darlek cap - I'm confused!

[ermie571]

Good afternoon,

I need assistance from those that understand the workings of the darlek cap.

I believe I have a brickwerks cap on there...but not 100% sure.

So, engine was removed due to exhaust gases in the coolant....engine has been sorted and is back in.....

oil at right place on dipstick

Coolant poured in....

its running now....and coolant is circulating. temp needle going to the LED, and very slightly to the right of it the thermostat is opening and the rad is warming up.

I have been watching the levels in the tank with the darlek cap. Before I fired it up, it was brim full. I started the engine. Let it idle for a few seconds, then revved it a little from the carb. Water level remained static or thereabouts. So I revved the thing a little more, and watched the temp guage slowly climb. Drove it round the block...needle did exactly what I thought it would do...ie climb steadily too just under half mast. At this point, rad is still cold, but I have heat coming through the heater.(needle has not done any dramatic shooting movement)

So, park up and let it idle some more. Begin to panic that the thermostat isn't opening....needle just to the right of the LED....EEK!....but then, just as I was about to turn it off....the radiator had heat at the bottom! TFFT! so....I then look at the tank with the darlek, (without opening it!) and the level has dropped to just above the inlet pipe. So not huge amounts, and I was expecting this. Rad pipes to the bleed screw warm...but not hot, and only water coming out. Was expecting some air...?

Now, the header tank is full to the fill hole with coolant. I thought that the darlek was supposed to suck in water from the header while driving if it needed it? Am I wrong here??

Anyway, I have left it to cool for an hour or so...while I nip into town. Will the darlek suck in water as it cools? Should it? I will top it up when its cool enough, if it needs it.

thanks for any comments.

Em
xx
thanks for reading!

[Nicola&Tony]

As far as I understand it, water in the cooling system expands as it gets hot. This increases the water pressure in the cooling system and the dalek cap expels water into the top-up tank once a certain water pressure has been reached. As the temp drops in the cooling system, the water pressure drops again which sucks water back from the top-up tank, through the dalek cap and into the main header tank again.

Sounds like you need to bleed the system a bit more so there's no air in the header tank?

Tony

[Ian Hulley]

I agree with the right dishonourable member for Tyneside North

Ian

[Nicola&Tony]

He he he! Phewf!!

Tony

[Oldiebut goodie]

To my understanding if the tank with the dalek cap is not brimmed there is no way that the coolant can be drawn back upon cooling as the contraction of the water has only the air to pull back. Not exactly the same as attempting to siphon with an airlock in the pipe but close to it. Having no air leaks in the pipe between the dalek and expansion is imperative also.

[kevtherev]

once in the header the small amount of air will be forced into the top up as the pressure builds up to around 15 psi wouldn't it?
sort of self bleeding.

[ermie571]

Kev, thats what I thought....that the unit does a little self bleeding!

Nicola&Tony - thanks....they nysterious workings are a little clearer!

Ian - always good to have someone back up a comment!

OldieButGoodie - thanks for you comments as well...they kinda explained why the tank didn't suck it back - too much air in the system.

Right...good news....after it had cooled, i very slowly released the darlek cap...and there was a slight hiss, and the level in the tank rose! So Mr darlek is working. Did it up again...will go an top it up to brim in a min, and have a another little drive.

thanks for reading and commenting!

Em
xx