JD X748 Sucking Fuel Like Candy

[Carl Bert]

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.

JDTank is right. These machines were designed to run the attached implements (mower, blower, tiller etc) at full RPM, read the manual or talk to your dealer. It's your tractor so you can obviously do what you want, but I believe it's going to be an expensive lesson in the long run. Just my opinion. Good luck

 

[JDTank]

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.

I am assuming that is a gas engine, that is a HORRIBLE thing to do.

Gas engines have the fan bolted to the flywheel. So, the amount of cooling the engine gets, is directly related to how many RPM's it is making. I see people bring me pressure washers all the time with the engines burnt up. When I confront them, they inform me that they turned the throttle down to decrease pressure. You NEVER do this! Now the engine is lugging at a low RPM, doing everything it can to stay running, with no cooling. The proper way is to increase the orifice size of your tips. Tips with a larger size will allow more volume, and less pressure. I should note here and now that a lot of people confuse orifice size with the degree of the tip. People walk into my shop all day long and just grab tips by color, "oh, I need a white tip" They have no clue you need the right size hole in the end of that tip to make your machine work correctly. In order to know which size you need, you need to know your machines Gallons Per Minute, and rated PSI.

That guy who is running his lawn mower extremely slow is killing it. The engine is lugging, working hard at a low RPM, and getting virtually no cooling.

 

[JDTank]

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.

I still think something is wrong with your machine. Your model of machine, the X748, has a particularly high load on it's hydro system. It is basically driving every component of your machine, and your running it at half throttle. Do you ever notice on construction sites that a 100,000 pound excavator is running at full RPM, even when making a small, delicate move. It's because that's how hydraulics work, it's all about pressure, and flow. You can't get either right without RPM's.

I cut 2 acres of grass today, half of that I took off 8 inches, big field. I filled my tractor before I started. When I was done, my gauge was just a hair off the full mark. I took off my fuel cap and boom, there's fuel, still pretty high up. This was all done at full RPM. I have exactly 32.4 hours on my machine. Maybe it's because my machine is only a 2WD. Either way, I run a long, long time before I need to even think about heading back for fuel.

Just a suggestion but I would take that puppy in to the dealership and let them go over it.

 

[eagle107]

I still think something is wrong with your machine. Your model of machine, the X748, has a particularly high load on it's hydro system. It is basically driving every component of your machine, and your running it at half throttle. Do you ever notice on construction sites that a 100,000 pound excavator is running at full RPM, even when making a small, delicate move. It's because that's how hydraulics work, it's all about pressure, and flow. You can't get either right without RPM's.

I cut 2 acres of grass today, half of that I took off 8 inches, big field. I filled my tractor before I started. When I was done, my gauge was just a hair off the full mark. I took off my fuel cap and boom, there's fuel, still pretty high up. This was all done at full RPM. I have exactly 32.4 hours on my machine. Maybe it's because my machine is only a 2WD. Either way, I run a long, long time before I need to even think about heading back for fuel.

Just a suggestion but I would take that puppy in to the dealership and let them go over it.

Well comparing a 100,000 pound machine is a lot different than a 1400 pound garden tractor. Just moving a machine that heavy you need RPMs and a lot more flow. The Yanmar engine has a lot of power and torque to move a 1400 pound garden tractor. I bet I put just as much strain on the pump running the tractor at full throttle and full speed as I do running it at half throttle and half speed. I actually hear the tractor strain when I have the tractor is running at full throttle with the pedal to the floor. When I hit heavy grass (4.5 inches of grass - the mower is set to 2.5 inch cut) at full throttle and full speed, the tractor actually starts to bog down. Let up on the pedal and tractor starts running better again, so maybe there is something wrong with it. I can tell you that the Scag tiger cat with a 25hp engine went right through that same grass area at full throttle and full speed without any problem. Now the Scag had a 52 inch deck while the X748 has a 60 inch deck, but the torque on the Yanmar Diesel engine should have enough torque to handle the extra 8 inches of deck. I am starting to think the hydro pump load on tractor is just too much for the engine to keep up with running the tractor at full throttle and full speed, and that is why the engine is sucking diesel fuel like candy and is bogging down.

 

[BleedingOrange]

I am assuming that is a gas engine, that is a HORRIBLE thing to do.

