Thermal Circllation

[T and S]

I read with interest in a different thread about thermal circlation. I've had my L185 a little over a year, and it had anti-freeze in it when I got it and still does.
However after reading up on it I've decided on going with straight water, plus adding a anti corrosion supplement.
My question now is around the radiator cap. I have a 13lb. cap on it now, but I am thinking that this system probably requires a specailized cap.
Anybody have any thoughts or more info on the radiator cap ?

 

[motorhead]

Your L185 has probably had antifreeze in it since day one. Why would you want to change to just straight water with additive? I had a B5100D with thermo siphon cooling (No water pump) and I ran a 40/60 mix in it. Never overheated.

 

[gurn]

I looked in my service manual of my L175 for info on the cap but found nothing. I agree with motorhead, about antifreeze. The heated liquid should still rise and fall and do the job of cooling just fine with all the benefits of modern coolant.

 

[kuboman]

50/50 antifreeze solution gives better heat transfer than straight water. Plus it won't freeze and wreck the engine.

 

[motorhead]

Found this on Messiks tractor parts: http://www.messicks.com/partdetail/15272-72020.aspx
They show a .9ATM or .9 atmospheres. 1.0ATM equals 14.7 psi.
It computes out to 13.23psi cap. You have the correct cap
I first looked it up as a L175 when I copied the link. It takes the same cap for the L185

 

[Russell King]

Sorry this will be a long post and I hope not to raise anyone's dander.

The manuals I have state that the L185 uses a pressurized system with the cap set at 12.8 PSI.

I was also reading and commenting on the use of anti-freeze on the natural circulation used on the L185. I recently purchased a L185 and it has anti-freeze installed. I live in central Texas so for most of the year freezing is of little concern here so the use of anti-freeze is not really needed for about 10 months of the year.

I doubt that the use of anti-freeze is necessarily bad but here we go with some basic facts:

Pure water will boil at 212 F and freeze at 32 F at sea level (1 atmosphere).
50% water/50% anti-freeze mixture will freeze at -34 F and boil at 265F at sea level.

Increase the pressure on either water or 50/50 and the freezing and boiling points change. Adding the 13 PSI cap will increase the boiling point of water from 212 to about 250 F. Anti-freeze boiling point also increases with pressure.

None of this really has any point on the use of anti-freeze in a cooling system and its operating point. The fact is that anti-freeze reduces the heat transfer capability of water. It is used in cars for numerous reasons but better heat transfer is not one of them.

In a 50% anti-freeze solution the specific heat capacity is decreased approximately 20%. The reduced heat capacity must be compensated by circulating more fluid when comparing a water system and an anti-freeze system. Since there is no way to increase the cooling capacity of the radiator/fan/pumping system on the tractor, the use of anti-freeze should raise the operating temperature of the system compared to water. If the heat transfer system was designed for the use of anti-freeze there should not be a problem. If the system was not designed for anti-freeze the heat transfer system will operate at a higher temperature.

Now - there is the use of thermostats to limit the flow of the fluid between the radiator and the engine. So this throws my mind for a loop on whether the use of anti-freeze would raise the operating temperature over pure water.

The owner’s manual IMPLIES that water should be used primarily and anti-freeze can be used when freezing temperatures are expected. Right now that is the main reason I am thinking to reduce or eliminate the anti-freeze in the tractor. And the fact that it is normally well above 32F here.

There were comments that the increase in operating temperature resulted in cracked heads. I imagine freezing water has cracked more heads than overheating. But either way I want to reduce the possibility of cracking the head in any situation.

I have access to some heat transfer experts at work so I will broach the subject of the thermostats and using antifreeze or water with them next week and post back afterwards.

 

[MagKarl]

The thermal conductivity of straight water is better than antifreeze. The coolant's job is to take the heat from the engine, and dump it to the radiator. The conductivity is the relative rate at which heat can be transferred through the fluid.

You should run the minimum amount of antifreeze needed to prevent freezing damage to your engine. 50/50 is the generally accepted mix to cover most everyone.

 

[kuboman]

I stand corrected Not sure where I got that from but I was thinking that lowering the surface tension of water helped in heat transfer, but anti freeze does not do that.

 

[T and S]

Interesting replies. I appreciate all of the info. I look forward to what Russel King finds out.

 

[T and S]

Thanks Vic! I will stay with anti-freeze according to your service bulletin. I have been using the 50/50 mix that prestone sells, so I will continue on.....

 

[Russell King]

I had read Service Vic’s reply and will continue to use anti-freeze since that is recommended.

I asked one of the heat transfer people at work about the use of water anti-freeze and having a thermostat involved and here is the explanation:
The engine generates heat and the cooling system must reject as much heat as the engine produces or the coolant temperature will continually increase. Most cooling systems are built larger than required to allow for fouling inside and outside the heat exchanger (radiator).

Assume that the engine generates 1 unit of heat, the cooling system is designed for water only with 10% extra cooling capacity. The system has a thermostat to hold the temperature at 180F. Start the engine and the water inside the block will increase to 180F and the thermostat will open and cool water will flow through the system. When it reaches the thermostat it will close the thermostat and the engine will heat the water in the block, the heat exchanger will cool the expelled water. Since the cooling system is more than capable it will cool the fluid below 180F so this cycle will continue over and over.

Now switch the water to 50/50 anti-freeze and the cooling system has become undersize since the fluid is not as capable of moving heat (only 80% as good as water). The engine will still generate 1 unit of heat but the cooling system will only be capable of removing .88 units of heat (1.1*.8=.88). The thermostat will open and close until the entire system is above the 180F set point. Then it will stay wide open and allow as much cooling as possible. This system will overheat since the heat source generates more heat than the cooling system can remove.

Now switch the design thoughts and design the system for 50/50 anti-freeze. The engine will still generate 1 unit of heat. The cooling system will be designed to have 10% excess capacity over the heat source. Taking the fact that the coolant is 80% as effective as water, the cooling system will become larger than the cooling system based on water. The anti-freeze cooling system will be sized around 1.3 compared to the 1.1 water system. The same cycle will occur with the system, engine will generate heat, fluid reaches thermostat set point, thermostat opens, water moves, thermostat closes…heat balance is maintained.

Now switch the system designed for anti-freeze to pure water and you have an over sized coolant system, it would be about 1.6 times the required capacity (1.3/.8=1.6). It will still operate at 180F since the thermostat will hold the water in the engine until it reaches it set point. This system would require the thermostat to hold the water in the engine because the cooling system would always be capable of cooling the fluid well below the set point in every cycle.

In conclusion, one system will operate at 180F with water but overheat if operated with anti-freeze. One system will work with anti-freeze or water and operate at 180F.

 

[kuboman]

There is no thermostat with a thermal system. Circulation depends on the rate of heating and cooling.

 

[Russell King]

You are correct. Each system will reach their steady state temperature, uncontrolled by any thermostat.