Transmission oil mixing with engine oil

2011 Tahoe LT / 4WD / 5.3L / 191k miles
Noticed my engine oil had a red tint to it not long after I changed it. Drives fine, oil pressure steady, not getting hot. If I didn’t check my oil I wouldn’t have ever known. What could cause this and what is the solution? I don’t have a clue where to start. Thanks in advance for your time and input. Oh and BOOMER SOONER!

Did you change oil brands??? Could just be the tint of the oil… Keep an eye on your fluid levels…

The only place I can think of the 2 fluids (engine oil and atf) is if the rad has the engine oil cooler in it, but even then they are on apposite side tanks from each other… No vacuum modulator on your 6L80 6 speed al electronic controlled transmission…

So as far as I know, there is no way that the engine oil and ATF can cross contaminate with out also including coolant…


Or, did the OP use an additive?
I recall that Marvel Mystery Oil is red in color, and some other oil additives may be similarly colored.


Check the transmission fluid level. If it is low, maybe it was topped off, but the trans fluid was poured into the engine oil fill location. When you say you “changed it”, did you diy’er that job, or did a shop do it? If shop, was it one of the national chains offering economy-price oil changes?

If you are certain trans fluid is contaminating the engine oil, suggest to replace the engine oil and filter before doing any more driving. Good chance to also monitor if the trans fluid reappears.

Transmission fluid is a great engine cleaner, but it will make the engine smoke pretty bad…

An old repo driver trick is to add 1 quart of atf to the engine and it will smoke like a freight train driving across the auction block, low bids and you can by it cheap… I know some repo drivers lol

So if not smoking, then I don’t think there is very much if any atf in the oil… VDCdrivers oil additive makes the most since…

1 Like

Very informative i greatly appreciate it!

I had the oil changed at WalMart before, but i changed it myself this time. i did use Castrol 5W30 High Mileage, i think WalMart put Pennzoil in it when they changed it. The transmission oil is a little low and my engine oil is a little high. No leaks, no smoking, no smell.

I would just keep a close eye on the levels for a while just to make sure, but I don’t think you have an issue…

1 Like

Why did you do that?

I’m pretty sure your vehicle calls for 5w30

1 Like

It’s definitely possible somebody attempted to top off your transmission fluid and poured it into the engine oil fill hole instead. In any event , suggest in future to either hire yourself to do the future fluid maintenance work as a driveway diy’er, or use a well recommended independent shop. Not all concur, but I hold to theory it is best for long term engine life to choose an oil brand & spec then stick with it for the life of the car. All the name brand oils are presumably good quality, but there could be incompatibility in their additives, brand to brand.

As long as the container of oil has this symbol on it,

and it’s the correct viscosity oil for your vehicle, you can use any brand of oil you want.


1 Like