SHOULD YOU TOW IN TOP GEAR / overdrive in your Mitsubishi Pajero? (or most vehicles for that matter)

There's a rumour going around that you shouldn't tow in overdrive so I put the rumour to the test!
While I can't currently monitor transmission fluid temperature directly, in this video we monitor the engine coolant temperature - which is very helpful because a transmission fluid cooler sits inside the radiator, so we can still indirectly monitor changes to the transmission fluid temperature.
We test towing in 4th and 5th gear while hauling our 2.5T caravan along the last part of the mighty Tanami Rd west of Alice Springs. The road's flat and sealed, the night's cool, so the conditions are perfect for a back to back comparo like this!

[@pvcs1754]

Also worth mentioning is the higher LHK reading when driving in 5th instead of 4th. Most people would believe using 5th will use less fuel but not when the torque converter is unlocked. One of my best mods was installing a TC lockup kit in my NT.

[@TheMusingGreg]

Yep good point, I found that too!

[@devonport68]

I’ve been curious about this for a while and just picked up our replacement caravan last week. I have a scan tool and set up auto temp, auto fluid temp and water temp. In 5th all three went through the roof and dropped considerably as soon as I dropped back into 4th. Towing 2.2t at a steady 95 on a flat highway. I’ll be staying in 4th from now on when towing the van.

[@TheMusingGreg]

Mate you are spot on! I didn't have such a good scan tool but I could see the same pattern through just the coolant temperature. Thanks for the verification, and drive safe!

[@Stormy_Knight]

Change in water temp is mostly if not all from a change in engine load. The engine is producing a lot more heat. With lower rpm trying to produce the same horsepower (to maintain the same speed), Exhaust Gas Temperatures (EGT) will have risen significantly in 5th over 4th.

[@TheMusingGreg]

Yep I'm sure you're right. Unfortunately I didn't have an EGT probe to confirm.

[@wwfgumby]

I can monitor transmission fluid temp easily in the Pajero (2015) using an Ultra Gauge. I have Auto Mate (by MM4x4) fitted to automatically lock the TC when appropriate. I've tested it towing a 2500kg van and if the car is left to do it's own thing and I try towing in 5th at say 95kph, the trans temp can easily reach 90+ and often well over 100 if there's a strain on the load like a long hill climb. Using a TC lock up and keeping it locked in 5th the trans temp hardly ever goes over 80c and mostly sits around 65. Fuel consumption is aslo improved. If it gets loaded above what is acceptable, Auto Mate drops the gear back to 4th or 3rd if required. You are correct in that towing in 5th is bad for the longevity of your transmission due to excessive heat build up and many people are blissfully unaware that it's happening. BTW, most vehicles don't show the trans temp warning light until it's over 140c and that's just too late. The fluid begins to degrade at around 115.

[@TheMusingGreg]

Thanks for that input Ian, very helpful! Yes I recently bought a bluetooth OBD2 adapter and the Torque Pro app which lets me monitor trans temperatures too, so I'll check this next time I'm out with the van. If I had my time again I would have bought an Ultragauge or Scanguage rather than the EDS tool in order to access custom PIDs. Locking the torque converter like your Auto Mate does would prevent the fluid overheating issue, though I wonder how much load it puts on the engine and drivetrain towing at lower rpm with all that diesel torque pushing through with lower rpms to dissipate the torque? A bit like driving a manual around town at 30kph in top gear, that would bog the engine down a lot. Not sure, just a thought.

[@richardwolski5899]

Cool. We put in a transmission cooler in our 2014 vrx pajero.... So i hope that helps... Ta

[@TheMusingGreg]

It will help for sure, but remember the Pajero already has a transmission cooler (well at least my 2012 model did so I assume it's standard). But far better to drop it back a gear and avoid building up that heat in the first place.

[@MarkNorman_NXTLVL]

Thanks for this, I am having issues with my paj from a yeehhaa moment. I had a new tune loaded in and was showing off to some mates. managed to do a 8.3 second 0-100 pull with the tune. I tried one more time and I felt the converter slip more. I have gone from 7.4L per 100km average to 8.6L per 100km now. this as-well as the decreased performance shows me therre is some sort of lock up issue going on with the torque converter. Might just change the fluid first as it is noticeable under high heat conditions ( i.e 34 degrees and driving for some time) Looking forward to getting the paj back to performance Yess I know its my fault for the tune and the launch haha M

[@TheMusingGreg]

Oh dear, best of luck with that! 8.3 is pretty quick for a Pajero, poor transmission!

