Bobcat 743 Overheating

[aaronmaurer2008]

I have 1989 Bobcat 743 I recently changed the water pump on it. I also checked the thermostat, there is also no obstructions on the radiator. I drained the oil and their is not any antifreeze in the oil. The engine in it I beleive is a v1702 Kubota. With the radiator cap off you can see the antifreeze flowing through the radiator. You can run it at full trottle just sitting their and it won't over heat but, after 10 minutes of running it it will overheat.

 

[Tazza]

As you have checked the radiator fins, i assume you checked the oil cooler too? the air passes through both.
It's possible the inside of the radiator is a bit plugged too, you said you can see coolant moving around, that doesn't mean it's flowing as fast as it should.
How high do you have the revs when using the machine? If they are too low, it can over heat.
Another thing is, the temperature sender may not be in great condition. The engine may not be over heating at all, it's just being told it is from a faulty sending unit.

 

[aaronmaurer2008]

As you have checked the radiator fins, i assume you checked the oil cooler too? the air passes through both.
It's possible the inside of the radiator is a bit plugged too, you said you can see coolant moving around, that doesn't mean it's flowing as fast as it should.
How high do you have the revs when using the machine? If they are too low, it can over heat.
Another thing is, the temperature sender may not be in great condition. The engine may not be over heating at all, it's just being told it is from a faulty sending unit.

When it's at high or half throttle it overheats the temperature sending unit isn't hooked up due to some wiring issue but I have a temperature probe and its getting 250 to 300 degrees if you keep using it. I have checked the oil cooler to and I didn't see any thing out of the ordinary but this weekend I think I'm going to pull it off if I can come up with anything else. Thanks

 

[SkidRoe]

When it's at high or half throttle it overheats the temperature sending unit isn't hooked up due to some wiring issue but I have a temperature probe and its getting 250 to 300 degrees if you keep using it. I have checked the oil cooler to and I didn't see any thing out of the ordinary but this weekend I think I'm going to pull it off if I can come up with anything else. Thanks

I'm with Tazza. Most overheating heavy equipment that I have experience with had plugged radiators, obstructing air flow through the rad.
Also, did you put in a new thermostat, or just check the old one? If you put the old one back in, did you do a boiling water test on it to make sure that it was opening fully?
One other thing to check is the lower rad hose / inlet to the water pump. Sometimes when the hoses get old, they can collapse due to the suction of the water pump.
HTH,
SR

 

[jerry]

I'm with Tazza. Most overheating heavy equipment that I have experience with had plugged radiators, obstructing air flow through the rad.
Also, did you put in a new thermostat, or just check the old one? If you put the old one back in, did you do a boiling water test on it to make sure that it was opening fully?
One other thing to check is the lower rad hose / inlet to the water pump. Sometimes when the hoses get old, they can collapse due to the suction of the water pump.
HTH,
SR

Did you change the water pump because of the overheat or did it occur after you changed it? Could be a problem with the pump if thats how it went. A non contact thermometer really helps if you can get or borrow one.

 

[reaperman]

Did you try a different radiator cap? If its the original cap it may not be sealing properly and wont build pressure.

 

[aaronmaurer2008]

Did you try a different radiator cap? If its the original cap it may not be sealing properly and wont build pressure.

I changed the water pump because it was overheating but, the bearings were shoot in the water pump any was when it started overheating the second time we need to use it so we pulled the thermostat out thinking maybe it was bad. It still would overheat. When it overheats the reservoir starts to hiss. I haven't tried the radiator cap yet but this weekend I'm going to change it and what it will do. I also heard that the ports in the head can get clogged any thoughts.

 

[Mikefromcny]

I changed the water pump because it was overheating but, the bearings were shoot in the water pump any was when it started overheating the second time we need to use it so we pulled the thermostat out thinking maybe it was bad. It still would overheat. When it overheats the reservoir starts to hiss. I haven't tried the radiator cap yet but this weekend I'm going to change it and what it will do. I also heard that the ports in the head can get clogged any thoughts.

Have you checked the blower housing shroud?

 

[mahans7]

Have you checked the blower housing shroud?

I just ordered a new 743 temperature sender which (per a BC service bulletin) requires a new temperature gauge from the Bobcat dealer, $8 + $30 respectively FYI.

 

[Tigerhaze]

I changed the water pump because it was overheating but, the bearings were shoot in the water pump any was when it started overheating the second time we need to use it so we pulled the thermostat out thinking maybe it was bad. It still would overheat. When it overheats the reservoir starts to hiss. I haven't tried the radiator cap yet but this weekend I'm going to change it and what it will do. I also heard that the ports in the head can get clogged any thoughts.

