Expansion Tank - black thingy behind cap!!

[Guest]

Hi - I'm a Newbie to this site.

I've got a 996 C2 Cab 2000/W that I have had for about 10 months.

Behind the expansion tank filler cap there is a black thingy! (suspect some kind of pressure release valve as it appears to be sprung) with a wire that appears to be for the purposes of pulling it up. The housing it sits in has ridges on it that seem to be for the purpose of locating and holding the 'wire puller' so that it holds it up/open.

Q1. What is it?
Q2. What position should it be in - up or down?

Apologies this is not very technical. Any pointers gratefully received.

Cheers

 

[Richard_Hamilton]

It is used for bleeding the air out of the cooling system, and should be in the 'down' position in normal use. The bleeding process is quite a complicated procedure, and would frighten the life out of me to do it, as it involves revving the b*ll*cks off it several times (under no load) over quite a long period. Apparently there are several pockets in the water jacket that can trap air after a coolant change.

 

[Guest]

Thanks Richard....much appreciated.

Kind Regards

____________
Keith
C2 Cab Tip
Silver

 

[Guest]

Actually, the bleed process is complicated... but you can run the car for weeks with the bleed valve open. Cup Cars do this all the time.

 

[Ian W]

......actually, once warm, they all run round with the bleed valve open all the time as the pressure in the cooling system forces it open anyway. Check it out next time your engine's fully warm - the bleed valve will be wide open.

Ian W

 

[Guest]

Thanks Loren and Ian W. This is all part of my diagnosis as to why I am losing coolant and signs of an oil leak (oil on top of engine behind and to the right of the oil filler cap.

Needless to say I am starting to fear such things as RMS!!!

 

[Ian W]

berrick

First the good news - oil on top of the engine isn't RMS. If that was starting to fail you would be seeing oil on the bottom of the engine, dead centre, where it joins the gearbox (i.e. the front of the car / back of the engine bay).

Bad News? Most likely cause of oil on top of the engine is the oil separator and/or return bellows (had 3 of these go on my 3.4). Good news again - bellows is only about 65p (and I'm not exaggerating much) but - bad news - it's a complete pig to get at. A good independent will want 3-4 hours (IIRC) to fit bellows and separator canister if necessary.

Most likely candidate for coolant loss would be the expansion tank itself. These have a nasty habit of cracking along the seam - right where you can't see it towards the back of the engine bay - and dumping coolant all over the place when the engine's really warm. They then come over all innocent and mended-looking as soon as you pull up and the car cools down. Sneaky little blighters.

Hope this helps

Ian W

 

[Guest]

Thanks again Ian W.

There is an independent near me Wrightune in Wallingford (saw a recommenddation on this forum for him) who I am planning to get to do the service that is due now (although I am going to have to wait until first week in June becuase he's so busy!) - but he's offered to stick it up on a ramp for me and have a look.

Thanks again for your A&G