Why The 306 Header Tank Cap Doesn't Work As Standard

[Garry 1]

I thought I would add a post explaining why in my experience, the 306 header tank cap will not work without a few mods on the XU10J4RS lump (Gti6/VTS).

 

I know it doesn’t work as I have a pipe that runs from the header tank over flow into a 1.5 litre plastic bottle that sits in the passenger footwell, so I can see when it leaks.

 

These are the caps I am talking about, the standard 205 one on the right, replacement 306 Xsi one on the left.

 

 

When running the standard 205 cap I found that the release spring inside the cap was not strong enough resulting the cap leaking when the car got hot or when turning the engine off.

 

I had read on this forum that others were using the 306 cap as it had a much stronger release spring. Which it has, the 205 one can be compressed with two fingers, the 306 one requires a lot more effort. But I found that the 306 cap still leaked.

 

Underside of the 205 cap

 

 

 

Underside of the 306 cap

 

 

 

When squeezing the coolant pipes I could air leaking from the 306 cap. I added a rubber washer to the inside of the cap (where the water can be seen on the pic). There was not one present on either of the 306 caps that I have (one from a pug dealer the other from a scrap yard), but I think there is supposed to be one as standard….. The washer gave a much tighter fit, but the cap still leaked.

 

The next thing I found was that the inner section of the cap did not touch the inside lip of the header tank, so I added a rubber washer to pack it out a bit and seal. See below:

 

 

The other major difference in the two designs is that the inside section of the 205 cap is solid whilst the 306 cap has holes in it, so I put some duct tap over the end to seal it off. This it how it looks now:

 

 

The result is a leak proof tank cap that will still release if the pressure gets too high, after a few trackdays and several cross country jaunts it does the trick.

 

The only concern for others would be to check your cooling pipes, by doing the above you are running the cooling system at higher pressure, which may mean you old cooling pipes may not be up to it………

[welshpug 1,621]

why didn't you get a new 205 cap? I just checked mine and that is pretty stiff as well, pretty much the same as my 306 cap, granted the actual pressure may differ.

 

the reason a 306 cap doesn't fit is the tabs, they don't allow the cap to pass the overflow pipe, which in turn means the cap doesn't get to the second stage (i.e doesn't seal)

 

 

If you want it to seal properly cut off the tabs and discard your gaffer tape.

Edited November 16, 2008 by welshpug

[jonnie205 1]

is that last pic not the worng way round welshpug? the thinner bit is tye sealed bit stage 2 and the fatter section is the 1st stage safety bit?

[welshpug 1,621]

nope you fit the cap and turn it clockwise to seal/lock it, the second fatter section pulls the cap tighter.

Edited November 16, 2008 by welshpug

[Matt Holley 11]

I just put a new standard cap on mine, no problems since

[welshpug 1,621]

1306 85 is the original 205 cap (replacement is as pictured above) releases at 1 Bar.

 

306 cap is set to 1.4 Bar (all use 1306 C7)

[Garry 1]

why didn't you get a new 205 cap?

 

Because I run a 306 engine and there must have been a reason for pug upping the pressure.

 

My header tank is the Ph2 type (the black one), not cream like yours.

 

I can get two clicks when tightening, ie full tightness. The overflow on my header tank points towards the bulk head, not forwards like the one shown.

 

I found that when it fully tightened, air could leak out just by squeezing the pipes.

[TurboSam 5]

I've been running a standard 306 cap on my 205 for about a year (inc 9 laps of the ring), and haven't noticed any coolant loss? Mine came with a rubber washer though.

[welshpug 1,621]

can't imagine why that would be, as the 309 gti16 uses the same cap as the 8 valve.

 

I think it must be that the XU10's run hotter, would still want to get a cap that fits properly though.

 

edit, just read your post again, rubber washer missing?! I would have taken that cap back

Edited November 16, 2008 by welshpug

[Super Josh 4]

Just fit an aftermarket cap from someone like quinton hazell. Same style as the original 205 cap, but 20 PSI release pressure. Job done

 

 

 

 

 

Josh

[DrSarty 90 1 Cars]

I suppose I was lucky. My 1.6 header tank cap fitted straight onto the BMW expansion tank I use and it all seems to run sweet as a nut.

[GTI6BOY 29]

we use the 306 cap and dont loose coolant.

[Henry Yorke 269 3 Cars]

I ordered a replacement standard cap from Peugeot and they supplied one of the later ones. I have never had any problems with mine either. Doesn't rust either! (Mine is on a phase 2 tank)

[welshpug 1,621]

yours would be like the one I pictured henry, i.e without the tabs, as I bought one from peugeot a few years ago too.

[Henry Yorke 269 3 Cars]

yours would be like the one I pictured henry, i.e without the tabs, as I bought one from peugeot a few years ago too.

Ahh, so Garrys solution will be to cut off the tab and all would be well?