Are you getting any bubbles or air in the radiator over time? I don't know the Kubota engines, but an infamous issue on Honda/Acura engines is what is called a "seeping" head gasket. There will be no water in the oil or vice versa, but one of the cylinders (usually the furthest from the water pump) will leak into the cooling system. The engines will still run well but after a short period of running hard, the engine will overheat because enough combustion gas will displace the coolant and cause the thermostat to close from air locking. You won't necessarily see coolant pushed out of the radiator either. Confirmation can be made by using a test kit on the coolant to check for combustion gasses. It's just another idea, and may be totally irrelevant to the Kubotas but thought I would mention it.

 

[Benjamin]

Did anyone ever figure out the issue here?

 

[Snowtom850]

I am curious also. I have a 763! with the same issue. I have pulled the head had signs of coolant in the far cylinder. The shop that checked the head said there was a small crack. They were able to repair it and resurface the head. Put bobcat gaskets back in. Still has same issue. Have to work it. Won't over heat even at w/o throttle until it starts working hydraulics. Even temp in radiator and plenty of air flow across coolers. Looking for any other ideas.

 

[brdgbldr]

I am curious also. I have a 763! with the same issue. I have pulled the head had signs of coolant in the far cylinder. The shop that checked the head said there was a small crack. They were able to repair it and resurface the head. Put bobcat gaskets back in. Still has same issue. Have to work it. Won't over heat even at w/o throttle until it starts working hydraulics. Even temp in radiator and plenty of air flow across coolers. Looking for any other ideas.

Could it be that your hydraulics are overheating?

Depending on which way your fan blows… the hydraulic cooler could be heating up your radiator.

 

[Jim A]

Jump solenoid to make hydraulic fan stay on continuously.
Use laser temp gun to check temp.
Make sure fan is rotating right direction.

 

[Snowtom850]

I don't have a hydraulic cooling fan that I am aware of. Belt driven fan that is moving tons of air. I have laser temp gunned it and everything is getting hot evenly. I feel like its something to do with the hydraulics also being it cools down as soon as I stop moving. have tried new fluid and filter on that too.
I pulls a ton of air through the coolers almost will pull my phone ( using flashlight) out of my hand and blowing out both sides of the exhaust. Air get warmer as heats up. The dealer keeps telling me the head and head gasket are the only thing that they see with this issue. I've owned this machine since 2009 have had no issues till last winter. and only randomly. now seems to be pretty consistent

 

[sherifflldon]

I don't have a hydraulic cooling fan that I am aware of. Belt driven fan that is moving tons of air. I have laser temp gunned it and everything is getting hot evenly. I feel like its something to do with the hydraulics also being it cools down as soon as I stop moving. have tried new fluid and filter on that too.
I pulls a ton of air through the coolers almost will pull my phone ( using flashlight) out of my hand and blowing out both sides of the exhaust. Air get warmer as heats up. The dealer keeps telling me the head and head gasket are the only thing that they see with this issue. I've owned this machine since 2009 have had no issues till last winter. and only randomly. now seems to be pretty consistent

Is there a reason you dont want to believe the dealer? Sounds like a water jacket problem of sone sort. Especially if it came on all of a sudden and is consistently doing it.

 

[Snowtom850]

I did believe the dealer. Took the head off and they found a crack fixed. Tested the head. Put back together same problem

 

[sherifflldon]

I did believe the dealer. Took the head off and they found a crack fixed. Tested the head. Put back together same problem

Sorry, I didn't read your previous remedy attempts.
One thread with this problem said they removed the thermostat. A (properly working) thermostat is designed to control the water flow so it can be cooled in the radiator. Removing and not replacing the thermostat will only exacerbate the problem. In that the water does not spend enough time in the radiator to be sufficiently cooled. Just throwing out an idea. Hope you can solve the problem. Skidsteers / mini track loaders are awesome machines. But their problems are awesomely difficult becauses of everything being crammed into such a small space. Good luck!!

 

[laurencen]

I did believe the dealer. Took the head off and they found a crack fixed. Tested the head. Put back together same problem

you can get a test kit to see if exhaust gasses are in the water, may be wirth giving it a try, our 743 was having the same issue, previous owner said head was checked and found no issues, we replaced the head and overheating went away

 

[KyMadMan]

A couple things to try. First, take out the thermostat completely and see if the issue still occurs. If not, bad thermostat. (Yes, they can be brand new and bad) Second, loosen the radiator cap or pull up the release lever if so equipped. Check issue, if not occurring get a new cap. If yes replace cap. Check the temp at both the inlet and outlet hoses on the radiator. Should be 2 different readings. If there is a major difference I would remove the radiator and try flushing it in both directions as you could have tubes restricted. I know this will sound stupid but not meant to be, make sure the hoses on the water pump are on correctly and not reversed.

Oh crap, I see this is a very old thread. My bad, but perhaps it will help someone else since it doesn't state if the issue was ever resolved.