Kubota engine cooling problems

[BMXER10]

I cranked it up yesterday and drove it all over the yard without the cap on. The radiator was bubbling a little bit and flowing, but not overflowing at all. I think the bubbles were forming from me hitting bumps.

Weird thing is i could not get it to heat up even close to redline. I drove it all over with the blades spinning. Not sure whats up with that. Might be because it wasnt hot and the grass wasnt tall enough to put much of a load on it.

I installed the smaller battery after this and im going to cut the grass on saturday and see how it does. It should be hotter on saturday so I will get a true test.

 

[milkman]

The battery pictured is WAY too big and too close to the radiator, no way for enough air to get through there, I see you got a smaller battery, hope you made sure the radiator fins are clean when you had the battery out, that and the new radiator cap will probably fix it unless it has been run hot too many times and blown the head gasket, I doube that's happened, they are pretty tough little engines. Let us know when you find the fix, I had a G5200 and it was an early '84 so I would bet yours is at least 20 years old, at $600 you got an excellent buy.

 

[DiezNutz]

One other thought.. that overflow hose under the rad cap - where does it go, and is it clogged?

 

[BMXER10]

One other thought.. that overflow hose under the rad cap - where does it go, and is it clogged?

I did use compressed air to blow out the fins on the radiator. i was able to examine all of them up close and they are pretty dang clean, just some dust came out. Its getting a radiator flush this weekend before I mow too.

I didnt check the overflow tube for clogs yet. It hangs down about halfway and drips down to the mower deck.

 

[BMXER10]

The battery pictured is WAY too big and too close to the radiator, no way for enough air to get through there, I see you got a smaller battery, hope you made sure the radiator fins are clean when you had the battery out, that and the new radiator cap will probably fix it unless it has been run hot too many times and blown the head gasket, I doube that's happened, they are pretty tough little engines. Let us know when you find the fix, I had a G5200 and it was an early '84 so I would bet yours is at least 20 years old, at $600 you got an excellent buy.

The new battery sits about another 1" further back and an 1 1/2" narrower. I pushed it all the way back and strapped it down good. Im going to post some more pics tommorrow of everything.

 

[milkman]

I didnt check the overflow tube for clogs yet. It hangs down about halfway and drips down to the mower deck.

The overflow tube on mine hung down almost to the bottom of the radiator and there was a plastic piece on the end of it that whistled when the the tractor got hot and the pressure went past the radiator cap and out the overflow tube, never had mine overheated, but blew on the other end of the tube one time and it was a whistle to let you know when it was hot.

 

[wrenchturner]

A lot of people have made good suggestions and I would like to add just a couple. Two more ways to test for a leaking combustion into the cooling system. Take off the coolant pump drive belt then remove the upper radiator hose from the radiator. Tilt the hose upwards then fill with water to the top. Start the engine then look for bubbles. On V type engines you can isolate the leaking head by removing the sparkplugs or injectors then remove the rocker arms so the valves are closed. Next, remove the schrader valve from the compression gauge hose then apply shop air to the cylinder. This way you can determine which head or cylinder is leaking by looking for the bubbles in the hose.

A friend of mine had a Kubota mower and had taken it to the shop and done all sorts of things. Finally by chance he noticed there was too much oil in the crankcase. He put the correct amount in and wa la, no more overheating.

 

[copperhead1967]

One other thing about the coolant mix ratio under 50/50 is designed to keep your metal parts from corroding. However the coolant itself may be old and worn out or of mixed types (Green and orange). I had a truck at work have all kinds of issues because one of the drivers mixed types of antifreeze. After a complete flush and new fluid, all was well. One other observation is you mentioned the thing never overheated when you drove around with the cap off. Bad or incorrect cap???

 

[SkunkWerX]

BMXer,

Let's back-up a moment, as you said you drove it around, with baldes spinning, and you couldn't get it to overheat.

From the last time it DID overheat, what have you done?

Sometimes when we start fiddling with things, we fix the problem, but don't realize that we did.

I suggest getting some paper and a writing stick.
Make two columns, first column is for any Action you take, like changing the battery. Second column, next to it, is for your observations, did it overheat?

