I don't understand the coolant bleeder/tank system

[JFP in PA]

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………..

[Dale_K]

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.

[JFP in PA]

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…………

[brp987]

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).

[Mark_T]

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.

[JFP in PA]

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........

[Mark_T]

What kind of psi and cfm do you need from your compressor?