Gas engines have the fan bolted to the flywheel. So, the amount of cooling the engine gets, is directly related to how many RPM's it is making. I see people bring me pressure washers all the time with the engines burnt up. When I confront them, they inform me that they turned the throttle down to decrease pressure. You NEVER do this! Now the engine is lugging at a low RPM, doing everything it can to stay running, with no cooling. The proper way is to increase the orifice size of your tips. Tips with a larger size will allow more volume, and less pressure. I should note here and now that a lot of people confuse orifice size with the degree of the tip. People walk into my shop all day long and just grab tips by color, "oh, I need a white tip" They have no clue you need the right size hole in the end of that tip to make your machine work correctly. In order to know which size you need, you need to know your machines Gallons Per Minute, and rated PSI.

That guy who is running his lawn mower extremely slow is killing it. The engine is lugging, working hard at a low RPM, and getting virtually no cooling.

Yes, you are correct again. It,s a gas. I,ve tried to convince him to rev it up, but can,t. Time will tell, and I,ll probably get to replace his engine. He mows about 5 acres, so I,m sure it will do harm even sooner.

 

[JDTank]

Well comparing a 100,000 pound machine is a lot different than a 1400 pound garden tractor. Just moving a machine that heavy you need RPMs and a lot more flow. The Yanmar engine has a lot of power and torque to move a 1400 pound garden tractor. I bet I put just as much strain on the pump running the tractor at full throttle and full speed as I do running it at half throttle and half speed. I actually hear the tractor strain when I have the tractor is running at full throttle with the pedal to the floor. When I hit heavy grass (4.5 inches of grass - the mower is set to 2.5 inch cut) at full throttle and full speed, the tractor actually starts to bog down. Let up on the pedal and tractor starts running better again, so maybe there is something wrong with it. I can tell you that the Scag tiger cat with a 25hp engine went right through that same grass area at full throttle and full speed without any problem. Now the Scag had a 52 inch deck while the X748 has a 60 inch deck, but the torque on the Yanmar Diesel engine should have enough torque to handle the extra 8 inches of deck. I am starting to think the hydro pump load on tractor is just too much for the engine to keep up with running the tractor at full throttle and full speed, and that is why the engine is sucking diesel fuel like candy and is bogging down.

Wow...does not sound like a X700 series! These things can go through almost anything and not even sneeze.

You have the 0.9L right? I think I remember you saying your machine is a 2012?

My X740 is a 2012, and every 1 - 2 weeks, I cut about 1 acre of grass that surrounds our barn. It grows insanely fast. If I leave it for 2 weeks, I am taking off 14 inches or so. My machine never bogs down. The only time I have ever heard it bog down, is when one of the blades hit a pile of dried up old straw that was compacted. It just dropped a few hundred RPMs and chewed it up like nothing. Since you are cutting at 50% throttle, I am not surprised it is bogging down. It needs full engine power and it isn't getting it. The PTO on these X700 transaxles robs some serious power from the hydro system. Shut off your deck while your moving forward and you will feel the increase in power and responsiveness. If your going to run 50% throttle, only do it when you need to move the machine in the garage, not when using the PTO.

If you have the hydro pedal to the floor, it will work the engine at any RPM. That is a LOT of fluid to move to keep the machine at 9 MPH. Put your foot to the floor at half throttle, and then again at full throttle. You will get a big jump in speed, because now your flow is where it should be.

I am sorry but no, you put more strain on the pump at half throttle than full throttle. These pumps have multiple pistons inside of them, if memory serves, I think it is 6. When fluid enters the pump at a low RPM, it is not spread across all of the pistons. The pistons that do get fluid have to work hard, this creates heat. Also, since your hydro fluid is moving slowly throughout your entire tractor, it is able to absorb more heat, because it is staying in places longer now. This all translates to very high oil and pump temperatures.

My comparison to construction equipment was based on the simple comparison between 2 machines. They both need high RPM's for pressure, and power. While they are 2 very different machines, they share the same basic concept of pressurized fluid running through pumps to move the machine.

You shouldn't need to rely on the torque of your diesel engine to keep you going. Yes, the Yanmar engines definitely have the torque to keep things moving at a lower RPM...IF this was a gear tractor. Since it isn't a gear tractor, the most important factor now becomes RPM.

 

[KennedyDiesel]

When I hit heavy grass (4.5 inches of grass - the mower is set to 2.5 inch cut) at full throttle and full speed, the tractor actually starts to bog down. Let up on the pedal and tractor starts running better again, so maybe there is something wrong with it. I can tell you that the Scag tiger cat with a 25hp engine went right through that same grass area at full throttle and full speed without any problem. Now the Scag had a 52 inch deck while the X748 has a 60 inch deck, but the torque on the Yanmar Diesel engine should have enough torque to handle the extra 8 inches of deck. I am starting to think the hydro pump load on tractor is just too much for the engine to keep up with running the tractor at full throttle and full speed, and that is why the engine is sucking diesel fuel like candy and is bogging down.

