4 Speed Auto Transmission - Towing and uphill driving

[SamSta Member Find all posts View Profile Close SamSta]

Hey all,

I recently purchased a 2000 Prado GLX 3.0L Turbo Diesel 4 Speed Auto with 330000 km on the clock. Due to below average uphill and towing performance, I've been troubleshooting a fuel supply issue (see discussion here ) however after quite a bit of troubleshooting and replacing various parts, I am starting to question if maybe a) my expectations are too high, b) these transmissions just suck or c) their is something off with the transmission/timing/ECU that's causing it to under perform on the uphills or whilst under load.

The truck drives beautifully on the flat - even better since replacing the fuel and air filters, cleaning the MAF and MAPS sensors and filters and replacing a suspected leaky fuel primer pump however after towing a relatively light trailer and a smaller caravan up a hill recently, the truck was fricken gutless and I am afraid of taking my ~1800kg caravan away in a few weeks in case the truck struggles or or cook the motor or something else.

I've been told "these engines aren't power houses compared to the common rail diesels" so maybe my expectations are too high? but I have a feeling I am not getting the full potential out of this truck on the hills and when towing. In particular, I suspect the transmission might be selecting the wrong gear for the situation when going up hill. It's like at 90km/h, it jumps from 4th down to 2nd, then when its ready to shift up, it goes from 2nd to 3rd (monetarily) then up to 4th (which is not suitable for the situation) then back down to 2nd? or something like that? I am new to these trucks so have no idea whats happening.

Usual driving around town is superb, reasonably zippy and no dramas. On a side note, I have had some cold start issues however I am confident I resolved that issue by replacing a suspected knackered/leaky fuel primer pump this afternoon. Tomorrow mornings cold start will tell!

Would love to hear others experiences with this engine/transmission combination.

Cheers

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

Yes, your expectations are way too high. The old KZ pulls OK as car only but really struggles when you add a trailing load.
But you can get the best out of them by understanding what the transmission is trying to do.
When towing, push the button In so she will only go up to 3rd gear (direct) and then wind out the rpm.
You will get up to 100 pretty quickly but then she’s pulling 3000rpm which I don’t like.
Hit the button as you ease off a tad for the change and she will go straight into locked 4 (overdrive) and may hold that speed or depending on load, you may have to ease her off further back to 90.
When you see a hill, hit the button before she bogs down and she will power over in direct with locked converter so long as road speed stays above about 80.
The idea with any auto is to get it up to converter locked speed, doesn’t matter if that’s 3rd gear (locks about 70) or 4th gear (locks about 85).
Those speeds are totally dependant on your accelerator position and the rate at which she’s trying to accelerate.
Locked converter also means a dramatic drop in transmission oil temperature which is cooled via your car’s radiator.
Slipping the converter means the radiator may not have enough cooling capacity and she might overheat, especially these older cars where the fan viscous hub is not working 100%.
Once you understand how the trany. works, you can drive it like a manual and you won’t be holding up too much traffic.
But if you put it in D and expect it to just go, she’ll overheat as well as give rubbish economy.
We towed our 1.5t off road camper through the Kimberley, top of WA, the Cape etc etc. Our most frustrating driving was around Sydney to Newcastle where traffic maintains a very high speed and it’s hilly. Your 90 won’t break any speed limits around there.

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

She also pulled this which weighs 2.3t.
Same method, push her up to 90+ then try for 4th. Ease off to a happy speed.
Tandems tow so well she wanted to stay at 90, so I just left her in 3rd.

[watsea Member Find all posts View Profile Close watsea]

Thanks Carco for your explanation of using the auto transmission while towing. I had towed a van of similar size to yours with my previous Series 90 which was V6 petrol. I think l learnt to use the gearbox in similar manner to your explanation because l noticed similar behaviour. Now I have a better understanding of the reasons. That car and van certain lost road speed on hills. The worst was on some of the freeway hills (mountains??) as you come into Adelaide on the S Eastern Freeway.

Generally, the fuel use was pretty high when towing the van, but that was expected.
Carco, my old 90 was the same colour as yours and had the Toyota bar in front, until it was bent by a roo. Replaced with a ECB alloy bar via insurance.

