P engine power and fuel consumption

[Nicolanders]

We are traveling quite a few miles down here in the South, so mileage becomes very important in the long run. We are wondering how to get the most for the buck when driving the Patrol.

Is there some info available on which RPM's you should try to run the engine at to get the best mileage, for the gears respectively? And which speeds would this translate to?

It would also be nice to know something about power output. Where do you get the most energy and torque from the engine?

Thanks

[miksum56]

Esteban where are you? For fuel consumption I feel good in mine at the 40-45 range. They are not known for being good on gas. Some of that is because (I feel) I've read over the years of owners running 55-65 mph. For my money that's Marks territory. My 2cents

[Esteban]

Esteban where are you? For fuel consumption I feel good in mine at the 40-45 range. They are not known for being good on gas. Some of that is because (I feel) I've read over the years of owners running 55-65 mph. For my money that's Marks territory. My 2cents

Mike is correct on his speed range, which translates to 64 to 72 Km/h. The Patrol engine reaches its torque at 2000 rpm, so that means around the speed Mike posted.

Since most of the driving will be in third gear, that speed will be the sweet spot. In 1st or 2nd gear, you shouldn't be too concerned, because it will be what it needs to be according to the inclines you're travelling. Beyond 90 km/h the wind resistance begins to take a toll in the fuel consumption.

For your information, these are the maximum speeds in each gear:

1st...... 40 km/h (25 mph)
2nd..... 80 km/h (50 mph)
3rd..... 120 km/h (75 mph)

So half of each of them is the best

[Nicolanders]

Wow, that is actually a lot higher than we thought.

So, is it correctly understood that the best mileage always is in the spot where you hit max torque? Also meaning that you will get the strongest pull from the engine at that spot?

This question might come because we're actually not completely sure on the difference between torque and energy-output - except that trucks and such always have more torque, race-cars more bhp

[moore_rb]

So, is it correctly understood that the best mileage always is in the spot where you hit max torque? Also meaning that you will get the strongest pull from the engine at that spot?

That is correct- most engines run with their best fuel efficiency, right at the peak torque RPM. So, like Esteban says: keep your Patrol right around 2000RPM while cruising, and you will maximize your fuel economy...

[faux40]

So, is it correctly understood that the best mileage always is in the spot where you hit max torque? Also meaning that you will get the strongest pull from the engine at that spot?

That is correct- most engines run with their best fuel efficiency, right at the peak torque RPM. So, like Esteban says: keep your Patrol right around 2000RPM while cruising, and you will maximize your fuel economy...

I'm going to write myself into a little frenzy... hang on!

I've always understood that the engine produces the most efficient power at the max torque point on the chart... But according to the P Engine service manual, it's optimum fuel consumption occurs at a slightly lower engine speed -- 1,600 RPM (the lower line on the chart):

Screen Shot 2014-08-27 at 8.39.43 PM.png

What this means is that you should generally have the best results if you keep the engine at 1,600 (if you look at the lower line on the chart, it's lowest between 1,400 and 2,200 rpm -- stay in that range if possible!). But at 1,600 rpm, you only have up to 65hp to work with -- that's the rate at which the engine can do work. At 1,600 rpm, you cannot achieve a speed that may require 70hp but can easily cruise along at a speed that requires only 30hp.

But for several reasons this doesn't necessarily mean that it's the most efficient engine speed at which to drive -- It's simply the most efficient hp generated. Overall fuel usage is much more complex. In reality, the truck's speed makes the biggest difference... there's always a trade-off!

At higher speeds, you cover more ground quicker, but the wind resistance is much, much higher so you must make more power just to maintain speed. At some speed (factored for all the external variables), the fuel per distance will be optimized -- Going any faster requires more power, so more fuel; any slower covers less ground but uses less fuel, however it doesn't save the amount of fuel to needed travel the same distance. Most likely this optimal speed will almost always happen around 1,600 rpm, but in which of the three gears depends on the environment...

I take a much more pessimistic stance than Esteban regarding at what speed takes a significant toll on mileage -- I'd guess the pain starts at less than half the 90kph speed Esteban posited. The aerodynamic profile of the Patrol is much like what you find with a high-speed brick. Wind resistance is going to be a major factor even at very low speeds -- throw in a hill or two and all bets are off!

It would be really tough, impossible for all practical purposes, to find the optimized fuel burn for the truck mathematically. There are just too many variables to account for - just to name a few: wind resistance, rolling resistance, braking, hills, turns, occupant and cargo weight, air temperature, air density, windows open vs. closed, vents open vs. closed, engine operating temperature, temperature of the air entering the engine, etc.

