Synthetics run cooler

Discussion in 'Mechanic and Repair' started by 44DCNF, May 9, 2008.

  1. 44DCNF

    44DCNF LawnSite Bronze Member
    Messages: 1,830

    Synthetics run cooler. That is no big news. I have been aware of it for many years. It's just the first time I have checked the difference with anything more than a vehicles dash guages. Vehicle instruments have shown lowered operating temps as well as increased idle speeds when switching to synthetics in the past. I am going to try to install an oil temp gauge on the mower, but an IR thermometer was used in this case.

    Exmark Metro 36", Kawasaki 12.5 FB460V.

    A proper comparison would have been between a petroleum and a synthetic 30W, however I changed from Castrol 30W to Amsoil 10W40, in a Kawasaki 12.5 and realized a drop of 8 degrees on average, in oil sump temps and block temps at various spots on the engine block. Measurements were taken against the side wall of block well above the oil level and also measured at the bottom of the sump where the oil sits. Mower was warmed up and then used for ten minutes of mowing each time. On the second run with the synthetic oil, a proslide was used to add more strain to the engine. Temps were taken upon completion of mowing for ten minutes and during a couple minute cool down period of idling the engine. Temperatures dropped as much as ten degrees during the cool down in each case, and were 6-10 degrees lower when tested with synthetic, than they were when checked with non synthetic.

    The mower has over three hundred hours on it. It was not using or leaking oil before. The manuals state that when using a multi viscosity oil, comsumption may increase. I will post back on any difference noted there. I may also put some 30W petroleum back in and take readings at the head and valve area. Rightfully that should then be compared to synthetic 30W. Maybe if I install the oil temp guage I will redo this test with pics and log the readings.
  2. Bill Kapaun

    Bill Kapaun LawnSite Senior Member
    Messages: 964

    Keep in mind that viscosity ratings are "nominal".
    A 30 weight oil may vary from 26 to 35 and still be called a 30.
    IF it had a viscosity between 36 to 45, it would be called a 40. It's basically the closest category that it fits in.
  3. tomo

    tomo LawnSite Senior Member
    Messages: 660

    as u r aware the sump mounted sender unit is the best way of determining the running temp .It would appear that the reduction in temp is around the 5f maybe upto 8f .
    In regards to oil temp drop that u mention [others also]
    The only true comparison to see if switching to sythetic actually drops temp is if the engine was running the same weight oil/ brand of oil and the only change was the type .All variables need to be removed from the test so a close comparison is acheived .

    The makers ""advertised"" viscosity is not exactly on the number so therefore each situation has to be judged induvidually

    nb ,also going to a thicker oil can also increase the running temp . The oil is thicker and harder to pump together with the increased friction from the oil gallery surface which generates greater pressure and therefore heat .
    Typically a 20/50 weight oil may do this but a 10/40 should not, in a mower engine .
    Other point to consider is the design of the oil system
    Is it ""all splash feed type"" or is it a FULL pressure lube type
    Beaware that some mower engines i suspect do run a partial ""full pressure"" lube to only some parts of the engine .
    The above is also an influence on the weights and type selected


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