"Engine load gauge"

[MV Moira]

The John Deere engines on my new-to-me trawler have gauges labeled "Engine Load" or similar, in percent. What does this mean? Specifically, what sensor(s) contribute to this reading? And why should I care?

 

[rslifkin]

In most cases I know of, engine load is a relative indication of power output. IIRC it's normally current power as a percentage of maximum power available at that RPM (not max power at rated RPM).

 

[SteveK]

Have not seen one of these but sure resembles the car vacuum gauge to save fuel.

 

[O C Diver]

The John Deere engines on my new-to-me trawler have gauges labeled "Engine Load" or similar, in percent. What does this mean? Specifically, what sensor(s) contribute to this reading? And why should I care?

Ok, so your engine has a computer (ECU). The ECU measures RPM and controls fuel injection. The gauge displays the load based on the current RPM. It does this by knowing the amount of fuel being injected (consumed) by the engine. So if the engine is able to produce 90 HP (at that RPM), but is currently only producing 60 HP, the gauge will display approximately 66% load.

Depending on the M value of your engine, the engine ECU can slow your engine down when exceeding percentage of load. For my engine, after 100% load for 5 minutes, it will reduce the RPM to below 80% load. At above 80% load for 30 minutes, it would reduce the RPM below 80% load. Typically my boat was running below 45% load.

Ted

 

[NWboater2]

Good explanation. My 6068 300 is typically high thirties to low forties at cruise of 1700 -1850 ish rpm.

 

[Dockmaster]

Yes, as mentioned this is the load % your engines are producing. Most engines prefer to cruise at 80% load and that's what is typically used when calculating duty cycles. There is usually not a sensor to measure load. It is derived using an algorithm from RPM's, fuel burn and others factors.

 

[MV Moira]

Ok, so your engine has a computer (ECU). The ECU measures RPM and controls fuel injection. The gauge displays the load based on the current RPM. It does this by knowing the amount of fuel being injected (consumed) by the engine. So if the engine is able to produce 90 HP (at that RPM), but is currently only producing 60 HP, the gauge will display approximately 66% load.

Depending on the M value of your engine, the engine ECU can slow your engine down when exceeding percentage of load. For my engine, after 100% load for 5 minutes, it will reduce the RPM to below 80% load. At above 80% load for 30 minutes, it would reduce the RPM below 80% load. Typically my boat was running below 45% load.

Ted

Wow! Ted, I think I understood most of that! So, if I get it: "load" is an expression of fuel usage vs. RPM? Higher "load" means that for a given RPM, more fuel than usual is being used? Higher "load" means that to attain a given RPM, more fuel has to be injected? And 100% would mean that throwing more fuel at it wouldn't increase the RPMs. If that's correct, I think I get it.

So (1) what's an "M value?" And where do I find it? There are fuel-consumption graphs for these engines from Deere, which call out an "M2" for this type--is this what you're talking about? And (2) that would imply that theoretically the engines could report net (in minus out) GPH if they wanted to. And (3) since there's a published GPH for these engines at various RPMs, then given the "load" number, could I back-calculate an actual GPH for a given moment? So if they're at 70% load, then looking at the graph I could figure that I'm using 70% of the expected GPH for that RPM? Or is that asking too much?

This site is such a resource!

 

[Jeff F]

The instrumentation you have also will display real time GPH and other interesting stuff. It's worth exploring the display options.

 

[chanprr]

Wow! Ted, I think I understood most of that! So, if I get it: "load" is an expression of fuel usage vs. RPM? Higher "load" means that for a given RPM, more fuel than usual is being used? Higher "load" means that to attain a given RPM, more fuel has to be injected? And 100% would mean that throwing more fuel at it wouldn't increase the RPMs. If that's correct, I think I get it.

So (1) what's an "M value?" And where do I find it? There are fuel-consumption graphs for these engines from Deere, which call out an "M2" for this type--is this what you're talking about? And (2) that would imply that theoretically the engines could report net (in minus out) GPH if they wanted to. And (3) since there's a published GPH for these engines at various RPMs, then given the "load" number, could I back-calculate an actual GPH for a given moment? So if they're at 70% load, then looking at the graph I could figure that I'm using 70% of the expected GPH for that RPM? Or is that asking too much?

This site is such a resource!

The tech sheet for my JD6090SFM85.

 

[O C Diver]

Wow! Ted, I think I understood most of that! So, if I get it: "load" is an expression of fuel usage vs. RPM? Higher "load" means that for a given RPM, more fuel than usual is being used? Higher "load" means that to attain a given RPM, more fuel has to be injected? And 100% would mean that throwing more fuel at it wouldn't increase the RPMs. If that's correct, I think I get it.

