406oc.co.uk

Earlier on this year i had an expansion cap crap out on me so replaced it and ever since I've monitored it and for ages i thought it was losing water until i came across a thread that told me i was over filling it.. (well ffs I've done nowt different with all the other cars I've owned)

Problem was i was doing so much driving i was scared to leave the house without it being up over the line it seems to settle at...During this time I've noticed a pressure build up it lets off a good POP when you undo it (is this normal?)
I've even started releasing the pressure through the black dust cap thingy on the hose.

I've always filled high and let the cap spit out the excess.

When the engine's hot, excess anything (coolant or air) will be pushed out of the cap when it exceeds a certain pressure. Afterwards when it's cooled down, there will be a mild vacuum in the system. It's likely this is the pop you're experiencing.

The dust caps are actually for bleeding. If you open them with the engine off and cool, you can introduce air pockets, which are bad (unless you're draining the system...)

mine does this and rather annoyingly, the 'level' that the car likes is below the sensor - causing the coolant light to come on and off at random times - done over 1.5k miles since I had the 406 and it seems it's just how the car likes to work.

( I still top up with half a litre every 3 weeks tho' )

Waxman wrote:mine does this and rather annoyingly, the 'level' that the car likes is below the sensor - causing the coolant light to come on and off at random times - done over 1.5k miles since I had the 406 and it seems it's just how the car likes to work.

( I still top up with half a litre every 3 weeks tho' )

sounds like your cap has had it and is letting too much be spit out

mjb wrote:

Waxman wrote:mine does this and rather annoyingly, the 'level' that the car likes is below the sensor - causing the coolant light to come on and off at random times - done over 1.5k miles since I had the 406 and it seems it's just how the car likes to work.

( I still top up with half a litre every 3 weeks tho' )

sounds like your cap has had it and is letting too much be spit out

I was thinking that too because when i topped mine up yesterday after 160 miles of driving it only took 50ml to get it back up over the mark it was at last week.

@Mjb. with the dust caps I've undone the one on the top of the engine slightly and you can hear air coming out... Then the cap don't pop so loud I'll check it again in a few days by just releasing the cap and see what it does then.

My worry is the hose does feel quite full after a run but i guess that's why their made of expandable rubber and not plastic.

mjb wrote:

Waxman wrote:mine does this and rather annoyingly, the 'level' that the car likes is below the sensor - causing the coolant light to come on and off at random times - done over 1.5k miles since I had the 406 and it seems it's just how the car likes to work.

( I still top up with half a litre every 3 weeks tho' )

sounds like your cap has had it and is letting too much be spit out

^^ I have a thread on here with the trials and tribulations of it, did my head it at first > It's been treated to a new cap and still does it. As long as it does not show signs of overheating and fans cutting in ( which is all working fine ) then it's back to the old school way of driving and just checking temps every now and then. - Done 500 miles in it last Sun without issue.

OP tho, yes - always makes a pop when I need to fill it

had all this over the summer period waterlevel light coming on every week but i do 1000 miles a week, pressure in the hoses , hoses quite hard after a run , pressure still in system if i released the cap several hours later , but always held 90 degrees even when the outside temp was at 35 in central london in the summer, fans never came in , was suspecting start of a head gasket !
one day put in a k seal, within 50 miles it blew all its water out , overheated but at least the fans worked , gave it a head gasket , 10.000 miles later had not had to put a drop of water in, and no abnormal pressure in the hoses ,
so all you guys out there with coolant loss problems and pressure in the system , stop thinking its a simple fix and think HEAD GASKET, by the way the old gasket was barely visible to any failure ,under a magnifying glass there was some deterioration around the seals , and i did not skim head or give it new bolts

the caps are for bleeding the coolant, iwouidnt undue them with the engine off, you will let air in if you do,

id get some ready mixed anti freeze and a pop bottle with the bottom cut off and bleed the system.