Oil sitting on top of coolant “overflow tank”

2010 4.0 95k miles
The other day i noticed my overflow looked dirty inside but the coolant was still pink, looked inside and saw what looked like oil sitting on top of the coolant *not mixed. I checked the radiator and the coolant was not milky nor is my oil. My motor has never over heated. The day I noticed was the day before I had a big trip, I drove about 5k and truck never over heated or skipped a beat. I check the trans and still red as ever. I removed the oil sitting on top of the coolant but getting back from my trip it returned. My oil was not low either. What are y'all thoughts? I read it could be a faulty oil cooler. But not sure trying to see if can figure it out before I take it in. I added some photos of the overflow how it looked and the oil spots and the coolant I removed

 

old coolant + corrosion

 

I thought the same and no when I tried to clean the overflow tank the top part of the overflow became milky

 

Coolant still clean

 

Head gasket?

 

Lol man ill be so pissed if it is at 95k but I'm hoping it ain't since it never over heated ever

 

@Texoma any thoughts?

 

A few thoughts in no particular order of importance. First, oil will float on water and coolant, so this is why it's showing up in the top of your coolant overflow tank. Second, it doesn't take much oil at all to show up like that. A little bit goes a long way. Since there is no oil in your cooling system normally, it has to be coming from someplace it already is - like your crank case. The most common way for it to get between those two closed systems is a failed head gasket. Why isn't your oil level going down if you have a failed head gasket and it's allowing oil to get into the coolant? Because the amount is too small to show up on your dip stick.

How do you determine if you have a failed head gasket? A cooling system pressure test will show it if the failure point is big enough. Time for professional help.

 

I wouldn't worry just yet. The coolant sample you took out looks fine, the reservoir plastic just looks a little "stained"

Remove the reservoir and wash it out with really hot soapy water, and then monitor it for a while

 

I hope its not too, sorry if it is. Overheating isn’t always a symptom or cause of a bad gasket though. You may have only won the bad lottery. Get some help with that though- they can test it. Hopefully its something else and not as big of a deal.

 

What's the pH of the coolant? 7pH is target, +/- 0.5pH is acceptable. Anything higher or lower is time to replace. Too long in that condition will start breaking down gaskets and metals.

 

Test the coolant for exhaust gasses.

 

So i tested it multiple times and i did not have any exhaust gas in the coolant used near half the bottle tested it for about 10 min and the fluid did not turn color

 

Have you ever heard of oil coolers going bad ?

 

If it came back after your trip, something is definitely not right. Did you check the ATF again? believe Blackstone or other similar business can test the coolant. Maybe have the ATF and motor oil tested for coolant also.

 

Do you have there website so i can send some samples

 

https://www.blackstone-labs.com/

Good luck! Hope it is not too bad!

 

Awesome appreciate y’all

 

What was the issue? Bad transmission oil cooler system?

 

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Texastaco2010 was last seen: Oct 11, 2022