Radiator filler Cap?

Change your supplier.

Well in all seriousness Derek there must another problem. Is the seating in the neck sound . Is it a plastic rad or an early metal one. ??
As it is a 993 with no matrix bleed on it you have got two rubber seals doing the job so I can only think over pressurizing due to a head gasket or the radiator filler neck seating isn't good or if its a metal rad is it leaking around the filler neck to header join. ?

woody wrote:Well in all seriousness Derek there must another problem. Is the seating in the neck sound . Is it a plastic rad or an early metal one. ??
As it is a 993 with no matrix bleed on it you have got two rubber seals doing the job so I can only think over pressurizing due to a head gasket or the radiator filler neck seating isn't good or if its a metal rad is it leaking around the  filler neck to header join. ?

Sorry, but I had to have a tongue in cheek reply to your first reply   

The seal on the non pressurised cap is twice the width than the spring loaded one, which I think maybe not  quite sealing properly. I rang up a piaggio dealer after seeing one on ebay for the 1.0l porter which looks identical to mine. Fingers crossed because there the same vans.

Should have gone to Specsavers. Seems to me Derek that its not just your van that needs attention but you aren't paying attention. I know what you are saying about the Solid cap. The rubber seal is a large one piece disc the whole size of the cap.
The Spring loaded cap also has the same diameter seal but obviously its a ring seal and then you have the small seal underneath the one way valve. Two seals the large one directly under the cap the same as the plain cap so it makes no difference if you fit the spring loaded cap --- except that it is giving you better sealing than the plain cap.
Am I making sense to you or have I misunderstood YOU .?? Regards Mr Know It All.

Sorry bud, but I have to disagree.   
The system is designed with a pressure relief into a catch tank, if both release and one goes to open air, it ain't rocket science(though it is physics )that the pressure release will take the path of least resistance and end up pissing out the top cap into the atmosphere.
It's what happened to my van so I'm sticking with my opinion.

It can't go to open air because there is no place to spill from.

If your caps keep leaking, resurface the top of the radiator with a flat block wrapped in fine sand paper.

Thank you for that HJ . Logi if you think about it on a normal car radiator system there is only one Radcap which on the filler neck -- Radcap housing -- whichever you want to call it --- has a bleed off pipe which goes to a sealed expansion tank or a catch tank which which isnt sealed. 

When the water in the radiator expands too much or the system is over pressurised by engine gases from a leaky head gasket or steam from over heating the valve as you so rightly say opens-- the line of least resistance and then because there is a TOP SEAL under the cap it SHOULDN'T get out under that but would travel down to the expansion bottle. 

The Hi-Jet bleed off pipe isnt a bleed off in the sense that it goes to a bottle -- it comes as you know from the top of the Heater Matrix. So it has nowhere to go on the Radiator. 
The excess pressurised water exits from the LOWER CAP housing into the overflow bottle. 

If you have got water coming out from under the RADIATOR CAP then the top seating is the problem or perhaps a fine split in the plastic neck. As you said IT AINT ROCKET SCIENCE TO UNDERSTAND THAT . You are a very competant person so you should be able to find the cause of the problem Old Fella.    

When I put caps on, I put Vaseline on the rubber seals and the "radiator neck" or "metal pipe under the passenger seat".

This stops the rubber seal from distorting as you twist it, because the copy caps don't spin round freely like the genuine daihatsu caps.

I don't have a problem, i have the CORRECT cap setup on mine

Oh well I have expressed my thoughts and experiences as have you Logi so I will leave a line under it there I think.  

Logi wrote:I don't have a problem, i have the CORRECT cap setup on mine

This seal twisting issue happens mostly on the metal pipe under the passenger seat, as you take in off and on more often.
And as you know, when ever your using any type of rubber seal it is recommended that you lubricate them.