[SamSta Member Find all posts View Profile Close SamSta]

Thanks for that info Carco! I'll keep playing around with the Power (ECT) button however I haven't noticed it making any difference. Maybe because I am engaging it during power loss on hills and not earlier on before it starts losing guts up a hill? I'll persist further and try n get my head around best techniques of how to drive this thing. Is there any chance my Power/ECT button could be faulty? It does engage the ECT light on the dash but there is no obvious sign it actually doing anything?....

Watsea, I live in the Adelaide Hills (Bridgewater) and the SE freeway is my reference point in this post We like to camp down at Rapid Bay amongst other locations and I am not confident my truck will pull my caravan up some of the steep hills around here without overheating of something giving. A buddy of mine pulled his 1200kg caravan up the SE freeway the other day and was sitting on 70km/h all the way up. He said it felt like the fuel was being restricted. (He has an 80 series land cruiser as a reference point). I get that feeling too driving it. Like its not quite running at its full potential. But sounds like that's normal. Just thought i'd check!

Thanks for the replies fellas

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

Not the power button, that just moves the shift points of the trany,
The O/D button is the one i'm talking about. It's on the side of your shifter, ready for your thumb.

[watsea Member Find all posts View Profile Close watsea]

Hi SamSta,

when towing a van with my 90, I always had the power button activated and deactivated the overdrive button, as Carco said, except for some downhill runs or some flats wth a tailwind. If the overdrive was activated, the vehicle's torque converter would easily hunt and the engine revs would change with no change of speed, obviously slippage of the torque converter.

Also, in hilly terrrain, use was made of the gear stick to change down earlier than the automatic shift, helps keeps the revs up and speed up, to a certain extent.

On our last trip to SA with the Series 90, as we drove into Hay, NSW, we spotted another 90, beside the road in town, and admired its seemingly good condition. However, their relatives were in the van site near us and we were told that the transmission had failed on that particular 90. They were towing a van slightly smaller than ours.

We often have been to Fleurieu Penisula, staying at friends' houses at Rapid Bay and Second Valley or staying with a van at Normanville for power to run the aircon. Leaving Rapid Bay could be interesting, if towing a van with a low powered vehicle.

[SamSta Member Find all posts View Profile Close SamSta]

Not the power button, that just moves the shift points of the trany,
The O/D button is the one i'm talking about. It's on the side of your shifter, ready for your thumb.

Ohhh you're kidding me! I feel like a massive dork. Didn't even notice that button was there as its kinda small and hidden when depressed. Was looking all around the console for it haha

Ok well that is interesting. I've been driving around with OD on the whole time. What difference should I expect with it turned off on hills?

Cheers Carco

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

Give it a work out. Get used to the speed you can feel converter lock in 3rd and 4th.
You will notice a big difference with O/D off when towing.
The KZ makes peak torque around 1900 and peak hp around 2400.
You’ll find towing at 2400-2500 is pretty sweet In 3rd, that’s about 90+

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

Now that you have the trany under control, you must look at the fan viscous hub.
It’s probably 20 years old and may work OK as a car but once you start towing, the engine’s heat load increases massively.
The 90’s cooling system is marginal at best so it needs everything working for it.
Unless you have an aftermarket coolant temp gauge, you’ll be relying on the dash heat gauge which is not too accurate. By the time the needle is in the red, she’s cooked.
I’d hate to see you stuck somewhere with a cracked head simply because the fan wasn’t doing its job. You wouldn’t be the first either, been there myself.
You can pick up an aftermarket hub for about $130 (Sparesbox) or you can add silicone oil (Toyota) to your hub at about $13 a bottle. Adding oil is what most owners do but it can be a bit hit and miss. Add too much and the fan will be working flat out all the time, robbing power and using fuel.
If you unclip the bottom section of the fan cowl, you can wriggle the fan/ hub assembly out through the bottom of the radiator and work on the bench.
Always give the two spring clips on the cowl a squeeze up with multi grips as they lose tension over time. Then the cowl can fall out and become jammed between fan and radiator, makes a hell of a mess. Been there too.
Also suggest you join the Mighty 90’s Facebook Page where there is loads of info. PP has very few 90 members so there’s not many recent posts.
Good luck with it all.

