Maximum Suggested Sustained RPM's for 12HT

[pathfinder_88]

I am just curious what everyone's thoughts are for maximum sustained rpm's on my 12ht. On those long, 110km/h stretches it'd like to be running 130km/h which puts me at 3,000rpm with the 285/75r16's. I've generally kept in in the 120km/h range to leave me under the 3k rpm. Other than hurting fuel mileage, if I am trying to save some time, is running at 3k rpm for an hour or two hard on these engines?

 

[roscoFJ73]

I just dont think they were designed for sustained engines speeds of 3000 or higher in mind(my opinon).
I dont even think a landcruiser is safe at high speeds.
Its tall,the brakes are crap even when they are working properly and the suspension will let you down if something goes wrong.

 

[prado t]

Sustained at 3000rpm . Its not gonna blow up or anything(If it is in good shape) Like rosco said a little dangerous at those speeds. Fuel economy and a little more wear and tear will be worsened. The 12H-ts are a real smooth motor so IMOP its not gonna damage it @3000rpm under moderate load.

 

[canucksafari]

Maybe not sustaining 130 kph at 3000 rpm constantly, but I think a 30 minute or 1 hour run is a good thing. It keeps the engine clean. With my two TD4.2s, I generally will do 120 on the flats and small hills. With the 5spd that's 2800 rpm. The engine just seems to get stronger with age. With my wife's auto, at 120 it is only doing 2200 rpm but I have taken off the over drive on longer hills and let it sit on 3000 rpm at 100 kph. JDM diesels are known for spending their lives mostly at or near idle. IMO, they need to be run good every once and a while to clean themselves out.

 

[amaurer]

130 is too fast. 110, IMO is about the limit for these old trucks, and frankly I'm happy to get that in my 73 considering the 42 tops out around 90.

In all fairness, "3000" rpm has a certain significance to the human brain since its a nice round number, but to the engine its only 15% faster than 2600rpm... all hell won't break loose once you cross that imaginary line. But its a simple fact that the engine will wear 15% faster.

 

[brownbear]

aim for 2300-2600. 3k is too high in my opinion to run a diesel. Any diesel.

I aim for 2000-2200 in my 3b. Yah a little older engine, but non the less a compression ignition engine.

 

[lynchmob]

I have personally put 200K km on my 3B BJ75 in the time I have had it. Its a 4 speed 4.1 gears 33x10.5 tires. Ive driven it 2400 miles at 120 in a single trip - and many other 1000mile + trips with no issues. Ive had it 125-130 for short periods on some of these trips.

I drive it 115-120 on the highway all the time - right around 3000 rpm. Its really up to you. If you take care of your engine and its in decent shape I dont see why it should be an issue.

 

[Dauntless]

3000rpm should be no problem for hours on end. My Hilux does 3700rpm for as long as I'm on the highway, with quite a bit of that time at WOT (4 speed gearbox). 197,000km and nothing blown up yet.

Same deal with my uncle's 2H powered HJ47 with 4 speed. It does 3400rpm all day with no issues. Nearly 500,000km on it now.

 

[pathfinder_88]

I guess what bothers me is that 3k rpm isn't all that far away from the redline of 4k-ish vs say a gasoline engine where I would have another 3k rpm of comfort! That probably isn't the right way to look at it though. I recall there is some procedure in the FSM, can't remember for what, that stated to floor the accelerator in neutral to run the engine to its max rpm. You sure as hell wouldn't be reading that in a gasoline FSM IMHO. Just a different ball game.

I have been put at ease knowing there are differring opinions.

Thanks guys.

 

[jamie_scotland]

I wouldn't worry too much about holding 3000 rpm. Its well within the normal operating range and as long as it's all in good order you won't do any harm. If there was an issue Toyota would mention it in the manual but all it states is avoid running in the red zone of the rev counter.

