Oily Moist under Transmission - Trailblazer 2017


Original poster
May 9, 2021
Hello Guys

I hope this message finds you well.
I just finished changing the engine oil in my 2017 Trailblazer Automatic Tranmission with about 115,000 KM on the Odo.
Other than minor hiccups such as lose airflow hoses which made the vehicle to go limp, otherwise she's served me well.

Whil exploring under the hood, I saw the follow picture

1. It was oily by the touch, and the color is black
2. I do not see any visible drips on the floor, therefore I assume this are moist and related to tranmission or coolant lines (honestly, I am assuming the two lines are from the coolant)
3. I have checked the level of trans-fluid throug the fill-hole , it was about the right measurement and the color of the fluid is towards light brown - red (I did a drop and fill of the trans fluid less than a year ago).

I was wondering , has anyone experienced this? What are the steps taken to have this fixed?
I actually can "ignore" it and just drive as per normal, but I would like to have this resolve or possibly know if there's anything I need to change to prevent further damage, if any.
And also, how much effort will it be if I decide to have this fixed? Will I be replacing a gasket or do I need to unfill all the transfluid..etc?

Appreciate your inputs..

Thanks alot



Dec 4, 2011
Ottawa, ON
Just so you know, this site is more specialized on the first generation TrailBlazer (2002-2009) and therefore we don't have specific knowledge of the later generation ones. We'll try to help as best we can with our general.knowledge of vehicles.

That looks like the transmission cooler lines. Maybe those seals are leaky? If it's just sweaty like that with no drip, I wouldn't worry about it.
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Lifetime VIP Donor
Supporting Donor
Oct 22, 2015
Tampa Bay Area
...and since your vehicle was not manufactured for the North American Market... Try poking around over in the Australian and New Zealand Holden Forums... there may be some who have had similar experiences on this platform. Here are a few additional, generic diagnostic suggestions:

(1) Use some Brake-Kleen or a comparable solvent to completely clean off those affected areas... especially well above the lowest places where the residue is in evidence and allow those areas to thoroughly dry.

(2) Then slide a Fresh Piece of Cardboard underneath the vehicle once parked and unattended each day for around One Week and then make a Daily Visual Inspection of the involved areas.

(3) Take some Daily Images over that week long study and this will give you a better chance to isolate the Point Of Origin of these Oil Residues and compare how fast or slow the Oil Deposition is occurring..

(4) As suggested by @Mooseman ...Don't worry about this issue too much if by the end of a Full Week of making these observations, you can see very little oil residue appearing in your photos. Remember... Your SUV is around Seven Years Old now...so you might expect there could be trivial leaks coming from places ABOVE and to the REAR of your engine that have places like an Oil Pressure Sensor installed that may have some leakage that then gravity drops down from above to decorate those locations.

(5) Stop back by...and let us all know how this fares... and post those images if you like.
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