4th or 5th gear towing

Submitted: Tuesday, Jun 09, 2009 at 13:13
ThreadID: 69649 Views:3072 Replies:10 FollowUps:7
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No, it is not about 5th gear towing and transmission failure as it is a Manual Pajero and they do not have 5th gear towing issues.
It is about fuel economy.
I will be towing a compertrailer weighting about 1.5 t from Dubbo, South Australia up to Darwin and back again.
With a standard tank and lousy economy out of the petrol 3.8 I can only carry 2 X 20litre jerry cans.
Would I get better fuel economy in 4th or 5th gear cruising?

Honky
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Reply By: Gronk - Tuesday, Jun 09, 2009 at 14:14

Tuesday, Jun 09, 2009 at 14:14
All depends what speed you want to sit on.....

Most of the road is flat, so at a speed of 100K's , 5th would be best ( and quietest )

What revs is it doing at 100K's in 5th and also in 4th ??
AnswerID: 369110

Reply By: Member - SR509 (WA) - Tuesday, Jun 09, 2009 at 14:43

Tuesday, Jun 09, 2009 at 14:43
Have a look at your torque charts for your model and see what revs it is in. Then put your gear to suit. Also no harm in working out some actual figures. My guess though for a petrol would be to tow in 4th as the max torque tends to be quite high relatively speaking.

AnswerID: 369112

Reply By: Baz&Pud (Tassie) - Tuesday, Jun 09, 2009 at 15:01

Tuesday, Jun 09, 2009 at 15:01
If towing a camper weighting in at 1.5 ton don't think i would be using 5th gear at all. There's not a great deal of difference in fuel consumption between 4th and 5th gear anyway.
Cheers
Baz
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AnswerID: 369114

Reply By: Madfisher - Tuesday, Jun 09, 2009 at 15:12

Tuesday, Jun 09, 2009 at 15:12
Depends on what diffs you have, our old nh Paj was so low geared 5th was the same revs as 4th in the Jack at 100. 100 is very comfortable in fouth in the Jack but not the Paj.
Cheers Pete
AnswerID: 369118

Reply By: Madfisher - Tuesday, Jun 09, 2009 at 15:12

Tuesday, Jun 09, 2009 at 15:12
Depends on what diffs you have, our old nh Paj was so low geared 5th was the same revs as 4th in the Jack at 100. 100 is very comfortable in fouth in the Jack but not the Paj.
Cheers Pete
AnswerID: 369119

Reply By: Member - mike H (WA) - Tuesday, Jun 09, 2009 at 15:39

Tuesday, Jun 09, 2009 at 15:39
Everyone above is correct but can I add that the absolute best way to maximise your fuel economy is to fit a good old vacuum gauge.
Ideally you would tow at the rpm at which the engine develops maximum torque but you also have to balance that with wind resistance and therefore engine load hence the vacuum gauge.
For example you may well be able to tow at 100kph in 5th gear quite happily with the engine at max. torque but even with a really torquey engine you will very likely find that you could reduce the speed a little and tow in 4th gear with the throttle backed off. This will substantially improve your fuel economy because the engine is not working as hard.
With the gauge you basically just balance road speed, engine revs with maximum manifold vacuum.
We use a version of the vacuum gauge in both turbo and non turbo piston engined aircraft and use it in just this way to maximise range and endurance.

Also if your 5th gear is an overdrive gear ie less than 1:1 you are reducing the available torque applied to the tailshaft compared to a 1:1 4th gear and therefore by definition the engine is working harder.
This subject is not quite as easy as it sounds but I hope this helps.
AnswerID: 369126

Follow Up By: tim_c - Tuesday, Jun 09, 2009 at 16:55

Tuesday, Jun 09, 2009 at 16:55
Doesn't a vacuum gauge just tell you how hard you're pressing the accelerator? In that case, you could just figure it out yourself - try 5th, then shift back to 4th and see which one you have to press the accelerator harder!
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Follow Up By: Member - mike H (WA) - Tuesday, Jun 09, 2009 at 18:12

Tuesday, Jun 09, 2009 at 18:12
Tim,
What a vacuum gauge actually does is to measure the air pressure in the intake relative to atmospheric pressure. Most EFI systems have a sensor that does much the same and the information is used by the ECU for ignition timing but more particularly, in relation to this subject, injector pulse width which is a complicated way of describing how much fuel is injected on each cycle.
The gauge is far more sensitive than your right foot and again relative to this subject will tell you if you are operating the engine under more load than you need to maintain your chosen speed but better than that you can use it to pick a speed that requires less throttle input and therefore less fuel use.
The gauge will for example also show an imbalance between each cylinder at idle and is also a very useful tool for engine tuning but like all these gadgets is only as good as the bloke who is trying to interpret what it is trying to tell him.
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Follow Up By: kiwicol - Tuesday, Jun 09, 2009 at 18:27

