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Discussion Starter #1
I just recently posted on another thread about how I thought my truck was loosing coolant. I filled it with distilled water (about a quart maybe a little more) to the fill line and I took it on a test drive last night to get it up to temperature and once I got back I saw the lever dropped a little which I know is normal. Well just now I went to see if it went back to max fill line and it hasn't, it was the same as last night. Is this normal or did I lose the coolant? Everything is operating normal like the ECT/EOT temps were 5 degrees apart at max (182/187), no white smoke, no coolant smell, and no oil/coolant mixture.

That being said, what is normal coolant level "activity" in the degas bottle on a normal operating truck with no load and no problems? And after it sits overnight should the coolant rise back up or stay at a lower level?
 

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the coolant level will "drop" when under pressure. It is normal.
 

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"resident smarty pants"
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The cold fill level should be constant (ie when the engine is cold, the level should be the same as the last time the engine was cold).

That being said, if your level was low and you added coolant, sometimes there is an air pocket that needs to "work its way out" and you will see the cold fill level drop some as it does.

BTW - according to Ford, it is best to "vacuum fill" the system - so that you avoid the air pockets.

If you had a certain COLD coolant level, and when you got back from driving the level was lower (even though you now have 200*F coolant), then you might actually have a leak ....... even though the degas bottle is now under pressure. If you were to open the degas cap when the coolant is hot, it will expand with the release of pressure. It will slowly drop back down as the coolant cools.

As the coolant heats up, it expands and pushes against the vapor space in the degas bottle - that is the primary reason the pressure increases. If you drive very hard, then there could be some flash boiling of coolant (definitely you will experience it if the coolant is 100% water) that would also increase the pressure. Under normal driving conditions, and with proper coolant concentrations, there is little chance of significant flash boiling.
 

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@bismic .. I recently did a coolant flush with distilled water only.. on one of the flushes I took the truck up the road with water only degas bottle completely full it whistled like a tea kettle then popped off through the cap.. could this have been damaging??? Truck runs fine and deltas are good ..thanks
 

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"resident smarty pants"
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Not from what you describe, I wouldn't think so.

Driving for very long with only distilled water can cause corrosion to begin, therefore when doing so, only short trips are recommended. Also (as stated) water will boil slightly more easily than coolant, but that shouldn't be much of an issue if the driving was not prolonged and you weren't doing WOT runs.

Water boils at 100*C (212*F) at atmospheric pressure; and at apprx 120*C (248*F) at 15 psig.

A 50/50 glycol solution boils at apprx 110*C (230*F) at atmospheric pressure; and at apprx 130*C (266*F) at 15 psig.

The difference in boiling points between pure water and a 50/50 glycol mix is around 10*C or 18*F. Not a tremendous increase but it is definitely helpful. Our degas bottles will typically run between 8-10 psig pressure with the degas bottle cold fill level slightly below the old MIN mark.
 

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Discussion Starter #6
The cold fill level should be constant (ie when the engine is cold, the level should be the same as the last time the engine was cold).

That being said, if your level was low and you added coolant, sometimes there is an air pocket that needs to "work its way out" and you will see the cold fill level drop some as it does.

BTW - according to Ford, it is best to "vacuum fill" the system - so that you avoid the air pockets.

If you had a certain COLD coolant level, and when you got back from driving the level was lower (even though you now have 200*F coolant), then you might actually have a leak ....... even though the degas bottle is now under pressure. If you were to open the degas cap when the coolant is hot, it will expand with the release of pressure. It will slowly drop back down as the coolant cools.

As the coolant heats up, it expands and pushes against the vapor space in the degas bottle - that is the primary reason the pressure increases. If you drive very hard, then there could be some flash boiling of coolant (definitely you will experience it if the coolant is 100% water) that would also increase the pressure. Under normal driving conditions, and with proper coolant concentrations, there is little chance of significant flash boiling.
Ok so your saying when it reaches the max fill line is due to flash boiling?
 

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"resident smarty pants"
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Not sure I understand the question fully.

The coolant expands a fair amount as it heats up. As a reference, I fill mine to 1/4" below the min line when cold and the highets level that I see when the coolant is up to full temperature is slightly above the min line.

If the level when the coolant is cold varies significantly, then (IMO) you have an air pocket (or had one).

If your cold level is at or below the minimum line and your level when hot gets to the max line then you may have air bubbles or possibly could have some flash boiling going on.
 

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Discussion Starter #8
Not sure I understand the question fully.

The coolant expands a fair amount as it heats up. As a reference, I fill mine to 1/4" below the min line when cold and the highets level that I see when the coolant is up to full temperature is slightly above the min line.

If the level when the coolant is cold varies significantly, then (IMO) you have an air pocket (or had one).

If your cold level is at or below the minimum line and your level when hot gets to the max line then you may have air bubbles or possibly could have some flash boiling going on.
Ok in my case, I filled to a little below the max line. It went down, to just under the min line and it's staying there no matter if engine is hot or cold. (No long trips might have to keep it hot for a certain amount of time idk about that). Today my temps got to 190. As soon as I pop the hood, coolant level is still the same. I open the cap, little pressure like that of opening a coke bottle for the first time and a little trace of steam came out, level did not rise. Outside temps have been cooler recently what's the relationships to coolant and outside temps?
 
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