Transmission Leak from Breather Tube

[Dehaka]

Had smokey nightmare today on Freeway. 1998 GMC Jimmy 4.3 Vortec SLT 4X4 4l60e 112,xxx miles, everything original

Saw smoke coming from passenger side from under the hood and then out the back of the vehicle. Pulled over and thought for sure it was a blown head gasket. Turned out to be ATF leaking out of a breather tube right next to the dipstick. Only does so at highway speed.

Fluid flushed and filter replaced 500 miles ago with Mobil D/M, differential, transfer case fluids also replaced. Shifts fine, no wierd noises.

What would cause fluid to come out of that particular vent??


Thanks in advance for any and all replies.

 

[PontiacHO]

Maybe useless to type this but have you checked the fluid level when trans is at operating temperature?
Fluid level either too high or low can cause this at times. If fluid level is correct trans may either be overheating and/or have an internal pressure leak. Also seen this happen with vehicles that had headers that “cooked” the trans case and cooler lines…. Thoughts at random.

 

[mattd]

Typically overfilled or overheating will cause this.

 

[JohnnyG]

1998? Make certain that the trans cooler, in the radiator tank, is not leaking. It could allow pressure into the trans and even coolant which is not good.

 

[andyd]

Johhny G is onto something. 25 yr old cars, anything is possible. Coolant in an AT is bad.

 

[Dehaka]

Maybe useless to type this but have you checked the fluid level when trans is at operating temperature?
Fluid level either too high or low can cause this at times. If fluid level is correct trans may either be overheating and/or have an internal pressure leak. Also seen this happen with vehicles that had headers that “cooked” the trans case and cooler lines…. Thoughts at random.

Yep fluid is exactly where dip stick says it should be.

 

[JohnnyG]

Yep fluid is exactly where dip stick says it should be.

Or the breather tube.

 

[Rand]

Yep fluid is exactly where dip stick says it should be.

do you check those hot with engine running?

 

[Dehaka]

do you check those hot with engine running?

yep after shifting through all the gears and pausing in between shifts.

 

[Rand]

well its 25 years old it has some deeper problem then.. overfilling would have been the best cause (easy to fix)

 

[clinebarger]

Assuming fluid level is correct.....Monitor trans temp via a scan tool. If it gets hot >230°, Let it cool back down then monitor TCC Slip RPM via a scan tool @ >45 mph, Should be +/- 5 RPM.

Guessing no Trans Component Slip DTC's (P1870)?

 

[jetman]

x2 what @mattd said previously