PSA Radiator Cap Efficacy/Service Life

addo · Post by **addo** » 07 Jun 2009, 23:56

I'm looking for informed comments on whether the modern style caps can lose ability to seal, or change spring tension with age.

Has anyone changed theirs on a car of maybe ten years age, and noticed a difference ascribably only to the cap?

Thanks, Adam.

Post by **CitroJim** » 08 Jun 2009, 07:18

Yes, I believe they do loose tension after a while Adam. I used to be in the habit of collecting caps from scrapyards but found that whilst some looked absolutely fine, they did not hold pressure and allowed water to run down the overflow pipe.

I'm the first to admit my observations were far from scientific...

Xantidote · Post by **Xantidote** » 07 Aug 2009, 21:12

Hi Adam,

Not sure what you mean by a modern style cap.

In case it helps, I had a cooling system problem on the Xantia in 2005 when car nearly 10 years old, and fitted new head gasket. However, continued to loose coolant until I placed a tin under the overflow pipe, and bingo, found the pressure cap was allowing leakage. The cap (original) was all metal, whereas the replacement was plastic (which I didn't really like) - no loss of coolant since then.

The overflow collection tin is still in place, and I check it now and then.

Martin

citronut · Post by **citronut** » 08 Aug 2009, 09:22

Martin
are you sure the metal one was the original cap fitted at the factory,
as i dont remember ever seeing a metal cap on a XANTIA of any year/model

maybe the meatal cap had been fitted by a previous owner if there were any????

regards malcolm

Post by **CitroJim** » 08 Aug 2009, 11:20

Original was the plastic cap with a handbook symbol on the top and arrows marked F and O.

The usual failure with these is that the inner pressure relief valve fails/gets blocked up. This causes the cap to either fail to hold pressure or causes far too much pressure in the cooling system. My V6 cap failed with the latter problem; bunged up with the horrible rad seal I found in the rest of the cooling system I suspect.

I don't like using the after-market metal ones. They all look very poor quality to me. Like something you'd expect to see fitted to a Morris Marina

Clogzz · Post by **Clogzz** » 08 Aug 2009, 15:23

My cap is metal, and was there when I bought the car second-hand in 1997.
I leave it loose at the first stop, where it doesn’t hold pressure.
No overflow or level dropping, and it’s 30ºC every day for over 3 months in summer.

Post by **CitroJim** » 08 Aug 2009, 18:28

That's not a bad idea Clogzz

As long as you're not too far above sea-level it'll not cause problems.

The only reason the system is pressuried is to raise the boiling point of the coolant. Anti-freeze in the form of ethlene glycol does the same thing as well if in the recommended 50/50 concentration. Mainly, the reason is to prevent the coolant boiling at very high altitude and/or if you have no anti-freeze in the system.

If the engine is really hot, it just may boil a bit when stopped and heat-soaked but even when really hot you're still a good 15 degrees from boiling and I'm sure you keep your cooling system and fans in tip-top order

What you do is a known dodge that some diesel owners resort to when their head gaskets are just beginning to show the first early signs of failure. It allows the pressure to dissipate and puts the "off with 'er 'ead" day back a few weeks or months.

Xantidote · Post by **Xantidote** » 09 Aug 2009, 23:19

Malcom,

your saying you're not aware that Xantia's had metal pressure caps makes me wonder if my memorory's playing tricks. It came with the car at 3 yrs old. Had quick look in my BoL, and that has 2 photos, 1 metal, and 1 plastic (like the replacement)!

From memory, it did have some symbols on the top, but unusual for me, I threw it away

Doesn't affact my finding it started losing pressure after car 10 yrs old of course

DickieG · Post by **DickieG** » 10 Aug 2009, 06:48

Like Malcolm I've never seen a Xantia fitted with a metal rad cap.

citronut · Post by **citronut** » 10 Aug 2009, 08:02

well if there is photo evidance in the BOL then they must ave fitted them at some stage in the XANT run,
as thats about the only thing the BOL has in common with the genuine dealers manual, as thats were hayny ass gets there picys from

regards malcolm

Clogzz · Post by **Clogzz** » 10 Aug 2009, 15:15

cooling system and fans in tip-top order

Oooh, yes ! They’re the second most important things after easy starting.
I used to put tap water and Castrol Radiator Corrosion Inhibitor in my previous old bombs with cast iron engines.
The radiator cap kept the pressure in, to prevent the water from simmering and evaporating.

On the Xantia, after draining the coolant, I drive the next day with water in the system, to dilute and drain the old remnants.
The drain tap feels harder with water, because glycol is meant to lubricate the water pump seal, and glycol concentrations over 50% become viscous.