Blanking cap
Blanking cap
Author
Discussion

keatsie

Original Poster:

326 posts

194 months

Friday 29th March 2013
quotequote all
Just had hot water coming out of the blanking cap on the swan neck? Never happened before and the engine temp seemed normal. Nothing coming out of the header tank overflow.

The cap seal looks ok, suspicious that the blanking cap should just start leaking or am I just being paranoid??

jmorgan

36,010 posts

314 months

Friday 29th March 2013
quotequote all
Mine started once but no water was obvious at first, the lugs that the cap locks onto on the swan neck were bent a tad so the cap was not sealing, my temp would rise and the system would force the air out. Took me a while to find it though.


Edit. What does the seal look like (not the aquatic version).

keatsie

Original Poster:

326 posts

194 months

Friday 29th March 2013
quotequote all
Seal definitely looks worn, but I am concerned about the pressure leak when the temperature was no higher than 80 degrees.

jmorgan

36,010 posts

314 months

Friday 29th March 2013
quotequote all
I used a straight edge, steel rule or a square and checked the seal on the swan neck. I also replaced a seal with a rubber blank that came with a pressure cap later on down the line. But as the system was not sealed due to the leak, the water expanded quite easily and would fill the expansion tank to the brim.

pwd95

8,459 posts

268 months

Friday 29th March 2013
quotequote all
They are basically not very good. Once you use them once or twice they don't seal very well at all.

pk500

1,975 posts

242 months

Friday 29th March 2013
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I replaced mine they are cheap enough so bite the bullet and buy one

adam quantrill

11,679 posts

272 months

Friday 29th March 2013
quotequote all
Also seal it down with a smear of blue stuff and never move it again - I always use the hose that goes to the expansion tank to top mine up if it needs filling there.

keatsie

Original Poster:

326 posts

194 months

Friday 29th March 2013
quotequote all
I will give it a go tomorrow, bit concerned I may have blown a head gasket after a good thrashing today. Although the temp didn't rise above 80 I don't see why the cap should have pressured water coming out, I would have thought it would have gone into the expansion tank...

jmorgan

36,010 posts

314 months

Friday 29th March 2013
quotequote all
I may be wrong here but from my experience and understanding when mine was playing up. If the cap is not sealing then the system is not pressurising, that is water is getting forced out as the water in the system expands and a loose cap is easier for water to get by than the 15lb (?) cap on the expansion. No pressure in the system then it will not force the spring?

RCK974X

2,521 posts

179 months

Friday 29th March 2013
quotequote all
If you (or your kids) cycle, a temp trick is to cut a couple of discs out of an old innertube and put these in below the cap - adds a bit of spring pressure and gives you a 'new' seal. I ran my wedge that way for a couple of months it worked so well !!

But do check you haven't got a blockage somewhere, as it might be caused by excessive pressure as well as a worn cap....

utternutter

80 posts

187 months

Saturday 30th March 2013
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buy a new one, cheaper than a new engine lol, really for peace of mind I would

bradderztvr

364 posts

177 months

Saturday 30th March 2013
quotequote all
Don't mess about trying to repair old cap, new ones are really cheap and on ebay. I got mine for £4.49, listed as a Jag E type 1967-1971, from Historic Car Parts.
The seal is really tight, but no leaks.
Good Luck

utternutter

80 posts

187 months

Monday 1st April 2013
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buy a new one, cheaper than a new engine lol, really for peace of mind I would

keatsie

Original Poster:

326 posts

194 months

Monday 1st April 2013
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On order, thanks all.

GV

2,366 posts

254 months

Tuesday 2nd April 2013
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What about a screw type cap? Surely there must be something on the market.