Rad Over Flow Bottle

[1960NSU]

Maybe this is a dumb question, don't know but I have to ask.What is the purpose of the Check ball thing in the rad/overflow bottle? Does it's only purpose have to do with working with the heater core to provide the interior heat? or does it have something to do with the cooling of the rad/engine itself?Why? In our resto of the NSU, the rad bottle sits too high to be used, so we are going to make a new bottle but if I don't have to make the new bottle with a check valve in it, it will be so much easier. Plus there will be no AC or heater in the car as well, so we don't need the extra inlet/outlet for the heater core tubing. the new bottle will be sized to hold the same amount of fluid if needed or made a bit smaller as the fluid amount will be less for not using the heater core and tubing.I hope I made some kind of sense, Any thoughts? ideas?Wendy

[Alex]

It's either to prevent backflow under some conditions, or I think more likely it's actually an air release. The ball floats in fluid and holds the passage closed, but will drop if any air bubbles get there. The estimable Tolsen did some work with it here. Read through that longish thread, I think it will help.

[1960NSU]

Alex, I read last night through all those posts, and thought I knew what it was used for, but then it went into thermostats and all other kinds of things, then I got lost on the whole concept of the little green ball, never did find out if Tolsen endied up removing the ball allltogether. Maybe I will PM him and see what he did.Wendy

[Alex]

I re-read most of that thread. I think the engineers read some entrails and waved wands in a few design aspects. The main purpose of the checkvalve appears to be to allow air to vent when filling the cooling system. The normal flow to rad from thermostat doesn't connect to expansion tank except through the checkvalve. A more normal tank open to a vertical tee from the rad hose will work fine. I think you can safely eliminate the checkvalve and simplify the coolant circuit. Use the heater matrix outlet from the thermostat to supply a small diameter bleed hose to the expansion tank, it appears any air bubbles in the system during operation leave via that route. An airlock may develop without a small flow out the heater line and a way for bubbles to escape. All you need is a slow trickle, too much flow will slow down warm-up.Be careful about not restricting the return flow from thermostat to water pump (Tolsen's restrictor plug) as well as the heater matrix flow. One or the other can be safely restricted, not both.Important question I haven't seen answered anywhere: Is the expansion tank or any part of the cooling system under any pressure ever? Many cars have the expansion tank open to atmosphere and connected to the radiator via a pressure relief, hence the tank is never pressurized but the system is. Does Wendy have to find a suitable pressure relief valve?Edit: Just looked at mine. The expansion bottle has a pressure relief and vacuum breaker. So either method is acceptable, a non-pressurized bottle with a relief valve and vacuum breaker between it and the rad hose, or a pressurized bottle, possibly using the stock cap. Just teed off the rad inlet hose is a suitable location, and the comments about a constant slow bleed from the heater outlet from thermostat still apply. Go visit a wrecker and look for a simple pressurized expansion bottle. Anyone know a particular model that uses that? Just a single bottom hose and a pressure relief/vacuum breaker cap.Second edit: Just checked the VW Transporter van at work. It has a pressurised bottle, with a low coolant sensor. So some or all VWs use that system.

Edited July 4, 2012 by Alex

[1960NSU]

Alex, now this is making sense to me, I have passsed this info on to my brother, thanks a bunch. Plus I will go the the wreckers today and see what I can find there as well. Wendy

[1960NSU]

Just a thought, if this expansion bottle is under pressure. Does it have to sit higher than the rad itself? or can it sit level with the rad. We were thinking it has to be higher than the rad, so this is why it won't fit in the NSU but if it is under pressure could it not sit level or near level? IF it can sit level we may be able to use the Smart bottle, and just use a longer rad to bottle hose. hmmmmHere is a pic of the bottle, as you can see it is too high.Wendy

[Alex]

I still think a simpler bottle may be best, with a trickle from the heater outlet to ensure bubble purging during operation. Get rid of the checkvalve and all the heat loss from the heater circuit.If the bottle is not higher than the rad I don't think it matters, except with regard to initial air bleeding when filling the system. That, you will have to figure out. The original smart system is known, but who knows with a custom job?

[1960NSU]

Alex I looked at the VW transporter bottle and yes it looks like it would work, just wonder on the hose diameter, any idea what the diameter would be on the VW, then I can see what the dealer/used guy would want for one?

[Alex]

Can't measure exactly as the hoses are butted right up, but it seems to be about 21 or 22 mm on the larger bottom connection, and 13mm on the smaller upper connection. (That is where you would lead the heater outlet purging trickle in.)Only four openings. The bottom and upper coolant barbs, the level sensor (handy to have a warning light, or just leave it there non-connected), and the filler cap at the top.

[1960NSU]

Oh thanks, I am going to go into town and see what I can find.

[1960NSU]

Well went to town looking for a solution on the rad bottle, wreckers were a bust, don't have any VW on the lot. So went to VW repair guy, who has been working on VW since Noah's Ark was created, and another bust there, tried to explain what I wanted the bottle for and was looked at like I had nine heads. His loss, for not making a sale. Oh Well, back to square one.So we are going to use the Smart bottle, just try to position it as level as we can with the rad, may be a challenge to get air bubnles out when filling but, may have to put an extension on the filler cap, get the bubbles out, remove said extension and go from there. I got the extension idea from a VW forum, on a post a guy was having trouble bleeding air bubbles on his transport and came up with the extension idea, and it worked for him. So no harm in trying.Thanks for the comments Alex, and all your help.wendy