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2.5TDi (and others) Thermostats

Discussion in 'A4/S4 forum(B5 Chassis)' started by PAULF, May 24, 2012.

  1. PAULF
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    PAULF Active Member

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    [May 24, 2012]
    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

    [​IMG]

    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

    [​IMG]

    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

    [​IMG]

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

    [​IMG]

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

    [​IMG]

    I have now ran the car about 100 miles, and it stays bang on 90 degrees.
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  3. scrag
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    scrag New Member

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    [May 30, 2012]
    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
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  4. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    [May 30, 2012]
    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?
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  5. PAULF
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    PAULF Active Member

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    [May 30, 2012]
    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.
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  6. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    [May 30, 2012]
    well the guage shows 90 at any temp between 80 and 100c anyway :p
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  7. PAULF
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    PAULF Active Member

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    [May 30, 2012]
    :lmfao:

    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'. :readit:
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  8. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    [May 30, 2012]
    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!
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  9. PAULF
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    PAULF Active Member

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    [May 30, 2012]
    Fair comment,

    (although how do you think I ended up airborne and bent the Panzer Plate?) :racer::superman::sob:
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  10. Mackers
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    Mackers Member

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    [Jan 21, 2013]
    hi again paul (3 times now i think) what is the I.D. of the tophose??
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  11. PAULF
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    PAULF Active Member

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    [Jan 21, 2013]
    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.
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  12. Mackers
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    Mackers Member

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    [Jan 21, 2013]
    i'm thinking of the volvo340 'stat as it operates higher than the Ren5.
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  13. PAULF
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    PAULF Active Member

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    [Jan 21, 2013]
    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!
    #12
  14. Mackers
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    Mackers Member

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    [Jan 21, 2013]
    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,
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  15. Ian2012
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    Ian2012 Active Member

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    [Jan 24, 2013]
    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
    #14
  16. adamss24
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    adamss24 Well-Known Member

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    [Jan 24, 2013]
    pm sent...
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  17. Mackers
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    Mackers Member

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    [Feb 11, 2013]
    adamss24.... got any hints for me too plsssss :p
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  18. adamss24
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    adamss24 Well-Known Member

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    [Feb 11, 2013]
    Yes mate, do it properly for 130 quid supply and fit genuine thermostat and seal...just like the factory intended !
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  19. nedge2k
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    nedge2k Member

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    [Nov 9, 2013]
    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 :)
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  20. trawicki1
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    trawicki1 New Member

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    [Nov 11, 2013]
    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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  21. nedge2k
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    nedge2k Member

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    [Nov 11, 2013]
    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: Nov 11, 2013
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  22. trawicki1
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    trawicki1 New Member

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    [Nov 11, 2013]
    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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  23. nedge2k
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    nedge2k Member

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    [Nov 11, 2013]
    I just used the QED housing, that t-piece is factory.
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  24. trawicki1
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    trawicki1 New Member

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    [Nov 11, 2013]
    mine doesnt have the t piece in at all so would just be the housing, thanks for your help
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  25. PAULF
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    PAULF Active Member

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    [Nov 11, 2013]
    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: Nov 11, 2013
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  26. trawicki1
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    trawicki1 New Member

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    [Nov 11, 2013]
    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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  27. trawicki1
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    trawicki1 New Member

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    [Nov 11, 2013]
    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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  28. nedge2k
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    nedge2k Member

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    [Nov 11, 2013]
    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.
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  29. PAULF
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    PAULF Active Member

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    [Nov 11, 2013]
    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.
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  30. trawicki1
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    trawicki1 New Member

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    [Nov 11, 2013]
    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?
    #29

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