Coolant Reservoir Cap

[DAC350]

Can someone please confirm on your S3 something for me. After driving to normal temps, turn off the engine and pop the hood. Does the cap on the coolant reservoir make a hissing sound? I know it's a pressurized system, but I didn't notice the noise until recently. It's not terribly loud, but you can definitely hear it when you put your ear to it. I actually took it to the dealer yesterday for a pressure test, but no leaks were found. I've been losing coolant very slowly and now I'm thinking it's evaporating from the cap if that is possible.

Thanks.

 

[S32B]

As long as it stays within the min-max line don't worry mate. Mine was half way between the min-max lines, so I bought some coolant and when I took the cap off the level went up to the max mark! You'll be surprised how little it takes to take it from the min-max line....less than a cup full.

I've just been out to look as I've not checked it since before I went up to Scotland in September, it was close to the min line so I've topped it up to the max, I suspect on my next run I'll hear it hissing like you have described. If it's too full it will just blow off.

This stuff is fine to use by the way: http://www.eurocarparts.com/ecp/p/c...t=awin+traffic&utm_campaign=Editorial+Content

EDIT* When you lock the cap back on, keep turning it until you hear/feel it click. It may just be it's not 100% tight/locked, it does go rather tight before the click!

 

[DAC350]

Thanks for the response. If you can double check for the hissing noise sometime that would be great. Just want to make sure my cap is not faulty.

 

[S32B]

Thanks for the response. If you can double check for the hissing noise sometime that would be great. Just want to make sure my cap is not faulty.

Will do mate, on my next run I'll pop the hood and listen, but I do expect it to hiss a bit now I'm on the max mark!

Did you check for the locking click?

 

[S32B]

If you can double check for the hissing noise sometime that would be great.

Hi mate, just dropped the wife off at her mates and then went for a 'spirited' drive around some nice lanes to get it nice and hot. I stopped the engine and popped the hood, no hissing from the cap! Just the noise of the hot engine and the normal bleeping (not sure what that's for tbh).

 

[AudiNutta]

How long after driving does it make the hissing for?

Having had somebody come back to you and say no, I will check mine tomorrow for you when I get to work.

It could just be a perished seal on the cap.

 

[DAC350]

Thanks for the video and checking everything! I'm not sure how long it's been hissing for, but I've been losing coolant very slowly for a month. The cap is locked, however I just took it off and cleaned the o-ring. So far, after cleaning the o-ring I no longer hear the hissing sound or have a coolant smell in the engine bay. Hopefully it was just dirt on the o-ring itself. If that is the case though, it's sad the dealership missed such an easy fix.

 

[AudiNutta]

Thanks for the video and checking everything! I'm not sure how long it's been hissing for, but I've been losing coolant very slowly for a month. The cap is locked, however I just took it off and cleaned the o-ring. So far, after cleaning the o-ring I no longer hear the hissing sound or have a coolant smell in the engine bay. Hopefully it was just dirt on the o-ring itself. If that is the case though, it's sad the dealership missed such an easy fix.

Sounds good, glad to hear you've got to the bottom of it! I can imagine you have been losing some over a period of time, from a pressurised vessel with a leak.

Give us a report back in a few times, to see if it's still not reappeared. Interesting how dirty could get to that seal anyway, but it's sorted now anyway.

 

[Rob2k68]

Had evidence of purple spots around my coolant reservoir last month or so which lead to me replacing the cap yesterday. The new one felt a much tighter fit so hopefully cures it.