Newbie with a Coolant question...

[Dubworth]

Good morning, I've recently joined the fold and purchased a very nice 1985 van with a 1900 DG engine and a high-top. I've noticed the last week I've had it that the 'top-up' tank is dry after a drive, even though I have topped it up before hand with the correct grade coolant. I am guessing this should maintain its level? When it tops up, it only ever requires around 500ml, about what it takes to top up the 'top-up-tank'
The van itself drives well and temperature never goes above halfway on the gauge, I get nice hot air through the fans if I turn the heating up.
I've read quite a few threads on here, and as a result I will be changing 'dalek' cap with a OE spec one from Brickwerks, and inspecting the header tank in the engine bay for leaks (I think it's quite stained so will look to have this replaced when I have the coolant flushed and refilled in the next few weeks). I would like to get to the bottom of this before I go and have a full flush and change carried out, are there any other areas/parts I should be checking? I have checked after the van has stood, no signs of it dropping coolant, nor is there any sign of it mixing with the oil when I check the oil filler cap and oil on dipstick.

Any help appreciated

[AngeloEvs]

I would bleed the system (see WIKI for procedure) as well as fitting a replacement Dalek cap. Assuming the system is properly bled and you are still having to add coolant then I would check under the Radiator, the various cooling connections from Rad to Engine and around the cylinder head seals for leaks.

[marlinowner]

You say the header tank is stained, they do have a tendency to develop hairline cracks which leak slightly and leave deposits as the water evaporates away as quickly as it leaks through. Still on the header tank, you can also get leaks around or through the coolant level sensor.

[Mr Bean]

Yes when I eventually changed my header tank out of frustration trying to seal the sensor I found a fine crack down the thread which allowed coolant to bypass the "O" ring seal. I assumed that this only opened up when the sensor was tightened. (Shouldn't be overdone being plastic and all!)

CS

[Dubworth]

Thanks everyone, I've ordered a new header tank and dalek cap, I'll get the system bled and those bits replaced and take it from there. Last night I replaced the hose and jubilee to the top up tank, as both had seen far better days, the expansion tank on engine appears to have older black style dalek cap as well, so I think a refresh is in order! Thanks again