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Thu Jul 26, 2012 6:29 am

Either my search skills failed me, or there has yet to be a thread devoted entirely to the idea of depressurizing the coolant system. I have caught whiffs of it buried inside many other threads, but I think this deserves to be discussed in one thread. I'd like to hear pros and cons.

Here is my understanding to date:

Pros - Why pressurize the system. The logic to the pressurized cooling system is that 15 PSI of pressure increases the boiling point of the cooling system. It also means that the cooling system will react consistently at different altitudes (since high altitudes have a lower boiling point).

Cons - Why pressure is bad. The downsides of a pressurized cooling system are, well, pressure. Pressure strains old components leading them to fail faster. I recently had many parts of my cooling system explode when a 'bad' cap was replaced with one that maintained pressure (and I suspect was bad in that it did not release pressure either!). The risks here are blowing hoses, heater cores, and if you are really unlucky, pushing a weak head gasket seal over the edge (although this seems far fetched to me - is it? surely there is a lot of pressure on the engine combustion side!). The final part of the con - and this is the worst one in my opinion - is that expansion tank caps go bad. If they go bad and hold pressure higher than 15PSI, perhaps blocking entirely, then they are going to blow some other part of your cooling system, weakest first, and lead you to a whole bunch of premature maintenance before you replace the blocked up cap.

The morymob mod is the only reference I have seen here, aside from the 'get home in a pinch' suggestion of loosening the cap (which could let coolant spill out onto the road). It would be fantastic if someone can post some pictures of the exact procedure here to create the depressurized expansion cap. The mod consists of drilling a small hole inside the seal at the top of the cap (not through the cap).

So, aside from morymob - who else runs their cooling system depressurized? How is it going for you? In my opinion, this sounds like a stark raving sane idea.

Thu Jul 26, 2012 7:44 am

One problem I can think of is that with an open system any small leak areas have the potential to let air in rather than seeping a small amount of coolant out. air pockets prevent proper circulation.

The stock system can be fairly reliable if properly maintained. If your having frequent issues perhaps you should consider replacing all you hoses and other plastic parts in the cooling system. That's what I did 5 years agon on my daily driver carat ( all new hoses, junctions, pipes and radiator). I have not touched anything on the cooling system since.

No manufacturer has offered a car with an open system in the last 80 years. That ought to tell you something right there.

Thu Jul 26, 2012 9:00 am

Syncrozilla wrote: One problem I can think of is that with an open system any small leak areas have the potential to let air in rather than seeping a small amount of coolant out. air pockets prevent proper circulation.

The stock system can be fairly reliable if properly maintained. If your having frequent issues perhaps you should consider replacing all you hoses and other plastic parts in the cooling system. That's what I did 5 years agon on my daily driver carat ( all new hoses, junctions, pipes and radiator). I have not touched anything on the cooling system since.

No manufacturer has offered a car with an open system in the last 80 years. That ought to tell you something right there.

This is a great reply.

Your van was designed to have a pressurised cooling system and it works extremely well when properly maintained. Replace the worn out parts of your van and drive with confidence! ;)

Thu Jul 26, 2012 9:01 am

A normal system will generally develop about 10psi internally, although higher transients can be expected. So the cap blowoff capability does not come into play most of the time, but does need to be there and working. The pressure containment accounts for the majority of the increase in boil point. What is often overlooked is the suppression of cavitation and spot-boiling that containment offers; I can guarantee that those running non-pressurised systems are experiencing increased spot-boiling in the cylinder head. How do I know? because minor spot-boiling occurs even within a pressurised system (and is one reason for the high-pressure transients), so it's going to be even greater without suppression. And I have observed numerous systems with a non-holding cap spot-boil badly enough that they were diagnosed as having combustion seal leaks when all that was being seen was coolant vapor, not combustion gases, reaching the pressure bottle. Spot-boiling results in decreased and uneven cooling effect at those hottest head surfaces, as well as erosion of the surfaces. Cavitation occurs mainly at the water pump impeller and can erode the impeller and volute, shortening water pump life and lowering flow rate as the pump loses efficiency.

