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Old 02-12-2011, 05:19 AM   #1
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I don't understand the coolant bleeder/tank system

On my American vehicles there is a pressurized expansion tank at the high point of the cooling system. There is no bleeder valve, just a medium size hose entering at the base of the tank and there is no bleeding during refilling. Just keep adding coolant until you get to the right level recognizing some air will migrate to the tank at first and you might have to add a little more coolant.

Therefore I don't understand the reason and function of the Boxster system. Why are there two "caps"? If you never touched the bleeder would any entrapped air move into the pressuized tank? What does the diaphram inside the bleeder do?

I'm considering a coolant flush and replacement on the 2000 S I bought a couple of months ago. I just want to understand the system before I start working on it and have never encountered a separate bleeder except I have seen distinct bleeders on the motor plumbing when the up and down routing of hoses and components left an isolated high spot in the system. My 1990 Thunderbird had a bleeder vent on the motor.

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Old 02-12-2011, 05:35 AM   #2
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If you don't have a Bentley book but plan on working on the 986, I'd get one. The procedures, photos and tips are really very good in preparing for any work. I'm confident it's covered step by step, I've looked at it but it was a while ago.
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Old 02-12-2011, 06:38 AM   #3
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Quote:
Originally Posted by Dale_K
On my American vehicles there is a pressurized expansion tank at the high point of the cooling system. There is no bleeder valve, just a medium size hose entering at the base of the tank and there is no bleeding during refilling. Just keep adding coolant until you get to the right level recognizing some air will migrate to the tank at first and you might have to add a little more coolant.

Therefore I don't understand the reason and function of the Boxster system. Why are there two "caps"? If you never touched the bleeder would any entrapped air move into the pressuized tank? What does the diaphram inside the bleeder do?

I'm considering a coolant flush and replacement on the 2000 S I bought a couple of months ago. I just want to understand the system before I start working on it and have never encountered a separate bleeder except I have seen distinct bleeders on the motor plumbing when the up and down routing of hoses and components left an isolated high spot in the system. My 1990 Thunderbird had a bleeder vent on the motor.
The reason for the bleeder assembly is quite simple: Large sections of the cooling system lie below the coolant levels inside the engine. As such, air can become trapped, particularly in the radiators way up in the front of the car, causing poor cooling, “hot spots”, and associated steam pockets, which lead to further air entrainment and potential engine damage. There are two possible ways to get the air out; the easiest, fastest, and most effective is to pull a vacuum on the system which will immediately purge all traces of the air; but what happens if you do not have a vacuum filling tool, or are stuck out on the side of the road with air in the system? You add a mechanical bleeder as high up in the cooling system as possible, which is where the tank is located. Manually open the bleeder and the system is running at atmospheric pressure and trapped air can vent as the coolant circulates.

Believe it or not, most hot water home heating systems have a similarly functioning device for the exact same reason………..
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Old 02-12-2011, 06:58 AM   #4
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A long time ago I was a licensed plumber and worked on many hydronic heating systems, including their expansion tanks and air separator valves. I guess that experience adds to my confusion of the Boxster system. The large hydronic heating plants have a specialized fitting that swirls the fluid inside like a little cyclone. The air is lighter and stays in the center and at the top of the center of the fitting is a discharge line that leads to the expansion tank(s). That line is left open all the time and you get air out of the system by venting the expansion tank. But I digress.

Say there was no separate bleed valve on the Boxster. A tee fitting on the highest coolant hose directs a new hose into the bottom of the expansion tank. It seems to me such a system would work (as it does on my Corvette). Think of the Boxster bleed being open all the time with the discharge line plumbed into the pressurized plastic tank.

I'm not trying to argumentative. I enjoy thinking through why engineers choose one solution over another and I want to understand why Porsche used the design found on our cars. Especially since I've never seen it on any other car I've owned.
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Old 02-12-2011, 07:37 AM   #5
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One function for the bleeder that you are overlooking is that it also is part of the coolant overflow vent, the one that pukes coolant onto the ground under the car when there is an issue. Yes, it is overly complicated, but that is just some of the “charm” or owning a Porsche. As for the “where’s and why for’s” of the chosen design, just remember that these are the same guys that created the AOS system as a substitute for the $3 PCV valve most OEM’s use…………
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Old 02-12-2011, 10:16 AM   #6
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I've seen this Uview vacuum refiller tool on ebay:

uview tool

Do you need to buy a vacuum pump separately? Hopefully a vacuum won't implode the coolant resevoir, or cause other problems. That would suck (so to speak).
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Old 02-12-2011, 10:46 AM   #7
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you don't need a vacuum pump for that tool, but you do need an air compressor.

Here's something similar, but cheaper:

http://www.tooltopia.com/uview-550500.aspx?utm_source=shoppingdotcom&utm_medium=cse&utm_term=UVU550500&utm_campaign=shopping_r1

Anyone have experience with these or want to make any recommendations? I was hoping Pelican might have something, but if they do I couldn't find it.
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Last edited by Mark_T; 02-12-2011 at 10:57 AM.
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Old 02-12-2011, 11:24 AM   #8
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The 550000 is a much better unit, comes with adaptors to fit anything and is made out of solid brass rather than molded plastics. For the extra $20 or so (Amazon.com) than the $79 plastic unit, you have a much more flexible and long lived tool.................. It is also the same tool Porsche sells for over $500.....



