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MTU 4000 thermostats fail position

Discussion in 'Technical Discussion' started by C4ENG, Dec 1, 2018.

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  1. C4ENG

    C4ENG Senior Member

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    MTU 4000s.
    Do the coolant thermostats fail in the open or the closed position?

    I know Cat 35 series thermostats will fail in the open position so you will not over heat but actually over cool the engine.
    I got a call from an engineer friend of mine as his MTU oil temps are alarming high (90-93C) on both main engines at high load. Coolant temps are good on both engines as the coolant also cools the oil cooler. The oil cooler was already serviced and not the issue. Techs now want to change thermostats on both engines after servicing oil cooler that was not the problem.
    Any help is appreciated.
  2. Capt J

    Capt J Senior Member

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    Not sure, but a dirty bottom/running gear will increase load at the same rpm point and increase oil temps as well.
  3. C4ENG

    C4ENG Senior Member

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    I am pretty sure the eng coolant and exhaust temps would go up as well if that was the case, and that is not happening from what he tells me.
  4. Beau

    Beau Senior Member

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    You folks are levels way over me, but If the coolant is running at normal levels, why would high oil temps indicate a thermostat problem. Particularly since its both engines - simultaneous failure are rare? The fluid that's being effected is the oil. I would go back to the coolers. We are assuming the oil coolers were serviced and reinstalled properly. Is there sufficient incoming water, is it exiting, impellar pieces, zing slugs, low oil level, dirty filters? If it is effecting both engines, is the problem non mechanical as Capt J suggests?
    Last edited: Dec 1, 2018
  5. Pascal

    Pascal Senior Member

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    If the oil coolers use coolant and not raw water, and if the coolant temp is good, then the issue has to be with the oil cooler and the lubrication system itself. It can’t be the Tstat, if it was then coolant temp would be high.
  6. Beau

    Beau Senior Member

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    Pascal

    Even if the oil coolers are using raw water, doesn't this fact pattern seem to eliminate the thermostats? It's reported that only the oil temps are elevated. The compounding fact is that the elevated temps are occurring in both engines - coincidental failures?
  7. Pascal

    Pascal Senior Member

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    Yes the fact that both engines are showing the same problem is weird.

    Each engine design has it quirks. For instance on 3412Es, the first symptom of restricted raw flow (impeller, clogged strainer or grass in the fuel cooler inlet) the first sign was higher gear temp even though coolant temp remained good. I guess some engines have additional coolant cooling capacity but less oil or gear cooling capacity
  8. Capt Ralph

    Capt Ralph Senior Member

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    The cooling side hose on these ZFs are such a small part of the total water flow, any restriction would cause a warmer clutch temp.
  9. C4ENG

    C4ENG Senior Member

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    The Thermostats where changed and they did sea trial today (Monday). The techs where right and that corrected the problem in both engines. Oil temp was running at 85c at almost full load for an hour straight.
  10. Beau

    Beau Senior Member

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    So that's great that they hit the solution dead on. Did they explain why that solution works, and why extra heat was evident in both engines? I always like to learn.
  11. Capt Ralph

    Capt Ralph Senior Member

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    Not a MTU guy. We usually call in FDDA when we get a rare MTU call (We do work on Series 60s ourselves). I do find it interesting that the clutches are cooled by closed coolant and thermostat controlled.
    I'm just short of pushing the B S button till somebody else comes on and explains the clutch cooling schematic.
  12. Beau

    Beau Senior Member

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    Capt

    What makes you say it's closed coolant system rather than raw seawater - that the thermostats were changed and oil temp dropped? Maybe, but I'd like to confirm that is true. This is screwy set of facts, to me. I don't think we have all the info. Recall that the claim is that both sides had the same symptoms. That means that several thermostats failed at the same time? (How many does each engine have? My Mans have 2 or 3 a piece) I'm a skeptic of the fact pattern - something is missing for me. Both engines is the trouble fact. One engine, I go away.
    Last edited: Dec 3, 2018
  13. Capt J

    Capt J Senior Member

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    They want to keep the clutches at a higher temperature to keep moisture out of them.

    The new C12.9's, the aftercoolers have their own thermostat, this is to meet emissions.
  14. Capt Ralph

    Capt Ralph Senior Member

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    I may have been distracted with my last clutch cooling thought.
    Usually clutches are raw water cooled thru their own H/E.

    Looking again at the O P; engine oil temperature...
    I'm still leery AND open to learn something new.
    These larger engine oil systems are cooled by the engines closed system coolant.
    My thoughts have to travel far (Mars?) to imagine different thermostats before the oil coolers.

    Just about all large D blocks I have worked on with integral oil coolers, the oil coolers are the first after the thermostats, H/E, circulating pump. Then then the blocks.

    Again, I am not a MTU tech and open to learn.

    "Recall that the claim is that both sides had the same symptoms...." At the same time??? Rite....

    Hello Admins;
    Is there a MTU 4000 tech in the house?
    George??
    Last edited: Dec 3, 2018
  15. Beau

    Beau Senior Member

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    Do the clutches use the same oil reservoir as the engines - it was engine oil temp that was elevated on both sides not gear oil, yes? So how many thermostats does each engine have?? We are now in that theoretical discussion area where we have flown by the OP. His problem is solved....
  16. Capt Ralph

    Capt Ralph Senior Member

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    Hang on.
    Back with fresh refreshments.
    While pouring I remembered something;
    I read somewhere a while back, MAN V8-900 had dual and different thermostats for something.
    I still can not imagine temp control on engine oil but I had to mention this as I rack my mind (whats left of it) thinking about these things.
  17. Capt J

    Capt J Senior Member

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    It keeps out sources of the coolers leaking saltwater into things such as the oil cooler, or the oil cooler developing a leak and blowing it out the seawater. Only the heat exchanger cooled by sea water, and that's the only item. It keeps temperatures of everything more stable, versus dealing with raw water of varying temperatures and hotter to meet tier III emissions. If the oil is a constant temperature, less expansion/contraction of metals.

    On Cat C12.9's the aftercoolers have their own thermostat. To keep them hotter and a certain temperature. They're fiat's what more do you want, retarded engineering.
  18. Capt Ralph

    Capt Ralph Senior Member

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    Modern clutches have their own oil.
    My 12V71s have 4, 2 for each head. but that's a 60 year old design.
    But my oil coolers are first after the circulating water pump.
    Last edited: Dec 3, 2018
  19. Capt J

    Capt J Senior Member

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    on the 4000's I have no idea, I know very little about them.

    On the C12.9 cats (1000hp), each motor has 2 thermostats and I had at least one of each fail on each motor in under 50 hours along with numerous other issues with those motors. A c18, THEY ARE NOT.
  20. Capt Ralph

    Capt Ralph Senior Member

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    Cat 12.9s don't use sea water for the air coolers?
    F. M.
    C18s & C32s use sea water. Side trickle raw water hose to the ZF clutch. 2 stats.
    Last edited: Dec 3, 2018

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