Mekanik Posted August 7, 2009 Share Posted August 7, 2009 We are having a debate this afternoon. Here is the question: On a vehicle with a de-gas bottle, will the coolant level drop or rise when the vehicle is warmed up. Now we aren't talking about a 6.0l with a venting bottle for whatever reason. It is just a genral question. At first I said that it would rise, but after listening to another tech who is a instructor at a community college I changed my mind. " Don't confuse expansion with pressure. " It kind of makes sense. If I were to pressure test one of these systems, the coolant level will go down because it is being compressed. Maybe I'm wrong. We have several techs here that are saying it will go up. What do you think and why???? Quote Link to comment Share on other sites More sharing options...
exmod110 Posted August 7, 2009 Share Posted August 7, 2009 drop.. the press builds up with a good cap, the hoses expand and the level drops... until you open the system. Quote Link to comment Share on other sites More sharing options...
Jim Warman Posted August 7, 2009 Share Posted August 7, 2009 Being a liquid, coolant can't be compressed... you can pressurize it... but you can't change it's volume. Now.... if there is a measurable amount of air entrained into the liquid, you might be able to measure the change in the volume of the emulsification - but it will be the air that is compressing - not the liquid. But, a funny thing happened on the way to the bar mitzvah... the liquid warmed up and expanded... And, like Don said, when the pressure built up, the hoses got "bigger"... In an ideal system, there wont be any air.... but the cooling system and the dynamics of the engine preclude any assumption of "ideal". Hot spots can flash coolant into steam .... vibrations can cause localized cavitation .... Hmmmm, time to install a clear hose for degas????? Quote Link to comment Share on other sites More sharing options...
Mekanik Posted August 7, 2009 Author Share Posted August 7, 2009 So Jim, your saying that ideally the level will go up? Quote Link to comment Share on other sites More sharing options...
dieseldoc Posted August 7, 2009 Share Posted August 7, 2009 It will go down. Here is the way too check. Test drive a truck to operating temperature. Mark the coolant level on the degas bottle or just watch it. Now slowly open the cap and watch it rise. I have seen this several times on my own 6.0 pick-up. As jim said hot-spots could cause the coolant to change to steam which will compress as well as the hoses expand as the system builds pressure. Quote Link to comment Share on other sites More sharing options...
Mekanik Posted August 7, 2009 Author Share Posted August 7, 2009 That makes sense, and I remember seeing the coolant level come up when opening the system. Quote Link to comment Share on other sites More sharing options...
Jim Warman Posted August 7, 2009 Share Posted August 7, 2009 Ideally, the level would remain static... but it wont because there is no real "ideal" in a machine like this. But at the same time, I'm not going to worry about it... We will generally see the level go down as pressure builds - because of the compressability of gaseous factions trapped in the system and entrained or perhaps emulsified into the coolant as well as the forced expansion of rubber goods. If we leave the cap off the degas bottle, we will generally witness the thermal expansion of the coolant. Let's not forget the water pumps effect on some of this stuff, too. Ever notice, "back in the day" you could squish more coolant into a crossflow rad by revving the engine? Vertical flow rads wouldn't? Quote Link to comment Share on other sites More sharing options...
GregH Posted August 7, 2009 Share Posted August 7, 2009 Water and antifreeze are compressable. If you take a given volume of coolant, and change the pressure applied to it, then the volume will change. Granted the change in volume will be slight, but it is measurable. Coolant will expand when heated, and contract when cooled. A given mass of coolant will have a certain volume at a low temperature, and a much higher volume at higher temperature - given that the ambient pressure is the same. The effect is easily visible without measuring equipment. The materials used in engine construction expand and contract with temperature changes. This results in reduced volume in the coolant passages - picture a box full of partially inflated balloons. A certain volume of free space will be present between the balloons. Now blow the balloons up a little more, and the available volume between the balloons will shrink. The effect is slight, but measurable. So, the phenomenon that is most visible is coolant expansion due to temperature changes. What is in the cooling system? Coolant and air, right? In a given, relatively fixed volume (aside from slight block expansion). Heat the coolant. The coolant will want to expand. The available volume is the same, so the pressure will increase. The air component will be exposed to increasing pressure from the coolant. Air, compared to coolant, is very, very compressable. This means you can drastically change the volume of a given mass of air without affecting the pressure very much. Since the air will compress easily, it will give in to the pressure exerted by the coolant. This will allow the coolant to expand, and rise in the degas jug. As long as the pressure in the system does not exceed 16psi (or whatever the cap is rated for) then the system will remain sealed and will drop to the original level and pressure when the temperature falls to the starting point. Another way to think of it: There is coolant and air in the system. When it heats up, the air in the top of the jug is pressurized. Where did the pressure come from? From coolant pressing on it from the bottom of the air cushion. Revving the engine makes the coolant level drop... The degas jug is typically tapped into the system on the suction side of the water pump (in the lower radiator hose or near it's connection to the front cover). This is for safety, because this is the lowest pressure area of the system. Rev the engine, the water pump sucks harder, and drops the pressure of the coolant in that area. Downstream of the water pump the pressure increases and expands the upper radiator hose, heater hose, and whatnot. This increases the volume of these areas, coolant fills the extra space, and coolant is drawn from the degas jug, dropping it's level. Crossflow radiators had the cap on the cold side of the radiator. Vertical flow radiators had the cap in the hot side. Quote Link to comment Share on other sites More sharing options...
Keith Browning Posted August 9, 2009 Share Posted August 9, 2009 That makes sense, and I remember seeing the coolant level come up when opening the system. I have also noticed this and made a mental note of it. Quote Link to comment Share on other sites More sharing options...
LARRY BRUDZYNSKI Posted August 9, 2009 Share Posted August 9, 2009 Quote: Revving the engine makes the coolant level drop... The degas jug is typically tapped into the system on the suction side of the water pump (in the lower radiator hose or near it's connection to the front cover). This is for safety, because this is the lowest pressure area of the system. Rev the engine, the water pump sucks harder, and drops the pressure of the coolant in that area. Downstream of the water pump the pressure increases and expands the upper radiator hose, heater hose, and whatnot. This increases the volume of these areas, coolant fills the extra space, and coolant is drawn from the degas jug, dropping it's level. I have read that this is why it's installed on the low side of the pressurized system. It only makes sense to protect the cooling system. Quote Link to comment Share on other sites More sharing options...
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