What does a hot transmission smell like?

Hi all. Truck has 157k miles, and seems to have been taken very nice care of. New to me in April 2023. It does have the towing package.

My trailer is an enclosed 6x10 single axle. My tools are in the trailer, but they don’t account for much. In all, I’d guess that I’m below 2k lbs GVW for the trailer. I left my father’s house in the valley, approximately 800’ altitude. While on flat ground, I had it in OD. As soon as I reached the base of the mountain, I hit the OD Button. Traveling around 45-55mph at 2,500 rpms +/- (depending on curves). It is a fairly steep climb, rising from 800’ to 2,600’ in about 5 miles.

After about 2 miles of climbing I started smelling what I thought were someone else’s brakes from descending the mountain in the opposite direction. About 30 seconds later, the smell became a bit stronger. At that point, we arrived at a section where the road became level before the rest of the climb. Immediately the smell went away. I drove about a mile on level ground until I could pull over. I expected to see smoke from under the hood, but nothing. The truck was at normal operating temps the whole time and no dash lights. I could barely even detect the faintest smell from under the hood. I pulled the trans dipstick and the fluid is still a nice, clearish pink, and smelled just like it does when it comes out of a new container.

Just to make sure, I also felt the wheels just to make sure I didn’t have a caliper sticking. Both front wheels were cool to the touch.

I got back into the road for the rest of the climb, but decided to take it easy. I kept the speed around 40-45 mph so it stayed out of 3rd gear. The rest of the ride home (about 10 miles of up and down small hills) it performed fine. Even used OD at 55-60mph.

Like I said, the smell was like hot brakes. Maybe just a hint of electrical smell. I’ve never smelled a hot transmission before, and had always assumed it would smell like burning oil. Anyone with experience in this?

Any help would be greatly appreciated, as I’m sick to my stomach right now. I can’t afford a trans rebuild after paying cash for the truck and trailer.

 

You can monitor trans Temps either with an app on your phone or a scangauge or similar. Not too expensive to do just for piece of mind. I have yet to do this myself though so I don't have any great recommendations.

 

Thanks, I’ll look that up.
I just spoke to a friend of mine who has many years experience as a mechanic and other jobs in the industry. He said it sounds odd, and the smell of hot trans smells nothing like brakes. He also said to smell brakes in the cab, it doesn’t necessarily have to be the front brakes. So now I’m wondering if I had a parking brake seized?

 

Totally possible. The '04 has a trans dipstick right? You may want to do a drain & fill, just to smell the fluid and see if it looks or smells burnt. Can't hurt anything.

I'd be popping off the rear driver side wheel though, and checking my shoes. And also verify the parking brake linkage.

 

You may have been smelling an other vehicles brakes. I've found this to happen to me more than a few times. I try to find out which way the wind is blowing when it occurs.

 

Most long steep grades smell like brakes.

 

Thanks. Yeah, I pulled the dipstick and the oil smelled just like when it comes fresh out of the bottle. I will be checking my shoes, though, just to verify.

 

If this has to do with the rear brakes dragging, you should be able to feel the rear drum(s) get hot after driving the highway for a few minutes even without being loaded unless this has something to do with the proportioning valve.

 

Do check your shoes, you might have stepped in something

 

So the saga continues, and it's become a little clearer, fortunately or unfortunately. This morning, I jumped in my truck to run to work with no trailer behind me. About 3 miles down the road, my VSC light and check engine light lit up.

I really appreciate you guys pitching in to try to help. But is there anyone who actually can point me in a direction without guessing? ie someone who has an experience similar? I would be willing to bet money that this is the source of my problem, but I don't know where to begin to look for the culprit. And of course, as you can see from my signature, you know what I'm afraid of.

 

What’s the code from the check engine light this morning?

 

And did you already go through your braking system and check for the things previously mentioned?

 

No not yet. I've been crazy busy with work and graduations (my boy) so today was the first day I've even driven it since the smell

I had to go to work. I'll have to get with my buddy who has a scanner. I'm wondering if the tongue weight of the trailer, coupled with the incline is what triggered the VSM? It doesn't make sense that it would, but I also dont understand completely how the system works.

 

Over here, places like Autozone will scan your truck for free and tell you what the codes are.

 

Well I feel foolish for jumping to conclusions of catastrophe. But at the same time, I have to ask "why did Toyota do that?" It was simply an evap code. But why all the drama of the VSM lights? After researching, I realized that's pretty much standard with these trucks?

 

congrats on the graduate!

 

Thank you! Yeah we’re proud of him. I started him riding 2 strokes at age 9. And I made him do his own maintenance. That turned into full motor rebuilds. Now he’s got some certifications as a diesel mechanic and will have his Class A CDL in the next few weeks. On top of that, he wants to only work part time here for the next few years so he can accompany me on volunteer building and disaster relief projects. I couldn’t be happier with him.

 

Your burning smell and the evap codes are unrelated. Hazarding a guess you either omitted to tighten the gas cap when you last filled up or you were overly keen and kept topping off the tank, a big no no for the canister.

Any more signs of burning? In my experience you are less likely to cook tranny oil if you keep the gearing low and the revs high than by ‘taking it easy’ on hard climbs.

 

Yes, I’m aware. Before running the codes, I assumed the CEL was for whatever created the hot smell. But when I saw evap codes, I was relieved. Re: canister. I’ve only filled up twice since I bought the truck. And it is my tendency to top off. Do you think the fuel saturated the charcoal if I indeed overfilled?

No. I’ve hardly driven the truck, as most of my tools are securely stored on the present jobsite. I drive my vehicles that get better mileage when I don’t need my trailer.

 

I'll take a stab at answering if you can tell me the code. If it was small leak, it may just be the gas cap, that you didn't tighten it until 1-click.

 

Yes, it was a small leak code. I’m going to go ahead and purchase another cap and clear the code. We’ll see…

 

I don't want to but I ordered a genuine Toyota gas cap about 3 years ago from Amazon and it did not spin cleaning like the original and the truck started throwing very small leak evap codes in less than a year. I ordered another cap from the dealer and it became obvious the previous cap was not genuine when I compared them. Been good ever since as long as I crank it down good after fill-ups.

 

I'm never certain about saturation issues and thus am one to err on the side of caution and not overtop gas. I know there must be a difference between some gas stations because some pump it like it's going out of fashion and others can take over five minutes to fill a tank which must surely affect when the autostop cuts in and until someone says differently I'll stop when the auto does, it hardly makes a difference for me topping off when I'm revisiting a gas forecourt, on average, every other day for the Tundra or every day for the Frontier.

 

I got one off RA and the code went away. So far so good for 2 years now.