Radiator cap Spring squeezes just few mm in depth=broken? +POPPING Noise when opened

Danny_G

Car is Peugeot 406 SALOON 2000

When opening the radiator cap of the car coolant, just as the last rotation turn is done,
it makes a popping noise.

(the car engine has been switch off over night)

so this is done the next day when the engine is cold.


when unscrewing the cap off, at the end before it comes off it makes a popping noise.

a) What could that mean?
why is it popping? what is it indicating ?

(NOTE The cap does NOT pop off when driving)



Bouncy Spring?

Also when pressing the bouncy spring part of it, it only seems to bounce up and back a 1-2 millimeters
mm.

b) does that seem too little?
I would think the spring would be show more distance of displacement? (0.8cm for example)...as it would be more bouncy ?


c) Is that usual?

d) or could it be damaged ?


Here is an image of the cap



Thank you your help



EDIT ADDED
the water level gets low after long drives (2-4 hour drives)

checking water level the next morning, the water level is less
(about 0.5 pints can be refilled of lost water)

so 0.5 pints has gone, hence asking about the cap

AdrianC

The job of the spring-loaded cap is to allow the system to pressurise - but not too high.

All it needs to do, once the working pressure is exceeded, is move enough to allow some of that pressure to release.

Is there an actual problem that you're concerned about? No loss of coolant, no overheating, no "mayo" in the tank?

tykesi

Wow. Overthinking much?

Jackmydad

"If it ain't broke don't fix it."
(Or even think about it in this case)
I've got a Peugeot with similar cap, and I don't think I've ever even looked to see how much "spring" it has, because the coolant system's given no problems. (So far at least!)

Danny_G

(added above also)

the water level gets low after long drives (2-4 hour drives)

checking water level the next morning, the water level is less
(about 0.5 pints can be refilled of lost water)

so 0.5 pints has gone, hence asking about the cap

AdrianC

The cap is not your problem. That explains the "pop" when you remove it - the loss of coolant has caused -ve pressure in there, which is being equalised when you release the cap.

I suspect you've got a leak somewhere - my immediate first guess would be corrosion or stone damage to the rad.

Jane_gs

does a pop perhaps hint that the cap has an issue?

and is making the water go into the overflow tank perhaps?

Jackmydad

You are filling the tank to the correct marked level and not right up to the top?
If so then the coolant is going somewhere.
If there are no obvious leaks then try a new cap?
And you need to top up with the right coolant mix. Not just water.

[Deleted User]

Hi,

the 'pop' is only because you are releasing pressure from the radiator.

The 'springy' is meant to squash down when you refit the cap and make a seal, then if pressure builds up it will be squeezed up to allow water to flow to an expansion tank, which can then be retrieved if radiator level gets low.

Danny_G

[Deleted User] wrote:

Hi,

the 'pop' is only because you are releasing pressure from the radiator.

so the fact that there is pressure in the radiator system (via the pop) what is that indicating?

DoaM

How long after the engine has been running do you release the cap? When the engine gets hot some of that heat conducts into the cooling system. As the cooling system is a closed system then the heat needs to be transformed because heat causes materials to expand ... it does this by pressurising the cooling system. (It's the laws of physics, captain).

If you release the cap whilst the system is still pressurised then you'll get a pop - this is entirely normal.