Let's say you normally cruise at 1,500 RPM and 45% load. If today you are towing a 16' jon boat, you might see 1,500 RPM but the load is now 55%. So the jon boat in tow is making the engine use more fuel and likely slowing the boat down some. A similar situation can occur with a dirty boat bottom or a fouled propeller.

On my engine there is a second alternator (12 VDC 220 amps). When I would leave the anchorage in the morning, the external regulator switched to bulk phase (220 amps full output). So while the boat speed didn't slow down, fuel consumption went up .3 GPH and load went up 10%.

So (1) what's an "M value?" And where do I find it? There are fuel-consumption graphs for these engines from Deere, which call out an "M2" for this type--is this what you're talking about?

M value is the HP rating and duty cycle both at high output and per year. As an example, my 4045TFM75 engine had 3 M values.

M1 is 104 HP @ 2,400 RPM continuous duty

M2 is 121 HP @ 2,500 RPM with reduced time at full output.

M3 is 134 HP @ 2,600 RPM with further reduced time at full output.

The only thing required to change the M value is to change the ECU.

And (2) that would imply that theoretically the engines could report net (in minus out) GPH if they wanted to.

Your ECU calculates fuel consumption as it's telling the injector pump exactly how much to pulse. Supposedly the fuel consumption is plus or minus .1 GPH. Go to your owner's manual to select fuel consumption as one of the 4 displays on your video screen.

And (3) since there's a published GPH for these engines at various RPMs, then given the "load" number, could I back-calculate an actual GPH for a given moment? So if they're at 70% load, then looking at the graph I could figure that I'm using 70% of the expected GPH for that RPM? Or is that asking too much?

This site is such a resource!

See real time fuel consumption display in your owner's manual. It was always displayed on my boat in the lower right corner. Between GPH display and the load gauge, you get several parameters that help you diagnose issues (like a dirty boat bottom) before they become problems.

Ted

 

[Coastal Cruiser]

Here is a thought for those who have the ability to get a load reading on your engine(s). I had a 4045 JD engine. Turbocharged and aftercooled. 200 hp.
At wide open throttle (limited electronically to 2400rpm) the load was in the low 90 percent range. Depending on sea state, 91-93 % load. To me this indicated an underpropped situation. Engine was running wide open and not producing all of the power it was capable of.
Removed the prop and had it repitched by Blair in Stuart. The very experienced people there nailed it. After the repitch (essentially changing the shape of the prop so it took a bigger "bite" on each revolution) the load at WOT was at or very near 100%. Perfecto.

Re the various "M" ratings on John Deere engines ( M1 through M4), the explanation of what they mean is in the JD literature.

 

[psneeld]

On some boats bacj in the early 2000s, the engine load was some sort of reading from the transmissions. I can only guess is they read some form of oil pressure there and it somehow was calibrated on power delivered to it.

Seems this is how the new computerized diesels measure it... from Google...
"dividing the actual fuel consumption by the maximum rated fuel consumption at full power over a specific period"

 

[MV Moira]

Thank you, one and all!

 

[rgano]

Ok, so your engine has a computer (ECU). The ECU measures RPM and controls fuel injection. The gauge displays the load based on the current RPM. It does this by knowing the amount of fuel being injected (consumed) by the engine. So if the engine is able to produce 90 HP (at that RPM), but is currently only producing 60 HP, the gauge will display approximately 66% load.

Depending on the M value of your engine, the engine ECU can slow your engine down when exceeding percentage of load. For my engine, after 100% load for 5 minutes, it will reduce the RPM to below 80% load. At above 80% load for 30 minutes, it would reduce the RPM below 80% load. Typically my boat was running below 45% load.

Ted

Do you suppose that a "load" gauge might also reflect a boost measurement?

 

[Jeff F]

Do you suppose that a "load" gauge might also reflect a boost measurement?

Interesting question. I'm pretty sure boost isn't reported directly, and my vague recollection is that it's not used or measured by the ECM.

The %load is a really simple measure - what's the current fuel flow vs the programmed max for that rpm. But to Ted's earlier point, it's a great all-round health check. If you didn't have sufficient boost the %load would spike.

 

[O C Diver]

Interesting question. I'm pretty sure boost isn't reported directly, and my vague recollection is that it's not used or measured by the ECM.

The %load is a really simple measure - what's the current fuel flow vs the programmed max for that rpm. But to Ted's earlier point, it's a great all-round health check. If you didn't have sufficient boost the %load would spike.

Do you suppose that a "load" gauge might also reflect a boost measurement?

No, the ECM has no input for turbo boost. It simply uses fuel consumption and RPM to compare it to the maximum fuel values for that RPM.

As Jeff indicated, you could see a loss of turbo boost, as fuel consumption would increase (% of load) (GPH on the video gauge) and probably modest black smoke exhaust from lower air volume (oxygen) in combustion.

Ted