Kubota M8540 vs M7040 re fuel consumption

[Marlon]

Not ignorant, just inexperienced. A couple of people who supposedly know more have told me that a bigger tractor NOT under stress will use less fuel than a smaller tractor under stress.

So, if I am to run a Topper that specifies it requires a PTO of 50-120HP (and weighs 640Kg but that shouldn't be relevant) would I use less fuel with the M8540 which has an engine displacement of approx 3769cc and IS TURBO charged DI and runs 540 PTO at 2205rpm, or the 7040 which has a smaller displacement of 3331cc and is NOT turbocharged but otherwise the same engine E-CDIS design but runs the 540 PTO at 2160 rpm.

 

[GeoHorn]

Do you really think the fuel consumption difference will make up for the higher costs of initial purchase price and also maintaining a turbo of the M8540?

And the 7040 is NOT “under stress” when it runs at PTO speeds. It’s designed to do that.

 

[Marlon]

Do you really think the fuel consumption difference will make up for the higher costs of initial purchase price and also maintaining a turbo of the M8540?

Thank you for your concern

And the 7040 is NOT “under stress” when it runs at PTO speeds. It’s designed to do that.

As I said, inexperienced, not ignorant, my current MX5200HST has an engine rpm of 2700, and has to run at the same 2700 rpm to spin the PTO at 540, and in doing so with a 6' rotary cutter which I was told would be fine, guzzles fuel like a session at the hotel on Friday night, so, was it designed to do that by the same designer who worked on the M7040??

Some facts might help me see why a 7040 will do efficiently what an MX5200 won't and those facts might also indicate if I need to go to an M8540, which I was only toying with to generate some facts base response so I could learn something that might make me choose between the real contenders, those being the M6040 and the M7040, or go to a turbo engine, or give up altogether.

 

[Dave_eng]

Manufacturers usually have the info you need in sales brochures.
This graph on engine performance and fuel consumption for a M9540 is the info you need to compare models and manufacturers.
Regrettably, although the sales brochure covers many models, the engine graph is only provided for one.

The lower line in the graph is showing pounds of fuel used per engine horsepower in one hour.
The point where the graph line is lowest is where the engine produces the most power for the least fuel consumption which is about 1,700 rpm.

I know this is all very technical jargon but it is really the only way you can compare different models and manufacturers.

Dave

 

[PoTreeBoy]

I doubt you'd see much difference between the 2 M's, doing the same amount of work. But the MX has two things working against it for some work: the HST is less efficient than a gear transmission, and the MX is tier 4 vs tier 2, which uses more fuel.

 

[Tx Jim]

My Kubota M7040 has a factory installed turbocharger. https://www.messicks.com/ku/85812
My M7040(3.3L) uses 2.5 g GPH of diesel pulling my JD 467 rd baler & my JD 4255 with 7.6L engine uses 3.2 GPH. I know it not the same but it's what I own & have checked for comparison

 

[Marlon]

Thanks for your experiences - I know fuel discussions can be endless and impossible to compare where there are different uses and weather conditions, but some indicators like the MX tier 4 vs the M7040 tier 2 are interesting and new to me.

I'd like to get some experienced and mechanical minded opinion on my thinking below.

In addition to the tier 4 vs tier 2 issue above which leans me to the M series over the MX, I have been thinking that any M series should be better than the MX for my broad acre (only 70-90 acres really) slashing because the MX 540rpm is 2700, the same as the engine max revs, so it's spinning it's head off, whereas the M6040 or M7040 (both non turbo in Australia) are achieving 540 rpm at 2160 engine rpms, that's 440 under the max engine rpm of 2600, so perhaps they are not spinning their heads off, and that alone will improve fuel use against the MX

What does anyone think of that please? And in addition, the colloquial opinion is that bigger engines not strained will be better than smaller engines, so if the above thinking is right then I should expect far better fuel consumption from a M6040 because

1. It's tier 2 rather than tier 4
2. It's engine/540 rpm are 2600/2160 as opposed to 2700/2700 for the MX
3. It's a bigger engine, 3.3l as opposed to 2.5l

and I should not have to go to the M7040 which will just be injecting more fuel to get the larger HP in order to pull a 12' Kubota flex wing (RC2512-2) which says it is for tractors with a PTO output of 40-100HP which should therefore make the M6040 suitable having a PTO output of 55HP.

So, what do you all think, am I a raving lunatic over thinking the fuel issue?

