2007 250 HPDI prop spins in neutral while idling on hose

[bphelps]

I have a friend with a 2007 250 HPDI. When he hooks the motor up on a water hose and lets it idle in neutral, the prop spins slowly...then after a few seconds, will start to get faster and faster. A mechanic friend of ours said this is normal, and is caused by the exhaust. Does this sound right??

[spider1]

Yep that is normal as long as it does not get to turning very fast like you would have it in gear at an idle.

[JUST-IN-TIME]

normal