I have just bought a new toy with a C20XE, and started to tidy up some bits, the cooling system is bugging me, although it works it feels wrong (If you know what I mean,) so, Starting with the rad, standard 40mm feed on the passenger side at the top, opposing bottom 40mm bottom hose hooks round into back of the water pump, that all seems OK and makes sense, where I would expect to find a 8mm pipe for overflow to a pressurised tank there is a 25mm pipe that runs into the top of a sort of ally swirl pot with a pressurised cap and overflow, there is also a 25mm outfeed from the bottom of this pot, which feeds back into the bottom hose via a copper T, Im guessing the tank is intended as an air trap and an easy way to fill, is there a better solution

[Edited on 16/1/23 by ian.stewart]

What you say you expect and what you describe having sound like the same thing??

An air bleed/de-gas pipe from top of engine/'stat/rad (or multiple T'd together) into a pressurised tank bottle with a larger expansion pipe from the bottom of tank T'd into bottom hose is pretty standard setup.

Have a look on the SBD website there's some good info on there

https://sbdmotorsport.co.uk/instruction_sheet_categories/vx-cooling-systems/

Thank you for that,
Looking at the SBD diagrams, it would seem that my heater is in fact plumbed incorrectly, one pipe is connected to what SBD suggest use as a vent/bleed, and on my spare manifold is not even drilled for water, the heater pipe should run down to the pump so there is a pressure difference to give flow at the matrix, I think the heater flow was stalled,

Sorry I miss read your post thinking you had a small pipe to the top of the tank. Where does that 25mm pipe come from?

The 25mm pipe comes from the top of the rad, and into the top of the expansion tank, then thru the tank out the bottom then tee'd straight onto the back of the pump, all the expansion tank has is 2x25mm hose fittings, one at the top and straight out the bottom, and a rad cap.
the rad has the usual diagonally opposite 40mm fittings, as par crossflow rad, but the extra 25mm pipe seems to me will just bypass the flow

You won't go far wrong with the SBD advice

They know their XE's

Yes, that doesn't seem right. Not a c20xe expert but...

You don't want/need flow through the header tank and would only normally have de-gas/bleed pipe of small diameter going to the top. The small size limiting the flow.

The heater circuit usually allows some bypass flow so that before the stat' opens there's flow through the block (without going via the rad). That gives more even warm up. So you need to sort that as well.

There are plenty of tin-top coolant bottles you can choose from to replace the ally one. Not only will you then have the right size inlets but you'll also be able to see the level (an additional issue with ally ones).

So, I keep looking, what I think I am looking at is a rad that has an oversize expansion pipe, (Will aid with filling the water,) aim the tank I have to the bin.... what it should go to is a pressurised expansion tank without any other outlets, other than overflow. or perhaps include a 10mm bleed from the highest point of the water system? then re route the heater pipe onto the back of the pump so ill get heater flow.
I do agree a nice clean plastic one would help with observation of water level.

The pressurised expansion bottle would normally have a small de-gas/bleed pipe into the top of it and a larger (15-25mm) pipe from the bottom into (normally) the bottom hose. That allows for expansion, retune of any water from the bleed and filling.

Have you got a pressure cap on the rad? If so, ideally that should be blanked and the bottle used as blow off. Otherwise it can suck air back in there every time it cools down (if the valve in thst cap is slightly weaked than the bottle cap).

You could swap to a polo rad'. That'd eliminate the cap issue and the oversize bleed pipe. Or eliminate the oversize rad bleed and bottle pipe problem by putting a restriction in the pipe to reduce flow.

Mulling over the issues I have, my idea is now, to keep the rad as it is, use the 25mm pipe feed to a pressurised expansion tank, fed from the bottom, mounted at a somewhere where it is higher than any point in the cooling system, so it will bleed air from the system and be my fill point, re route the heater pipe from the inlet manifold onto the back of the pump, blank off the position from where the heater was/is fed, with possibly a bleed screw, and give it a go, the KISS acronym has always been in my mind when dealing with cooling, I may well shroud the rad too so air will do thru rather the around it