German Auto Solutions 1.2 bar coolant cap

[Ewazix]

......
And if you dont think that there is a relation between temperature (regulated by the thermostat) and pressure, do some reading:
https://en.wikipedia.org/wiki/Clausius%E2%80%93Clapeyron_relation
https://en.wikipedia.org/wiki/Antoine_equation
As these guys figured it out a few hunderd years ago.
But I gues they were know it alls too...

Can nobody outwit the Wiki-Man :wink:

 

[GuidoK]

It has nothing to do with 'outwitting'.

 

[Kamuela]

Here's a data point. I had a slow loss of coolant I couldn't find with UV tracer dye, maybe 50 ml/month. Finally replaced the cap, loss stopped. I hypothesize that the relief pressure of the cap had dropped to the point where it was venting the water portion of the antifreeze mix (water boils lower than ethylene glycol, and has a higher vapor pressure at a given temperature, so it was in effect acting as a still. This is how antifreeze is recycled, by distillation to remove the water). I never saw any indication of overheating, or found any trace of dye outside the cooling system, including around the cap; just a slow decrease in coolant level, although the cap would still have some pressure if I released it warm so it hadn't totally failed. I would expect a lower relief pressure on a new cap could have the same effect, a gradual loss of coolant, but I have no idea whether 1.2 bar is low enough to make a difference. That's still a pretty high pressure, 17 psi, which is about what most American iron runs for radiator caps, so it's likely OK, but I don't want one anyway.

Now I've gone and done it; should learn to never get involved in 'net "discussions."

 

[Ewazix]

Here's a data point. I had a slow loss of coolant I couldn't find with UV tracer dye, maybe 50 ml/month. Finally replaced the cap, loss stopped. I hypothesize that the relief pressure of the cap had dropped to the point where it was venting the water portion of the antifreeze mix (water boils lower than ethylene glycol, and has a higher vapor pressure at a given temperature, so it was in effect acting as a still. This is how antifreeze is recycled, by distillation to remove the water). I never saw any indication of overheating, or found any trace of dye outside the cooling system, including around the cap; just a slow decrease in coolant level, although the cap would still have some pressure if I released it warm so it hadn't totally failed. I would expect a lower relief pressure on a new cap could have the same effect, a gradual loss of coolant, but I have no idea whether 1.2 bar is low enough to make a difference. That's still a pretty high pressure, 17 psi, which is about what most American iron runs for radiator caps, so it's likely OK, but I don't want one anyway.

Now I've gone and done it; should learn to never get involved in 'net "discussions."

No I think it's a valid observation and I've effectively been agreeing with GK (yes ) that a low pressure cap with no other changes is not a proven good-idea. My proposition is that used with waterless coolant it MIGHT be because waterless reduces working pressures, this has some potential benefits for the longevity of systems that are now nearly 15 years old and garage queens in some cases.

As I said it would be good to hear from anybody who has converted to a LP cap.

 

[GuidoK]

Here's a data point. I had a slow loss of coolant I couldn't find with UV tracer dye, maybe 50 ml/month. Finally replaced the cap, loss stopped. I hypothesize that the relief pressure of the cap had dropped to the point where it was venting the water portion of the antifreeze mix (water boils lower than ethylene glycol, and has a higher vapor pressure at a given temperature, so it was in effect acting as a still. This is how antifreeze is recycled, by distillation to remove the water). I never saw any indication of overheating, or found any trace of dye outside the cooling system, including around the cap; just a slow decrease in coolant level, although the cap would still have some pressure if I released it warm so it hadn't totally failed. I would expect a lower relief pressure on a new cap could have the same effect, a gradual loss of coolant, but I have no idea whether 1.2 bar is low enough to make a difference. That's still a pretty high pressure, 17 psi, which is about what most American iron runs for radiator caps, so it's likely OK, but I don't want one anyway.

Now I've gone and done it; should learn to never get involved in 'net "discussions."

I think thats slight vapour/steam seepage past the o rings or diaphram from the radiator cap. I've had that problem too (I'm also on my second radiator cap, instantly stopped the minute lowering of the coolant level over months). Over time rubber hardens or is pressed into a certain form and that reduces its function as a seal. Its not that the radiator cap has lost its release pressure dropping below the working pressure of the coolant system otherwise it would be gushing/blowing out. I think this is just a tiny pinprick hole that releases a minute amount of steam.