Expansion Bottle; what's it all about?

[Lucky]

Bollocks. Back to square one

[ian65]

Bollocks. Back to square one

nah, loads of cars use bottom fed expansion bottles..... just keep your coolant clean and flush the bottle out every now and again.

[Hobbawobba]

I was wondering recently about this same thing. Saw some cool looking catch cans and thought something similar would be nice instead of the standard bottle. Not too fussed about it though.

And for no reason apart from vanity, here's mine after the equivalent of an expansion tank spa day ... the patented steradent and dishwasher treatment

Just gave a few parts the same treatment Came out really nice. Shame it doesn't wash surface rust away from the outside of the blue box

[KiwiDave]

[gt_james]

Wondering if I can tap into the knowledge of the experts on here.

On my white car I seem to be having an issue where the coolant level in the radiator goes down a bit and triggers the coolant level light.

It seems that there isn't a leak or any gradual coolant loss, the amount of coolant in the car stays constant. I think when it warms up, it pushes a bit of coolant into the expansion bottle, but then as it cools down it doesn't suck it back into the top of the radiator, so on the next drive, the coolant light comes on while it's cold, and goes off after a few miles, the level is slightly down when cold. Can sort this by manually pouring some back into the top of the radiator from the expansion bottle, but it will happen again next drive.

I have replaced the radiator cap for a stainless one, I have checked the nipple in the top of the radiator neck, the rubber hose and the straw in the bottle are all clear by blowing through them, nothing blocked. I wondered if there was an air lock and that I needed to syphon the coolant up the rubber hose, so I took the hose off at the rad, syphoned it up the hose and connected it to the nipple again, but none of this seems to have helped. I have wondered about trying to get it up to temperature, then holding the expansion bottle much higher than the top of the rad whilst it cools down to try and promote it syphoning back to the top of the radiator with a bit of hydraulic head.

Any other ideas, or obvious fixes to this issue please?

Cheers, James

[Richnzj]

Is your coolant system all stock with the only change the rad cap ?

[gt_james]

yes, and I changed the rad cap after this was happening in an attempt to fix

[Richnzj]

OK yeah the cap has 2 valves it should let out the fluid under expansion but also allow the fluid back in under vacuum from what your saying the expansion tank is not getting enough vacuum to pull the fluid back in to the rad
When the rad is cooling down ?

[Hobbawobba]

OK yeah the cap has 2 valves it should let out the fluid under expansion but also allow the fluid back in under vacuum from what your saying the expansion tank is not getting enough vacuum to pull the fluid back in to the rad
When the rad is cooling down ?

That's the gist I'm getting aye. Try a new silicone hose from rad to bottle aye. It could be split and sucking air back in to the rad on cool down?

[gt_james]

Hose closing up under vacuum could be a possibility, will try changing it and see if that sorts it.