How does an Expansion Tank Work?

[dlundblad]

Last weekend and into the beginning of the week, I performed 4 drain and fills with distilled water on the cooling system of the Jeep. The system holds 15 quarts and 8 quarts drain out when the lower radiator hose is pulled. (I skipped the petcok)

I refilled the heater core, radiator and expansion tank with 8 quarts of straight G-05. (8 quarts of straight coolant with a 15 quart capacity.) The expansion tank was nearly filled to the top, but as the system burped itself over the first drive and having the heater on, it went down to a normal level. Then, once again having the heater on full blast and driving (heating/ cooling) over the next couple days, it fell halfway between hot and cold marks once hot and just below the cold mark when the engine is cold.

My question is, when the system is hot and the radiator cap allows coolant to travel to the expansion tank, what sort of mixing happens? Would the coolant in the tank be mixed just as much as what's in the rest of the cooling system by now? I'd like to top off the expansion tank with 50/50 to the correct level, but if it isn't thoroughly mixed just yet, I would like to hold off and not dilute the straight coolant since I would like it to be mixed with the whole system.

 

[demarpaint]

I'd top it up with the 50/50 mix and call it a day. It will mix through within a reasonable amount of time. I can't say for sure how long but I topped my Liberty expansion tank with distilled water because it was a little low when the engine cooled off after a recent cooling system service. I took about an hour ride, shut it off, drove it the following morning, and in the afternoon when I checked again the color of the coolant in the expansion tank matched the color of the coolant in the radiator. When I added the distilled water the color in the expansion tank was lighter than the color of the coolant in the radiator. HTH

 

[bullwinkle]

It'll push some out hot, & suck some back in when it cools if everything is sealed well. My theory is, just don't put straight water in the expansion tank in winter!

 

[SHOZ]

Very little mixing would happen. If you are changing coolant why leave the old stuff in the expansion tank?

I usually flush twice with distilled water then drain, pur in a gallon of 70/30 and the rest is 50/50. Comes out to around 50/50 when done.

If there is air in the engine then it will blow that out and suck in the tank coolant when it cools. But as long as there is air it doesn't push much coolant out of the engine. If the system is sealed well, then over time the air will dissolve in the coolant as it heats up and is under pressure , then when it is pushed out and depressurizes the air becomes undissolved. If there are any minor leaks, the system will loose vacuum on cool down and it doesn't work very well.

 

[CharlieBauer]

In your case, I'd top up with distilled water.

Your system now has 53.33% new coolant plus 2.9% old coolant so 56.2% total. Adding distilled will improve cooling without affecting freeze protection.

And you've presumably used the 2 gallons of coolant you got for this job. So why buy any more that you won't need? Coolant life is the same in the jug as it is in the cooling system. So that 90% of coolant you leave in the jug will be mostly wasted.

 

[dlundblad]

Originally Posted By: SHOZ
If you are changing coolant why leave the old stuff in the expansion tank?


Where'd you read that I did this?

 

[dlundblad]

Originally Posted By: CharlieBauer
In your case, I'd top up with distilled water.

Your system now has 53.33% new coolant plus 2.9% old coolant so 56.2% total. Adding distilled will improve cooling without affecting freeze protection.

And you've presumably used the 2 gallons of coolant you got for this job. So why buy any more that you won't need? Coolant life is the same in the jug as it is in the cooling system. So that 90% of coolant you leave in the jug will be mostly wasted.


I've never heard of cooling performance based on antifreeze percentage. This is the thermostat and radiator fans job.

In fact, Zerex allows up to 70% for the lowest freezing temp.

As far a extra coolant, I already have half a gallon of 50/50 on hand from last fall.

 

[CharlieBauer]

Originally Posted By: dlundblad
I've never heard of cooling performance based on antifreeze percentage. This is the thermostat and radiator fans job.

In fact, Zerex allows up to 70% for the lowest freezing temp.

As far a extra coolant, I already have half a gallon of 50/50 on hand from last fall.



For the same volume, water has more heat carrying capacity than coolant. Sure the other elements in the cooling system will regulate the temperature, but the more water in the mix, the more efficiently heat will get carried away.

This is a different characteristic than freeze point and boil over protection.

You can feel and measure this for yourself when blowing hot air in the cabin especially if you do a flush and go from 50:50 to mostly water and back to 50:50 again.

So unless you need freeze protection better than that provided by 50:50, I would top up with distilled to move you closer to 50:50 than you are now.