The higher viscosity of glycol mix does aid in boil/cavitation suppression, but not as much as pressure containment does. The temptation might then be to increase the glycol component to have higher viscosity, but that would work at cross-purposes because glycol is much less efficient a heat absorber/rejector as plain water. Antifreeze mainly performs its eponymous function, boil point increase being relatively minor compared to freeze point decrease, and it offers controls to corrosion, cavitation, aeration, and other negative factors that were serious problems in early water-only systems.

Some people do run open systems and get away with it, as these effects are not immediately apparent but they are occurring nonetheless. As power demands and especially elevation increase, though, the negative effects become greater; at high elevations such as where I reside, open systems have been immediately problematic.

People often point to the Evans open cooling approach and use that example as a free pass to run their own system open, overlooking the fact that the Evan's coolant has a proprietary additive package designed to manage these and other effects.

So bottom line is, open system can be done and things don't immediately blow up, but there are unseen negative effects occurring constantly that would be better-controlled with containment. A pressurised system lets the engine be operated safely in a much wider range of heat and load conditions, and that is why no manufacturer has sold a vehicle using a non-pressurised cooling system since the advent of such a thing, it's overwhelming benefits were so obvious to the vehicle designers.

If you want to run an open system just to prevent leaks and ruptures, just be aware that you are only applying a band-aid, there are no leaks and ruptures when the system components are kept in good condition.

Thu Jul 26, 2012 9:16 am

thanks. this was the kind of information i wanted to get. so, clearly, anything that reduces the risk of coolant boiling in the system will increase engine life.

i did not understand the principle behind cavitation, but wikipedia gave me an idea (i think). my layman one sentence: cavitation (bubbles forming and dissolving rapidly) increases the errosion of a surface (such as the engine cylinders and heads). http://en.wikipedia.org/wiki/Cavitation

there are many threads on overheating and ideas for improving the cooling system. it is interesting to note however that the idea that even though the coolant does not appear to be boiling, this 'spot-boiling' will likely increase as the temperature of the cooling system increases.

Thu Jul 26, 2012 1:55 pm

I drilled a hole in my pressure cap as a band aid fix for when my front heater core started leaking. I wanted to relieve the pressure to slow the leak untill I could pull the dash and replace the heater core. I also ran straight water so I wasn't dripping anti freeze inside the van.

After the first drive where the engine got fully up to temp, I shut down the engine and could hear a gurgling and there were some bubbles in the pressure tank, the water was boiling in the heads after shutdown and probably while driving too. I just parked the van untill I could fix the heater core. I'm running a subaru but the same thing should happen to a wbx too.

It's a band aid and a temporary solution at best.

Thu Jul 26, 2012 3:15 pm

I keep a drilled cap in the glove box. If I could get it I would probably try a low pressure cap, like 4-7psi. I have long run low pressure caps on all of my older more conventional water cooled vehicles with great success.

Thu Jul 26, 2012 8:00 pm

I prefer a pressurized system for sure.

Thank you Tencent for your post.

Thu Jul 26, 2012 9:16 pm

ya thanks a lot for the info I had wondered about it for a while now...

so what about this proprietary additive...something to use an a wbx or other engines ?

Fri Jul 27, 2012 4:15 am

Guess i'll add my 2-cts here on no-press.Done it sincr '93 on ALL my wbx's,5,to date and no blown,split etc parts. One, a '94 was driven almost 14 yrs and i put well over 100K on it, had 330K when i sold.Each has their own theory(?) as what goes on in the engine but NONE have over heated or was a problem. I also stated each time to insure the cooling system was up to par to start as it should be anyway. U do it your way and i will keep on keeping on, i rest my case.

