This post made me curious about coolant flow. I read up on it in my Dodge Service Manual, here is the description:

"The coolant recovery container works in conjunction
with the radiator pressure cap. It utilizes thermal
expansion and contraction of coolant to keep
coolant free of trapped air. It provides a volume for
expansion and contraction of coolant. It also provides
a convenient and safe method for checking coolant
level and adjusting level at atmospheric pressure.
This is done without removing the radiator pressure
cap. The system also provides some reserve coolant
to the radiator to cover minor leaks and evaporation
or boiling losses.
As the engine cools, a vacuum is formed in the
cooling system of both the radiator and engine. Coolant
will then be drawn from the coolant tank and
returned to a proper level in the radiator."

So I guess I was partially correct on coolant flow. According to Dodge the reservoir returns coolant to the radiator, not the engine.

Jimmy

 

Right... That action is being caused by the engine (Water pump) but the fluid is sucked from the tank to rad then cycles through the engine...

When you turn your truck off heat builds up in the engine and pressure increases (Not sure what they are talking about vacuum..) I guess you could try and use that word.. and coolant is forced out by the wide open Radiator Cap through the hose and into that tank..

Restart the motor and it will draw fluid from it.

Also to say its used as an overflow is technically correct. If too much pressure (Caused by Heat buildup and the boiling of the liquid) occurs more fluid from the rad would go into the tank.. the tank has an overflow on it and this would be overheating.

 

You did not say which engine you have. If it's a 3.9 the coolant capacity is 14 quarts, which is 3.5 gallons. If it drained out 2 gallons that is just about right I guess. What you need to do now is try to remember or calculate how much of the coolant still in the engine is coolant and how much is water. From your original post it sounds like the coolant that is left in the engine now is probably watered down and diluted a pretty good bit. You might need to buy a couple of gallons of coolant, add one gallon to the system and see where that brings the coolant amount. Then maybe dilute the other gallon of coolant with water 50/50 or a little stronger maybe and then add that in a little at a time until the coolant level is correct. Then you can buy a coolant tester hydrometer at any parts store that will tell you what the temperature protection level is and you can use that to check the coolant to water ratio, there are charts online that will help you figure out the ratio based on your temperature protection specs.

I went through problems a lot like this when I did my water pump. It was a nightmare, the first water pump I installed I had the coolant mixture correct but there were problems with the pump so I had to take it off and install another pump and that is when I got the coolant ratio all screwed up. My truck ran like crap and used a lot of gas because I had too much coolant so it was running way too rich because it never got to normal operating temperature. I had to drain and fill and check it with the hydrometer until I got it correct and it was a PITA.

Jimmy