For those of you with Kaw FD620D engines…….

Probity

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I have a very very basic operating principles question for you regarding the FD620D crankcase ventilation system.

In post-1960’s conventional naturally aspirated auto engines with a PCV system, fresh air (usually filtered) is allowed to enter the crankcase (via valve cover breather caps or some other means). This air and crankcase vapors are then expelled via the PCV control valve plumbing back into the intake system to (hopefully) be combusted. If you consider the crankcase as a lung, there is an “inhale” flowpath and an “exhale” flowpath. Like attached:

For the FD620D, considering just the crankcase, I feel I fully understand the “exhale” operation and flowpath – (a) crankcase vapors exit via the reed valve in the “breather chamber”, (b) the metal baffling in the chamber hopefully does a basic air-oil separation job and liquid drains back into the crank via the drain hole in the chamber, (c) remaining vapor exits the breather chamber via a hose to some point upstream of the throttle body. And at idle there should be some vacuum on the crankcase as measured with some form of manometer.

But it appears to me there is no “inhale” flowpath for this engine. There’s no breather cap on one of the valve covers, the oil fill cap on the other valve cover is sealed to a degree. Where else can fresh air be introduced to the crankcase?

So – am I correct in thinking that in the FD620D, fresh air does NOT enter the crankcase? Or am I missing something……
 

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StarTech

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You are correct that fresh air does not enter the crankcase. The engine PCV system just discharges the blow by gases so the has a small vacuum at times which creates pressure impluses which the OEMs use to drive the vacuum operated fuel pumps.
 

Probity

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You are correct that fresh air does not enter the crankcase. The engine PCV system just discharges the blow by gases so the has a small vacuum at times which creates pressure impluses which the OEMs use to drive the vacuum operated fuel pumps.
Many thanks for the quick reply! I'm being a little disingenuous as I'm thinking about my brand new (less than 10 hrs) Mule 4010 4x4 with a FD620D DFI vs. having a lawn mower/ZTR application. I'm trying to be proactive about addressing throttle body issues (crudding up)/"I've got oil in my airbox/filter!"/etc. that Mule 3000/3010/4000/4010's are known to have as a result of typically operating them exactly opposite of how people operate their mowers/ZTR's. Most Mule use typically involves a lot of short-ish runs (don't get engine temps up), a lot of idle time compared to WOT time. Just the opposite as to how I operate my Ferris IS700Z with a 3600 rpm screamer FS691V (3 hrs WOT cutting time, 5 minutes warm up/cool down time). Putting another air-oil separator (aka catch can) between the crankcase breather chamber and the airbox intake is what many people do and claim this prolongs the time between needing to clean the crud from the throttle body. But I wanted to first fully understand how the crankcase vent system works on my Mule and couldn't for the life of me figure out how (if) the crankcase actually "inhaled" fresh air somehow. Now I know.
 
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