[@MarkNorman_NXTLVL]

@@TheMusingGreg thanks 😇 I'll let you know if it's just converter or locking clutches . But the GB itself is still a solid unit 😇

[@jamiefrangos9233]

I have noted your speed at 80. On my NW it does not like 80km/h in 5th and seems to labor slightly on light throttle going up a very slight incline on a freeway prior to pushing the foot down enough to kick down into 4th. The funny thing is that's without towing.

[@TheMusingGreg]

Hi Jamie, Yeah that's about the same with my NW I'd say, especially if you've been cruising for a while when the transmission may be reluctant to kick down. The torque converter would be unlocked anyway under those conditions, which is OK if it's not heavily loaded, but I would just manually pull it back into 4th and let the torque converter lock back up and just cruise up the hill with a few more revs. You'll typically use a bit more fuel with the revs higher but if the torque converter is unlocked in 5th the revs may end up similar and you just put a bit more load on the transmission in 5th. I'd opt for slightly more fuel burn and a cooler trans. Cheers, Greg

[@jamiefrangos9233]

@@TheMusingGreg thanks Greg, will try doing that more often I think as its nice to have that power on tap from that speed in 4th. Enjoying your work keep it up.

[@TheMusingGreg]

@@jamiefrangos9233 My pleasure Jamie, thanks for being a subscriber!

[@mustangdude11]

Hey Greg, Your temp test doesn't prove slippage in the lock up converter, what the temp rise was possibly due to is the changed load conditions with the engine in a different part of it's torque curve changing need for slightly more cooling due to higher load. Two degrees rise to 90 degrees is minimal, the same as when you hit a rise in elevation whilst towing or driving in soft sand. It's really showing the window the thermostat operates in, the thermostat constantly opens and closes trying to keep a stable temp but being its operated by a wax pellet the accuracy isn't perfect. It's a mechanical device that fluctuates a lot. To see if the torque converter lock-up function is slipping, watch the rev counter and compare it in top gear towing and not towing. I like your videos and narration. Well done.

[@TheMusingGreg]

Thanks for the reply mate. You're correct that a coolant temperature rise doesn't prove converter slippage, however I had done this test multiple times and always saw the same result. We'd done by this stage about 50,000km in the vehicle so I had a good idea of how the temperature behaved, and I know the coolant temperature doesn't fluctuate when conditions are constant. As I mentioned in the video, the road was flat and the coolant temp had been at 88 degrees for several minutes in 4th without any fluctuations, so it was stable under those conditions. Yet within 25 seconds of switching into 5th it climbed one degree, and then up another within another minute. Dropping back to 4th the temperature came back down to 88. Given I'd repeated this test multiple times in stable conditions and saw the same result each time, it was a fair demonstration of the point. What I should have done, as you mentioned, was to show the tacho as well because when watching the tacho, you can see the tacho jump up initially when you shift into 4th, and then pull back slightly as the torque converter locks up. When you shift into 5th with the converter locked the tacho drops down as you'd expect, and then jumps up a little as the converter unlocks. The purpose of this video wasn't actually to prove the torque converter was locking or not, though it would have been helpful to add that in; but having pre-determined that under those conditions (and many others actually too) it was locked in 4th and unlocked in 5th, the purpose of the video was to show the temperature effect of the locked / unlocked state. Finally, this doesn't mean either that the torque converter is always locked in 4th. If you're climbing a steep hill at 70kph in 4th, chances are it's going to be unlocked, so you'd need to apply the same rationale and drop back to 3rd to try to get the revs up and lock the converter. Of course slippage is normal and on a steep climb you might need to have that, it's just not desirable long-term on the highway. So a few learnings for me to clarify in future videos! Thanks for the input! Cheers, Greg

[@streetleswa8053]

notice how fuel consumption also increases in 5th

[@TheMusingGreg]

Yep true, all that extra slippage in the torque converter

[@captkev55]

Sorry I am so dumb, didn't understand a word of this. All I can say is I have been touring Australia for seven years, with my 2.5 tonne van for over 100,000 klms in top gear with my manual 2011 Diesel Colorado with out a hitch. Happy Days.

[@jackrussell7058]

It is an auto transmission issue, it could be solved at factory with a higher lockup limit on the torque converter when towing. Hence either use a lower gear or fit a lock up kit as the internal gearbox temp gets too high. I use a manual for heavy towing for just that reason.

[@TheMusingGreg]

You're not dumb Kevin, it's just not relevant for your situation as you've got a manual gearbox, not an automatic transmission with a torque converter.