2004 chevy blazer, 175k mi
there is a fluid collecting on the bottom of my precat and burning when driving. is this fluid automatic transmission fluid?

oil coolant lines replaced by the dealer with OEM GM oil lines and the bottom (including precat) was subsequently washed 200 miles ago
dealer recommended noted somewhat of a transmission fluid leak and replacing the automatic transmission gasket.

or is this an oil leak? what am i looking at here?

 

Was it the engine oil remote cooler lines that were replaced or the transmission cooling lines thst were replaced. The engine oil lines are on the driver's side whereas the transmission fluis cooler lines are on the passenger side.

I would guess that it is more likely a leak of transmission fluid.

If there is enough of the fluid to have a few (unburnt) drops, dabbing them with a white paper towel should allow you to see the color of the fluid. If red, it is transmission fluid.

The transmission cooling lines although metal, can wear through if there is metel-on-metal contact. I was able to catch where a sharp corner on the iderlet arm bracket almost wore through one of my transmission cooler lines because of that.

 

engine oil remote cooler lines were replaced 200 mi ago, on the driver's side.

oh dear, i had my idler arm replaced recently, maybe that is relevant?

 

I would say a close inspection of the trans cooling lines is in order.

Regarding the idler arm, that is quite a bit forward, ahead of the front lower control arm, so that a leak would be a fair amount forward of where the leak appears to be. However, while driving, the wind could drive the leaking fluid back so it could be up at the idler arm.

My almost leak was from the tubing rubbing on the top of the mounting bracket for the idler arm. However, to install the idler arm, the lines could have been moved with them rubbing against any number of things.

 

Wiped it with white printer paper, this is photographed in full sunlight. The left spot is directly from the precat, the right spot is wiped on the carboard below.

 

The fluid at the corner of the paper looks reddish. If it is, that is not engine oil and is most likely transmission fluid.

 

Yep, I think it is transmission fluid.

Edit: I spent some time moving a flashlight around. I see no wetness on the transmission coolant lines and no obvious mechanical defect.

The bottom of the automatic transmission pan has reddish drops of fluid on it. The side of the precat closer to the automatic transmission pan is wet.

So I think this is the automatic transmission pan gasket.

 

ay carumba. the GM filter + gasket apparently are on backorder. Hopefully my transmission will survive ok with an AC Delco instead?

 

Oh good. A bad gasket seems reasonable.

ACDelco is the same as GM so you are good.

I replaced my pam gasket and filter once. It was a super painful to do because of a cross member on the way. Also you can't get all the old fluid out. For that reason I have a local transmission shop do it.

 

So this dude swapped an OEM GM transmission filter for an AC Delco and you can see the difference between the parts--the OEM had long finger-width ridges in it.


Hopefully the filter design hasn't been "improved" too much. 🤞