Tuesday, Jun 09, 2009 at 18:27
The best guage to fit is a exhaust guage temperature ( egt ) the hotter the temp the more fuel you are using. Very easy to figure out which gear and foot setting. Quite amasing watching guage as you very minutly back off the throttle and see the temp drop. Col
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FollowupID: 636634

Follow Up By: Member - Matt & Julie (VIC) - Tuesday, Jun 09, 2009 at 23:11

Tuesday, Jun 09, 2009 at 23:11
Would a cruise control help ?
Cheers

Matt & Julie


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Follow Up By: Member - Graham H (QLD) - Wednesday, Jun 10, 2009 at 10:53

Wednesday, Jun 10, 2009 at 10:53
Cruise control wont help and will use more fuel than just driving it.

I tow a 2.8 t van and have a EGT fitted. On a flat road in 4th temp is 300-325
If I drop into O/D it immediately goes up to nearly 400.
Conclusion Engine is working harder in O/D as it out of optimum torque range.
Fuel compsumption hardly differs and in actual fact got the best consumption on a day when I did 549k all in 4th


Hope this helps
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FollowupID: 636734

Reply By: Member - Jeff M (WA) - Wednesday, Jun 10, 2009 at 01:38

Wednesday, Jun 10, 2009 at 01:38
I'll just say that I towed my 2.5T Roadstar with my petrol/gas prado V6 to Esperance and back to Perth in 5th gear and now I have some play in my drive train (read transmission). When I stop and restart I get a noticeable clunk in the transmission. Not serious (I hope) but a concern nonetheless given I leave on Sunday to do half a lap and 21,000KM. Mechanic said not to worry but gave no guarantees I wouldn't have problems down the track. 4th gear for me from now on.
AnswerID: 369250

Follow Up By: Abraxxas - Wednesday, Jun 10, 2009 at 08:40

Wednesday, Jun 10, 2009 at 08:40
Jeff, I recently had the same issue with my Prado after towing the caravan for half a lap. Dealer pumped more grease into the tail shaft and the problem disappeared?
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FollowupID: 636711

Reply By: Member - Oldplodder (QLD) - Wednesday, Jun 10, 2009 at 07:55

Wednesday, Jun 10, 2009 at 07:55
For best economy sit on 80 to 90km/hr in 5th.
Back to 4th for any hills.
Otherwise drive as you would normally for economy by being very light on the throttle. :o0
My figures towing our CT are 11l/100k at 80km/hr, 12 to 13 at 90 to 100k, 14 to 15l/100k at 110k, so speed and wind resistance has a lot to do with it. Add another 1 to 2/100k for hilly country and again for head winds.

Have a good trip.
AnswerID: 369257

Follow Up By: Member - Graham H (QLD) - Sunday, Jun 14, 2009 at 17:00

Sunday, Jun 14, 2009 at 17:00
Maybe if you are towing a piddlly little camper trailer.
Certainly not towing a 2.8t van, as I posted above, towing in 4th the motor is cooler and the fuel consumption doesnt vary from 5th gear towing.

Towing in 5th can make it lug and then it uses more fuel and runs significantly hotter and also strains the tranny.

Today I used cruise control for about 80k and it made the EGT go up to 480deg in one part. Reason is it feeds more fuel when going up slopes to keep the speed up whereas driving with the foot one tends to drop speed a bit on the upslopes and thus keep temp down and use a bit less fuel.
Simply an observation backed up by the temp gauge.
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FollowupID: 637338

Reply By: traveloz005 - Sunday, Jun 14, 2009 at 01:03

Sunday, Jun 14, 2009 at 01:03
I towed a small 1300kg pop top camper with a Toyota Troopy in 5th gear ... between 90 and 100 kph and never under load without changing down to 4th ... Toyota tough .. yeah .. replaced the gearbox .. and now use only 4th .. with better fuel economy ...
AnswerID: 369869

Reply By: Member - Nick (TAS) - Tuesday, Jun 16, 2009 at 20:16

Tuesday, Jun 16, 2009 at 20:16
Hot off the press.We are currently touring for three months and I have observed the following towing our Tambo Cooper with 1HZ with turbo and I/C.
Towing in forth at 85kph 2500rpm I get EGTs around 300deg C post turbo
Towing in 5th at 95-100kph 2200rpm I get EGTs around 350degC post turbo.
I now tow in 4th
AnswerID: 370405

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