Thermosyphon System Conclusions..

[Alexisferos]

The point of this post is to share my conclusion after a lot of reading and tests with the thermosyphon cooling at old Kubotas (and other tractors).

A year now i have in my hands a small beast a Kubota L1501dt similar to the L185dt.
And this beast make read and learn a lot of things, the most amazing is its cooling system and i think that i have found the right answer to everyone with a cooling system like that, a lot of old tractors have this, they working at this days,
the L210 the B6*** or the B7*** etc.

Kubota makes me think that he had measure the liquid capacity needs to cool the heat of the engine so they design the radiators bigger, to absorb the extra heat and stay within the limits at all the time.

Since those tractors don't have a temp gauge no one knows the operating temp at high load, they have a whistle and all the manuals say that if you hear it its time to stop.

But a version of b7100 (thermosyphon) at Sweden,Finland,Denmark comes with factory installed temp gauge, the gauge is installed in the head near the injectors
photo

and this is the place that i have put mine

that temp gauge reads up to the 130C (266F) and has the normal operating temp until 110C (230F) it even has a yellow zone with five degrees celsius, so the overheating we can say that it starts about 115C (239F).

This temps are keep up with all the tests that i have read from Nebraska university for some Kubotas, they even keep up with my temps, and with some other users.
Now a small parenthesis, some users may see different temps +,-7 degrees Celsius , the think is that a lot of factors must been in mind, like, where the sensor is placed, and how is the mix of antifreeze in the radiator, more antifreeze the bigger the temp you see.

My tests are in a very good and professionally cleaned radiator with 50/50 antifreeze and distilled water, two temp sensors and a laser gun.
first sensor is in the water lines in the head, next sensor is reading the water temp at the upper hose.

And the results are.
I keep log for 3 continuous working hours in every test for some months now.

3H mowing around at full speed the maximum temp is.
Gauge at head 208F
Water gauge 197F
Laser between injectors 205F

3H with the pto hard working
Gauge at head 226F
Water gauge 214F
Laser between injectors 221F

Indicative the idle temp at the head gauge plays around 185F

Now all of this must confirmed mathematically and by Greek physics.

Our systems are pressurized with the radiator cap, as the coolant gets hot it expands creating pressure in the system. The hotter things get, the more pressure created. The radiator cap allows pressure to build up in the cooling system, pressure reduces the creation of localized hot spots within the coolant passages of the cyl block & heads which can lead to formation steam pockets and therefore air locks in a system, when it reaches its top point will vent that pressure to the overflow.
Typically each pound of pressure over atmospheric will increase the boiling point of water by 3 deg..
This means doing the math that a 13 lb. cap will add 39F deg. to the boiling point of our coolant if it was straight water ~250F. -This is at sea level-
Add now 50% antifreeze - [keeps water from freezing in the winter (by lowering the freezing point of the water) and at the same time raises the boiling point of the water.]

Remember that a 50/50 ratio of coolant has a boiling point of 223 degrees. Straight water has a boiling point of 212 degrees.
Both however are boosted significantly by the pressure in the system.
A standard 0.9 bar (13lb) cap adds ~40 degrees to the boiling point of either fluid.
So the coolant in our KUBOTA will not actually boil until ~251 degrees, or ~262 degrees if it has antifreeze mixed in.
This numbers confirmed with some post that i have read from users that have hear the whistle and have Temp Gauge

Conclusion.

With strait water we don't hear the whistle until 251 degrees F.
With 50/50 that most users run we can go up to 262F

Im not saying that i like this numbers but i don't see them also,
i see maximum under 230F at very hot (Greek) days and with continuous load even with some clogged radiator. Never above that.

So if you see under ~240F the Whistle things you are all good.
Sorry for the big post.

 

[Lil Foot]

Excellent post, very informative, thanks for answering some of my own questions on thermosiphon cooling.

 

[85Hokie]

Excellent post, very informative, thanks for answering some of my own questions on thermosiphon cooling.

Alex,

I second the excellent post !!! Awesome job and excellent info. I have a new to me B7100, and I have the problem with the grass in the radiator and the heat problem. I too want to add a gauge. Your info is priceless.

I have noticed that if the ratio of antifreeze is off it will make a big difference!
My radiator was a bit low, so I added a little bit of straight green stuff, then it was low again.....added a little more green stuff.....

cutting grass - heard the whistle on a hillside, scared the shyte out of me ......read some posts about going 70-30 ......

I drained the radiator via the petcock, got about 1/2 gallon of the cleanest fluid I have ever seen!!! Added water to that amount and stirred it back up and added it back, ratio is something less than 50-50 I think - no problems so far, but that damn thing does get hot!

