JD X748 Sucking Fuel Like Candy

[eagle107]

I have a 2012 X740 with the 54 inch deck, and my numbers are MUCH lower than yours. However, I think I can see a few reasons why.

The X748, as someone already pointed out, has a hydro AWD system. Your AWD machine has a 6 GPM charge pump. My machine being a 2WD, has a 4.5 GPM charge pump. So, your front wheels must constantly be fed power via the hydro system. The charge pump is considerably larger, specifically to handle the extra GPM needed on a hydro driven axle like the front one on your X748.

My deck is a 54 inch. While minor, bigger blades take more effort to turn, and catch more wind when turning, requiring more effort yet to keep speed. Your deck is a 60 inch correct? If you have the 7-Iron deck, that deck weighs something like 330 pounds. My 54C deck weighs 150 pounds. You are carrying 180 pounds more weight around your yard all day long than I am. Considering the weight of these machines, it probably works out to about a 15% increase overall, which is big.

I cut about 1.5 acres around the house area, and I would say I use probably a gallon of fuel. I keep my speed fairly low to maintain cut quality, and I think that helps save fuel as well. When your mower deck is engaged, it robs a large portion of power from your hydro system. If you try to cut with a high ground speed, I wouldn't be surprised if your fuel economy is worse because of it.

So overall, your machine is working harder to move more weight, with a hydro driven AWD system, pumping more hydro fluid, and turning bigger blades, it all adds up. Your consumption does seem a little high to me, even after all that. Although, if your machine is new, it will take some time to break in a diesel. I have 30 hours on my 2012 diesel now, and I am guessing it will take at least 300 before it is broken in and running as efficient as possible.

Yeah, I was thinking along those same lines. The X748 is about 300 pounds more than the Scag Tiger Cat, the AWD is not the most efficient system on these little tractors and of course the deck is bigger and heavier. Well I guess I still burn the same amount of fuel cutting the grass as the Scag, just that it is costing me more in fuel now. Unfortunately, I needed a deck as heavy duty as the Scag's Velocity Plus deck with all the twigs and limbs I chop up/hit when cutting in the woods; so far the 7 Iron is handling the cutting tasks. Only time will tell if the JD engineered but Chinese made balling bearing aluminum spindles on the 7 Iron deck will last as long as the Scag's US made tapered roller bearing cast iron Mazak spindles; god, that Velocity Plus deck was just awesome and strong.

 

[JDTank]

Well, I can say this much, I have never, not once, heard of a 7-Iron deck with a failure in any aspect.

Give that machine a few hundred hours, once it breaks in I think you will see a fuel economy improvement. I still believe these X7's are the best garden tractors out there, anywhere. Everything has it's pros and cons. I wouldn't give mine up for anything.

 

[jd4310man]

It seems to me that any new diesel engine that is tier 4 compliant is going to burn more fuel. In the "Good old days" when diesels were engineered to run efficiently and reliably, fuel economy wasn't a big concern. They want these engines to drink down the fuel and get lousy economy, they engineer them that way under the guise of "cleaner burning".
I doubt that a few hundred pounds would make a significant increase on fuel consumption as any tractor is low geared for pulling weight. Now running the engine at high rpm all the time will most certainly have the most in fuel consumption, I would say for average mowing conditions, 3/4 throttle should do fine. Lower the engine rpm the better efficiency an engine can get. To compare these small indirect injected diesels to a larger direct injected diesels, the indirect is less efficient than the direct because the direct injection atomizes the fuel spray finer than the idi. Idi's rely on the higher compression and swirl chamber to mix the courser fuel charge. But essentially it goes back to the whole emissions thing. I have a z665 mower and it too has the china spindles. What a low blow for Deere. But they work just fine. Its hard not to buy Chinese as everything is made there, even on an "American product".

 

[JDTank]

It seems to me that any new diesel engine that is tier 4 compliant is going to burn more fuel. In the "Good old days" when diesels were engineered to run efficiently and reliably, fuel economy wasn't a big concern. They want these engines to drink down the fuel and get lousy economy, they engineer them that way under the guise of "cleaner burning".
I doubt that a few hundred pounds would make a significant increase on fuel consumption as any tractor is low geared for pulling weight. Now running the engine at high rpm all the time will most certainly have the most in fuel consumption, I would say for average mowing conditions, 3/4 throttle should do fine. Lower the engine rpm the better efficiency an engine can get. To compare these small indirect injected diesels to a larger direct injected diesels, the indirect is less efficient than the direct because the direct injection atomizes the fuel spray finer than the idi. Idi's rely on the higher compression and swirl chamber to mix the courser fuel charge. But essentially it goes back to the whole emissions thing. I have a z665 mower and it too has the china spindles. What a low blow for Deere. But they work just fine. Its hard not to buy Chinese as everything is made there, even on an "American product".

