How to best start JD 4720 in cold weather

[mmurphydds]

I had a 2005 JD 4320 that had a glow plug preheater for cold weather (or any weather) starting...push in the key switch, indicator light on dash lights up, count to 20, start-er-up. I get that, no problem or confusion. Now I have a 2011 JD 4720, theoretically the same machine with higher turbo-boost. But they went and did something different with the starting protocol, and the manual is really no help in terms of explaining it. They call this newer system an "air-box preheater".

So here's the question: How does this new system work or differ form what I had before?? The new system has a scrolling text in the dash display that says "Wait to Start" when the key switch is pushed in. But when the weather is cold, it seems that the "Wait to Start" text never goes away, just keeps scrolling. Am I just not waiting long enough? And what exactly is happening while I'm waiting...I assume a coil somewhere is heating up intake air?? How is this system better than the tried and true method diesel engines have been using since just about forever??

The engine starts fine, sometimes takes longer to crank than others, I can't tell if the new system is working or not...not like the older model's glow plug heater that let the engine pop right off when you started it up. I don't want to gum up the works or damage anything by mistreating it.

I feel stupid with all the electronically controlled stuff that is not well documented...what ever happened to a choke cable/lever...or a well written manual to educate the users. So, I'd be grateful for user tips and some education from some of you guys that are a lot smarter than I am!!

 

[Wooddust]

Mine started last winter sitting outside in zero degree weather. I too had the same insecurity but its a "non starter" issue with mine

 

[mmurphydds]

Yeah, we had a lot of -20F weather this winter and I never failed to start...I just want to know how it all works, what's the difference from the old system and how to operate the new system the way it is intended to be used...

 

[doxford jim]

I don't have a JD 4720 tractor but I do have a Cummins engine in my Dodge truck. The air heater, if the same as the Cummins engine, has a grid element inside the intake manifold. When the switch is turned on, electric current is sent to the grid which glows like an electric fire element. This in turn heats the air inside the manifold. When you go to start, the warm air is then drawn into the engine cylinders, which when compressed by the moving piston, heats up further and allows the engine to fire.
These are pretty foolproof and make for easier maintenance. It seems the heating elements last longer than the glow plugs.
Your tractor might be different, but from your description I would say it is a similar set up to what I have described above.

 

[Dave M7040]

I am making an educated guess with my comments.
It is possible your newer tractor has a "Thermostart."
A Thermostart is a very efficient glow plug used in most of the Yanmar tractors and a number of British originated tractors. Instead of relying on just a heating coil like other glow plugs, this unit also drips a small amount of diesel fuel onto the red hot coil. This produces thick smoke, lots of heat, and occasionally small flames. All of these things help the engine to start in the coldest weather. The thermostart is trying to feed the engine hot air as it cranks over.
The older one may have had glow plugs which heat the air inside each cylinder to aid starting.
Did your old engine have a glow plug for each cylinder or just one in the intake manifold?
Dave M7040

 

[mmurphydds]

I am making an educated guess with my comments.
It is possible your newer tractor has a "Thermostart."
A Thermostart is a very efficient glow plug used in most of the Yanmar tractors and a number of British originated tractors. Instead of relying on just a heating coil like other glow plugs, this unit also drips a small amount of diesel fuel onto the red hot coil. This produces thick smoke, lots of heat, and occasionally small flames. All of these things help the engine to start in the coldest weather. The thermostart is trying to feed the engine hot air as it cranks over.
The older one may have had glow plugs which heat the air inside each cylinder to aid starting.
Did your old engine have a glow plug for each cylinder or just one in the intake manifold?
Dave M7040

I have no flippin' idea, Dave, but the old one worked great and I never even thought about it until this winter when I realized the new one was different and I didn't know what I was doing.

 

[mmurphydds]

I don't have a JD 4720 tractor but I do have a Cummins engine in my Dodge truck. The air heater, if the same as the Cummins engine, has a grid element inside the intake manifold. When the switch is turned on, electric current is sent to the grid which glows like an electric fire element. This in turn heats the air inside the manifold. When you go to start, the warm air is then drawn into the engine cylinders, which when compressed by the moving piston, heats up further and allows the engine to fire.
These are pretty foolproof and make for easier maintenance. It seems the heating elements last longer than the glow plugs.
Your tractor might be different, but from your description I would say it is a similar set up to what I have described above.

Thanks, Jim makes good sense. If I don't get a reply from someone who knows for sure, I guess I'll have to do the walk of shame and go ask the dealer and show them what a Rube I am.

 

[Dave M7040]

Start by looking for a heavy gauge wire going to the air box/air filter housing. If you find one, next look for a small fuel line. If you have both you have a thermostart.
Dave 7041

 

[arlen4720]

The new 4720's have 4 glow plugs just like the old ones did. You probably know that it is the same John Deere 2.4 L Powertech block. The most significant change is that the fuel injection system is completely different. The new ones have 4 unitary injector pumps; 1 per cylinder, and the engine is electronically controlled AND electronically governed. Like you said, the turbo boost is higher in the new ones also. The old ones had unitary pumps also, but the new ones are simpler. You can take a look on JD parts and look at the V-3, V-8, and V-11 engines. You will see how simple the fuel system is on the V-11's

The glow plugs are activated automatically for a variable length of time depending on the fuel temperature and the engine coolant temperature. You get the "wait to start" message when they are heating. If it's cold out, you may see the message for 30 seconds or so. Then when the engine starts, the computer can tell if the RPM is unstable and will energize the glow plugs until things smooth out.
You can activate the glow plugs manually too by pressing the key in, but you will get the same "wait to start" message. The message will display as long as you have the key pressed in.
When it's cold out, I like to let the computer do it's thing, then I hold the key in for another few seconds, and I hold the glow plugs in WHILE I crank the engine.
I have been completely amazed at how well the 4720 starts in cold temperatures, and how well the electronically controlled engine runs during warm up. Very little smoke, and very stable RPMs.

Just curious what made you think that the engine had an intake pre-heater?

I'm attaching a page from the service manual that explains the operation a little better than I did. I also attached a couple of pages from JD parts of the fuel system of a 4120 and a newer 4720. The old 4720 was almost the same as a 4120 or a 4320. The 4520 and 4720's are pretty much the same. For good measure, I attached a parts breakdown of the glow plug system for the V11 (post 2009) engine.

 

[mmurphydds]

Just curious what made you think that the engine had an intake pre-heater?

The manual mentions an engine air heater system (page 27 of the manual)...I guess I got that wrong, huh??