Odd Gear Oil Smell When Driving with Window Down

Earlier this year while on a camping trip I noticed a peculiar smell when I rolled the window down a bit while driving. I first thought it was all the cowshit in the pastures but - no pastures or cows in the area. Smelled like gear oil was leaking from somewhere. I pulled over and checked all around underneath but found no leaks. Nor did I smell anything out of the ordinary.

Twenty miles farther I got a CEL. Wound up replacing my injectors to fix it, but the smell still exists. I can smell it whenever I drive over 20-30 mph. No other problems with the truck. If I keep the windows rolled up I don't smell it anymore.

Has anyone else had a similar problem and if so, what was the cause?

 

You probably have an air leak around your shifter boots. When you roll the window down, the cab becomes a low pressure spot and will suck air through any hole in the floor

 

Sounds like it it time to get it nice and hot and spend some time laying underneath. Could be a whole bunch of things. Look for small oil leaks that may be dripping on top of the exhaust pipes. Stuff like that. Good luck.

 

Have you checked your fluid levels? Diff(s), transmission, transfer case, engine oil? How’s the drive shafts doing? Wheel bearings?

 

Check the rear and the sides of the valve cover/s for leaks, if they are and oil is getting on the exhaust manifold, you will very likely smell it, especially if the seals are getting old in the cab.

 

Those were all good suggestions!

I'll check for leaks around the shift boots. Never thought of that before. That might explain why I don't smell anything when I drive slower that 20-25 mph. Next, I'll crawl underneath while the engine is hot and look for burn spots on the exhaust.

All fluid levels are normal. No other symptoms that I would know of that would indicate a wheel bearing or U-joint problem.

I saw no oil seepage from the valve covers, or anywhere else when looking around from the engine compartment, and when I recently replaced the injectors I didn't see anything there either.

@fxntime - Where are the cab seals that you wrote I should check?

 

Since you didn't say L4 or V-6, this advice is for V-6: check cam seals on the rear of the heads. It can drip right on top of the exhaust if they leak even a little bit. Just changed mine. Small extension mirror and light will be helpful.

I think the "cab seals" was just a general reference to things like door opening seals, shifter boot, heater hose grommet to cowl, AC tubes, window glass runs, engine main wire harness to cowl, etc, etc. There are a lot of places sealed by rubber.

 

I’m curious if you ever figured this out?

My 2014 does the same thing.

It doesn’t have any leaks and it is definitely gear oil, not motor oil.

Please let me know what you may have found

 

Nope, I still smell it and I never figgered it out

 

I can usually smell my CV boot grease when they tear. It doesn't smell quite the same as diff fluid. Also, you'd probably notice cv grease all over the place.
Side note: no more torn cv boots since I did the boot slide mod a few years ago.