Pressurized vs Non-pressurized Cooling Systems

[oddball]

There's an entertaining fight going on that deserves its own thread instead of mucking up everyone's repair/help threads.

Should an auto cooling system run unpressurized? Is it acceptable to run unpressurized, and if so, for how long? It is likely to cause issues, or to fix problems?

The argument for non-pressurized is systems with aging and fragile plastic parts tend to develop very small cracks that expand under heat and pressure, causing leaks and overheating. By running unpressurized, the cracks are less likely to form since the parts aren't under pressure stress, and any existing cracks are less likely to open.

I think the LS V8 does not lend itself to running unpressurized very well.


First, the engine doesn't get very much coolant flow:
1) The cooling path is very complicated, without considering the heater circuits, hindering free fluid flow and exchange with the radiator.
2) The water pump has notoriously low flow rate, hence the need of an Aux pump

This means coolant moves relatively slowly through the engine, which means it will accept more heat. Running unpressurized has a much lower boiling point. Combine poor flow with a lower boiling point, and the engine should experience spot heat and boiling, particularly around the exhaust valve seats. The really bad part of spot boiling is it can create an air pocket that is self-reinforcing. Poor flow means its more difficult to collapse that pocket. Also note that the CHT is on the intake side of the head, which may continue to flow properly while the exhaust is experiencing boiling.

IMO, running unpressurized is more likely to cause long term damage, especially a warped head or block. If the engine is babied then it may survive fine, but elevated exhaust temps would stress this configuration significantly.

I suppose my main question is if a system is overheating when pressurized, how does running non-pressurized resolve the overheat?

 

[Kumba]

I haven't seen an unpressurized or open loop cooling system on an engine that wasn't manufactured in the 20's or earlier. I know some early diesel's had a small cooling tower that was used to cool the cylinder heads.

There's two other important factors not mentioned in your post. Those would be the Thermal Efficiency and Transition Point of the Metals.

On the thermal efficiency angle, a warm engine is going to atomize fuel better and have a more complete burn since less heat is lost to the block/head/piston during the combustion cycle. So with a hot chamber, the fuel will ignite easier, burn faster, and have less emission since the burn is more complete. Counter-intuitively, a hotter engine does NOT make more power. This is because the fuel is not burning for the full combusion cycle in order to make sure unburnt fuel isn't pumped out the exhaust port. This is mostly for fuel efficiency and emissions. Conversely, on a drag car, you want the block as cold as possible that will allow for decent fuel atomization and a thermal load capacity to take wide open throttle without detonation. You also want your fuel to burn for the complete combustion cycle almost to the point of back firing to make sure the piston is always under as much pressure as possible. This is why drag cars don't warm up before they run, and will even just push the cars to the line and only start up for the burn-out.

As far as the Transition Point this has to do with the Coefficient of Friction and how it relates to temperature. There is an optimum temperature at which metal has the least amount of friction and therefore wear. Too cold or too hot and the metal wears faster. This temperature range at which a metals friction is lowest is called the "Transition Point" where you transition from lower to higher coefficient of friction. So in a street car it's important to have all the different metals of the engine running in a certain optimum temperature in order to get the best wear and longevity out of the engine. I am going purely from memory of when I worked in a machine shop years ago but I think the optimum CoF for iron (nodular/cast) was around 225 farenheit. I don't remember what aluminum was and this really only plays a roll on rotating parts. An aluminum engine block itself isn't really factored into CoF since the bearings and steel cylinder sleeves and all that are what takes the wear.

Modern cars run around 200 degree thermostats. If you weren't able to pressurize the cooling system you would have to use something other then Water as the base of the coolant mixture. Water at 14-psi boils at 248-degrees Farenheit. With a 50:50 antifreeze mix you can get 263-degrees Farenheit. Unpressurized you'd only get 212-degrees Farenheight at sea level. Less at higher elevations. There just wouldn't be enough thermal capacity in the coolant to keep the engine at an optimum temperature for efficiency, emissions, and longevity.

