Towing in overdrive (5th)

[PradoJim Member Find all posts View Profile Close PradoJim]

I've done some google searches and forum searches in the past re this issue but found no adverse comments. However, I recently read the manual (you know, if all else fails). It states that the automatic 5 speed should be in "S" mode (manual shift) and no higher than 4th should be selected when towing (the manual must also be driven no higher than 4th gear).

However, I find the reasons intriguing. The book says it's because of reduced engine braking and alternator output. Really ? If that's the only reason I'd be happy to keep towing in overdrive. I've had no charging issues on 5 hour tows and the van brakes are pretty strong, I don't really need that tiny bit of additional engine braking. Fourth becomes annoyingly noisy after a while and the fuel consumption considerably worse.

Does anyone know of "mechanical" issues as to why you shouldn't town in top gear on the 150 ? IE Gearbox failures or related ? I'm towing 2.5 tonne (well under the 3 door limit).

[krypto Avid PP Poster! Find all posts View Profile Close krypto]

My understanding is it is because 5th gear is an overdrive and the mechanical components are weaker.

[PradoJim Member Find all posts View Profile Close PradoJim]

My understanding is it is because 5th gear is an overdrive and the mechanical components are weaker.

Yes, that would be a reason that I would understand. However, it's not the reason given by the Toyota manual. Are they reluctant to talk about weaker components (if that's the case) and hide it behind "engine braking" and "charging" excuses or is there genuinely nothing wrong with the drivetrain and the aforementioned are the only reasons to avoid it ?

Anybody out there who's done a lot of heavy towing ? What gear have you been using and how's the car holding up ? I do know of one bloke with an older Patrol who blew a gearbox towing and only after that was told by Nissan that top gear wasn't up to the task. The salesman had told him the car was fine to tow in top (no surprise there).

[bazzang Junior Member Find all posts View Profile Close bazzang]

I own a 2014 GXL Diesel manual and tow in top gear all the time on flat roads. When the car starts to slow going up hills I go back to 4th. This is only with a relatively light off road camper trailer (1.5t) not a large heavy van. No issue since new and the car now has a little over 60,000kms on it.

[carco Advanced Member Find all posts View Profile Close carco]

As it's an auto there's no weaker gear than any of the others, they're all planetary gears.
The usual reason not to tow in top gear is to prevent the auto from dropping out of convertor lock.
When the convertor clutch locks you have solid drive, just like a manual. But the engine may be lugging hard and so the engineers designed the trany computer to have a bit of a think and if she's clearly not getting on top of the load, she'll drop out of convertor lock..
Now the convertor is slipping, engine is revving higher making more hp. Everything is going well except that slipping convertor adds a lot of heat to your transmission oil.
So to keep everything happy, if you manually select the lower gear, the convert will lock, no added heat to the oil and the engine's making good hp.
It's just a bit noisy.
You often find an engine working effortlessly at slightly higher rpm will give better economy than that same engine lugging way hard at the lower rpm. Better oil pressure, fan is spinning faster making for better cooling and so on.
I only have the 4-speed and it's always towing in whatever gear she'll pull the easiest. When I see it's not making headway, I drop back out of O/D to locked 3rd where road speed and rpm are almost the same as slipping the convertor in 4th. I can monitor my oil temps and that trany oil will start cooling the instant you have convertor lock.
The 5-speed with D4D will really slog it out, but if you want to maintain decent road speed you usually have to drop back that gear and let her rev a bit.

[mjrandom Out of control poster! Find all posts View Profile Close mjrandom]

Carco is spot on. If I am on the highway I leave it in Dumb, if it gets hilly or twisty back it goes to S and 4 or 3. Back to D when it levels out. I keep a goid eye on the tacho and terrain. Fit an extra cooler for the transmission too. I am knly towing 1.5t usually but with the loaded car trailer I will pick routes more carefully.

[PradoJim Member Find all posts View Profile Close PradoJim]

Thank you all starting with krypto. Great answer from Carco and thanks for backing it up mjrandom and actual experience bazzang.

I think it adds credence to what I was going to do.......ie what you recommend. D for the flats and on any grades, don't wait for it to make up its mind, drop it back. I've understood how a car working less in a lower gear can actually get better consumption than one labouring at lower rpm in a higher gear, but so far, on the flat, she burns a lot more fuel in 4th than 5th. Oh, and thanks for pointing that out, all the same gears on the auto. Forgot about that.

Thanks gents, question answered.