I once did a run across Germany one night in my 1-HDT 80. Was running late to catch a ferry and went from one fuel stop to the next (at least 300 miles) without really dropping below 100mph(160 km/h)! Was surprisingly comfortable and my gf actually slept most of the way.

Not saying it was sensible or a good idea but the truck actually run better/cleaner for a while afterwords. A good hard run always seems to improve a diesel.

Jamie

 

[Ropeman]

The max power figure is given at 3500 RPM, you won't kill your engine but you'll do your mpg no end of harm running at 3000 rpm.

The limiting factor for long stretches at high revs is going to be your bladder and the steering, which gets more than a little vague above 75mph* on my 60.


*The steering gets vague too

 

[Dieseler]

What are 285/75/16s comparable to,I have 35s on mine run 110-120 often and know in reality I am in the 130kph range due to the bigger tire and I am in the 2500-2800 range I also have a 5spd trans.
I would assume if the red light on the tach next to the green light comes on you are in the danger zone

 

[blis]

What are 285/75/16s comparable to,I have 35s on mine run 110-120 often and know in reality I am in the 130kph range due to the bigger tire and I am in the 2500-2800 range I also have a 5spd trans.
I would assume if the red light on the tach next to the green light comes on you are in the danger zone

youre doing way more than 130kph at 110 on speedo with 35's, i know my hj61 does around 105kph at 90 on speedo with 33's...

oh, i wouldnt worry about doing 3000 on 12ht for extended periods, heck, even 3500 is ok...

 

[canucksafari]

Speedos on stock vehicles are also always out a bit. The only way to know how fast you are going is to check it with a GPS. On mine, I found that 110 on the speedo with stock gearing and stock tires was only about 102 on the GPS. I haven't been in a vehicle yet where the speedo was dead on the money. Also, it helps to partially explain why fuel economy numbers are all over the place.

 

[pathfinder_88]

285/75R16's are a 33" tire. The 130km/h is via my gps...speedo reads about 125km/h I believe.

 

[pathfinder_88]

What are 285/75/16s comparable to,I have 35s on mine run 110-120 often and know in reality I am in the 130kph range due to the bigger tire and I am in the 2500-2800 range I also have a 5spd trans.
I would assume if the red light on the tach next to the green light comes on you are in the danger zone

The red light is an overboost light and comes on at 14 or 15psi...it flashed a few times when I was setting up my boost controller but I seem to have it set just under what causes the light to come on.

 

[crushers]

disagree
and
disagree

I just dont think they were designed for sustained engines speeds of 3000 or higher in mind(my opinon).
I dont even think a landcruiser is safe at high speeds.
Its tall,the brakes are crap even when they are working properly and the suspension will let you down if something goes wrong.

 

[crushers]

ummm, that is only 75%
and the recommended red line is 4200...

if you have good oil pressure then you won't have an issue.
<ust let us know if it was a main or a rod bearing that finally let go.>

me, i have no issue of driving 3000 rpm in a healthy diesel. if the condition is questionable then slow down.

as for speed being an issue, it is a long wheelbase with a low center of gravity. if you are a capable driver then drive it. if you suck then slow down.

of course you could change to 3.7 and lower the rpms...

mind you if the truck is in good mechanical shape this is relevant, if the truck "needs work" then keep it off the road altogther.

I guess what bothers me is that 3k rpm isn't all that far away from the redline of 4k-ish vs say a gasoline engine where I would have another 3k rpm of comfort! That probably isn't the right way to look at it though. I recall there is some procedure in the FSM, can't remember for what, that stated to floor the accelerator in neutral to run the engine to its max rpm. You sure as hell wouldn't be reading that in a gasoline FSM IMHO. Just a different ball game.

I have been put at ease knowing there are differring opinions.

Thanks guys.

 

[pathfinder_88]

She runs perfect and has great oil pressure which I monitor with the madman

 

[crushers]

if you want to drive at those rpms for extended periods then my i suggest an aftermarket coolant temp, oil and pyro gauge install?
just to play safe...