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

[AZScrambled]

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 :

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

 

[SenorNoob]

Every time I've seen transmission fluid mixed with coolant it's pink...

 

[gaz]

@AZScrambled
Sorry my man, that is oil in your coolant.

Consider yourself fortunate if it isn't in your engine/crankcase...STOP DRIVING and correct this IMMEDIATELY!!

 

[AZScrambled]

Ugh, I was hoping it might be transmission fluid.
So if it's engine oil where's it coming from ? The head gaskets passed the radiator glove test and the oil pan shows no water. Where else could the oil be coming from ?

 

[alwaysFlOoReD]

The glove test is for combustion pressure. Pressurized oil galley into water jacket? Could be any place.

 

[85_Ranger4x4]

Ugh, I was hoping it might be transmission fluid.
So if it's engine oil where's it coming from ? The head gaskets passed the radiator glove test and the oil pan shows no water. Where else could the oil be coming from ?

Does your truck have an oil cooler?

Otherwise I would lean headgasket.

 

[ShhhhhDougsHere]

Take out all your spark plugs out.
Pick a cylinder and put a compression tester on it.
Crank the engine over 5 or 6 times. Get out and see if the compression in the compression tester slowly sheeps out. Give the compression a good 5 to 10 minutes or more to see if it sheeps out or not.
Repeat for each cylinder.

That's advise I got from 1 of my brothers a long time ago when I was up in the air about if I had a blowed head gasket or not.

 

[AZScrambled]

Thank you !
I'll run a compression check on each individual cylinder and see if it holds after 10 minutes.
Is it possible that a blown head gasket can have a leak between an oil passage and coolant passage while still having good cylinder compression ? The engine has never overheated so it seems strange that the head gasket would fail between oil/coolant passages while keeping the cylinders sealed.
In the past I've always seen blown head gaskets with loss of cylinder pressure which made sense. In this case I'm trying to understand how the head gasket could fail between oil/coolant passages - and how to avoid it happening again. Sorry for the odd question but this type of head gasket failure is a new one for me.
Thanks again !

 

[ShhhhhDougsHere]

First you have to take into account everything that everyone has said in reply to your first post.

You have not replied about what @85_Ranger4x4 asked

Does your truck have an oil cooler?

Otherwise I would lean headgasket.

If your truck does have an oil cooler that goes through your truck's radiator, it can be just like the transmission cooler part of the radiator.
It can deteriorate and contaminate the radiator.

Blown head gaskets can do funny things.

The head gasket could be leaking at any point.
It could maintain cylinder pressure but it may not be accurate. And that pressure would and could decrease over time.

The one fact you know for sure is you have something getting into your coolant and sorry to say it is about 85% surety that it's oil.

Warning: you don't want to run your vehicle while you have this problem for excessive amounts of time it could cause severe internal damage.

After doing a compression test on each cylinder and seeing if it decreases over a period of time you're 10 minute window, as you pointed out that you would use.
I would do another test, if you have an engine that the oil gets cooled by going through the radiator.

I would drain the radiator and put in straight water.
Run the truck for a couple minutes and then check the water for oil contaminants.
I'm sure the first time you do this there will be oil contaminants in the water so drain the water and repeat the process.

You may have to repeat this process a few times to get out the contaminant that's in the coolant passages the radiator the heater core and so on and so forth.
If you continue to get oil in the actual water and you do have passages in your radiator to cool your oil disconnect the oil lines in some way.
Then some how connect the two lines together without connecting them to the radiator.
Bypassing the oil cooling process the radiator does.

Warning: if your truck is set up to have the oil cooled through the radiator having the lines to disconnected from the radiator can cause damage if you allow things to get too hot.
So don't allow the engine to get hot while doing these tests

Flush the coolant system out again and see if you get any oil in there at this point. Once again repeat this a couple times to verify if you're getting oil in the water/coolant or not.
If you're still getting oil in there at this point you know it's not the oil coolant passages in the radiator.

I know I wrote a book. Sorry hopefully this helps you.

P.S.

You stated your truck has never overheated.

Unless you're the only owner of the truck you cannot say for certainty that it has never overheated.

It may have overheated multiple times from the previous owner and they not tell you when you bought it.

 

[ShhhhhDougsHere]

I added to my last post in this thread. Please read the P.S. part if you have not already read it.

 

[85_Ranger4x4]

First you have to take into account everything that everyone has said in reply to your first post.

You have not replied about what @85_Ranger4x4 asked

If your truck does have an oil cooler that goes through your truck's radiator, it can be just like the transmission cooler part of the radiator.
It can deteriorate and contaminate the radiator.

Ford only ran the transmission fluid in the radiator.

Engine oil cooler is a part of the engine usually, housing that has like a mini radiator inside of it they run engine oil thru and engine coolant over.

I know they did it on Explorers, I have never locked horns with a newer Ranger to see if they did it on them or not.

 

[Blmpkn]

Every time I've seen transmission fluid mixed with coolant it's pink...

This.. but... Also pulling the trans dipstick and having a look..

 

[ShhhhhDougsHere]

@85_Ranger4x4
Thank you for teaching me something new.
I truly appreciate it.

 

[ShhhhhDougsHere]

@Blmpkn
That too is a good test.
And very easy as well.