Cub Cadet 782D / Kubota D600 overheating

[Oaktodd]

I picked up a non-running Cub Cadet with a D600 in it. This thing has sat many years not running. I pulled it in the shop and found the injector pump had 2 stuck plungers. I got that repaired and bleed the injectors. I also found the bottom radiator hose plugged up solid with crud. I then pulled off the water pump and flushed a bunch of crappy looking stuff out of the inlet and outlet of the block. I also found the thermostat wasn't in there. I had an old one from another tractor, checked it and found it opens around 170ish, so i put it in. I got the tractor running and it runs pretty good but will peg the temp gauge if I let it run long enough. I even pulled the thermostat and it makes no difference. Could my block be plugged up with gunk causing my issue? My next step I'm thinking is to pull the head and inspect the water passages. TIA

 

[85Hokie]

You flushed the radiator ?....... did you do a temp check at the upper neck and lower neck of the radiator?

My guess your radiator is one potential problem

 

[North Idaho Wolfman]

Any smoke?
Any bubbles in the radiator?

Kubota's are know for cracking the heads if they overheat.

 

[lmichael]

Could be a number of things. IDK if Kubota engines are prone to having a bad head gasket or cracked head allow exhaust gas into the cooling system. But lets eliminate the easy stuff first. With that much gink in the system you may need to resort to a chemical flush, and make sure coolant flows. Maybe even a new radiator, as well. Also the water pump impeller may be partially eaten away

 

[Oaktodd]

Oops, I forgot to mention. With the rad cap off, engine very near to overheating, the water at the top of the rad was 105*. I checked it with a Fluke 52 meter. It felt cool at the bottom. If I place my finger near where the temp sensor is on the head I can only hold it there for a few seconds so I'm thinking it's 140+ there.

 

[Oaktodd]

No unusual smoke or bubbles in the rad either.

The bypass nipple was clogged up on the water pump but I got that cleaned. I used a piece wire to try and get any crud off of the impeller but I can't tell if I did because you can't see in there.

What is a good flush? Is this stuff any good or do I need something more heavy duty?

THERMOCURE Cooling System Rust Remover & Flush | CRC

THERMOCURE cooling system rust remover and flush removes rust scale and deposits from radiators, water pumps, engine blocks, and more.

www.evapo-rust.com

 

[GreensvilleJay]

this...
I also found the bottom radiator hose plugged up solid with crud.

for SURE the block HAS to be plugged with crud...

I'd clean the block at least 3 times over 2 -3 days. When truly 'clean', garden hose water will flow fast out of the block .

 

[mikester]

Answer TRUE or FALSE:
"I use hard tap water to top up my coolant levels"

 

[GreensvilleJay]

neighbour use muriatic acid to clean a 'used 1 season ' swim pool gas heater exchanger. I could not believe how PLUGGED that was....

 

[lmichael]

Answer TRUE or FALSE:
"I use hard tap water to top up my coolant levels"

Likely the case but OP does not have a full history on the machine.

 

[Oaktodd]

Okay, yesterday I rigged up a flushing system after I removed the thermostat and radiator. I pumped CLR into the water pump and ran the outlet back to the bucket.


I ran that for about an hour and decided to run the engine with the cleaning solution circulating. After about 5-10 minutes of run time my temp gauge almost pegs but my circulating solution is only about 145. I IR scanned the block in several places and it reads about the same temp.


Here is the decal under the hood showing the temp gauge operation. It shows that I should be over 230 but I'm nowhere near that.


Looks like I may only have a gauge/sensor issue.

Are there any good aftermarket temp gauges/sensor that will screw into the original location on the head? If not, I have changed the gooseneck on some of my other diesel cubs and placed an aftermarket setup in it.

 

[GreensvilleJay]

Well I'm HAPPY you've got a nice clean cooling system !!!
The gauge looks like a 'common' 2 1/16" round hole device, have no idea about the quality of current units.
If the gauge/sensor is mechanical (no wires..) ,be sure not to bend the 'cable' too sharp. Electrical ?, you'll need both sensor and gauge.

 

[MOOTS]

Welcome Todd. I still have your clutch compressor you lent me. And I still haven't worked on my 128.

 

[Oaktodd]

Welcome Todd. I still have your clutch compressor you lent me. And I still haven't worked on my 128.

Oh ya, someday I'll get that from you but I haven't needed it lately. Thanks

 

[Oaktodd]

Well I'm HAPPY you've got a nice clean cooling system !!!
The gauge looks like a 'common' 2 1/16" round hole device, have no idea about the quality of current units.
If the gauge/sensor is mechanical (no wires..) ,be sure not to bend the 'cable' too sharp. Electrical ?, you'll need both sensor and gauge.

Yes, it's electric so I'll probably switch over to something else. Thanks

 

[Vigo]

If its electric you could try cleaning connections and looking for any damaged insulation on the wires. Usually with coolant temp sensor circuits extra resistance will read colder not hotter but i cant say ive checked every single type.

The fittings where coolant temp senders screw into engines are almost always NPT because if torqued correctly they are self sealing. Course, some people’s idea of torqued correctly is make all the threads disappear into the hole which sometimes results in a CRACKED ENGINE BLOCK so uh.. results sealing npt fittings vary by competency level.

 

[North Idaho Wolfman]

Most Kubota's have BSPT threads, a lot of the universal kits come with that adapter as it's fairly common.
NPT fitting will thread in about 1 1/2 threads then start to bind, they do not thread in properly and will either break or leak.