I don't think asking whether or not to run an unpressurized cooling system is a real question. I think the real question is why Ford used platic parts so extensively throughout the cooling system. The answer to that is simple: Cost. It's much easier to injection mold a complex part out of plastic even if you know it will fail in 5-8 years then it is to cast and machine something out of metal. Literally all you do after you injection mold the part is put metal inserts in for the attachment points, run a belt sander over the mating surfaces to remove flashing, and the put an o'ring anywhere you want a seal.

 

[LSV8FAN]

Remember that hoses are also recommended to be changed after about 10 years, although I had a '94 Buick Roadmaster with a pressurized recovery tank (Degas bottle) and didn't have the hoses replaced in the 19 years that I owned it; I did have to replace a steel coolant tube because it developed pitting and started leaking. On the other hand, the Degas bottle on the Buick had much thicker walls than the one on the LS.

 

[LS4me]

I don't think asking whether or not to run an unpressurized cooling system is a real question. I think the real question is why Ford used platic parts so extensively throughout the cooling system. The answer to that is simple: Cost. It's much easier to injection mold a complex part out of plastic even if you know it will fail in 5-8 years then it is to cast and machine something out of metal. Literally all you do after you injection mold the part is put metal inserts in for the attachment points, run a belt sander over the mating surfaces to remove flashing, and the put an o'ring anywhere you want a seal.

It was also to save weight. Manufacturers are looking to save ounces to meet CAFE standards, not pounds. Remember Lincoln deleted the rear sub enclosure to save weight.

 

[joegr]

I haven't seen an unpressurized or open loop cooling system on an engine that wasn't manufactured in the 20's or earlier. I know some early diesel's had a small cooling tower that was used to cool the cylinder heads...

It's not impossible that Don knows something that all these engineers for all these years don't know, but it is very unlikely. It is far more likely that he has tried something that has worked only in his very limited circumstances. When the first part broke on my 04 (nipple for the engine degas hose), I did leave the cap loose so the hose wouldn't pop off. I did this for about one week, which was how long it took for all the plastic parts to arrive. I put the cap back on tight after that. I suspect (don't have proof) that you could soak the parts in hot coolant for five to seven years and see the same failures as you do on a pressurized car system.

I would like to add to the discussion the fact that mixing in more antifreeze into the coolant makes it less effective at removing heat from the engine. Water transfers heat better than antifreeze. Pure water would be best from a heat transfer only point of view. Of course, we mix in antifreeze because we don't want it to freeze in the winter, we want to reduce corrosion all year long, we want a little extra margin before the coolant boils, and we want to lubricate the water pump(s). Some time back, it was determined that a 50/50 mix was the ideal compromise, and it would seem that the years have proven this to be true.

 

[cammerfe]

Or, to add to the discussion, use propylene glycol instead of ethylene glycol as the coolant. It's available at heating supply stores and is used in home radiant heating systems. I won't 'pitch' it here but if the subject interests you a little Googling would be worthwhile. The brand name for automotive systems is Evans but it's several times as expensive as the 'home' product.

KS

 

[don-ohio]

Boys, just keep blowin those Degas bottles. It's YOUR business if you wanna keep replacing parts.Meantime,I'll just be driving my LSes to Florida or wherever I want with no concern about blowing parts or overheating. I've only been doing this since the 80s,guys, so yeah it might fail me one of these days before I die.LOL! don-ohio ^)

 

[Kid_Lyrics]

I should've seen this coming.

However, I will say. With my luck of overheating, I had the cap on tight, creating pressure. I could not drive more than 12 blocks from my house without smoking coming out profusely.

I then decided that I NEEDED to make it to work that day. I drove back home and decided to shoot my shot.

I loosed the cap one turn from tight and drove all the way to work.

On the way there I would:

1. Stop at least 3 cars away from the stop light to keep some sort of air getting to the engine.
2. If there were no way to effectively do (1). I would drive off the main road I was on into a gas station or offset road just to keep air.
3. Keep the heat on high even tho I do not have heat nor ac at the moment.

Now, I'm not sure if it were because of all the weird extra work I did or just a stroke of luck. I made it to work doing 60mph the entire way there including dropping down to 45mph when on public roads.

I immediately opened my hood when I got to work anticipating a large cloud of smoke from the engine and what do I get? Nothing, Not so much as steam.

I did notice a bit of a loss of water in the degas bottle which of course I have 4 bottles in my car. The loss was no more than the space between the Hot and Cold Max Fill lines.