If you want to stretch your range, you'd be better off thinking of ways to reduce average fuel usage (a.k.a. hyper miling):

• Gentle starts and acceleration
• Keep the top speed reasonable -- I have no idea what the sweet spot is on this beast -- 45 or 50mph? Remember, in a perfect world, each time you double your speed, your wind resistance goes up four times. In other words, it takes four times the energy to overcome drag at 50 than it did at 25. In reality, it's probably worse!
• Constant speed cruising (I expect it to be near 1,600 RPM -- but that's a guess)
• Avoid stopping whenever possible -- When possible, predict where you need to end up and coast there so you can avoid needing the brakes (think of braking as simply wasting the energy you asked the engine to make and paid for in fuel!)
• Reduce drag -- no roof rack, closed windows (some folks go crazy here -- add streamlining, tape body seams smooth, reduce radiator slats, remove the exterior mirror, lower the vehicle and add an air dam to reduce airflow under the truck)
• Tailgate big trucks (I'm talking about nearly touching the bumper kind of tailgating) as you can share the slipstream they created... of course, this particular method may result in a fatal crash. If you want to survive, I'd avoid this one!

Personally, I think you should put a few Jerry cans of fuel on the roof, roll the windows down and enjoy this trip of a lifetime and forget about mileage and range... and keep sharing the stories!

John

[Swerve]

My main tip is take a mental note where your accelerator pedal is.

I've noticed on the freeway it sits around 3/4 pressed. If you can drive slower etc, and have it only 1/2 pressed, Id say you will save fuel. Also run higher tyre pressures (less drag) but will be bumpy

[Nicolanders]

I'm going to write myself into a little frenzy... hang on!

Yes please!

Very interesting the chart you have. But it actually seems to show that fuel consumption is level between 1600-2200 rpm. The increase has to be very low, a few percentage points at worst. It is nice to have a "window" like that to stay within. But really this is also just what intuition tells you. It does not take any advanced physics to know that a roaring P-engine chugs like an elephant

Also very good point that you "pay" for your horsepower, higher consumption does not necessarily mean fuel wasted.

You make a very good point on the wind resistance. We have thought about that too. Having not only the roof rack, but also the roof tent - which really is shaped like a brick - surely makes for some massive wind resistance. So it would be nice to know when it really starts to kick in. As you point out, wind resistance increases exponentially with velocity, so there is probably some point where it goes completely off the charts. It would be nice to have an idea on how much more you consume going 70 kph instead of 60 kph.

We are not really worried about these things, they are not in the way of enjoying the trip. It is just good to know when you have to travel more than 10,000km - it adds up! So having an idea will save you a lot in the long run - even without sealing the windows shut with silicone and throwing away the mirrors

By the way, how does the P-engine work when engine breaking? How much does it consume? Sometimes we go down very long slopes. Would it consume less putting the transmission in neutral, or engine braking? (we know that there are other things to consider here as well)

[Esteban]

It's so entertaining to read your adventures and look at the pictures. Awesome.

By the way, how does the P-engine work when engine breaking? How much does it consume? Sometimes we go down very long slopes. Would it consume less putting the transmission in neutral, or engine braking? (we know that there are other things to consider here as well)

It will consume a little less putting in neutral, but you'll end up paying for brakes later on. Be aware that you have been and will be facing some long stretches of steep inclines, and overheating the brakes in that condition is very easy. It's not fun when that happen. Strongly recommend to use the engine for braking when possible. We know that you also have to deal with the noise in the transfer case, so be flexible and don't overuse the brakes.

[moore_rb]

By the way, how does the P-engine work when engine breaking? How much does it consume? Sometimes we go down very long slopes. Would it consume less putting the transmission in neutral, or engine braking? (we know that there are other things to consider here as well)

It will consume a little less putting in neutral, but you'll end up paying for brakes later on.

I have to disagree with Esteban on his first point- I totally agree with the second point- that the cost in brakes is far more excessive than any equivalent cost in fuel, when going downhill.

But, When using engine (compression) braking while descending hills, less fuel is consumed than it takes to keep the vehicle idling on level ground, due to the throttle being completely closed, and zero vacuum being applied to the carburetor venturi.

In fact, since the Patrol has no power components (no power steering, no power brakes, and no steering column lock); Compression braking downhill in a Patrol could actually still be accomplished with the ignition key turned totally OFF.