Engine Flush Question

[bdunigan]

I now flush my twin QSB6.7 425 units after each run…5-7 minutes each. SB flush caps on the sea strainers. I have noticed that the cool fresh water really cools the heat exchanger and after cooler. 

Is there any chance this quick swing from hot to cold can stress/damage/crack these components?

Topic

[Bill Desmarais]

I freshwater flush my QSB 5.9 480 after each use.

The engine is generally shutdown 20-30 mins before flushing.

I cannot see in my mind’s eye why a 30 degree difference in water temp coursing through the SWAC side of the engine could be create a thermal issue.

I can’t sleep if I don’t freshwater flush after each use. 🙂

1 user thanked author for this post.

bdunigan

[bdunigan]

The dock water I use for flushing is well water and runs cool….say 60 degrees or so…if not a bit cooler. My seawater is 85. Coming off a run, the engines, of course, are sitting around 155-160. Certainly the after coolers and heat exchangers are not this hot but they are very warm to the touch. I would guess maybe 120-130 but am not sure. So, in a matter of 5 minutes, the flush process cools these components roughly 60-70 degrees (if I have my temps right). Maybe I shouldn’t be concerned but thought I would inquire.  

I guess I am worried about ‘thermal shock’ which I am told is defined as rapid heating or cooling by 18 degrees F per minute. So, doing the math, cooling these components by 90 degrees in 5 minutes could be bordering on thermal shock. Of course, I don’t think I am cooling them this much so maybe I am OK.

[Gene Fuller]

I would not expect the fresh water to have a temperature much different than the seawater temperature that you have been operating in.

Is there some reason your fresh water is especially cold?

[Author]

Replies