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Thread: HowTo -> M62 thermostat mod (lower engine temp)

  1. #1
    Join Date
    Nov 2007
    Warsaw, Poland
    My Cars
    '00 BMW 740i

    HowTo -> M62 thermostat mod (lower engine temp)

    Both of my M62-powered E38s have been facing problems with cooling system inefficiency.

    Electronically controlled thermostat on those cars tries to maintain coolant temperature at 108-109C, providing that the engine is working under light-to-moderate load (and this is the case during most of time). Detailed description may be found here.

    While such solution improves a bit emissions and fuel efficiency, it reduces the longevity of the engine itself as well as all the plastic/rubber elements like hoses, gaskets, etc.
    What is more, on a 10+ year old car (so possibly with not so efficient radiator, etc.) this control system loses its initial precision.
    What is yet more, in case of sudden high load (e.g. when you floor the car after longer stay in a traffic jam), the engine which has just been working at 109C, will get more heat until the electronically controlled thermostsat manages to reduce the temperature to safe 8x-9xC levels.
    In effect we may be soon walking on thin ice of potentially dangerous for the engine temperatures (110C and more). Also, continuous staring at TEST 07 can kill fun of every ride.

    Thats why I turned to some simple mod which allows to reduce operational temperature of the M62 engine considerably. I prepared some DIY write up, here it goes.

    The solution has been implemented on a post-facelift VANOS European-market M62 engine. There are some minor differences between pre- and postfacelift engines.
    Although I did my best to describe the modification as accurately as I could, I do NOT guarantee ANY result and CANNOT be held responsible for ANY damage caused to a vehicle person or property by following write up.

    Skill level:
    - disassembly of fan, water pump etc. is required so probably not the job for absolute beginers
    - some works have to be done by specialized machinist shop

    Parts needed:
    - water pump (new or the one from our engine)
    - new water pump gasket (11511731372 - part 02)
    - thermostat housing integrated with the thermostast and a heater (the one from our engine)
    - thermostat for M60 engines sold on some markets (with opening temperature at 85C) (11531729720 - part 07 where S823A=Yes)
    - new thermostat gaskets, 2 pcs. (11511705408 - part 08, O-ring 4.0 x 76.5 mm)
    - bolts M6 x 45 mm, 4 pcs.
    - coolant


    This is a M60 thermostat, which is NOT electronically controlled and opens at 85C:

    ...and this is original water pump for M62 engine (postfacelift, prefacelift one differs a bit)

    As we can see, the M60 thermostat doesnt match with M62 pump. We will need to measure its maximum diameter D1.

    Now we have to have our pump machined by the specialized shop, to make a socket for the thermostat:

    Socket diameter should be equal to D1 measured before, and the socket height H1 = 4.2 mm. It is best idea to give them both pump and the thermostat so they can check the fitment and eventually correct.

    Now we should be able to put the thermostat with a O-ring gasket into the socket:

    Now we have to measure the internal diameter D2 of the gasket and the maximum height H2 on which the round part of the thermostat protrudes beyond the surface of the pump.

    Lets take a look on thermostat housing now. This is the housing with the integrated thermostat and the heater removed (with angle grinder). Remainings of the thermostat should be plained a bit, to make them not protrude beyond the surface of the housing.
    Now we have to measure the diameter D3 between the edges shown below:

    Such prepared housing still wont fit the water pump because of the thermostat shape.
    The solution is to have an appropriate spacer done by the machinist shop (shown below).
    The thickness should be H3 = 13 mm, the bigger diameter is equal to D2 measured before, the lesser one equals D3, and the deepness of the bigger hole must be at least H2.
    There should be also a small hole made to make a space for the valve on the thermostat (see the pic below).
    Bolt holes do not have to have thread, and their pattern must correspond with the pattern of the pump and housing. The housing fits the pump only in one position.
    External contour of the spacer is not really important, it may be just square.
    The material is aluminium.
    Again, it is the best to give the whole combo to the machinist shop.

    Now we put the thermostat with a O-ring gasket into the socket, and then the spacer on the thermostat:

    ...and then we put the modified thermostat housing with another O-ring gasket on the spacer:

    This is how it looks:

    When assembling, we now need bolts which are longer than original ones:

    And this is how the modified pump looks afer attaching everything back together.

    Additional info:
    - no, the M60 thermostat housing does NOT fit the M62 water pump
    - in addition to 85C thermostat, there were also 95C units installed in M60 engines (11531702279 - part 07). It was the case for North American markets, non catalytic converter cars as well as some others. It should cost you less at BMW dealership, but the gainings from such mod are also reduced.
    - those of you who can buy Wahler products in their countries do not need to pay 3-to-4 times more for the thermostat at BMW stealership. Just look for Wahler 4516.85D type, this is exactly the same part (they make it for BMW).
    - I met some guy who claimed to do similar mod with no need of machining the spacer. Now I guess it might have had something to do with his car being pre-facelift and/or with this other thermostat.
    - E39 M5 has a thermostat which opens at 79C with no electronic control. Unfortunatelly it is completly different and it would be a major PITA to make it fit our cars

    Before this mod, I had TEST 07 readings as high as 110C.
    NowI have driven about 200 km in moderate-to-heavy city traffic since installing new thermostat and Im really impressed. Usually I read numbers like 94-95C in the moderate traffic, and 92-93C when Im able to floor her a bit. Max temp I noticed was 96C when stopped after a longer drive.
    I recommend this simple mod to all M62-powered E38 (and E39) owners.
    Last edited by IcemanBHE; 05-21-2010 at 04:07 PM.
    Best regards,


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