    1999 A4 B5 1.9 TDi FWD Saloon, Green
    2000 A4 B5 2.5 TDi Quattro Avant, Maroon, 'Panzer' Plated (currently sporting wrecked engine)
    2000 A4 B5 2.5 TDi Quattro Saloon, Blue, 'Panzer' Plated, Cruise Control retrofitted, OEM 6 Disc Changer retrofitted

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    it will have the return pipe back to reservoir, i am in conatc with carl and looking to get the same as yours, and from the pics yours looks identical pre mod as mine.

    i am new to these cars so am finding my way, i have read a bit about the viscous fan, should the fan be spinning from cold? forgive me if this is a silly question

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    Quote Originally Posted by trawicki1 View Post
    it will have the return pipe back to reservoir, i am in conatc with carl and looking to get the same as yours, and from the pics yours looks identical pre mod as mine.

    i am new to these cars so am finding my way, i have read a bit about the viscous fan, should the fan be spinning from cold? forgive me if this is a silly question
    have just noticed yours also has the t piece paul. mine has no t piece and just has the return pipe from the top hose going straight into the header tank. i guess it will still work fine if plumbed in as yours is

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    Quote Originally Posted by trawicki1 View Post

    i am new to these cars so am finding my way, i have read a bit about the viscous fan, should the fan be spinning from cold? forgive me if this is a silly question
    yeah all viscous fans behave that way. when cold you should be able to stop it by hand if it is correctly. still not a great design though, replace with electric to free up some ponies.
    2.5 TDi (AKE) Allroad

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    Quote Originally Posted by trawicki1 View Post
    it will have the return pipe back to reservoir, i am in conatc with carl and looking to get the same as yours, and from the pics yours looks identical pre mod as mine.

    i am new to these cars so am finding my way, i have read a bit about the viscous fan, should the fan be spinning from cold? forgive me if this is a silly question
    Quote Originally Posted by trawicki1 View Post
    have just noticed yours also has the t piece paul. mine has no t piece and just has the return pipe from the top hose going straight into the header tank. i guess it will still work fine if plumbed in as yours is
    As long as the 10mm hose goes from the 'hot' (engine) side of the housing to the expansion tank it should be fine.
    There will be flow past the 'stat bulb which will open when it reaches it's set temp.

    The fan will spin at idle with very little cooling effect due to the inherent friction in the viscous coupling.
    A real man will test it with his fingers - if you still have them afterwards, the coupling is ok.

    A sensible man will shove a copy of Womans Own magazine into the fan slowly after starting the engine from cold. If it gets shredded, the coupling is broken. If the fan stops, the coupling is fine.
    1999 A4 B5 1.9 TDi FWD Saloon, Green
    2000 A4 B5 2.5 TDi Quattro Avant, Maroon, 'Panzer' Plated (currently sporting wrecked engine)
    2000 A4 B5 2.5 TDi Quattro Saloon, Blue, 'Panzer' Plated, Cruise Control retrofitted, OEM 6 Disc Changer retrofitted

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    i wil try the fan test tomorrow, but dont think i will use my fingers as it seems to be spinning very fast, it spins freely when the engine is off as i have spun it by hand then, i take it if the fan is overspinning that is another big job to do that involve removing the front end?

 

 

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