Large mystery oil leak, Kohler Command 21hp

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Aug 26, 2009
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Hoping someone here will know what this likely is. A new large oil leak, about a quart or so in 1.5 hours. Only leaks while running. Doesn't drip down into a pool anywhere. Seems to soak the back half of each side of the engine pretty evenly. I took off some the guards to get a better look. I was hoping to spot a source but couldn't. I looked around the web for someone with the same problem on the same engine, no luck.

I dropped some dye in but it was too late at night to fire it up.

 
I am dealing with a leak myself on a 19 HP Briggs. What I would do, make sure all fasteners are tight and the breather is not blocked. The crank seal could be bad but I would believe that would leak badly all the time. You need to degrease the engine and investigate, you have too much crud to really see anything. Make sure it's not the filter which I'm sure you checked already.The block could be cracked. As I am facing, you might have to pull the engine so you can really go over it and find that bad leak you have.
 
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I had a Kohler Command 22 HP v-twin that did the same thing. Engine was on a Cub Cadet GT2550 lawn tractor. Whenever the outdoor temp was lower (in the 60's) in the spring I had very little usage. Once summer came and hotter temps it drank oil like crazy. I never tracked it down as a new John Deere was calling my name. Think I'm done with Kohler power.
 
Probably the shaft seal underneath the fan/flywheel. It's worth checking the valve cover gaskets since Commands are notorious for leaks there but that shaft seal is only other seal on that side of the motor that can leak and when it leaks the fan blows the oil everywhere. I have a CH22s on a JD zero turn and it looks exactly like that every time that seal needs to be replaced.
 
Dude that things a mess! take shields off clean real good then run with shields off and observe..

Most of the shields are off. The main one on the back doesn't look like it will come off unless the engine is out.
 
As others have stated clean it and keep looking. My bet is on a rear main crankshaft seal. The flywheel and air is blowing the oil around. These engines won't leak a whole lot when sitting but when they are running the oil galleries are pressurized and this will cause the seal to leak a lot. I had to change the bottom main crankshaft seal in the spring. The first spot oil flows from the oil pump on my 15HP Kohler is the crank journals.

Just my $0.02
 
No option but to pull the engine and clean everything. Clamp on workbench, provide a fuel source and start the engine. Leak should be obvious. I'm betting like others have said the crankshaft seal behind the flywheel. Easy to change, but hard to get access as everything has to be removed.
 
Everyone who said Rear seal was correct! Flywheel is winging it everywhere. Engine will have to come out. Doesn't look that difficult but I know these Kohler engines have other issues. Is anything else I should do to it while it's out?

This leak did coincide with an oil change from Castrol 20w50 to Mobil 5w40. (had the 20w50 in it to slow the prior leak from the front seal).

It doesn't start leaking noticeably until the engine gets real hot. Oil is incredibly thin at full temp (300 degrees).
 
As others have stated clean it and keep looking. My bet is on a rear main crankshaft seal. The flywheel and air is blowing the oil around. These engines won't leak a whole lot when sitting but when they are running the oil galleries are pressurized and this will cause the seal to leak a lot. I had to change the bottom main crankshaft seal in the spring. The first spot oil flows from the oil pump on my 15HP Kohler is the crank journals.

Just my $0.02

I was also wondering something else. If you pull the dipstick tube it will blow a ton of compression and oil vapor out. The PCV at the carb is putting out pressure too, so it seemingly is working. I considered modifying a valve cover for a small breather but when its hot so much oil vapor comes out the fill hole in the other valve cover that I can't imagine a breather could function correctly. Was wondering if this engine being worn is making excess pressure and helping push oil past older seals.

Since I don't ever work on small engines I don't really have a reference point of what is normal/not normal.
 
I was also wondering something else. If you pull the dipstick tube it will blow a ton of compression and oil vapor out. The PCV at the carb is putting out pressure too, so it seemingly is working. I considered modifying a valve cover for a small breather but when its hot so much oil vapor comes out the fill hole in the other valve cover that I can't imagine a breather could function correctly. Was wondering if this engine being worn is making excess pressure and helping push oil past older seals.

Since I don't ever work on small engines I don't really have a reference point of what is normal/not normal.

if you remove the dipstick when the engine is running it will blow oil out and make a hell of a mess! This is normal in a small engine.

If you shut the engine off and there is a significant amount of wafting vapor in the case and dipstick tube it might be a blown head gasket. It needs to be a lot. Some vapor is normal. If you have good compression and no loss of power it’s likely fine. If you have a concern about rings it should be burning oil and might even smoke while running.


Just my $0.02
 
Clean it real good like everyone says, and then run it. The cause could be many different things. How old is it?
And the post above tnt motorsports is on to a possible cause.
 
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