 

[Tx Jim]

I prefer larger CID(L) engines vs the smaller displacement engine. I would definitely pick the Tier 2 emissions over Tier 4 emissions hands down. JD produces some tractors with about 125 HP utilizing a 276 cid(4.5L) engine

 

[GeoHorn]

Changing tractors, trucks, cars, etc …. to achieve a slightly better fuel consumption is usually a poor economic decision,… because the up-front costs of the purchase will likely never off-set the “pay as you go” …minor differences in fuel economy.

My wife wanted to trade her 2010 vehicle which got 24 mpg for a 2021 model that claimed to get 34 mpg. (If you can believe sales brochures and that the average person can match the driving skills and conditions of the Federal tests.)
So we did the math and found out that it would mean that after spending an additional $22K for the new car …(the difference in price of the new versus the selling price of the old)… that even at $5/gallon it would take the life-expectancy of 3 of the new vehicles before the BREAK EVEN point. And THAT would take almost 26 years if she drove 20K miles per year.…and the purchase price would be in REAl dollars and RIGHT NOW and UP FRONT…. as compared to the gradual and future purchase of the fuel.

If your only major concern is price differentials of fuel consumption…. and if your present ride does the job…. keep what you’ve got.

 

[Marlon]

If your only major concern is price differentials of fuel consumption…. and if your present ride does the job…. keep what you’ve got.

I'm not trying to go from 21mpg to 22mpg, I'm trying to get to a position where I can slash a 20 acre paddock using less than approx. 26 gal of diesel which from what I have gauged here is way more than it should take, which I have to do frequently now.

So What I have seemingly determined from my own common sense and what I have learned on this site is that my problem is:

1. Current tractor is hydrostatic, so not direct drive, so uses more fuel
2. Current tractor revs at 2700rpm to run PTO at 540, so uses a lot more fuel than the M6040 to run the PTO at 540rpm
3. Current tractor is Tier 4 rather than M6040 Tier 2, again supposedly uses more fuel
4. Current tractor has PTO of 43HP which is not high enough for any topper I can find, or the Kubota RC2512-2 winged cutter I am thinking of, let alone the Howard 6' on sled slasher I am using at the moment, so uses more fuel as it is stressed doing the work
5. The M6040 I am thinking of is Tier 2 and engine displacement is approx 850cc greater than the MX and so for the same work, the larger capacity engine should alleviate the stress and do the job more efficiently, there again less fuel, and aside, I'd like to know if anyone thinks I really need the M8540 with a displacement of 3800cc to avoid a stressed tractor, I'd like to NOT have to go that big
6. Current tractor is lighter and on R4 tyres and more often requires 4WD

The current tractor was great for what I needed when I got it, but circumstances have changed the work I am expecting it to do and experience to date says it is not up to that work and will send me broke at the rate it is guzzling fuel trying to do it.

It's not just a cost exercise, and on Orange Tractor, I'm trying to get confirmation from people with more tractor expertise than myself to tell me if all the above is right or not and if the M6040 with a displacement of 3300cc and a PTO of 55HP running at 2160prm to achieve 540rpm, will suit my needs (eg the RC2512-2) at an acceptable fuel consumption

 

[Marlon]

The only reason I was looking at the M8540 was because a dealer was suggesting it, and looking at the downloads of manuals for the M series, the M8540 had these amazing figures of PTO 540 at 2035 rpm against engine rpm of 2600, as opposed to the M6040/7040 which had PTO 540 at 2160 against engine rpm of 2600, and buried in my ignorance, I was interpreting / assuming the less revs to achieve PYO 540 as meaning less fuel.

However, when I went back to the dealer with some questions, he said his sales documentation which contained all the specs as well, quoted the M8540 PTO as 540 at 2205, greater than the M6040/7040, so

1. which is correct, the manuals I have downloaded from multiple sites including Kubota site, or the dealer
2. Am I chasing a rabbit down a hole with the above interpretation / assumption on 540 rpm effect on fuel consumption, and
3. If the manuals are wrong and the dealer is right, can I trust the same source with regards to the PTO revs required for 540 for the M6040/7040 which state them as 540 at 2160 rpm, so can anyone confirm the revs required for the M60/70 to spin the PTO at 540?

Why is buying a tractor so hard??

 

[Dieseldonato]

Your not going to save any fuel. You need to burn a certain amount of fuel to produce a certain amount of power. The larger tractor is heavier and will require more power to move its own weight.
Do you need the extra hp? Obviously not. Your current tractor does the job.

