Allison 6sp spewing oil from top

812sf

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Feb 10, 2024
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Jason1969
I’ve got a hummer h2 with a Dmax swap. Tran’s tune is from Duramaxtuner. When warm and driving moderately hard like at at high speeds, it spays oil out the top from somewhere. All over the underside of the body and down the transmission.

im going to change the oil tomorrow just to verify the fluid level. It doesn’t seem it’s coming from the vent but it almost has to be.

Can a trans tune cause this?
 

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2004LB7

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Dec 15, 2010
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More than likely the vent

What temp is it getting when lit leaks? Where on the dipstick is the fluid level?
 

812sf

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Feb 10, 2024
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Jason1969
Not sure what temp it starts leaking. As far as I can tell it’s in the correct hot zone with engine running.
 

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Dozerboy

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Jun 23, 2009
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TX of course
Allison's tend to "over heat" and puke fluid if over filled. It's always been recommended that you want the fluid level at the lower end of the hot cross hatch area. I always verify my transfluid level in the summertime, because this time a year I can hardly get my trans warm enough. The hotter you can get the trans , the higher and more accurate the fluid levels gonna show.

Of course you could just have an issue with your vent or something too.
 

Chevy1925

don't know sh!t about IFS
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Oct 21, 2009
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You want the level to be at the bottom of the hot hash marks when the trans is at 175-180*.

You are better off having the trans under filled some than overfilled. Windage is an issue inside which causes issues like you have. Also can cause cavitation in the pump as the windage puts air bubbles in the fluid
 

812sf

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Feb 10, 2024
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Jason1969
I pulled the pan and put in a new filter and fluid. Put a little under 8 quarts in and drove it hard. Still is shooting oil out I assume under higher load because you can’t see a leak while idling. The gauge never got hotter than the below pic ~150f. It was still registering in the cold range and I could hold my hand on the pan and it wasn’t very hot By the time I got home and checked it.

now I’m thinking I have a cracked housing or a pinhole leak.
IMG_6271.jpeg
 

Chevy1925

don't know sh!t about IFS
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Oct 21, 2009
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Yeah it might be cracked. Are your u-joints in good shape? May need to get a mirror and look around up top
 

812sf

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Feb 10, 2024
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Jason1969
I’ve spent hours looking at the top with a mirror and camera. No smoking gun. It actually doesn’t seem like it’s coming from the vent. It’s. It the t case vent either. Also checked the two sensors on the side. I always get hard to solve problems like this.