[Pontirag]

Originally Posted by Stuckinda60s

. A frozen engine can also overheat because the ice keeps any water remaining in the system from carrying the heat away. I've seen frozen engines boil over.

I can personally vouch for this fact. as can anybody who lives in an part of the country where the winter tempertures drop below freezing.

I had a 326 in my 66 GTO. I did not have antifreeze in the coolant so I parked my car in the garage. the overnight tempertures droped below freezing and remained ther through the early morning. in the garage the temperture remained above freezing. as I started to work that morning the engine heat kept the water in the block warm, but with the sub freezing temperture and the wind chill at 45 MPH blowing through the radiator. It froze up and burst just about every seam and soldered joint. while the water pressure from the blocked up pump and the quickly escalating temperture blew every gasket and seal in the engine. when the steam blew out from under the hood it emeaditly froze up on my windshield and all over the sides and rear of the car. just enough green from antifreez and brown from rust to give the gold goat this bazaar emarald green and cofee brown hue. I could not fully appreciate it from inside the car because it covered the windshield too.

Typically this happens every winter to many people back east the first time the weather drops below freezing. In fact that day described above caught so many people out that it was a very heIIish day at our gas station. the customers were lined up out to the street and they all had the same symptoms and same problems.

that little 326 only had 47,000 miles on it and the radiator was a 4 core a/c unit. I took it in the shorts for lack of 8 bucks worth of antifreeze.

[Stuckinda60s]

Bret, you've got some good points. But you've also got some misconceptions.

Originally Posted by screamingchief

Also there is the fact that the whole entire cooling system is'nt under the same exact pressure,as a matter of fact pretty much half the system is acutally under negative pressure,and then there are pressure drops across the radiator core as the coolant cools to account for,so that nifty science lab experiement means next to nothing in terms of how all that handy physics knowledge relates to a cooling systems actual operation.

First, there's no such thing as "negative pressure". There is gauge pressure, absolute pressure and there is vacuum. Check it out.

If you think that half of the system is under "negative pressure", then why don't you go for a high-speed run, pull over and then remove the radiator cap with the engine running. After all, that's the low-pressure side of the system, right? Whether or not there is air in the system, there is always positive pressure in a properly operating system when it's above ambient temperature. Expansion of the coolant is what causes the pressure. Any air in the system is compressed the same as if it went through an air compressor. The reason why systems can operate at 220-230 degrees and not have any steam is because they are under pressure. If the suction side of the pump was under vacuum, the water would flash into steam and the pump would become vapor bound. Trust me, it's a fact and it completely conforms to the LAWS of physics. That's what causes cavitation in a pump suction. It can happen at very low temperatures.

If you think that the suction hose can collapse because of vacuum, that's not exactly true. What you are calling negative pressure is, now read this carefully, IN RELATION TO THE PUMP DISCHARGE PRESSURE. There are times when the coolant flow, because of radiator restriction, etc, can not keep up with the pump speed. If there are no voids to fill then the pump will slip and steam bubbles may form at the suction eye. If there is air, it may be further compressed and the lower suction pressure in the hose can cause collapse. That's why the hose may collapse when you rev the engine up, until the water can rush in to fill the void. Most of the times I've seen this happen is when the radiator cap is off. If you think about it, you'll probably recall that the coolant level in the radiator dropped when you revved the engine, as well. That shows that the system is not full. IF THE SYSTEM IS CLOSED AND FULL, THE HOSE SHOULDN'T COLLAPSE BECAUSE THERE WILL BE NO VOIDS TO FILL AND A LIQUID CAN NOT BE COMPRESSED. A properly operating and sized system will not have the hose collapse.

You're right, the system is dynamic and, at times can replenish itself when the engine is running. That would happen if it cooled enough to require water due to shrinkage. Generally speaking, though it won't do that.

Water at atmospheric pressure boils at 212, right? Does that mean that you can open your cap at 200-degrees? I wouldn't advise it because the system is under pressure. What causes the pressure? Even though the temperature is too low to boil and make steam, It's under pressure due to expansion. As you said, the hoses will absorb some of the pressure and acting somewhat like a balloon force some of the hot liquid out of the system if the pressure is relieved. Any air COMPRESSED in the system compounds that action. You can open the system, but you have to vent off that pressure before you remove the cap. Right??? That's true even though the cap is the low-pressure side.

As far as contradictions? Let's just say that air will always flow upward in the system, If there is a clear path for it to do so. That's true whether the system is operating or not. If there is a void with no outlet at the top, the air will be trapped. Maybe I didn't explain myself very well, but there really aren't any contradictions if you read it with an open mind.

[v869tr6]

I posted this bleed system " spill proof funnel " in another post but will put it here also, I must lead a sheltered life because I never have seen it before.
http://www.lislecorp.com/divisions/p...=1&category=19

http://www.youtube.com/watch?v=NReU4...eature=related

[Skip Fix]

"lol, silly me.... The comparison between a honda engine/cooling system and a pontiacs has to be the biggest apples to oranges deal to date."

Silly me Both use thermostat housings and they are both close to the highest point in the cooling system, and if I remember my freshman chemistry air is lighter than water and most other liquids-why brake calipers have bleed screws at the highest point to let the air out.

[Nickv]

I drilled a small hole at the top of my thermostat housing and installed the bleeder form a 98 Grand Prix.. Problem solved for bleeding air from the system, especially after a drain and refill. case closed.

[Shiny]

Warning.. long geeky post with much speculation.

I don't have an opinion about the airbleed debate but the topic is interesting to me technically (engineers compromise their integrity for reasons).

I was surprised to read the source of pressure buildup was attributed to coolant expansion. Most liquids don't expand much with temperature. A quick check online says water, for example, increases volume by 0.00012 per degree F. Here's an online volume expansion calculator that says 2 gallons of water heated from 70 to 190 F will expand to 2.03 gallons. I don't think that is much. Yes, if the "container" was totally rigid and did not expand, that liquid expansion would create tremendous pressure. But the "container" is far from rigid and its volume also increases with temperature. Metals expand with heat so the cooling system volume will expand. The rubber hoses are not very stiff and they will also increase volume.

More likely to me, the increased pressure in this closed system (pressure measured relative to air pressure outside the cooling system) is "predominantly" caused by increased "saturation vapor pressure". Here's another online vapor pressure calculator that shows water vapor pressure increases from 0.4 psi at 70F to 9.3 psi at 190F.

This pressure increase will only happen if the evaporated water has no-where to go (closed system) and can reach "equilibrium" with the liquid water.

I think most radiator caps vent at higher pressures (maybe 15 psi?) and I have no clue what "real" pressures are inside cooling systems but IMO the pressure isn't caused primarily by volume expansion of the liquid coolant. Coolant volume expansion may be a factor but I speculate vapor pressure increase is a bigger one.