Fri Jul 27, 2012 4:24 am

Here's a table of the impact of pressure on boiling point (from http://avenger-valkyrie.org/techinfo/antifreeze.htm)

Code:
Effect of System Pressure on Boiling Point

Coolant 0 psi 4 psi 8 psi 12 psi 16 psi 20 psi 24 psi
Water 212F 225F 233F 242F    252F 260F 265F
33% 220F 230F 240F 253F    260F 268F 273F
44% 224F 234F 245F 257F    265F 272F 279F
50% 226F 236F 248F 259F    267F 275F 280F
60% 231F 241F 253F 264F    273F 280F 285F

Fri Jul 27, 2012 5:59 am

morymob wrote: Guess i'll add my 2-cts here on no-press.Done it sincr '93 on ALL my wbx's,5,to date and no blown,split etc parts. One, a '94 was driven almost 14 yrs and i put well over 100K on it, had 330K when i sold.Each has their own theory(?) as what goes on in the engine but NONE have over heated or was a problem. I also stated each time to insure the cooling system was up to par to start as it should be anyway. U do it your way and i will keep on keeping on, i rest my case.

Thanks. It is great to hear the long term reports on this. I've met several people who have suggested this to me.

Morymob - did you change any of the other components such as the thermostat or radiator fan switch?

I don't think the pro/cons have changed much from the first post above. The only new point for pro pressure is a lower risk of cavitation and thus wear from spot boiling. Though, I am not convinced that a 30-45oF change in boiling point is going to stop spot boiling in an engine with a temperatures that are much much higher. tencentlife isn't this reasonable or off? I get it that more temperature means more chance of spot boiling, but by how much?

I do see the argument for consistency at different altitudes. Being high altitude might drop the cooling system into boiling over when it's running in normal temperature ranges. based on the numbers above, i'd guess that less pressure may drop boiling point to 215oF with 50/50, or to 200oF with water, which may be a little close to the target 190oF operating temp.

Fri Jul 27, 2012 6:09 am

Try some water wetter, it will help cool things down.

I also recycle Evans coolant from race cars....some only use it for one race and change it.
It displaces heat very well.

Fri Jul 27, 2012 6:22 am

I've been reading about Evans and am intrigued. Given that I have spent close to $400 in VW coolant over the past month, 5he cost of Evans seems like it is on par with the cost of the offical VW blue blood (if not cheaper!?!)

I searched for more info on Evans here but I didn't find any tales and issues with people who had long term experience using it. Insynchro - have you been using it for a long time? Is there any cause for corrosion fears for VW engines? I presume you mean the racing blend (obviously if you're recycling it from race cars).

Fri Jul 27, 2012 6:35 am

No issues to report.
I use it for a year max in the vans.
I flush each summer as I have plenty of it around.
You can tell by smell it the stuff has boiled.
If so, I do not reuse it.

Evans hooks up my race team, so we have plenty of it around.

:arrow: no H in syncro :arrow: :wink:

Sat Jul 28, 2012 3:55 am

All other cooling sys parts left stock, changed one thst,3rd wbx,it was bad when purchased. The metal disc is thepart needed to have vent hole.Don't have the long hard high elevations here some do but the shorter hard climbs haven't caused a problen and i run over them all times of the yr.

Sat Jul 28, 2012 4:47 am

I have looked at Evans coolant before, and have been personally unwilling to experiment with it due to a single factor: the lab test results on Evans' website show that selection of cooling system rubber components is important.
http://www.evanscooling.com/assets/Uploads/Evans-Coolant-1000-hr.pdf

Some rubber compounds perform very poorly. It is difficult enough to find ANY hoses that work for some parts of the system (Syncro oil cooler, front radiator hoses, etc.) without the added difficulty of ensuring that the rubber is compatible with Evans coolant. How do you determine what rubber compound is used in the commonly-available hoses and o-rings?

Mike

Sat Jul 28, 2012 7:08 am

I have replaced most rubber hoses with custom hard lines and silicone hose.
There is a thread recently posted by GEEBEE, who is willing to make all hoses out of silicone for the Vanagon.
I have a few of his hoses already.

All coolants and coolant conditioners will eventually soften rubber hoses.

Loctite sealant and stainless hose clamps are recommended.

Anyone converting to a new engine has the chance to upgrade during the conversion and not brake the bank.