Towing caravan with 2002 Prado TX Turbo diesel

Submitted: Tuesday, Nov 26, 2013 at 13:36
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About to take possession of a windup caravan which will weigh about 1400kg loaded.

Will be towing with a 2002 Prado turbo diesel which has automatic gearbox ( 4 speed I think). This has the 1KJ-TE engine. It is not chipped

I am interested in any advice on what speed or rpm to maintain to ensure best fuel economy.

I will be in no hurry and will be travelling for 12 months at least so happy to cruise at lower speeds.

Prado has 265/70/16 tyres, roofrack, winch, bull bars and 2" lift in case this has a bearing. I have seen some advise that says stick to 80km/h and other advise to keep revs above 2000 rpm.

Thanks in advance
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Reply By: bluefella - Tuesday, Nov 26, 2013 at 14:52

Tuesday, Nov 26, 2013 at 14:52
What RPM's is your vehicle doing at say 90km in third gear if it is around the 2300 to 2400 that is what I would be using.


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Reply By: Member - Bruce C (NSW) - Tuesday, Nov 26, 2013 at 15:43

Tuesday, Nov 26, 2013 at 15:43
As Bluefella says, tow in 3rd gear in a 4 speed box and keep the revs in the best torque range for the best results and best fuel economy.

You should have no problems towing that lightweight unit anyway.

Seems strange to be towing in a lower gear and get better fuel economy doesn't it, but,
I have carried out experiments many times by towing in top or overdrive and found the fuel going down quicker, especially on flat country. I only tow in 4th now (5 speed box) and get good economy for the setup I have.

When towing it is advisable to drive by the tacho and keep the revs in that torque "sweet spot" for best results.

Cheers, Bruce.
At home and at ease on a track that I know not and
restless and lost on a track that I know. HL.

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Follow Up By: Paparata R - Tuesday, Nov 26, 2013 at 16:04

Tuesday, Nov 26, 2013 at 16:04
Thanks Bruce and BlueFella,

Based on the details at this link Prado specs should I be aiming at keeping the rpm to 2000 as the Maximum Torque Nm @ RPM for the 1KZ-TE is at 2000 rpm. In the same link they comment "Useful torque between 2000 - 3000 rpm but little elsewhere"
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Follow Up By: Member - Bruce C (NSW) - Tuesday, Nov 26, 2013 at 17:41

Tuesday, Nov 26, 2013 at 17:41
OK then, you should be running the engine between those figures while towing and towards the top end when pulling hard such as up a hill etc.

I would assume that there would be plenty of useful torque beyond 3000 RPM but the best of it would be between 2000 and 3000 from that info you provided.

Remember that the faster the engine is revving the better the turbo is working, within those limits of course. The more an engine labours the more fuel it is using needlessly and the turbo is spinning below its optimum in that situation.

After an hour of driving you will get the feel of the combination when towing and you will quickly learn what works best for that combination of vehicle and trailer. Just don't be frightened to use your gears if needed.

I use my auto like a manual when towing and I find it works best for me.

Cheers, Bruce.
At home and at ease on a track that I know not and
restless and lost on a track that I know. HL.

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Reply By: Athol W1 - Wednesday, Nov 27, 2013 at 09:41

Wednesday, Nov 27, 2013 at 09:41
Paparata R
One of the most important things to consider with any vehicle fitted with an Auto Transmission is the transmission oil temp. Toyota Prado diesels usually only have the basic transmission cooler inside the radiator, whereas the V6 petrol has an additional oil to air cooler fitted. It is not unusual to find that the oil in a Prado Diesel is very discoloured or burnt black due to overheating, even in vehicles that have never been used for towing.

I strongly recommend that you have an additional cooler fitted to help keep transmission temperature to a reasonable level, and also do not use your top gear (or overdrive gear) when towing. It is generaly recognised within the motor trade that for every 10 degrees that you can lower the operating temperature of the transmission then you double its life, and it is impossible to freeze transmission oil.

If your vehicle is fitted with a OBD11 diagnostic port (generaly near the steering column under the dash) then I would suggest that you get a Scangauge 11, which will allow you to more closely monitor engine functions (including coolant temp, current fuel use updated every 2 seconds, and transmission temps (in most Toyota's)) and then you can drive the vehicle to get the best results all around.

Enjoy your trip from a fellow traveller.

Athol W
Retired motor mechanic
AnswerID: 522171

Follow Up By: Paparata R - Wednesday, Nov 27, 2013 at 11:11

Wednesday, Nov 27, 2013 at 11:11
Thanks Athol,

this will sound like a dumb question but I am going to ask it anyway.

With the auto on the Prado being 4 speed is 3rd equivalent to selecting D with overdrive off?

I will get a transmission cooler fitted but looks like a scanguage II is not compatible with my Prado
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Follow Up By: Athol W1 - Wednesday, Nov 27, 2013 at 15:50

Wednesday, Nov 27, 2013 at 15:50
Paparata R
That is most likely correct, most autos with more than 3 forward gears used an overdrive as their highest gear, and generally those using 6 or more forward gears have more than one overdrive gear..

Regards
Athol W
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Follow Up By: Nomadic Navara - Sunday, Dec 01, 2013 at 16:41

Sunday, Dec 01, 2013 at 16:41
The most important thing in keeping fluid temperature down in an auto box is not letting the torque converter do too much work. Some people think of a torque converter as just something that slips and allows you to get some drive from your motor when things are working at slow speed. A torque converter is actually a hydraulic gear box.

Its action is similar to a mechanical gear box. When you are travelling slowly you change down a gear or two. This allows your mechanical gears to convert the engine torque to a higher torque albeit at a much lower output speed than the engine speed. In our turbo diesel engines when we are travelling with an engine speed above 3,000 RPM the torque converter will not do much work, the converter output speed is nearly as fast as the input speed and the stator will be free wheeling and also turning at the same speed as the rest of the converter. If you are travelling with the engine speed below 2,000 RPM the stator will be locked by its free wheeling clutch. The transmission fluid wil be travelling in a motion that increases the torque through the converter. The output speed will be slower than the input speed, just like happens in a manual box when you shift down. Better description in these pages.

The problem is that more heat is produced in the torque converter when it is working harder and increasing the torque. If you are climbing a hill and your motor speed is around 2,000 RPM or a little more your converter will be doing a lot of work and thus producing more heat. If you manually select a lower gear and spin your motor up to 3,000 RPM or a ittle more the converter will be doing less work and produce less heat.

If you use this technique and keep your engine speed up on hills there will be no need for an extra heat exchanger.

PeterD
Retired radio and electronics technician

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Reply By: david bt50 - Sunday, Dec 01, 2013 at 14:28

Sunday, Dec 01, 2013 at 14:28
i have a 2002 prado i am towing a coromal 6.9mt total weight of around 2.5 tonne which is the limit of the prado. i also have a 3.75 tinny on top i travel at 95 kph at 2500 revs fuel economy 5km to the litre. I find travelling at this speed it is a bit easier when you come to hills. Toyota say never to tow in overdrive.
AnswerID: 522412

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