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2006 exmark backfire

Discussion in 'Mechanic and Repair' started by jarroo's lawncare, May 31, 2006.

  1. jarroo's lawncare

    jarroo's lawncare LawnSite Member
    Posts: 116

    my new exmark is backfiring and dieseling, i bought it brand new this year. it has 60 hours on it, i put it on idle and let it run for short time before i turn it off. it has the 25 hp kohler command on it. any help would be great.jarroo
  2. Jman

    Jman LawnSite Member
    Posts: 217

    The owners manual says to shut it off half to three quarters throttle. I say shut it off WIDE OPEN!!!
  3. lawnmaniac883

    lawnmaniac883 LawnSite Silver Member
    Posts: 2,613

    Shut off at approximately 2800 rpms or 1/2 throttle.
  4. ed2hess

    ed2hess LawnSite Fanatic
    Posts: 13,192

    I agree 100% shut it off at full speed....the unit cools faster when it is wide open any way.
  5. Restrorob

    Restrorob LawnSite Fanatic
    Posts: 11,023

    Perhaps you didn't see this from a previous thread so I thought I would re-post it.

  6. thecrankshaft

    thecrankshaft LawnSite Member
    Posts: 172

    Rob, you are leaving out the fact that the cooling fan moves a lot more air over the cooling fins of the engine at 3600 RPM compared to 1200 RPM. I am not convinced by your test results as of now. Nor do I trust those non-contact thermometers.
  7. lawnmaniac883

    lawnmaniac883 LawnSite Silver Member
    Posts: 2,613

    So what if the fan moves more air at 3600 than at 1200? That was a good expirement rob and those numbers seem fairly accurate. Remeber though, the numbers on the outside dont reflect the numbers on the inside. The outside valve covers have air flowing over them, the piston doesnt have that.
  8. thecrankshaft

    thecrankshaft LawnSite Member
    Posts: 172

    Oh, I'm sorry. I thought this was an air-cooled engine. My mistake.
  9. lawnmaniac883

    lawnmaniac883 LawnSite Silver Member
    Posts: 2,613

    LOL, my point is that the air being moved over the engine is linear with engine rpms which is linear to the heat being generated. More rpms = more heat. Since the fan only cools the outside of the motor the internal temps are going to be higher at WOT than at 1600 rpms.
  10. Jman

    Jman LawnSite Member
    Posts: 217

    You have to remember we aren't actually running WOT (wide open throttle) Actually when the engine is running 3600 rpm's, with no load applied, the throttle plate is only open about 7 to 10 degrees. There for with very little air and fuel added to the engine, no heat increase is seen. When an engine is under a load and the throttle plate is open 25-50 degrees, a lot of fuel is added, heat is created and then has to dissipate thru the cooling fins. Remember it is the fuel being burned which causes the heat as a by-product of producing power. When an engine is shut down after running under a load there is what is called heat soak. The engine temperatures actually rise for a short amount of time since no cooling air is coming across the engine.
    From what I am reading with the responses that it is ok to take the coolant away, I would assume you guys would be willing to drive a $40,000 truck on a 500 mile drive, pull into your driveway, jump out and quickly drain half of the antifreeze out of the radiator and let it sit and idle to cool before you shut it off.
    Like the crankshaft said "air-cooled".
    The whole trick to doing a temp test is under load conditions, build up the heat like it does in mowing conditions.

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