Given the option I'd get the larger tractor just because it had more power, I wouldn't for a second think it will burn less fuel then the smaller tractor doing the same job.
The turbo requires no more or less maintenance then any other part of the engine. Fearing it is absurd. Plus it uses wasted exhaust energy to pump more air into the engine, so it could be argued it's a more efficient engine.

P.s. buying a tractor is easy, either get the smallest one that will handle the job, or the biggest one you can afford.

 

[Marlon]

Your not going to save any fuel. You need to burn a certain amount of fuel to produce a certain amount of power. The larger tractor is heavier and will require more power to move its own weight.

To a point I agree , but with regards to "Your not going to save any fuel" , VERY OBVIOUSLY, the hydrostatic tractor working the PTO at 2700 rpm which is the engines max chews up the fuel whereas the feedback is that a non-hydrostatic working at 500rpm UNDER the engines max rpm will not, so it's not just HP to consider but the engine and transmission design

Do you need the extra hp? Obviously not. Your current tractor does the job.

So I might not need extra HP (but in this case I will since I'm also looking at a larger slasher) but I certainly for the same HP, need a tractor designed to do the job all day, and not just do it for short times infrequently

Yes, I'm trying to determine the smallest tractor to do the job, but the DIFFICULITY is in determining what that smallest tractor is, and it's not just HP to be considered and I say that with authority given my hours on the hydrostatic tractor frequently interrupted by my opening my wallet to re-fuel, so will the design of the M6040 reduce that frequency as many seem to be saying it will?

So, for clarity, I repeat what I had previously posted above to draw comment on the specific points.....

Am I correct in the following points and will a M6040 be the right choice (smallest to do the job efficiently?)

1. Current tractor is hydrostatic, so not direct drive, so uses more fuel
2. Current tractor revs at 2700rpm to run PTO at 540, so uses a lot more fuel than the M6040 to run the PTO at 540rpm
3. Current tractor is Tier 4 rather than M6040 Tier 2, again supposedly uses more fuel
4. Current tractor has PTO of 43HP which is not high enough for any topper I can find, or the Kubota RC2512-2 winged cutter I am thinking of, let alone the Howard 6' on sled slasher I am using at the moment, so uses more fuel as it is stressed doing the work
5. The M6040 I am thinking of is Tier 2 and engine displacement is approx 850cc greater than the MX and so for the same work, the larger capacity engine should alleviate the stress and do the job more efficiently, there again less fuel, and aside, I'd like to know if anyone thinks I really need the M8540 with a displacement of 3800cc to avoid a stressed tractor, I'd like to NOT have to go that big
6. Current tractor is lighter and on R4 tyres and more often requires 4WD

 

[GeoHorn]

Your not going to save any fuel. You need to burn a certain amount of fuel to produce a certain amount of power. The larger tractor is heavier and will require more power to move its own weight.
Do you need the extra hp? Obviously not. Your current tractor does the job.

Given the option I'd get the larger tractor just because it had more power, I wouldn't for a second think it will burn less fuel then the smaller tractor doing the same job.
The turbo requires no more or less maintenance then any other part of the engine. Fearing it is absurd. Plus it uses wasted exhaust energy to pump more air into the engine, so it could be argued it's a more efficient engine.

P.s. buying a tractor is easy, either get the smallest one that will handle the job, or the biggest one you can afford.

He obviously wants the bigger tractor because in post #10 he lists all the limitations perceived of his current ride and avoids mention of any limitations of the proposed larger tractor.

Two things continue to pop up: One is the implication a turbo is no more at risk of trouble than a non-turbo engine. I do not think that is correct. While turbos have improved over the years, they still introduce a few things VS the non-turbo: One is that a turbo raises the compression and therefore the stresses (and yes, the efficiency) of the base engine. It does that by taking energy from the exhaust…which contrary to common belief, is Not “free”. It creates back-pressure and it absorbs heat and that heat must be addressed with engine oil as a coolant and none of that activity is either “free” of cost OR “free” of added maintenance risks.

Secondly: These engines are not equal displacement. The larger engine will suck in more air and therefore more fuel (in order to obtain the appropriate fuel/air ratio) than the smaller, with the variable thrown in of the turbo which itself “packs in” more air to that engine...(which also requires additional fuel to obtain the proper fuel-air ratio)… But the effective displacement differences of the two engines will alone result in a difference of fuel consumption at any specified “per cent” of rated power.

