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355 Oil thermostat rebuild / replacement

Discussion in '348/355' started by cactussed, Aug 30, 2023.

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  1. cactussed

    cactussed Formula Junior

    Mar 12, 2008
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    #1 cactussed, Aug 30, 2023
    Guys
    It seems my thermostat has stuck at 100 degrees.
    Has anyone successfully deconstructed and then rebuilt the original thermostat? I'd rather not pay hundreds of pounds to replace what is essentially a £10 part, simply because its for a Ferrari...
     
  2. Qavion

    Qavion F1 World Champ
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    #2 Qavion, Aug 30, 2023
  3. m.stojanovic

    m.stojanovic F1 Rookie
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    #3 m.stojanovic, Aug 30, 2023
    The Oil Thermostat consists of the parts #17 to #21 on the diagram below. Please confirm that this is what you are referring to.

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  4. cactussed

    cactussed Formula Junior

    Mar 12, 2008
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    #4 cactussed, Aug 30, 2023
    It’s part 18…
     
  5. yelcab

    yelcab F1 World Champ
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    #5 yelcab, Aug 30, 2023
    What's to rebuild with 18? That's just a hard piece that moves up or down depending on the force of the spring (19) which depends on the oil temperature.
     
  6. m.stojanovic

    m.stojanovic F1 Rookie
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    #6 m.stojanovic, Aug 30, 2023
    Part 18 is the thermostatic element which has a "waxstat bulb" inside it which expands with temperature and moves the element which, in turn, controls the oil flow through the radiator. Why do you suspect it is stuck at 100 degrees? It can be stuck closed, stuck half-open or stuck fully open.

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    Looks like the waxstat bulb is removable but finding a new one that would fit will be a problem and you would need to know at what temperature it starts opening and at what rate it opens. These waxstat bulbs are sold separately for various types of oil thermostats, some examples:

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  7. cactussed

    cactussed Formula Junior

    Mar 12, 2008
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    #7 cactussed, Aug 31, 2023
    So, having disassembled, I have 2 problems. The first is that the thermostat assembly was stuck in the housing, hence my oil temps not regulating as they should. The why eludes me.
    Upon disassembling, there's a long valve itself, with 2 bells at either end held on by circlips. Under that is the actual waxstat valve itself, which is far longer and thinner than anything off the shelf.
    It appears that the wax stat valve part itself has also failed as it doesn't move in a pan of water.
     
  8. cactussed

    cactussed Formula Junior

    Mar 12, 2008
    286
    #8 cactussed, Aug 31, 2023
  9. cactussed

    cactussed Formula Junior

    Mar 12, 2008
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    #9 cactussed, Aug 31, 2023
  10. cactussed

    cactussed Formula Junior

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    #10 cactussed, Aug 31, 2023
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    the valve itself
    Is the whole long bit, on which the end had split presumably allowing all the wax? To escape, hence no longer working.
     
  11. cactussed

    cactussed Formula Junior

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    #11 cactussed, Aug 31, 2023
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    And that’s what’s inside. Presumably the wax expands under heat, forcing the (very long) plunger out and pushing the whole assembly up and down the housing, thus directing the oil flow to the cooler as needed…
     
  12. m.stojanovic

    m.stojanovic F1 Rookie
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    #12 m.stojanovic, Aug 31, 2023
    You have provided very good info. Yes, the wax, like in the water thermostats, expands a lot when it is melted by the heat and pushes the plunger out. During cooling and solidifying of the wax, the long spring on the plunger returns it. Unfortunately, this waxstat unit appears to be quite unique so I think retrofitting something is out of the question. I see a used unit at Eurospares for GBP 200.
     
  13. cactussed

    cactussed Formula Junior

    Mar 12, 2008
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    #13 cactussed, Aug 31, 2023
    I’ve ordered it today. In the meantime, I’m going to investigate wax pellets…
     
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  14. cactussed

    cactussed Formula Junior

    Mar 12, 2008
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    #14 cactussed, Sep 5, 2023
    Replacement stat installed. Oil temps and pressures now rock solid (middle of the gauge) including under spirited driving conditions. It also warms up far quicker also, Amazing how one small item can make such a difference to the running of the car,
     
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  15. fdekeu

    fdekeu Formula Junior
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    #15 fdekeu, Sep 6, 2023
    Problem solved ;-)
    Possibly the valve needs more than 100°C to open
    This info may be useful for other owners in the future
     
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  16. m.stojanovic

    m.stojanovic F1 Rookie
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    #16 m.stojanovic, Sep 6, 2023
    As you can see on the pictures, the old waxstat had cracked allowing all wax to leak out which was why it couldn't open.
     
  17. johnk...

    johnk... F1 World Champ
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    #17 johnk..., Sep 6, 2023
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