We have to remember though that these small machines are hydro operated. Hydro robs a lot of power.

Also, I don't suggest running your machine under at least 85% throttle at any time. The charge pump is designed specifically to operate at full engine speed. When the engine speed is decreased, the load is spread unevenly against the pistons inside the pump. This generates a LOT of heat, and is generally hard on the hydro system. This is the downside to hydrostatic transmissions, they are designed to operate at full throttle regardless of work load.

 

[KennedyDiesel]

Well, I can say this much, I have never, not once, heard of a 7-Iron deck with a failure in any aspect.

Give that machine a few hundred hours, once it breaks in I think you will see a fuel economy improvement. I still believe these X7's are the best garden tractors out there, anywhere. Everything has it's pros and cons. I wouldn't give mine up for anything.

A few hundred hours to break in???

We have to remember though that these small machines are hydro operated. Hydro robs a lot of power.

Also, I don't suggest running your machine under at least 85% throttle at any time. The charge pump is designed specifically to operate at full engine speed. When the engine speed is decreased, the load is spread unevenly against the pistons inside the pump. This generates a LOT of heat, and is generally hard on the hydro system. This is the downside to hydrostatic transmissions, they are designed to operate at full throttle regardless of work load.

85% throttle minimum?


I'd be curious to know where you came up with these figures?

 

[eagle107]

Guys,

Just an update. I had my mom cut the lawn at half throttle yesterday both the front and back parts of the lawn (she cuts slow anyways). The fuel gauge showed that she used less than a quarter of a tank, she had no issues steering the tractor or with the transmission and the cut quality did not suffer at all; the 7 Iron deck tore right through the thick grass even at half throttle and the engine never bogged down. Now that is how a diesel should work; just sip that fuel! I think we found the happy medium for running our X748 and fuel usage; 1/2 throttle cutting normal thick grass, 3/4 throttle cutting higher/longer thick grass and full throttle cutting very high/insanely high thick grass. Thanks for all the comments and help.

 

[JDTank]

A few hundred hours to break in???



85% throttle minimum?


I'd be curious to know where you came up with these figures?

Hydrostatic transmissions are designed to run at high RPM for maximum efficiency, and serviceable life. Cutting grass at half RPM may seem like a good idea, but your working that hydro pump hard. Hydro pumps last longer running at rated input RPM's, not a figure in your head you decided you like better.

These are diesels, not gas engines. In these small Yanmars, 200 hours is actually considered a short time to break them in. The FI gas X700's would break in much quicker, being a gas engine.

Why would you want to cut at half throttle? Your deck speed is cut in half, which limits your discharge distance, and affects your airflow. Since your blades will be spinning at half the RPM they should be, you will not get near as much lift. This also cuts your airspeed under the deck way down, and in turn, discharge distance falls on it's face.

 

[BleedingOrange]

JDTank, I hear exactly what you are saying. I have a 455 lawn tractor, and I run it full engine speed while cutting my grass. I,ve got a neighbor across from me, that thinks it,s better to idle his John Deere tractor and crawl along at the slowest speed possible. I can almost see the grass growing up behind him as he mows along at a snails pace. I,m expecting to hear his machine blow up every time he heads out to cut the grass.Painful to hear and watch him move so sloooooow. He,s 73 years old. I asked him why he idles his machine while cutting and going so slow and he says that,s what an old farmer told him to do, so that,s the way he does it. I just scratch my head and wait for it to blow.

 

[eagle107]

Hydrostatic transmissions are designed to run at high RPM for maximum efficiency, and serviceable life. Cutting grass at half RPM may seem like a good idea, but your working that hydro pump hard. Hydro pumps last longer running at rated input RPM's, not a figure in your head you decided you like better.

These are diesels, not gas engines. In these small Yanmars, 200 hours is actually considered a short time to break them in. The FI gas X700's would break in much quicker, being a gas engine.

Why would you want to cut at half throttle? Your deck speed is cut in half, which limits your discharge distance, and affects your airflow. Since your blades will be spinning at half the RPM they should be, you will not get near as much lift. This also cuts your airspeed under the deck way down, and in turn, discharge distance falls on it's face.

That does not seem to be a problem with the 7 Iron deck and it seems to cut fine at that throttle speed. My mom cuts the lawn slow with the tractor anyways so it does not seem to be an issue. For her to run the tractor any faster is just a waste of fuel. As for the hydro pump, we will have to wait and see what happens over time.

 

[bubbacuse77]

I know I have noticed a difference in lift when cutting at lower throttle settings. I can understand needing the higher throttle settings when using the machine for PTO things like snow blowing or other high power uses. However my X749 will cut high grass and go up a 45 degree grade without even loosing rpm at half throttle. Maybe they should start putting a two speed transmission on the decks to get higher tip speed at lower throttle settings when you have an over powered machine.