Kubota R520 cooling problem


Tree House enthusiast
Aug 23, 2008
19 y o machine, has always run perfect, but cooling issues last 6 months. Machine normally ran cool always, regardless of workload or ambient temp. Repalced radiator and thermostat. Runs cool some of the time but still acts up. Hot ambient temp can play a role but the thing that reliably seems to make the engine temp start to rise quickly is driving it on a hill. And it's not the workload of climbing the hill, it just seems to be the angle. I can watch the temp gauge steadily rise if I stay on the hill instead of going back to level ground and it would go right up to redline if I let it.

Full coolant?

Does the fan have a clutch?

Is a wire shorting out in certain positions due to gravity?

How's the water pump? Belt tension?
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  • #3
Coolant pretty full, if I add more it pisses out the overflow. Water pump seems good. Belt tension good. I don’t think it has a clutch as the fan runs full time. Good idea re wire, idk
What happens if you're 180° on the hill? Eg, it overheats facing up, how about facing down?
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  • #6
Definitely facing up, I gotta check out 180 and facing down
How long have you had it; the whole 19 years? I ask, because some vehicles can be very particular about how you fill them with coolant, and can trap air if it isn't filled the way it likes. A friend of mine had a car that had to have the front end raised to fill it, or it would overheat. Maybe look in the manual to see if they specify any special instructions.

Another option would be attitude change affects the waterpump, and it quits/slows pumping. I don't understand how that could happen, but maybe?
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  • #8
Yes I bought it new. I have heard about air bubbles, I'll check the manual.
Yeah, sounds like you've got a bubble somewhere. See if pushing the nose up with the bucket, while sitting still, reproduces the problem.
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  • #10
Would that be different than just being on a hill?
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  • #11
Nothing of note in the manual
Call the dealer service department. They might know about something finicky.

Any coincidence of maintenance and the problem?

Are you checking the overflow or the radiator for the coolant level?
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  • #13
All good queries and suggestions.

Yeah I'm gonna call svc dept. My mechanic thinks the next step is head gasket but i'm not feeling it, yet.

Yes, checking radiator for level, though when I fill it to the top, alot pisses out of the overflow.
I think the hill test will be interesting. If it works going downhill, that would point to air in the system imo. Facing uphill, the air will go to the waterpump, and flow will be reduced.

For filling, I like to do it with the engine running. Fill the radiator til it takes no more, then fill the overflow to the appropriate level. Can't say if it's right or wrong, but that's generally how I do it. If that doesn't work, try the same thing, but with it facing uphill. That'll put the air at the radiator with fewer places to hide. If that doesn't work, :shrugs: I don't think a head gasket is attitude dependent, but I'm not even a poor mechanic.
Head gasket will make dirty mayonnaise looking gunk appear on your oil dipstick and the inside of your oil fill cap. Or oil appear in your coolant. Head gasket is kinda unlikely.

I mentioned pushing the nose up with the bucket because you can replicate grade, without driving the tractor. First I would lift the front wheels as high as I could with aforementioned bucket, turn off the tractor and check the coolant level at the radiator. Once I verify there's little to no room in there, start the tractor and monitor the temps. I make this recommendation so you're not driving around to diagnose and potentially getting your tractor stuck somewhere inconvenient whilst you repair what you hope is the problem lol.

Your milage and experience may vary with your local service center, some are more competent than others, and some are fairly priced. Being a stubborn hillbilly, I tend to work all the way to the end of my talent, and then push a little further.
I would do a compression and leakdown test before doing a head gasket, why is he thinking head gasket? Oil in the coolant or sludge on the oil dipstick? Mayo looking froth on the radiator cap? Bubbles in the overflow tank? I assume they flushed it when you did the radiator? Why did you replace the radiator, same problem? What did the radiator look like inside when they pulled it, full of crap? Is the fan good, or is it missing teeth, how about the shrouds that go around it? Hoses good and not collapsed / soft? Did someone mix coolants or use the wrong one? New and correct psi radiator cap, correct temp thermostat? Thermostat clogged with sealant from the install? Smoke bad (especially white) on startup? Have you overheated it where a head might be warped? Bad or dirty injector? Bad coolant sending unit or wire? Did you tell it you love it, or maybe even try talking dirty to it? :lol:

Might have crap clogging something or a weak water pump, a head gasket is a possibility but i would be damn sure before hand, that's opening a pretty big can of might as wells (while you're that deep you might as well check/swap other parts since it's open, not to mention inspection and machining if needed which may mean pulling the engine...). Does it run ok? If you fill the coolant completely to the full level what happens? I would also pull the water pump and check that before just ripping the head off, that's not something you just wanna go swapping parts on til it's fixed. At least drain the oil and coolant to see how it is (which you'll need to do if you're getting to the water pump or thermostat), use a very clean buckets (different buckets obviously, likely brand new from a hardware store) and reuse it if it's still good, if it's a head gasket you gotta do both anyways and that way you can see if it's contaminated. If it's not and everything else is good i would be tempted to flush it and see what comes out. If it's all clogged up you might be into pulling the head anyways, but then again you might not be, there's a lot of little things that can go wrong too. I'm a huge fan of trying to find the actual problem first rather than just bolting parts on til it stops.
Me too, so i try to do it all myself, even if i can't. I'll break down occasionally on some stuff and pay for help, but mainly I've been able to get it done myself. I'll struggle and struggle and then i learned something new. What one man can do another man can do! It helps that i have some buddies that are mechanic wizards too, and have been at it forever since I'm poor. One of them is a retired engineer who actually wrenches on stuff all the time, he's literally seen it all. I usually don't bother him, but when you're at the end of what you can find he can usually get you straightened out.
I have mostly given up on hiring work done. I even set my toe on front end, not that they couldn't do that right, but for a hundred and something I can do it myself. Kind of fun figuring stuff out.....sometimes!

Can you see flow in the radiator when it is level? You could check for flow on incline, if you can.

I had a water pump on a slant six that I could see nothing wrong with that didn't pump at all. Impeller would not slip or wobble as hard as you tried by hand. New pump-no more problem.

Does the belt that runs the water pump run anything else that could be causing it to slow down? Is the fan hard to make it slip by hand?
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  • #22
I just read all this stuff... the answer to the problem is likely in there somewhere, I 'spect.

Right now I'm too shot to reply much but Imma look into all the stuff thou hast writ.

The reason I asked about coolant changes is because I have seen water pumps with the impellers eaten away from corrosion. They don't leak and look ok from the outside but don't push very much coolant. If this has come on gradually over a long period of time then the water pump is a distinct possibility.

On the other hand, I'm just guessing and could be 100% wrong.
Coolant maintenance is easy to overlook. I have been guilty. My neighbor changed his hydraulic oil in his tractor religiously. I told him how important changing coolant was in a diesel. He didn't buy it. GM v6s had a poor intake gasket that I think was made worse by not changing coolant. Caused me a pia. Live and learn.
Hah! Made me look up the coolant change interval on my Avant loader with a Kubota engine. Kubota says every 2 years and mine is 2 years old. Then I realized I have had my F150 for 4+ years and never changed that, either. So off to Amazon to order coolant for the truck and loader.