Another thing is to note the ambient temperature outside each time you test it. if it overheats when it's 90F degrees, but not when its 75F degrees, that might point toward airflow issues. So, just be mindful of air temp changes, and any changes you make that may affect your problem.

I agree with Volfandt's and others posts about making sure you check for water pump and thermostat operation. Sorry that I mentioned the compression check, my mind was racing ahead as I thought about an engine that had been continually over heating, but, as eveyone has posted, there are plenty of simpler ways to check for a bad head gasket. You don't want to pull the injectors if you don't need to. Most importantly, we don't want to compound or create other problems along the way.

Sounds like you have changed to the smaller battery, or are ready to, so, just make that note, and do another OverHeat test, to see if you affected the machine.

If it doesn't overheat with the smaller battery, you may well have found your problem.....but, I'd put that Big Battery back, to prove 100% that was certainly the problem.

So, back to the question, when you drove it around and it DID NOT overheat, what was different? Had you moved the battery? Changed coolant levels, blown out radiator...etc etc etc????

Keep us posted, I think you are going to find it this weekend!

 

[SkunkWerX]

One other observation is you mentioned the thing never overheated when you drove around with the cap off. Bad or incorrect cap???

Here is a classic example of being able to prove the trouble!

If it did NOT overheat with the cap off, then place the cap back on, and see what happens? If it overheats, could be the cap...or a related coolant problem.

 

[DiezNutz]

Under *normal* circumstances it would be more likely to overheat with the cap off/leaky cap. The cap keeps the system under pressure, thereby raising the boiling point of the coolant. The lower the boiling point of the coolant (bad or no cap), the more likely it is to...well...boil... instead of cooling the engine.

So I'm a little baffled at why it didn't overheat with the cap off, if the cap is the problem. I think as a number of us have already suggested, there are multiple factors at play here... for instance we still don't know the effect of the right-sized battery.
SkunkWerx's suggestion of making incremental and systematic changes and observing the results is the right way to proceed.

 

[BMXER10]

Under *normal* circumstances it would be more likely to overheat with the cap off/leaky cap. The cap keeps the system under pressure, thereby raising the boiling point of the coolant. The lower the boiling point of the coolant (bad or no cap), the more likely it is to...well...boil... instead of cooling the engine.

So I'm a little baffled at why it didn't overheat with the cap off, if the cap is the problem. I think as a number of us have already suggested, there are multiple factors at play here... for instance we still don't know the effect of the right-sized battery.
SkunkWerx's suggestion of making incremental and systematic changes and observing the results is the right way to proceed.

I have come to the conclusion that its a woman. Thats why its unpredictable. I cranked it up, let it sit for 10 minutes at full throttle. It didnt heat up very much at all. So I hopped on it, turned the deck on and drove around the yard for another 15 minutes, still stayed at a low temp.

The grass is going to be at normal height on saturday so im going to cut it, wish me luck.

 

[DiezNutz]

I have come to the conclusion that its a woman.

Hmm... that would cover all the angles in that old expression about having trouble with anything with tires, or other things. Good luck.

 

[milkman]

I have come to the conclusion that its a woman. Thats why its unpredictable.

When you get tired of fooling with her, I'll give you what you paid for her plus what you you paid for parts and come load her up and get her out of your hair. At least she heats up quick.

 

[BMXER10]

Well it was really freaking hot on Saturday with lots of humidity. I set the cutting height pretty low so the tractor got a good workout. It took a long time to heat up this time. You can see the before and after picture. Its definitely running cooler! I think its still running a tad hot, but Im honestly not sure where it should be running at since its always run hot.

BEFORE:

AFTER:

 

[DiezNutz]

That's still a bit too hot (assuming your sender & gauge work properly). Did you notice the coolant boiling as before?

 

[BMXER10]

That's still a bit too hot (assuming your sender & gauge work properly). Did you notice the coolant boiling as before?

It couldnt hear the boiling sound that I was getting before. The overflow tube never let any fluid out this time either.

Im pretty sure this gauge is accurate. It would never let fluid overflow until right when the gauge hit that red line. Any way to test it???

 

[Bronc]

Pulling this out of the archive to see if you ever found what was causing your overheat condition.