MX4800 Check Engine light

troverman

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MX6000 HSTC; 2020 Kubota Z421KW-54 zero turn mower
Jun 9, 2015
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I was mowing a field last week, pretty dry and tall hayfield. After a couple of hours I noticed the temp gauge was creeping up, but I figured I could make a few more passes without the needle moving to the red zone...finish the section I was doing, then clear the radiator screen.

Well, after a few more passes, the gauge had crept up further but was still well out of the red zone. The "EM" check engine light illuminated. I finished my pass and shut the machine down, cleared all the radiators / coolers, then idled the engine at about 1000RPM. The temp gauge dropped back to normal and I recommenced mowing, but the EM light stayed on for another pass or two before finally going off.

Since when do you get a check engine light for an 'almost' overheat? Only thing I could think of was fuel temp is monitored and when the fuel cooler got plugged up the fuel temp became too hot? Maybe I'm overthinking this. I don't even know if such as sensor exists.

Lastly, and this is the third time this has happened, why is the tractor pouring a steady stream of coolant out of the overflow tank well before the gauge gets to the red zone?
 

SidecarFlip

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probably because the gauge is inaccurate. If it's pumping coolant out the overflow from the coolant bottle, it's HOT. Coolant expands when hot and if the bottle is overflowing (which it has to because it has nowhere else to go), my suggestion is you stop and clean your screens and clean out your rad before the gauge starts climbing.

I'm pretty sure the coolant sensor and the gauge are not in agreement but then you ignoring the heat indicator to 'get one more pass' isn't good either.
 

troverman

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probably because the gauge is inaccurate. If it's pumping coolant out the overflow from the coolant bottle, it's HOT. Coolant expands when hot and if the bottle is overflowing (which it has to because it has nowhere else to go), my suggestion is you stop and clean your screens and clean out your rad before the gauge starts climbing.

I'm pretty sure the coolant sensor and the gauge are not in agreement but then you ignoring the heat indicator to 'get one more pass' isn't good either.
Well, the three other Kubota tractors I've owned won't push out a drop of coolant even with the needle just a hair below red. I'm not interested in overheating an engine and warping a head, but there is a range on the gauge for a reason. This MX is different. I'd be surprised if the gauge isn't accurate consider the MX is a 100% electronic tractor, but my previous experience with Kubota told me it was safe to proceed a bit further.
 

North Idaho Wolfman

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Can you read any codes?

Burping out fluid on that new of a tractor means something's not right.

Have you checked fluid level in the radiator when cool?
 

troverman

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MX6000 HSTC; 2020 Kubota Z421KW-54 zero turn mower
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Can you read any codes?

Burping out fluid on that new of a tractor means something's not right.

Have you checked fluid level in the radiator when cool?
I have no way to read codes. Coolant level appears fine, although it's probably lost some now. It makes sense the engine is getting hot with the level of chaff in the radiator screen and coolers; heck the radiator itself is getting some blockage since the screen is ineffective.
 

Russell King

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You may want to put a cheap air conditioner filter in front of the screen to help keep it clean.

I have found one that is blue and has no frame so can be easily cut to size


Sent from my iPad using Tapatalk
 

lugbolt

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Is the fan belt tight? That'll cause heating...fan won't turn fast enough. Pushing coolant out is one of two things usually. Hot, or radiator cap not holding pressure. Does it have any warranty? If it does, have them look at it before the engine has any problems. Those are real expensive to have to work on......
 

troverman

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The increase in temperature seems inline with how plugged the radiator screen is, and that all seems normal - my gripe is with the gauge seemingly not reporting how hot the engine actually is, unless the radiator cap is weak and leaking out early. Otherwise, the main thrust of my post was why did the Check Engine light come on.

Yes, this is a 2018 tractor and still has warranty.
 

sheepfarmer

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I think it would be worth your while to have dealer check sensors and gauges. If I recall from some other posts correctly, it is possible for a tractor to be too hot to regenerate correctly, and this could cause you problems long before you have a cracked head.
 

troverman

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About 30 minutes before I had the overheating problem / Check Engine light, the tractor performed a regen, took about 25 minutes, that part seemed normal. I've never had an issue with regens on this tractor.

Maybe I'll take it in, but most dealer's service departments aren't that great. The only advantage they have is they can pull codes and look at live data.
 

wgator

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Otherwise, the main thrust of my post was why did the Check Engine light come on.
According to my operators manual for L4701, that is a Kubota universal symbol for "emission control" and my manual says when that symbol lights: Emission indicator
If this indicator lights up, take the steps to lower the water temperature. This helps keep the emission clean.
So it seems the problem was as you stated, the high water temp caused the emission indicator to come on.
 

troverman

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MX6000 HSTC; 2020 Kubota Z421KW-54 zero turn mower
Jun 9, 2015
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According to my operators manual for L4701, that is a Kubota universal symbol for "emission control" and my manual says when that symbol lights: Emission indicator
If this indicator lights up, take the steps to lower the water temperature. This helps keep the emission clean.
So it seems the problem was as you stated, the high water temp caused the emission indicator to come on.
That emissions light is basically the Check Engine light. I can't understand how high water temp would increase emissions, unless the engine uses more fuel to try to cool the cylinders.
 

North Idaho Wolfman

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That emissions light is basically the Check Engine light. I can't understand how high water temp would increase emissions, unless the engine uses more fuel to try to cool the cylinders.
An overheating diesel engine burns fuel too quickly, sort of like an old gasoline engine with pre ignition knock. ;)
 

Fordtech86

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The increase in temperature seems inline with how plugged the radiator screen is, and that all seems normal - my gripe is with the gauge seemingly not reporting how hot the engine actually is, unless the radiator cap is weak and leaking out early. Otherwise, the main thrust of my post was why did the Check Engine light come on.

Yes, this is a 2018 tractor and still has warranty.
ECUs are not very smart. They don’t know that the engine is actually overheating and they don’t know that the radiator is plugged and that it’s blowing coolant out. All it knows is that what it’s seeing from the coolant temp sensor is not within the parameters that it wants to see. It can’t determine if it’s a mechanical issue or electrical issue such as a wiring issue or sensor issue. It will turn the light on to tell you it didn’t like what it seen.

Without knowing what the code is though it’s hard to say. I’m just assuming it set an engine over temp code.
 

troverman

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MX6000 HSTC; 2020 Kubota Z421KW-54 zero turn mower
Jun 9, 2015
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An overheating diesel engine burns fuel too quickly, sort of like an old gasoline engine with pre ignition knock. ;)
I doubt this would be the case on a common-rail engine, since we are only talking what, about +40-50F above normal at most? Plus electronic injectors can control not only how much, but at what stage fuel is injected...
 

Bark

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Older post but I just had the exact same issue. Warm day, mowing up hill both ways, temp gauge crawling towards hot than the EM light came on (with the dust I thought it said EN). Anyway, radiator screen was fairly covered with Chaff. After cleaning it the light went out and engine is at normal temp.
My 80 year old Ford 9N never has this issue;).