B7500 HSD bogging down & overheating

enonhall · Aug 19, 2004

I have read the previous posts on overheating, but I am not sure my symptoms match those exactly.

I have a 1-1/2 year old Kubota B7500 HSD. In the past month it has started overheating almost immediately when mowing.

I can run it all day without the PTO engaged...no problem.
I can run it all day with the PTO engaged and the mower deck off the ground...no problem (not that I do this).
The minute I start cutting grass (even short, thick grass) the engine bogs down, black smoke emits from the engine and the temp gauge shoots almost immediately to the red.

The coolant will boil and overflow. Once left to sit, the engine cools pretty quickly. But when I restart...it all starts all over again.

I replaced the mower deck blades (they were in bad shape) and the belt (which had actually came off) two weekends ago. Didn't help. I can only assume that I got the new belt on tight enough. I asked for a tension gauge (which the manual says to use) when I bought the belt and the guy behind the counter said "nobody uses those...just make sure it's tight, but not 'banjo string tight.'" I think it falls somewhere in that range of tightness.

I keep the radiator screen clean, but I have not yet blown out the radiator itself with compressed air. Will try that this weekend. I had also planned to pick up a thermostat Sat am too, just in case that could be the problem.

Any help that anybody can provide me would be greatly appreciated! My grass is getting knee deep while I try to solve this one weekend at a time.

Thanks!
Bill

slowzuki · Aug 19, 2004

There is something wrong with your cooling system, don't keep overheating it, it will damage the engine!

I suggest cleaning the radiator screen, it could be plugged solid, check the fan, the viscous clutch (if it has one) may be shot. When it is cool make sure it has the correct coolant amount and mix in it.

The PTO load causes the engine to develop more power which your cooling system can't keep up with.

Ken

Bob_Skurka · Aug 19, 2004

I wonder if there is something wrong with the PTO itself? If the engine bogs down & overheats when you engage the PTO, my suspicion is that there is something broke INSIDE the tractor and it is creating undue strain on the engine which creates the excess heat due to the engine bogging down. That is my guess. Then again, I sell candy to kids, so I never claimed to be too smart!

Henro · Aug 19, 2004

I have a 1-1/2 year old Kubota B7500 HSD. 

Warranty is 2 years everything, 3 years powertrain, isn't it?

Why not let the dealer fix it? Worst it should cost is the pick up and delivery...

enonhall · Aug 19, 2004

It doesn't really bog down when the PTO is simply engaged, but it does when a load is put on the PTO...cutting grass.

And I'm not running it while overheating, Ken. It starts overheating...I stop fast.

enonhall · Aug 19, 2004

Getting it hauled away to the dealer is definitely an option I will exercise if I need to. I just wanted to make sure that I wasn't overlooking something silly on my end. Would be painful to be without it for a couple weeks. (Not that it's doing me any good right now! /forums/images/graemlins/tongue.gif )

Is it possible that the mower belt isn't tight enough and that's putting strain on the PTO/engine? It sure seems tight...

Bob_Skurka · Aug 19, 2004

I think this is a warrenty issue.

enonhall · Aug 19, 2004

It would not overheat with the mower engaged sitting in the driveway. I have tested this with the mower deck up in the air out of the grass.

Bob_Skurka · Aug 19, 2004

Sounds like something is causing the a serious binding issue? But why would the blades free spin with the deck up and then bog down so badly when they engage a little grass? Like I said, I sell candy to kids . . . I don't have to be too smart to do that for a living.

Henro · Aug 19, 2004

In that case it could be something as simple as a stuck thermastat...even then...on a new tractor you might want the dealer to fix it cause you paid for the warranty in the purchase price...

Sounds like as soon as you ask the engine to do a little work it overheats. But it will run forever at reasonable temps when it is not working, right?

If something keeps the coolant from circulating, the engine will soon overheat because the coolant can't get to the radiator fast enough to expel the heat.

It is probably a simple enough thing to check yourself. But you need to be careful...it would be unfortunate if you voided your warranty (don't know if a tractor is the same as a laptop or not) because you did something on your own...

enonhall · Aug 19, 2004

( Sounds like as soon as you ask the engine to do a little work it overheats. But it will run forever at reasonable temps when it is not working, right? )

Exactamundo.

sandyc · Aug 19, 2004

As a thought, I would drop the mower and remove the belt and make sure that the spindles for each of the blades turn freely, same for the idler pulley. Could be that you have a frozen or soon to be frozen shaft. There is a thread regarding the lack of grease from the factory/dealer.

Good luck

sandyc · Aug 19, 2004

Whoops...almost forgot...make sure the u joints are well greased as well. With the mower deck up the drive shaft is pretty much aligned. Once you drop the deck you are stressing the u joints

gduff · Aug 19, 2004

It sounds like you are checking all the right things. (I.e. radiator screen etc.) Just a couple of thoughts that you may have already checked... Is the outside grill on the tractor clean? Your lawn may be kicking up some debris that is plugging it. (More apt to happen with a rotary cutter than a mower, but worth a check)
Is your grease/fluid level in your mower deck correct? Do you have a bent or damaged blade or a damaged bearing?
I agree that if you cannot determine this quickly it is time to get it to the dealer.

DieselnHooters · Aug 19, 2004

can you run some other PTO driven implement? If they run fine then you know the problem is the mower.

enonhall · Aug 19, 2004

( can you run some other PTO driven implement? If they run fine then you know the problem is the mower. )

Good point.

Gonna have to cut the grass with the bush hog at this rate anyway...

Henro · Aug 19, 2004

Just another thought...but if it is the mower, and the engine is overheating because it is being overworked by a defective mower component, then something on the mower should be getting real hot, since you don't appear to think the problem is true load caused by really high grass or something like that.

So you might try feeling the mower gear boxes and the belt, and this way locate the bad part of the MMM, if indeed there is a bad part...touch gingerly...

The brush hog test is a good idea. If you get the same results with two implements, the problem is unlikely an implement...

JerryG · Aug 19, 2004

Can you get to where you can see straight into the fins on the radiator? A lot of times, it will look like a radiator is clean from an angle, but the plug will be deep in the fins. If that is the problem, post back and I will tell you a easy way to get it out.

BillyP · Aug 19, 2004

I can run it all day without the PTO engaged...no problem.
I can run it all day with the PTO engaged and the mower deck off the ground...no problem (not that I do this).
The minute I start cutting grass (even short, thick grass) the engine bogs down, black smoke emits from the engine and the temp gauge shoots almost immediately to the red.


According to the above statement, it sounds like something in the deck isn't right. You could have a bad bearing in one of the spindles but that would cause belt slippage. Sounds more like a problem with the main gearbox on the deck.

If it overheats a little before starting to bog down, I'd check the radiator fins. If they are stopped up with grass and such, it can cause an overheating problem (especially under load).

My first guess would be something in the deck is binding, when you start cutting grass.

By the way, never shut off a hot engine. Always take the load off and let it idle for a few minutes. This will give the radiator time to cool the water and keep it from boiling.

Good luck

slowzuki · Aug 19, 2004

I just reread this, head to the dealer, if the deck is fine, something is wrong with your injection pump.

To me it sounds like the pump may be out of time, this can cause overheating and smoke production, without any power being developed.

Or the air filter may be severely clogged, but it likely wouldn't start very easy.

The dealer can sort it out.