[SamSta Member Find all posts View Profile Close SamSta]

Now that you have the trany under control, you must look at the fan viscous hub.
It’s probably 20 years old and may work OK as a car but once you start towing, the engine’s heat load increases massively.
The 90’s cooling system is marginal at best so it needs everything working for it.
Unless you have an aftermarket coolant temp gauge, you’ll be relying on the dash heat gauge which is not too accurate. By the time the needle is in the red, she’s cooked.
I’d hate to see you stuck somewhere with a cracked head simply because the fan wasn’t doing its job. You wouldn’t be the first either, been there myself.
You can pick up an aftermarket hub for about $130 (Sparesbox) or you can add silicone oil (Toyota) to your hub at about $13 a bottle. Adding oil is what most owners do but it can be a bit hit and miss. Add too much and the fan will be working flat out all the time, robbing power and using fuel.
If you unclip the bottom section of the fan cowl, you can wriggle the fan/ hub assembly out through the bottom of the radiator and work on the bench.
Always give the two spring clips on the cowl a squeeze up with multi grips as they lose tension over time. Then the cowl can fall out and become jammed between fan and radiator, makes a hell of a mess. Been there too.
Also suggest you join the Mighty 90’s Facebook Page where there is loads of info. PP has very few 90 members so there’s not many recent posts.
Good luck with it all.

Cool, thanks for that! Fortunately I've just run into a Diesel Mechanic that is keen to do some work on my truck in exchange for my old transit van so will let him know about that. He owns the next model up from mine so knows the cars well. I've also got some solid advice from this bloke (https://youtu.be/09qoNGKPFIw) regarding some reasonably straight forward upgrades to improve towing. Yes have been looking into aftermarket temp gauges. I found this one on ebay that monitors all the key things including an EGT gauge so will be investing in one of those I think rather than a bunch of individual gauges cluttering up the dash. I am not on Facebook atm and hopefully might stay that way. It is hard though when all the good chat groups are on there. Will see about that one!

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

I fitted one of those to my 90.
They’re quite a lot of work to install, most sensor wires are too short. They’re extremely thin so extending them means finding suitable small wire.
Will need a tee for the oil pressure and as it’s in a dreadful position, I’d suggest buying the flex. stainless hose extension kit with attached block that can be bulkhead mounted. You then fit your stock pressure switch and the new pressure sender in that block.
My EGT sensor went a bit crazy after I massively overheated the engine limping her home with cracked head. Had pre turbo EGT’s of 700-800.
You can drill and tap your manifold in situ to fit the sensor or if you go for a 3” dump and exhaust, it will come with a suitable bung. That will mean you’re reading post turbo temperatures. Scott’s Rods had by far the cheapest 3” system.
When I get the other computer going, I can post photos of where I mounted the processor.

Re- your diesel mechanic mate, his model, the 120 doesn’t have the same cooling woes that the 90 has and more seriously, the 120 has a lower ball joint design that won’t drop your suspension on the road. If you’re unaware of this potential problem with 90’s, better do some research ASAP.
Don’t be tempted to buy any lower ball joint other than Toyota. You can get them from Glen on the Mighty 90’s Facebook page at excellent prices. Same goes for other suspension components.

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

For my coolant, I drilled and tapped that lump on the housing.
It looks like it was meant to be there.

[SamSta Member Find all posts View Profile Close SamSta]

I ended up installing a 3 bar map sensor, boost controller and Saas EGT/boost gauge with EGT probe about 100mm below the join between dump pipe and exhaust. Nice upgrade! Have taken it out for a few runs. Pulls hard on flat. Sits nicely on the highway. Very very happy with it's performance. However still falls on its arse on long hills. Spoke to a local performance tuner. His advice was if the EGT is around 450°c on long highway inclines, we can up the fuelling to resolve some of the power loss on hills. Today it was sitting at maximum 505°c on my test stretch of road (long gentle incline - 110km/h zone). Dropped from 120 km/h to around 95-100 and was being left for dust by other cars. Feels very much like the fuel is being restricted. Going to take it in for a fine tune on the dyno and see how it goes.

On the plus side though, I'm really happy with the mods I've done already for general driving around the hills where I work and live. Feels a lot more like a petrol engine performance wise so I'm finding I'm barely touching the accelerator. Just cruises around nicely in traffic. Be interesting to see how it's going on fuel!