We use these just about everyday in the shop, and on everything from 986/987's to motorcycles. And, no, the vacuum will not collapse the tank........
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Last edited by JFP in PA; 02-12-2011 at 11:29 AM.
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Old 02-12-2011, 12:07 PM   #9
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What kind of psi and cfm do you need from your compressor?
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Old 02-12-2011, 12:32 PM   #10
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As it creates vacuum by air flow over an eductor nozzle assembly, it depends more upon volume rather than pressure. As such, any level of flow will do, the higher the flow rate, the faster it develops vacuum; but it always gets to the same level (24-27 inches). The manufacturer recommends at least 90 psig air delivery for optimum performance with larger volume cooling systems, such as Porsche’s. It is a neat tool, and it will pull a totally empty Boxster cooling system down to around 25 inches of vacuum in about 90 seconds, and then refill the system in about 3-5 min., leaving absolutely no air behind. And, as mentioned earlier, it will work on any cooling system. Real time saver around the shop and no “come backs” due to trapped air or coolant levels dropping later.
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Old 02-12-2011, 01:45 PM   #11
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Yes the cooling system is a little odd. Crazy Germans. Remember that Porsche has been building air cooled motors for over 60 years and the 986/996 is essentially a first generation water cooled flat six production motor so we are guinea pigs to some extent. Chevy has been doing water cooled motors since 1914?? so by now they have the bugs worked out.

Do pay attention to purging all the air out as air entrapment and hot spots in this motor mean cracked heads or worse.
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Old 02-12-2011, 01:50 PM   #12
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I guess what I'm really asking is how big of a compressor and tank do I need to run this. Mine's kinda small - great for filling tires and blowing off dust but not adequate for most air tools.
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Old 02-12-2011, 02:32 PM   #13
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I've seen people run them off rather small portable compressors, so it can't require all that much. Other than the recommendation for 90 psig, I'm not aware of any other requirements. You may want to drop them an email as I'm sure this question comes up all the time........

http://www.uview.com/index.php
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Old 08-01-2013, 06:25 AM   #14
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Draw vacuum after coolant flush.

I have just replaced the coolant in the 2000 Boxster and thought I would bleed the system manually via the comments here. I'm not absolutely sure the system is free of air pockets and have ordered the suggested 5500 unit. If I draw a 25# vacuum on my already filled system will it still draw out any entrapped air or do I have to refill the system using this tool? Thanks
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Old 08-01-2013, 09:22 AM   #15
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Originally Posted by rebeltown View Post
I have just replaced the coolant in the 2000 Boxster and thought I would bleed the system manually via the comments here. I'm not absolutely sure the system is free of air pockets and have ordered the suggested 5500 unit. If I draw a 25# vacuum on my already filled system will it still draw out any entrapped air or do I have to refill the system using this tool? Thanks
It works best while filling the system because it totally prevents any air entrapment, but you can use it on a full system to pull out any major air pockets.
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Old 11-22-2016, 07:31 AM   #16
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I know this is an old thread but.......

I don't have a workshop air compressor and I want to flush and refill my coolant and would happily spend on getting a vacuum refilling system but not both pieces of equipment.

Is there a vacuum system that does not need an external air compressor or alternatively has anyone devised a way of using a vacuum system without a compressor maybe with a 12v tyre inflator or some other devious way to provide the air power?
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Old 11-22-2016, 07:44 AM   #17
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Borrow an air compressor ? Or go to an Indie to get this job done.
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Old 11-22-2016, 12:23 PM   #18
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Quote:
Originally Posted by Mark_T View Post
I guess what I'm really asking is how big of a compressor and tank do I need to run this. Mine's kinda small - great for filling tires and blowing off dust but not adequate for most air tools.
I borrowed a small 8 gallon unit, and it pulled the required vacuum no problem. A smaller one would likely work too, just would take longer to evacuate.
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Old 11-22-2016, 03:30 PM   #19
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RR, I live in a city with a pop of about 700K. Just Googled tool rental and found 18 places I could rent a compressor at a fair price. I looks like your in the UK and would think there it would be about the same. You might find someone who has a compressor but no bleeder and do a loan.
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Old 11-23-2016, 05:32 AM   #20
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I use a 6 gal pancake compressor and a UView. I think that is probably the smallest you could go. I did 2 Distilled water flushes and then filled with 50/50 pink stuff
I felt like I had to run the purge valve a couple cooling cycles anyways as I was not familiar with the temp behavior after this and new WP and low temp thermo replace.

The hardest part here in NJ is getting rid of the stuff, 12 gallons. Auto parts stores don't take it. Finally had a House hold recycling day where the county takes things like paint and antifreeze

I would like to know better how one uses the Uview with a full system to help remove any potential trapped air.
Anyone done Vacuum on a full system???
I have just started seeing condensation under trunk lid and I had a drop or 2 come out the overflow after driving an hour and half. It's been 4-5k miles since all the coolant work with no issues. Temps run cool
I have a new tank as of last Dec (2015),WP, thermo Flush. I had put an '04' cap on 3 years ago.
I just order a new cap to see if that is it

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