bypass valves mk2

yo, iv got a 91 mk2 gti 8v

at the mo my heater isnt blowing hot air. iv got a feeling its got the famous crappy matrix bypass valves. just to make sure are they the two parralel hoses runing through the bulkhead with 2 valves and a smaller hose linking the two? if so iv heard you can just take the valves out but have been warned that you may have to uprate the matrix? is this true? as i really cant be fecked to replace the matrix. would it be easier to just replace the valves?

cheers, rod.

 

yes it's those valves, replace them with a bit of pipe and then run the car up to temp and see if it works without them, then if you aren't going to change the matrix get some more valves. otherwise it can be very dangerous...

my jetta used to blow cold air if the coolant was low, or if it had an airlock too...

 

Is this:

17855 PRESS COMPENSATING LINE G2 27.90

GSF's part number? Can't seem to find a description that sounds like "Bypass valves".

What do VW charge for them?

Edit: Yes that is the right GSF part number. Had to buy from them as VW said they couldn't get any at the moment.

 

Is there a picture/diagram/anything in the Haynes manual for the bypass valves?

 

Valves are obsolete from VW now.

 

So options...
1. Clean valves
2. Remove valves, replace with regular piping
3. Replace matrix with MK3 matrix??

 

Oh. Thought 3 was a solution in its own right.

Damnit. That's a huge job...

Is it possible to get second hand bypass valves?

 

Are the valves not cleanable?

Still can't find them in Haynes...

 

I figure if I'm going to have to replace the matrix anyway I may as well try and bypass the valve first I mean the worst that could happen is second degree burns on my feet and legs since I'm so short, so does anyone have pictures/diagrams to help me locate and remove the valve?

cheers

 

Looking from the front of the car, you`ll see two pipes coming out on the right hand side of the bulkhead.

One goes to the side of the head (matrix feed), and the other (matrix return) goes to the metal water pipe.

Now, everyone refers to the set-up as `bypass valves`, but (being pedantic for a second) there`s only one `bypass` valve, that`s fitted in the matrix feed pipe. The other piece is a `check` or `non-return` valve that prevents the relieved pressure from flowing into the matrix from the return side.

If you have the valve fitted you`ll see it about half-way up the matrix feed pipe. It`s a metal body with a small bore pipe leading to the plastic t-piece in the return pipe (it`s this small bore pipe that the relieved pressure passes through when the valve opens).

They`ll probably only be attached with Jubilee clips, so removing them is simple.

Replace them with a couple of 3-4" lengths of copper pipe (there`s always debate about which diameter to use, but 22mm rings a bell).

Just don`t do what someone I know did and join the wrong ends together...

He ended up bypassing the matrix completely and wondered why he still had no heat....

Hope that helps!

 

I've never heard of anyone cleaning the valves successfully. I tried it with kettle descaler, among other things...

I've replaced valves with copper pipe, with no problems. Only a tiny fraction of the cars ever blew the heater matrix. While it would be pretty unpleasant if it happened, it's very unlikely.

22mm pipe is the nearest I've found. Ideally you'd want 20mm, as 22mm is a bit of a stretch for the hoses, but I haven't found anywhere that sells 20mm pipe.

 

I didn't find a metal T-joint ... there's a metal T-joint but it's not really a T... it's like an elbow joint and then after the elbow joint there's rubber hose that leads to the other big pipe.

Um... so, I know I'm an idiot, but which one is the valve? The joint? Pix plz =(

 

The metal piece is the valve...like I already said...

 

I think I get it now!

[I did say I'm an idiot?]

Cheers! Now I gotta ask my friend how the jubilee clips work ha...