I was thinking of the inline rad hose with gauge - BUT - I want to verify that the ID of the hose....some say 32mm some say 34mm.......

I will print your info - and thanks again!

 

[Ezlife45]

A couple of comments.

Don't know what the antifreeze does to the boiling point but looking at a standard steam table, water at 15 psig boils at 250 F. The pressure has nothing to do with localized hot spots.

There are locations throughout the block where you may have higher temperatures than others, thinner cylinder walls, etc. If you had no radiator cap thus no pressure, the "hot spot" will have localized boiling much sooner than you'll notice steam coming out of your open radiator. As the hot spot boils the liquid, it vaporizes into steam. As the steam is subcooled by the surrounding liquid in the engine block, it will turn back to liquid. By having a functional radiator cap that is building pressure, the liquid will follow a steam table (for water) or the boiling point curve for an antifreeze mix. A pressurized system will boil at a higher temperature. That helps prevent localized boiling inside the engine block.

Now the thermosiphon works based upon the difference in specific gravity. Looking at a steam table, you can see that as temperature increases, the density of water goes down. Also, heat rises. Therefore, as the block is heating the liquid, the "lighter" hotter (less dense) liquid rises to the top. Eventually the liquid in the upper portion of the engine/radiator is fairly hot. As air passes over the radiator, the temperature is lowered, and thus the density of the fluid is increased. This denser, cooler liquid is then able to enter the engine. The heavier, denser and cooler liquid helps displace the hotter lighter fluid from the engine and the thermosiphon continues...

 

[phaser]

Great post Alex!!!

If you can spare the time, more information on parts and the gauge you used, and with photos would be great.

.

.

 

[Tooljunkie]

I would also be interested in the steps used to install your temp guage. This is a very informative thread. Thumbs up!!

 

[Alexisferos]

The hotter things get, the more pressure created. The radiator cap allows pressure to build up in the cooling system, pressure reduces the creation of localized hot spots within the coolant passages of the cyl block & heads which can lead to formation steam pockets and therefore air locks in a system, when it reaches its top point will vent that pressure to the overflow.

A couple of comments.
The pressure has nothing to do with localized hot spots.

let me rephrase that for you.
its simple, if you have pressure, with the difference of the temperature as you refer (i dident concentrate to the difference or the temp because its absolute normal since the fan blows air and cools the water) you have movement,
less pressure slower the movement, the point was to explain the usage of the radiator cap and how important is to be in perfect condition.

There are locations throughout the block where you may have higher temperatures than others, thinner cylinder walls, etc. If you had no radiator cap thus no pressure, the "hot spot" will have localized boiling much sooner than you'll notice steam coming out of your open radiator. As the hot spot boils the liquid, it vaporizes into steam. As the steam is subcooled by the surrounding liquid in the engine block, it will turn back to liquid. By having a functional radiator cap that is building pressure, the liquid will follow a steam table (for water) or the boiling point curve for an antifreeze mix. A pressurized system will boil at a higher temperature. That helps prevent localized boiling inside the engine block.

we say almost the same thing.
with the little English that i know i can understand that we need pressure to avoid the steam and the hot spots, etc..

Now the thermosiphon works based upon the difference in specific gravity. Looking at a steam table, you can see that as temperature increases, the density of water goes down. Also, heat rises. Therefore, as the block is heating the liquid, the "lighter" hotter (less dense) liquid rises to the top. Eventually the liquid in the upper portion of the engine/radiator is fairly hot. As air passes over the radiator, the temperature is lowered, and thus the density of the fluid is increased. This denser, cooler liquid is then able to enter the engine. The heavier, denser and cooler liquid helps displace the hotter lighter fluid from the engine and the thermosiphon continues...

simple in Greek.. you know thermosiphon its a Greek word i know exactly its meaning.
and yes it does what you just say.
thermosiphon called the method of passive heat exchange based on natural convection, which circulates a substance (liquid, or gas such as air) without the necessity of a mechanical pump.

 

[Alexisferos]

I would also be interested in the steps used to install your temp guage. This is a very informative thread. Thumbs up!!

its simple but i will try to show you, or explain all the steps.

 

[Diydave]

Actually it was a pretty good system, as it came from the factory. what often brings about failure, is in a mowing situation, clippings and chaff can accumulate between the radiator, and battery, causing an overheat. I think, there was also an import law, at the time, which made it have liquid cooling, to be legal to import them. This motor could easily have been air cooled, with the proper fins, shrouds and fan...