Already noted is the better efficiency of the direct-drive transmission over the HST…. but by the argument-style and points made by the OP,….He clearly favors replacing his current tractor and is seeking support for that desire. I would believe the factory data over the dealer.

 

[Dieseldonato]

I'll ask you this. Can you afford the higher hp tractor? If so I'd buy that one. Don't get hung up on the semantics. It will give you room to grow in the future.

 

[Tx Jim]

Turbo charger on my '91 JD 4255 that I've owned since Feb '93 is the original turbo & has 11'600+ hrs of use. The turbo on my '11 Kubota M7040 is original @ 1645 hrs of use

 

[Dieseldonato]

He obviously wants the bigger tractor because in post #10 he lists all the limitations perceived of his current ride and avoids mention of any limitations of the proposed larger tractor.

Two things continue to pop up: One is the implication a turbo is no more at risk of trouble than a non-turbo engine. I do not think that is correct. While turbos have improved over the years, they still introduce a few things VS the non-turbo: One is that a turbo raises the compression and therefore the stresses (and yes, the efficiency) of the base engine. It does that by taking energy from the exhaust…which contrary to common belief, is Not “free”. It creates back-pressure and it absorbs heat and that heat must be addressed with engine oil as a coolant and none of that activity is either “free” of cost OR “free” of added maintenance risks.

Secondly: These engines are not equal displacement. The larger engine will suck in more air and therefore more fuel (in order to obtain the appropriate fuel/air ratio) than the smaller, with the variable thrown in of the turbo which itself “packs in” more air to that engine...(which also requires additional fuel to obtain the proper fuel-air ratio)… But the effective displacement differences of the two engines will alone result in a difference of fuel consumption at any specified “per cent” of rated power.

Already noted is the better efficiency of the direct-drive transmission over the HST…. but by the argument-style and points made by the OP,….He clearly favors replacing his current tractor and is seeking support for that desire. I would believe the factory data over the dealer.

The turbo if sized correctly should have a 1 to 1 ratio of exhaust out to air in, in any sense its using waste gas to power itsself. Otherwise were just releasing wated energy. The dynamic compression ratio is irrelevant. Most turbo engines have a slightly lower compression ratio then non turbo engines. Not a hard and fast rule, but a general rule of thumb. Most manufacturers also use better parts in a turbo engine, piston cooling jets, blah blah blah. There's no reason to not buy something because if the turbo. They are literally used every day on dam near every industrial, construction, locomotive engine out there. It not the 70's anymore. Really only lower out put engines don't have them.
Any way. I do agree he's looking for justification. By all means get the bigger tractor. It will do the job fine.

 

[mcmxi]

The turbo if sized correctly should have a 1 to 1 ratio of exhaust out to air in, in any sense its using waste gas to power itsself. Otherwise were just releasing wated energy. The dynamic compression ratio is irrelevant. Most turbo engines have a slightly lower compression ratio then non turbo engines. Not a hard and fast rule, but a general rule of thumb. Most manufacturers also use better parts in a turbo engine, piston cooling jets, blah blah blah. There's no reason to not buy something because if the turbo. They are literally used every day on dam near every industrial, construction, locomotive engine out there. It not the 70's anymore. Really only lower out put engines don't have them.
Any way. I do agree he's looking for justification. By all means get the bigger tractor. It will do the job fine.

Yep. I've owned and own lots of turbos. My '02 F250 with 160k miles is on the original turbo with no sign of issues. I do let the engine run before shutting down to allow the turbo temperature to reduce. I do that for both of the tractors too. I have zero fears or concerns with turbo engines.

 

[mcmxi]

I would get the bigger tractor for a number of reasons given the OPs intended use. It'll be more comfortable for sure, and based on my limited experience pulling an RCR1884 behind the MX and M, it'll probably be more fuel efficient.

 

[Dieseldonato]

Yep. I've owned and own lots of turbos. My '02 F250 with 160k miles is on the original turbo with no sign of issues. I do let the engine run before shutting down to allow the turbo temperature to reduce. I do that for both of the tractors too. I have zero fears or concerns with turbo engines.

I wasn't referring to you, I was a heavy diesel mechanic for years and an avid fan of the diesel engine. I've put more miles on service trucks then I care to admit. Last one being an 07 3500 dodge with nearly 400k on it when I left service work. Original everything on that engine. Fuel and air system.