I'm not encouraging this, nor am I saying this works. I will say after driving there and back, I didn't have the issues I had every other day.

I'll try it again when I go back to work again this week. I am indeed babying the engine. When I say baby, I mean...... baby. As scared as a paranoid-ocd-epileptic- teenager.

Oh, the drive from my home to work is approx 40mins.

 

[Kumba]

Boys, just keep blowin those Degas bottles. It's YOUR business if you wanna keep replacing parts.Meantime,I'll just be driving my LSes to Florida or wherever I want with no concern about blowing parts or overheating. I've only been doing this since the 80s,guys, so yeah it might fail me one of these days before I die.LOL! don-ohio ^)

Whatever works for you. I'd rather spend the money and not worry about it for another 100K+ miles.

On a side note, I don't know of too many people who have had to re-work the cooling system more then once as long as they used Motorcraft degas bottle. I know there's plenty of horror stories about the dorman bottles though.

 

[Kumba]

I did notice a bit of a loss of water in the degas bottle which of course I have 4 bottles in my car. The loss was no more than the space between the Hot and Cold Max Fill lines.

Yeah, with the system open you will boil off water and have to replace it frequently. Probably just something you'll have to check every time you get gas. The LS will go into power reduction mode if it gets too hot and shut down every other cylinder using intake air to cool itself. The one thing helping you is that it's still relatively cold up north. If it were the middle of summer with 100-degree heat waves then that would likely be a different story.

 

[Kid_Lyrics]

Yeah, with the system open you will boil off water and have to replace it frequently. Probably just something you'll have to check every time you get gas. The LS will go into power reduction mode if it gets too hot and shut down every other cylinder using intake air to cool itself. The one thing helping you is that it's still relatively cold up north. If it were the middle of summer with 100-degree heat waves then that would likely be a different story.

Yea, that's what I was hoping for. However, that's why I keep so many bottles in my car INCLUDING one full 50/50 just in case. Yea, I've read that 12345 run and 678 alternate to allow cool air in the engine itself. Hopefully I can get this fixed before it gets way too hot up here again.

 

[FDR]

Yea, I've read that 12345 run and 678 alternate to allow cool air in the engine itself.

I assumed it it would alternate every cylinder so that every cylinder only fires once in 8 strokes, as opposed to 1 in 4 (intake compression combustion exhaust, intake compression nothing exhaust). It would seem strange to only deactivate 3 cylinders, especially all on one bank, to desperately try to cool an engine with no coolant

 

[joegr]

I assumed it it would alternate every cylinder so that every cylinder only fires once in 8 strokes, as opposed to 1 in 4 (intake compression combustion exhaust, intake compression nothing exhaust). It would seem strange to only deactivate 3 cylinders, especially all on one bank, to desperately try to cool an engine with no coolant

You are correct, he is not. The idea is to pass fresh cool air through each cylinder between firings.

 

[Kid_Lyrics]

You are correct, he is not. The idea is to pass fresh cool air through each cylinder between firings.

Well, it's not my fault the information I read was incorrect. OH well. It's every other cylinder. Same difference.

 

[FDR]

Well, it's not my fault the information I read was incorrect.

No one blamed you, don't worry about it lol. joegr's response was just blunt. My post was more of a question

 

[Kid_Lyrics]

No one blamed you, don't worry about it lol. joegr's response was just blunt. My post was more of a question

Lol, I took no offense to it. I was just making the statement. Isn't it amazing how text can be misinterpreted?

 

[1LoudLS]

joegr's response was just blunt.

I prefer the term efficient.

Joe doesn't mix words or beat around the bush, he just gives you the answers you need as simply as efficiently as possible!

 

[1LoudLS]

I want with no concern about blowing parts or overheating.

if you really had zero concern, I doubt that you would have bought any extra parts to keep in your trunk...

 

[don-ohio]

Hoping the best for you,KidL...........I knew you'd never make it with pressure. Once you get the fan fixed,any rotten parts replaced, and filled with 60/40 and loosen Degas cap, your problems will subside.
don-ohio ^)

 

[Kid_Lyrics]

Hoping the best for you,KidL...........I knew you'd never make it with pressure. Once you get the fan fixed,any rotten parts replaced, and filled with 60/40 and loosen Degas cap, your problems will subside.
don-ohio ^)

Well see, If I replace and refill, I'm definitely going to tighten my cap lol. I wouldn't waste coolant like that or at least, it seems that would be one occurrence.

