Towing in 5th gear auto??

[Mike-4103 Junior Member Find all posts View Profile Close Mike-4103]

Hi guys,

Why should you not tow in 5th gear??

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

Hi Mike

I can't see any of our usual fountains of knowledge answering so here goes from a non mechanic....
the auto on the 150 doesn't naturally lock until you get to 2400 or 2500 RPM so, even though you have max torque at say 1800 RPM, the auto does not have the engine locked to the drive train and some slippage is occurring. Slippage in turn generates heat and heat is the enemy of the auto transmission. If you are not towing, and you are travelling along a flat road, even if the auto has not locked the heat build up is not too intense. As soon as you add the weight of a trailer/caravan the slippage increases and you get the heat build up. By the way, the same thing happens if you are travelling up-hill and your auto holds the high gear for too long (see other threads about this scenario)
Cheers
Mark

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

It has been covered in detail before in both the 120 and 150 section. Search and you will find the answers.

[discoveraus Member Find all posts View Profile Close discoveraus]

Hello Mike 4103,

The easiest answer is because the owners manual says not to. If you ignore the manual and tow in 5th. and damage the gearbox the dealers will know instantly from the damage sustained and will walk away from the warranty.

Technically, snowman is correct, towing with a slipping torque convertor for extended periods will cause overheating of the box, will degrade the transmission oil and cause expensive damage inside the gearbox. You will also find that the gearbox will need to change to 4th. often and this will creat mors wear and tear as the box hunts up and down gears on every slight rise and fall of the road.

Driving in 4th. at 100 kmph you will rarely have any gear changes as the engine is at optimum revs for almost anything and because the gearing is optimum the torque convertor rarely needs to slip. All is happy and economy will not be affected.

regards

Ross

[Mike-4103 Junior Member Find all posts View Profile Close Mike-4103]

So heat is the only issue, the dealer would have a lot to prove to void warranty, now that would be a good argument,

I only tow a small camper been using 5 th no issues at just watch the temp on the scan gauge

Thanks guys

[Vk3zgw Junior Member Find all posts View Profile Close Vk3zgw]

Try a little experiment with your scan gauge. Drive a flat road in D5 at around 95kph on cruise. Note the scan gauge reading for LHK (ltrs per 100k's)

Then do the same in 4S. You should be seeing 2500 rpm for that speed and a lower LHK reading. Also the ATF temperature will be lower when towing.

That's what I've found with my 2010 GXL 4D

[Anth120playdo Banned Find all posts View Profile Close Anth120playdo]

Just drive the vehicle. That is if you go up an incline & converter unlocks, click it over to 4th till the road flattens out.