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Is this engine oil or tranny fluid in my coolant? - and where's it coming from?


AZScrambled

10+ Year Member

Joined
Jun 21, 2010
Messages
1
Points
3,001
Vehicle Year
2002
Transmission
Automatic
Sorry for the long post but can anyone help me figure out why my radiator coolant looks like a chocolate milkshake? I'm not sure if this is engine oil or auto transmission fluid floating around inside my radiator neck.
Here's a couple pictures :
IMG_1958.jpeg

IMG_1955.jpeg

A little background :
2002 Ranger Edge, 190K miles, 3.0L V6, auto trans.
Truck runs perfect. Starts right up with a touch of the key, idles smooth as silk, has amazing power, never overheats, shifts great and just passed Arizona emissions with flying colors and no engine codes. Everything's perfect - until I did my routine engine checks yesterday and saw this brown mess in my radiator.
Here's what I've checked so far :
- Blown head gasket check. Removed a couple inches of coolant and covered radiator neck with rubber glove while clamping off overflow tube. Cranked engine several revolutions but no movement at all from the glove so no cylinder pressure escaping into cooling system - head gaskets appear to be fine.
- Changed engine oil. No water at all in engine oil. Just the normal brown color I always see when I change the engine oil.
- Dropped transmission pan to change fluid and filter. No water at all in transmission fluid. Just the clear pinkish color I normally see when changing my transmission filter.

I'm not even sure if this milkshake scum is oil or tranny fluid so after scratching my head for a while here's my questions :
- If it's engine oil could this be from a timing cover gasket leak ? I've seen this mentioned in a few posts although I'm not entirely sure how a bad timing cover gasket would let oil into the coolant. The underside of the engine is clean and dry with no oil leaks if that matters.
- If it's transmission fluid could it be leaking inside my radiator ? I've read that the transmission cooler lines inside the radiator can deteriorate and leak transmission fluid into the radiator coolant. Would transmission fluid turn brown like this when mixed with coolant ?

I don't want to throw parts at this problem until I know if it's oil or tranny fluid first. At least then I can narrow down the cause a little.
Honestly, I'm hoping its tranny fluid since replacing the radiator isn't that bad a job....

Hoping someone on the forum has seen this before. Any help would be great !!
Thanks !!!!
Jerry
 

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