 

[don-ohio]

Well,if you think when you get done,that your parts will stand 16psi,go for it.
BUT, you will NOT evaporate your coolant at 60/40 mix enough to even notice it for quite a while. WATER evaporated under no pressure,but you got to work. When your cooling system is RIGHT,like mine,you won't notice evaporation. And you won't blow parts.I've done this too long,KidL.....I know the score.
don-ohio ^)

 

[Kid_Lyrics]

Well alrighty then.

 

[Kumba]

Well,if you think when you get done,that your parts will stand 16psi,go for it.
BUT, you will NOT evaporate your coolant at 60/40 mix enough to even notice it for quite a while. WATER evaporated under no pressure,but you got to work. When your cooling system is RIGHT,like mine,you won't notice evaporation. And you won't blow parts.I've done this too long,KidL.....I know the score.
don-ohio ^)

I dug around a little and found some baseline numbers for coolant and water mixes.

Boiling points:
------
Water at atmosphere boils at 212-degrees Farenheit.
Water at atmosphere with 50/50 coolant mix boils at 226-degrees.
Water at atmosphere with a 60/50 coolant mix boils at 231-degrees.
Water at 14-psi boils at 248-degrees Farenheit.
Water at 14-psi with 50/50 coolant mix boils at 263-degrees.
Water at 14-psi with 60/40 coolant mix boils at 267-degrees.

Heat transfer of water:
----
Straight Water - Baseline of heat transfer, one of the most efficient coolants available
50/50 Coolant/Water mix - Around 86% as efficient as plain water
60/40 Coolant/Water mix - Around 83% as efficient as plain water
100/0 Coolant/Water mix - 65% as efficient as plain water


So you are going from the OEM recommended setup which boils at 263-degrees and is 86% efficient at transferring heat to one that boils at 231-degrees and is 83% as efficient. So not only have you made the cooling system more prone to hot spots and boiling by reducing the operating margin, but you've also decreased the amount of heat that it can remove from the engine. This means that the coolant overall will run hotter then it would under the pressurized setup.

The other thing to remember is that coolant temperature is an average as measured at the outlet. The actual coolant temperature inside the engine can spike depending upon what's going on. So while the car may idle or cruise around in the 190-200 range, driving up a mountain or through phoenix or anything stressful can easily get you into 220+ territory.

I wouldn't risk an engine repair over $600 worth of cooling system components that are going to last 100K+ miles. That seems like the wrong way to prevent an issue or save money.

The only reason people think the car has a bad cooling system is because they bought a 10+ year old car. You own anything for 10-years or 100K-mi and **** is going to break.

If you had bought the car new you would likely only be bitching about the COPs, DCCV, Trans Solenoid Block, and Rear Toe Links. A good chunk of those never made it to 30K before the nightmare started.

 

[oddball]

Kidl, nothing directed at you, nor BigRig, nor Don. I think it's an interesting topic to look at the actual physics of the cooling system and how it's designed. I used to do just about anything to limp a car home in the past - once pulled the Cutlass with no driveshaft about 15 miles. Now I make good use of my AAA membership.

Don, I'm more interesting in spot boiling and long term damage. Would this cause an exhaust seat to burn? Exhaust valve to seize? One would have to look at the engineering models, or at least section a head, to get a decent idea of how significant the issue might be. Now on 70's engines with big water pumps, wide open coolant passages and heater sections well isolated, there's a lot more flow, so I'd expect more even cooling even unpressurized. However, four corner cooling is a common modification on older engines, specifically to even out the cooling in the head. Granted, the older systems have the coolant enter the block while newer systems usually enter the heads.

 

[joegr]

...
Water at atmosphere boils at 212-degrees Farenheit.
Water at atmosphere with 50/50 coolant mix boils at 226-degrees.
Water at atmosphere with a 60/50 coolant mix boils at 231-degrees.
...

Things get even worse if you don't live/drive at sea level.
I think that just maybe they knew what they were doing when they pressurized it.