 

[Alexisferos]

as for the installation of the gauge i will try to explain as much i can.
the idea to make a hole in the cylinder head came in my mind after i saw a Kubota D1101 cylinder head at ebay with an extra hole near the bolts,
(what is that i say) and i thought that this engines are used in many applications and maybe someone wanted a gauge for temp
this is the picture.

now i already had my cylinder head off so i see that at the place where the hole is you can monitor the water line in the head.

no hesitate, i bought a new drill bit 12mm and a (kolaouzo) i don't know how its called in English

after i drill carefully the head and create the coil with the (kolaouzo)
i wash the metal parts from the hole and the head.

a bronze washer installed before the adapter that came with the analogue gauge.
look how the head was and how i install the adapter.

my gauge is analogue i just went to the first auto store and bought it, no connections is plug and play.

a hole must be made in the dash if you are looking for the factory look.

it even has a buld for the night so i connect it with the same source as the hour meter, now i can monitor the temp at night also..

a lot of other Kubota heads have that place taped there. with a new drill bit you can open a monitor hole in your cylinder head.
this a d650-d750 head...

this is the story..

 

[North Idaho Wolfman]

a (kolaouzo) i don't know how its called in English

after i drill carefully the head and create the coil with the (kolaouzo)

Amazing that with all the fancy words that are derived from greek words, Kolaouzo = Tap or Thread Tap.

 

[Alexisferos]

Amazing that with all the fancy words that are derived from greek words, Kolaouzo = Tap or Thread Tap.

thanks for the information..

 

[Ezlife45]

Alex...

If you made the posts you put here and English is not your first or primary language I tip my hat to you.

I have conversational level capabilities in a second language, but in no way can I discuss or convey technical information as you have done here.

Good Job!!

 

[Alexisferos]

Alex...

If you made the posts you put here and English is not your first or primary language I tip my hat to you.

I have conversational level capabilities in a second language, but in no way can I discuss or convey technical information as you have done here.

Good Job!!

off course and i write my posts.
Greek is my primary language (born and live here) ,
but i speak and write in good English and Russian at the level you see.

thanks for your good words..

 

[phaser]

Alex, thanks for your install details and photos. Good job!

.

 

[Tomcat]

Very informative. Kudos Alex!

 

[In Utopia]

Great post, thanks for sharing.
Got me inspired to put the whistle back on my L175 which wasn't there when I bought the tractor.
Saw a site that has them, but I need more info on the rest of the system from the overflow outlet to the whistle.
Previous owner had the radiator repaired and never replaced the whistle system.
Found a picture of the whistle itself in the manual, but not other details.
Help would be appreciated.

 

[Diydave]

Simple, a tube runs from slightly above the rubber seal, of the pressure cap, in the outer surface of the radiator neck, down to the bottom of the radiator, just under the sheet metal. I can't remember for sure, but my guess would be left side of rad, as you sit in the seat. Steam from an overheat comes out the top of the radiator, into the tube, and blows the whistle. if someone switched the radiator, you might need to drill a hole in the neck, and solder on a downward facing elbow, to carry the steam to the whistle. I think the tube is somewhere in the neighborhood of 3/8" diameter. If I am wrong, just check the OD of the whistle you have, and use that to size the overflow tube and elbow...

Oh, and the whistle mounts to one of the lower rad side bolts, at a 45 degree angle, apx, with the output end of the whistle pointing back toward the operator...

 

[In Utopia]

Simple, a tube runs from slightly above the rubber seal, of the pressure cap, in the outer surface of the radiator neck, down to the bottom of the radiator, just under the sheet metal. I can't remember for sure, but my guess would be left side of rad, as you sit in the seat. Steam from an overheat comes out the top of the radiator, into the tube, and blows the whistle. if someone switched the radiator, you might need to drill a hole in the neck, and solder on a downward facing elbow, to carry the steam to the whistle. I think the tube is somewhere in the neighborhood of 3/8" diameter. If I am wrong, just check the OD of the whistle you have, and use that to size the overflow tube and elbow...

Oh, and the whistle mounts to one of the lower rad side bolts, at a 45 degree angle, apx, with the output end of the whistle pointing back toward the operator...

It's the original radiator, so the overflow is still there. Right now I have a piece of clear plastic tubing running down the side of the radiator allowing any overflow to go to the ground.
I'm guessing the clear vinyl tubing with clamps on both ends is sufficient?

 

[Diydave]

It's the original radiator, so the overflow is still there. Right now I have a piece of clear plastic tubing running down the side of the radiator allowing any overflow to go to the ground.
I'm guessing the clear vinyl tubing with clamps on both ends is sufficient?

If the tubing is snug enough, the only clamp you need is to hold the whistle in place, at the bottom, this is not a high pressure situation, flow of steam causes the whistle to operate...