Kubota GR2120 losing power when hot

[pumasong]

Hi there,

Looking for some ideas really as I'm scratching my head a bit with this problem. The back story is the GR has been fine for since I bought it in 2019, but has developed a problem in the last few months. When mowing our garden (about 1 acre, regular lawn) it's fine for about 20 minutes, but then starts to lose power, so much so that if I keep the mower engaged it will stall. It will restart, and will just about run without the mower engaged, but it runs really rough, misfiring etc. I tend to stop at this point and come back later.

Things I've done to try and resolve:

- Replaced air filter element
- Replaced complete fuel filter (not just the element)
- Checked all fluid levels (coolant/engine oil)

When it's not misbehaving it runs sweet, no smoke other than a little puff on startup, and nothing else to note even when mowing at full power. It's a 2011 model I think but only has approx 380 hours on it.

Any ideas welcomed, I'm quite happy to do work myself but struggling to think where to look next!

Thanks

George

 

[zoltanthegypsy]

I wish these things had a full set of instruments. If it's "simply" heat, one thing to check is the fan belt. They wear "skinny" and slip. The fan spins and appears to be working but it's going too slow to move enough air.

Not saying that's the issue, just something to check. Been there.

Z.

 

[JWR]

My Kubotas are all the B or BX types which have very different mechanical configurations BUT ... a few comments anyway:
1) You probably have a screen or some kind of protection from grass and crud to your radiator. Pull that screen up and out and keep it free of debris which can be a main factor in overheating.
2) Is the radiator boiling or overflowing? Without gages that is the hard way but does tell you when it is overheating !!
3) It is a real no-no to run the thing overheated because you stand a change of engine damage like warping the head, ruining the rings, etc.
4) The deck itself could be binding or clogging. Make sure it is thoroughly cleared/cleaned out. That won't make the engine run rough but might be excessive load causing it to overheat, etc.
5) Hmmm... there are manyu posts and manyh stories regarding fuel starvation. Your's may be one of those. As fuel is used it must be replaced in your vented tank by air. If it is NOT replaced by air a vacuum forms in the tank fighting fuel flow. Not sure on yours if the tank is vented OR if the just the fuel cap is vented. Either way -- unscrew the fuel cap and try running it through your normal routine and see if the problem persists. [Can probably just loosen the cap where it barely stays on while you are running OR just remove it...] If the problem goes away then figure out if the vent (or the vent in the cap if it is made that way) is clogged.

So my advice is figure out first if it is overheating. If so fix that of course. If not overheating check for fuel tank vacuum. If none of those ... it is more of a puzzle. Not enough hours on it to think of other complex issues ... unless it has been run WAY overheated for long periods and done engine damage. Even then it would not add up to what your describe.

See what you can find and let us know.

 

[pumasong]

Thanks guys really appreciate the input. Overheating sounds possible, it does always happen after running for some time. The fan is definitely spinning and I've seen no sign of the coolant boiling, so there's that. I did consider the "fuel tank vacuum" scenario previously and loosened the filler cap but that didn't seem to help.

I have an infrared gun-type thermometer, I wonder whether I could use that to tell whether it's overheating? I'll check the belt as that sounds an easy place to start.

 

[JWR]

Thanks guys really appreciate the input. Overheating sounds possible, it does always happen after running for some time. The fan is definitely spinning and I've seen no sign of the coolant boiling, so there's that. I did consider the "fuel tank vacuum" scenario previously and loosened the filler cap but that didn't seem to help.

I have an infrared gun-type thermometer, I wonder whether I could use that to tell whether it's overheating? I'll check the belt as that sounds an easy place to start.

Yep. You can use the temp gun to check temperature. I would try the radiator inlet area from the engine which ought to read around 180 deg I would think when the engine is fully warmed up and been running a while . The aluminum neck to the thermostat is a good spot too. I do not know what temp the head of the engine runs when up to full operating status but that is where most temperature gages would go if you had one. At least you could get a reading there and call it a reference point.

The belt should be very snug / tight to the feel with the finger tips. That is pretty unlikely to be causing problems. Can't hurt to check.

There have been a bunch of reports on various model tractors of debris in the fuel tank that floats around and eventually occludes the fuel exit port from the tank. These spots are typically impossible to see (and the fuel tanks are encumbered by awful amounts of sheet metal and crap to get them loose...) so it may be hard to get to or find out. I have heard small plastic bottle caps, leaves, plastic lid seals and all sorts of things getting sucked to the fuel outlet and then restricting fuel flow. This crud rarely makes a complete seal thus the engine still runs but half starved for fuel. Loosening the fuel line and blowing through it in reverse up through the tank would give you good full running at least for a while if that is the issue. At least then you would know if it is worth pulling the tank and doing a major cleanout. Some people have rigged a jug and line to supply fuel instead of from the fuel tank to test for this disease.

So more things to check.

 

[dstig1]

I would agree that it could be a heat issue. You need to really clean out the rad and all screens. Start with air, but then you will need to get a hose on it to fully clean out crud. There are fin cleaners that are made for heat exchangers but they are often acidic and slightly etch the metal, plus you need to be careful getting it on everything around the rad leading to corrosion. Don't use a pressure washer as it will bend over all the fins and destroy it.

The other issue that pops up here a lot is debris in the fuel tank that does not cause a problem until enough fuel has been drawn that it starts to plug up the outlet and leads to starvation. When you shut down, the flow stops, it floats back out a bit but will repeat the same sequence next time. I think the only way to deal with this is to pull the tank and clean it out good. But what a mess to do.

 

[pumasong]

So I had a chance to do some more testing at the weekend. My observations:

- The problem isn't related to overheating - I ran the mower as usual making regular temperature readings at the point where the water pump meets the block, but also on the block itself. Even under load the temp didn't go above 175F

- The mower deck moves freely, I can easily turn the blades by hand. I don't believe the problem is to do with abnormal load from the deck.

- The issue starts the same length of time into work - about 20-30 mins.

- It also doesn't seem to be a tank/vacuum problem - ran the mower with the cap removed and it still did it.

Having said all this, it feels to me very much like fuel starvation - there's no additional smoke, and when it's happening, if I disengage the mower deck, the problem persists for a bit. Since I've changed the fuel filter, and much as I hate to say it, feels like the logical next step is to drain and pull the tank to see if I can get any muck out of there? Maybe blast with an air line?

 

[pumasong]

* bump *

anyone have any further thoughts? really trying to find a reason not to have to take the tank out and drain it

 

[thclimer]

If I'm looking at the correct Kubota, it looks like your fuel filter is translucent. When this issue occurs are you able to see the fuel level in the filter? If that level is decreasing from when you started it would seem like there is a blockage upstream.

Upon further review it looks like you have 2 fuel filters (item #100), one prior to the pump (#130) and the same one after the pump. Have you replaced both of them?

 

[loggin]

* bump *

anyone have any further thoughts? really trying to find a reason not to have to take the tank out and drain it

You could try siphoning some fuel from the bottom of the tank, moving the hose around at the bottom, into a clean container and see what comes out..? I would use a 1/2 inch hose so the opening and flow are great enough to suck out the debris.