John deere 3720 turbocharger question

pfeener · May 3, 2015

I have a 2009 John Deere 3720 which seems to run just fine. Has plenty of power and not a lot of smoke. It has a little over 600 hours on it. Recently while I was examining the tubocharger, I noticed that the waste gate seems to be stuck in place. I can work on it to free it up, but I got to wondering if such a small turbo every develops enough boost to open the waste gate anyway. Anyone know how much boost a 3720 turbo should develop. My guess is around 10PSI and the waste gate actuator needs around 15 or more PSI to begin to open. So my thought is even if I free up the waste gate actuator it may not ever open anyway and maybe that's why, because it never opens, that it's stuck now. Thoughts?

sunnyside360 · May 3, 2015

Good question, but I don't have the answer. However, I do have a 2007 3720 Cab tractor with just over 600 hrs like yours which has been problem free. Use it mainly for mowing large lawn (6+ acres) in spring/summer/fall and blowing or brushing snow on long driveways in winter. It is kept in a garage when not in use. Will have to check to see if the turbo is stuck like yours.

pfeener · May 3, 2015

Yes, it's an interesting question. I'm sure I can remove the muffler and heat shield and I could work on the waste gate shaft and get it freed up, but if it's never used, then it doesn't really matter. All turbochargers, that I know of anyway, are manufactured with a waste gate to reduce the boost pressure if it gets too high so as not to damage any of the pieces parts. But just because the waste gate is present doesn't necessarily mean it gets used. On a small 3 cylinder diesel with a top RPM of around 2500, I think it's reasonable to question whether it will ever develop enough boost to open the waste gate. Also question to sunnyside360; Do you hear any "turbo whine" with the throttle wide open? I don't really hear any on mine and others have said they don't either with these small engines and turbos.

sunnyside360 · May 3, 2015

pfeener said:
Also question to sunnyside360; Do you hear any "turbo whine" with the throttle wide open? I don't really hear any on mine and others have said they don't either with these small engines and turbos.

Never heard any turbo whistle on either the 3720 or the 4320. However, I do hear the turbo whistle on the larger Kubota M110X tractor engine.