D722 Electrical Oil/Temp/Fuel Solenoid

[Aefriot]

We have a D722 driving a lineshaft. Currently it has been configured with the fuel solenoid grounded to the block. The solenoid gets power once the oil pressure comes up to "minimum" for the current oil switch. The temperature sensor/switch was replaced at some point with a non-oem switch and was broken when we received the engine. We installed a mechanical temperature gauge. Today, the water pump/fan/generator belt broke. By chance, the engine was checked on (it is in a separate room) and steam was being pushed out of the radiator. The engine was shut down immediately. The gauge read no more than 230-240F. We were lucky.

Thinking about the wiring and about a way to operate the engine that more ensures the engine will not overheat again and remembering that the D722 engine wiring schematics had a one-wire temperature sensor/switch we thought it a better way to wire the engine is to run ground to a thermal disconnect. The engine would have to have oil pressure to start and run. Plus, the temperature would have to be under the temperature cut-off limit of the thermal switch. Does Kubota, or anyone else for that matter, offer a thermal switch for such a purpose? At what temperature should this switch open to shut down the engine?

Thank you

 

[lugbolt]

I have no input on thermal shutdown, most of that stuff is ECU based in my experienced. The sensor is just a thermister, meaning it's resistance changed with temperature.

Kubota seems to have a cast material that is sensitive to excessive heat--and with that said, I have had to replace a ton of cylinder heads because of overheat conditions (cracked). The typical complaint is that it keeps overheating...and what I usually found was that either the gasket was leaking or the head was cracked, and combustion gases were entering the system causing excessive pressure and/or pump cavitation leading up to overheating. So, if it were mine, I'd probably start/run it with the radiator cap off and watch for bubbling. If you get bubbles that don't quit within 30 seconds to a minute, you know you'll probably be looking at pulling the head for inspection of it and the gasket. I have never seen a Kubota engine contaminate the engine oil with coolant due to failed head gasket or cracked head, almost all of them just won't quit overheating as stated.

 

[North Idaho Wolfman]

You should be able get one off of ebay.
I might have one laying around, they are used on the old refer units as protection from an overheat.

 

[Aefriot]

My friend is Amish and certainly not up on ECU control. I could design and assemble an electronic monitoring system, but he would not prefer that since it is beyond his understanding. In fact, keeping the engines operating with minimal control oversight is preferred. Engine protection from overheating on a refer makes sense. Something similar for my friend is desired.

For the cutout switch, I am not sure of the temperature that, if reached, should disconnect power to the fuel solenoid. I am not sure of the temperature of the switch. The engine will work hard and create heat. I wish to have the it be able to operate to 100% potential before shutting down due to excessive heat. I am not familiar enough with the engine to know at what temperatures they operate at safe for their operation.

I suspect we could operate the engine at its maximum requested output for a few minutes then record the coolant temperature with the current gauge and add ten degrees. If the engine shuts down prematurely, we can add few degrees.

I think someone else has this experience...I am looking to benefit from other's knowledge. So, maybe I can just look to the refer manufacturers for the correct part.

Thank you

 

[GreensvilleJay]

hm. have a look at HVAC, boiler or infloor(radiant) heating controls. All will have a suitable sensor.
Every clothes dryer has 2-3 of them ( KLIXON) a simple 'thermodisc' switch clamped to the 'hot' area. Normally closed, allows power through, gets too hot, it opens kills power, auto resets when cool again. They come in fixed temperatures+-xxdegrees. That style could be clamped onto the head. The 'boiler/PEX' style would be installed in a 'welladapter',same ar temp probe for engines.
My gut says the sensor should be say 5-10* above the thermostat value ?
While I design/built energy controls 3 decades ago, I agree with the KISS principle so a 'KLIXON' style would be best.

 

[Aefriot]

Again...a potential solution .

I have to wonder, though, is the external surface of the head the same temperature of the coolant? What is the difference? I can take my digital thermal gun to read the temperature to read the maximum normal temperature where it is at its highest and purchase a "KLIXON" or similar for a few degrees above that.

Thank you GreensvilleJay

 

[Aefriot]

I just contacted Thermo King and the parts guy said there is no thermal switch on the engine, only a temperature sensor. The on/off cycles are controlled by the ECU.

Maybe he is too young to remember non-ECU units? I will try a local truck repair shop who has seen a lot of older equipment.

 

[GreensvilleJay]

External head temperature will be cooler that the coolant, and will vary depending on where on the head you measure. Simply use an IR temp gun and take several readings, including coolant temp.
If the head is 10*F cooler, get a switch for the tstat rating( say 160* ? I'd put the new KLIXON at the hottest point on the head . Idea is coolant is 160, head 'sensor' might be 150....'overheating begins'... coolant goes up to 180, head gets to 161, KLIXON comes one... shuts engine down.
KILXON units have 'hysterisis' ...come on at say 160, reset at 155 (see the specs...),this 'deadband' allows for 'things' to get back to normal.
As a start I'd go with whatever the tstat is...so 160*F stat...use 160*F KLIXON

 

[Aefriot]

Thank you GreensvalleyJay

 

[GreensvilleJay]

always happy to help if I can !

 

[Aefriot]

I have ordered a 160*F KLIXON. We will see where that leads. I think the hottest portion of the exterior head will be 20*F cooler than the coolant. I am not positive, but it is a starting point. I feel better we are moving ahead with securing the engine to be able to be left unattended for extended periods of time. Engines are too expensive to treat like they are throwaway devices.

 

[GreensvilleJay]

Not to be paranoid but.....if a rad hose failed, engine, could it die before it 'overheats' ?
Now you'll need a 'loss of coolant' detector....
Dang , how about a 'broken fan belt' detector ?
sigh, one could get carried away but..... something to consider.

If this is remote, having a set of hoses and belts might be a good idea. As long as they're there, you'll never need them !

 

[Aefriot]

I hear ya about being paranoid. It is easy to create trouble where there is none. Too many systems to track other systems will get complicated. We know if it is made by man, it will eventually fail. I suppose we should replace parts (belt [done] and hoses) that are known to fail in the long term (5+ years) with high quality parts now before they fail. Then again on a schedule (5 years or so) since this is a remote engine that once it has been started and warmed up, it may not be heard for hours if loud equipment is operated. Engine trouble may not be noticed before permanent damage is done. But you are right about the coolant level. Low coolant could be trouble and not show itself until it is too late. Perhaps, a mechanical switch soldered into the top of the radiator. Rather, a fitting that a switch can be fastened. Thank you for reminding me of alternate engine perils.