Catch Tank Rule Problems - VW Porsche and others please comment

[Gary L]

So you want me to drill a hole in my closed system and create a weak point so that I can prevent something that hasn't happened yet? I think we should require coolant catch tanks on air cooled beetle too. There is no breather valve on the VW system. So there is no place to vent it from. To do so, would illegally modify the cooing system IMHO.

If you have a pressure cap (by that I mean one that is designed to open at a pre-set pressure), you already have a hole in your "closed system". Consequently, it is no different than the '66 Mustang setup... when something goes wrong, it is going to piss coolant on the track. By design.

[Greg Amy]

If you have a pressure cap (by that I mean one that is designed to open at a pre-set pressure)...

They're not designed that way, Gary.

The VWoA group uses an expansion cap with a one-way valve, designed to allow air *in* when in vacuum, but block exit of any liquids, gas, or pressure *out*. I only mentioned the "last resort" for the cap because that's what typically fails first (if you don't pop a hose). I've link a photo at the bottom.

But this is not necessarily germane to the conversation. I think Bob's point is that we now have a requirement for a "catch can", a catch-all (har-de-har) rule that doesn't necessarily apply to all systems. I was simply pointing out that the rule was not intended to apply to systems such as the VWoA's; you certainly don't want to hack into these systems to add a catch can, it would be problematic, dangerous, and flat stupid.

If anything, the rule will be enforced intelligently, i.e., tech inspectors will recognize this rule doesn't apply to these systems; if not then it will need to be adjusted accordingly. - GA

[Gary L]

They're not designed that way, Gary.

I agree... but what you've pictured is not a pressure relief cap. And I would agree, that type of system should not require a catch tank.

I'm referring to those systems that have an expansion tank with a normal radiator pressure cap on that expansion tank, designed to relieve coolant pressure at a preset value. I suspect this is the very type of system that Bob R. was referring to in his original post, when he brought up the Saab, Porsche, et al. I know I can certainly point at one car that has such a system. I race it... the ubiquitous Volvo 140.

[Greg Amy]

I'm referring to those systems that have an expansion tank with a normal radiator pressure cap on that expansion tank, designed to relieve coolant pressure at a preset value.

Roger, I agree. That's what this new rule is designed to address. But, it throws out this all-encompassing, all-assuming net...

BTW, Porsche's system is the same as VW's; in fact, many Audi and Porsche expansion tanks are actually the same part number as a Volkswagen Rabbit's (VW, Porsche, and Audi all share common engineering roots)...

GA

[JeffYoung]

I've only scanned some of this, so forgive me if I am off base.

My car has a radiator without a cap, and a hose to an expansion tank which does have a cap. The expansion tank has an overflow hose that dumps to the ground.

My read on the rule is that it is simply trying to prevent the latter, which I agree with -- overflow coolant should go to a 1 quart overflow "tank" (or Gatorade bottle as the case may be) with at least 1 qt of vapor space. And that is what I shall do -- just run the overflow line to a one quart Haterade bottle.

On the VWs, you aren't dumping coolant anywhere by the very design of the system and while I agree that doesn't fit "nicely" within the rule, since it is clear from the design of the system that coolant "overflow" isn't going going to ground, then all seems to be ok (to me anyway).

[Gary L]

I've only scanned some of this, so forgive me if I am off base.

My car has a radiator without a cap, and a hose to an expansion tank which does have a cap. The expansion tank has an overflow hose that dumps to the ground.

And the system that I am referring to is like yours, but there is no hose, nor a nipple for same... simply a hole in the neck of the tank that is uncovered when the cap relieves pressure at the preset value.

Greg - I may be wrong, but I would almost bet if you go back far enough, you'll find the same system (as my '71 Volvo) on the German cars... an expansion tank with a regular radiator pressure cap on the tank instead of the radiator. As I said in my first post on the subject, the wording of the proposed rule could use some work.

[Greg Amy]

Greg - I may be wrong, but I would almost bet if you go back far enough, you'll find the same system (as my '71 Volvo) on the German cars...

Believe it or not Gary, VWoA has used the same exact general design from the very first water-cooled VW, the 1974 VW Rabbit. In fact, the expansion tank was the same exact part number from that '74 all the way through all the A1 model lines (Rabbit, Scirocco, Jetta), gasoline and diesel. The only differences were tank and radiator shape and size for chassis-specific placement, like the longitudinal placement in the Dashers, Audis, Porsche 924/944, and the space requirements of the A2 Golf chassis onward...and all through it they used the same exact expansion tank cap. Hell, my 2000 S4 still uses a variant of that same exact design and I'd not be surprised if Audi and V-dub still do it for new stuff today.

In fact, this system is so efficient that many other pure-race cars use Scirocco radiators and expansion tanks...

I will admit I haven't seen an early 1970's Audi 100Ls in probably 20 years, but if someone is racing one of those then the cooling system is the LEAST of their worries...

[Gary L]

...and all through it they used the same exact expansion tank cap.

Then someone needs to tell the suppliers about this.

Here's what the internet parts places seem to think is the correct tank for the early (I checked '77-82) Porsche 924, and it definitely does not appear to have the screw-on cap, rather the pressure relief type I'm talking about. Like Jeff's tank, this one even has a nipple to hook up an overflow hose.