A few questions about how to build my cooling system!

[montyjohn]

Hi, I'm rebuilding a JPR Wildcat using a BMW M52B28 TU engine from an 1999 5-Series E39.
I'm just about to finish off the cooling system and there's a few things I'm not quite sure about.

Couple of notes first:
The BMW cooling system is pressured to 2 bar (29 psi) which is huge.
I'm using an aftermarket radiator based on a Cortina Radiator that has a 20 psi cap (BMW radiator has no cap).
The BMW expansion tank should only be half filled. This allows the water to expand and compress the air. There's a feed from the top of the radiator that drains to the expansion tank to allow the system to self bleed.
The 8mm feed from my radiator is not quite at the top of the radiator as it would be on a BMW radiator. It's about 15mm away from the top. This means that any air in the system can collect at the top of the radiator before it will make it's way to the expansion tank.
BMW engines normally lean over by 30 degrees towards the exhaust. I'm running mine vertically.
The system is shown in the diagram below.

So I have a few questions:

Question 1: I don't have a BMW to check this against, but I'm not sure what the radiator level should be compared with the engine and expansion tank. Does anyone know the correct order for this type of system, as I believe it may be different to a typical classic layout.?

Question 2: Does it matter that my radiator will have some air at the top of it? The top doesn't provide any cooling anyway on a Cortina style radiator.

Question 3: Since my aftermarket cap is 20 psi, I was thinking about piping the cap pressure relief outlet to the feed that drains to the expansion tank. That way the entire system is governed by the BMW 2 bar cap on the expansion tank (which I may reduce to 20 psi also). Does this sound sensible?

Question 4: Anything else that looks wrong with what I'm proposing?

[witko999]

If you have airspace in your radiator which is above your bleed line, then air will accumulate there. The cooling system may still perform adequately like this but it's not the ideal situation.

It also might be a good idea to add another bleed line from a high point elsewhere in the system, such as the top of the engine or the pipes to the heater matrix. This will aid filling and help to avoid any airlocks. You can 'T' into the existing bleed line to the expansion tank.

I believe that you should only have one pressure cap in the system, so a plain cap would be better on your radiator.

Make sure your expansion tank is as high as possible, or at least higher than the rest of the cooling system.

[witko999]

Also, it may be possible to permanently blank off the cap of your Cortina radiator, but retain the overflow pipe, and use that as your bleed line. You could then blank off the other bleed line on the radiator, and it would evacuate all the air from the top.

[montyjohn]

witko999 said:

Also, it may be possible to permanently blank off the cap of your Cortina radiator, but retain the overflow pipe, and use that as your bleed line. You could then blank off the other bleed line on the radiator, and it would evacuate all the air from the top.

Thanks for the info. All makes sense.
I've had a look at the radiator cap to understand how it works, and I think the only way I can use the bleed pipe and Tee it into my bleed line is if I weld the neck with an alloy blanking plate.

I'm going to treat this as a last resort and see how I get on with air at the top of the radiator and keep the blanking option in my back pocket.

Thanks.