So how fast (ground speed) are you trying to cut at? Pedal floored?

 

[eagle107]

Wow...does not sound like a X700 series! These things can go through almost anything and not even sneeze.

You have the 0.9L right? I think I remember you saying your machine is a 2012?

My X740 is a 2012, and every 1 - 2 weeks, I cut about 1 acre of grass that surrounds our barn. It grows insanely fast. If I leave it for 2 weeks, I am taking off 14 inches or so. My machine never bogs down. The only time I have ever heard it bog down, is when one of the blades hit a pile of dried up old straw that was compacted. It just dropped a few hundred RPMs and chewed it up like nothing. Since you are cutting at 50% throttle, I am not surprised it is bogging down. It needs full engine power and it isn't getting it. The PTO on these X700 transaxles robs some serious power from the hydro system. Shut off your deck while your moving forward and you will feel the increase in power and responsiveness. If your going to run 50% throttle, only do it when you need to move the machine in the garage, not when using the PTO.

If you have the hydro pedal to the floor, it will work the engine at any RPM. That is a LOT of fluid to move to keep the machine at 9 MPH. Put your foot to the floor at half throttle, and then again at full throttle. You will get a big jump in speed, because now your flow is where it should be.

I am sorry but no, you put more strain on the pump at half throttle than full throttle. These pumps have multiple pistons inside of them, if memory serves, I think it is 6. When fluid enters the pump at a low RPM, it is not spread across all of the pistons. The pistons that do get fluid have to work hard, this creates heat. Also, since your hydro fluid is moving slowly throughout your entire tractor, it is able to absorb more heat, because it is staying in places longer now. This all translates to very high oil and pump temperatures.

My comparison to construction equipment was based on the simple comparison between 2 machines. They both need high RPM's for pressure, and power. While they are 2 very different machines, they share the same basic concept of pressurized fluid running through pumps to move the machine.

You shouldn't need to rely on the torque of your diesel engine to keep you going. Yes, the Yanmar engines definitely have the torque to keep things moving at a lower RPM...IF this was a gear tractor. Since it isn't a gear tractor, the most important factor now becomes RPM.

Not sure how you came up with me running the tractor at 50% throttle when it bogs down. It looks like you misread my post. Let me point it out again:

"I actually hear the tractor strain when I have the tractor is running at full throttle with the pedal to the floor. When I hit heavy grass (4.5 inches of grass - the mower is set to 2.5 inch cut) at full throttle and full speed, the tractor actually starts to bog down."

It just seems the hydro pump running the both the front and back transmissions is putting too much load on the engine to keep up with running the tractor at full speed (~8.5 MPH) and cutting heavier 4.5 inches thick grass; mostly likely that is why the engine is sucking diesel fuel like candy. The tractor did not bog down running it at 50% throttle because my mom only runs the thing at ~3 MPH. The issue now is to figure out if this how the X748 is suppose to run or is there is actually an issue with it.

As for the other stuff regarding the hydro pump, I do not know if your information is truly factually or just conjecture as I do not work on hydro pumps or engineer them. However, there are so many different types of pumps and hydrostatic transmissions out there that you really need to review the engineering documents to figure out how a specific transmission will react to lower and higher RPMS, how heat is dispersed and etc. May be Tuff Torq or JD has something out there that explains all of this. While this is an apple to orange comparison, my JD 4520 can cut grass in ePTO mode at half throttle/half RPMS without any issue and that is also a hydrostatic transmission.

 

[eagle107]

So how fast (ground speed) are you trying to cut at? Pedal floored?

I run it with the throttle at 100%, the pedal is floored (8 - 8.5 MPH) and cutting grass at typical height (4.5 inches not 8 or more inches), but the grass can be thick. Running both my X748 and my uncle's X748 this way and they both eat fuel. Run the X748 like my mom does at 50% throttle and 3 MPH, the tractor seems to sip the fuel.

 

[ccsial]

I have some dry sandy areas that I mow at about half throttle when it is dry out. I do this to prevent sucking up so much sand. I do this for about 15 minutes.

So in light of the turn this topic took, I looked in my manual and it only mentions running at full throttle with the PTO engaged. I suspect this is to insure there is enough power to run the attachment. I'm pretty sure the transmission does not really care if the PTO is engaged or not.

I called two dealers about this practice and both said it will not cause any damage unless I was climbing steep hills while doing it. I was going to ask this question on the JD web site but it appears they don't want you to do that since it says to call your local dealers for tech support. So I will continue this practice that I have been doing since 2007 and 350 hours.