 

[dlundblad]

So even though the thermostat opens at 195*F, the air will feel hotter with a higher water concentration? That's what you're saying?

 

[DoubleWasp]

Sounds like he is saying that under tougher conditions, 50/50 will be less likely to creep past the thermostat's rated temperature than a higher mixture of coolant.

Most of my trucks have radiators the size of a bad. Fat chance seeing those thermostat Temps when fully loaded in Florida heat. Never get high enough to worry about, but definitely get up past the 190° thermostat rating.

 

[CharlieBauer]

Originally Posted By: dlundblad
So even though the thermostat opens at 195*F, the air will feel hotter with a higher water concentration? That's what you're saying?


The same volume of water will hold more heat when that water has more water and less coolant. How the thermostat reacts to that I am not quite sure but for the water going to the heater core, I don't think the thermostat comes into it.

The last time I did a flush with distilled water, the air blowing in the cabin got incredibly hot as well as hotter with each successive drain and fill.

Here in CA we don't do well when it turns colder in winter, so having hot air in the cabin quickly is important for survival.

 

[dlundblad]

The thermostat has everything to do with the heater core temperature. A stuck open thermostat symptom is poor heat.

I am betting your distilled water flush flushed some crud/ old coolant out of your heater core, (you live in California after all; the heat isn't used as much as it would be here.) thus causing more heat.

 

[CharlieBauer]

Originally Posted By: dlundblad
The thermostat has everything to do with the heater core temperature. A stuck open thermostat symptom is poor heat.

I am betting your distilled water flush flushed some crud/ old coolant out of your heater core, (you live in California after all; the heat isn't used as much as it would be here.) thus causing more heat.


Sure a stuck open thermostat would result in poor heat, but that clearly is not relevant for the point being discussed.

As to having crud / old coolant, I doubt that is the explanation. As I mentioned, the temperature with the final 50:50 was also not as hot. The system is also very clean and more than up to date on maintenance. And you'd be surprised but the heat does get used year round.

 

[dlundblad]

I still don't buy it. Your heat didn't feel hotter because of the water %.

As said before, it's all in a thermostat, which if functioning correctly, doesn't care about coolant/ water %.

As far as relevancy, please.. your first post in this thread had absolutely nothing to do with the OP.

 

[CharlieBauer]

Originally Posted By: dlundblad
I still don't buy it. Your heat didn't feel hotter because of the water %.

As said before, it's all in a thermostat, which if functioning correctly, doesn't care about coolant/ water %.


Ok, let me ask you a question.

If you run 100% coolant, is it bad? And if so why is it bad and what exact mechanism is the reason it's bad?

 

[kschachn]

Originally Posted By: CharlieBauer
If you run 100% coolant, is it bad? And if so why is it bad and what exact mechanism is the reason it's bad?


It's undesirable for several reasons. For one the heat capacity is lower by a significant amount as you yourself posted above.

Also the freezing point is higher:

The boiling point of 100% ethylene glycol is higher but it doesn't get you anything in practical terms since if your cooling system was operating at that temperature you'd be in trouble anyway (speaking for a normal passenger car engine).

Passenger car cooling systems are designed for the range of coolant/water mixtures allowed by the manufacturer. I also suspect that water is required for some of the corrosion inhibitors to function correctly but that's just a guess.

 

[CharlieBauer]

Originally Posted By: kschachn
Originally Posted By: CharlieBauer
If you run 100% coolant, is it bad? And if so why is it bad and what exact mechanism is the reason it's bad?


It's undesirable for several reasons. For one the heat capacity is lower by a significant amount as you yourself posted above.


Good start. Now can you extend that and help the OP understand how differences in heat capacity of coolant leaving the block would alter the amount of heat available in the heater core?

 

[Jetronic]

Originally Posted By: dlundblad
I still don't buy it. Your heat didn't feel hotter because of the water %.

As said before, it's all in a thermostat, which if functioning correctly, doesn't care about coolant/ water %.

As far as relevancy, please.. your first post in this thread had absolutely nothing to do with the OP.


I'm running about 25% AF in my cooling water, and I noticed the same thing...

 

[Yah-Tah-Hey]

And I thought the oil and filter members were a little anal.

 

[HTSS_TR]

Originally Posted By: dlundblad
I still don't buy it. Your heat didn't feel hotter because of the water %.

As said before, it's all in a thermostat, which if functioning correctly, doesn't care about coolant/ water %.

As far as relevancy, please.. your first post in this thread had absolutely nothing to do with the OP.

Agreed.