Fluid venting through cap in reservoir cap

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BrentW

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Aug 8, 2017
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I have a Scag TC2 61 in with a 29 hp Kohler efi. I started noticing oil venting from the tank cap at a pretty good rate. I thought maybe the 20/50 oil was getting dirty so I drained and filled. Capacity shows 4 quarts but I barely got it to hold 3 quarts. Filled it to 2 inches below the filler neck. Took it for a spin around the yard and it is still venting a lot of oil. There are no leaks and the machine functions perfectly. Any clue of my issue? Also I replaced the cap with another new scag cap.
 
"... started noticing oil venting from the tank cap at a pretty good rate"
.
I ASSUME (??) that this is the transmission hydraulic oil ????

If so the oil is getting hot & expanding. The extra volume of oil is venting, as it must do.

The only ways I can think that this could occur is:
  • Wrong oil to start with - getting hotter than it should.
  • Too much oil in the reservoir/tank in the first instance. - are you absolutly sure you did not overfill?
  • The oil is getting hotter than usual, blocked oil cooler and or fan not working.
The last is the most likly - solution is to clean oil cooler and or replace defective fan.

One more less likly possibility is additional load on the system - Are you towing a trailer? Are the brakes comming off when you move the tillers into drive position?

"Capacity shows 4 quarts but I barely got it to hold 3 quarts."

The 4 quarts is probably when the whole system is completly empty of oil ie not just the reservoir but also pumps, motors, oil coolers and hoses. Unless you drained everything some oil will always remain the the system.

:devilish:
 
It calls for 20/50 for the hydro and engine oil. Fans are working. No towing anything. I am starting mulching my yard and that does slow me down a little by adding a load. This problem started toward the end of summer before mulching but has gotten progressively worse now.
 
the engine is listed as a wet sump engine so it would not have an external oil tank. Things that commonly cause oil to act that way:

moisture in the oil that boils and blows out oil

moisture in the oil that causes it to froth. Frothed oil takes up more space so it would force oil out of the tank

Leaking suction line or cavity where air is being pulled into oil, causing displacement and frothing. As an example, let's say there is a seam that leaks on the low pressure / suction side of an oil pump. It will suck in air because it is easier to do so than pull in oil. That air takes up volume.
 
sgkent said:
the engine is listed as a wet sump engine so it would not have an external oil tank. Things that commonly cause oil to act that way:

moisture in the oil that boils and blows out oil

moisture in the oil that causes it to froth. Frothed oil takes up more space so it would force oil out of the tank

Leaking suction line or cavity where air is being pulled into oil, causing displacement and frothing. As an example, let's say there is a seam that leaks on the low pressure / suction side of an oil pump. It will suck in air because it is easier to do so than pull in oil. That air takes up volume.
Click to expand...
I think he is referring to oil purging out of the drive reservoir tank.
 
sgkent said:
the engine is listed as a wet sump engine so it would not have an external oil tank. Things that commonly cause oil to act that way:

moisture in the oil that boils and blows out oil

moisture in the oil that causes it to froth. Frothed oil takes up more space so it would force oil out of the tank

Leaking suction line or cavity where air is being pulled into oil, causing displacement and frothing. As an example, let's say there is a seam that leaks on the low pressure / suction side of an oil pump. It will suck in air because it is easier to do so than pull in oil. That air takes up volume.
Click to expand...
It is not leaking anywhere other than out of the hydro cap. Would a suction line leak also leak outward?
 
It sounds like the oil is aerating and foaming due to a bypass condition in the pump(s). This could be a blocked filter/screen condition or worn internal pump parts. Lower the reservoir level, then run it and pull the cap and look for foaming
 
Auto Doc's said:
It sounds like the oil is aerating and foaming due to a bypass condition in the pump(s). This could be a blocked filter/screen condition or worn internal pump parts. Lower the reservoir level, then run it and pull the cap and look for foaming
Click to expand...
Hydro oil is supposed to be 3” below the top of filler neck in reservoir tank for that system. You said you filled it to 2” below. Try lowering oil level and see if that helps.
 
I will give that a try. The manual calls for 2 inches and that is where it has been for the first 600 hours of service without any problem.
 
"There are no leaks and the machine functions perfectly. "

If there is air in the hydraulic oil, it would not perform as the OP stated - got to be something else. :devilish:
 
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