OK, based on my findings last week, I got a new header tank. It was suggested that my non pressurized tank is not so sensitive to verticle placement. So, does this seem like a decent place to put the header tank or does it need to be mounted higher still? Mind you, this is the type with a single bleed nipple, not like the VAG bit I used previously. Any help is appreciated.

--Thanks, Chris
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I would mount it so that the highest point in the rest of the system is no higher than the mid point on the tank. You need to fill the system so it must be at least in line with the higest point, and then add enough unfilled space for expansion when the system heats up.

Hi Chris - what tank did you get?

If it's either of those you suggested on the last thread, then you don't have to mount it high up as it's an overflow bottle (expansion bottle). When the coolant expands in your system it'll be purged into the bottle from under the cap. In this situation it's actually better if the bottle is a wee bit lower.

However a pressurised 'degas' system need the bottle to be at the highest point in the system so that any trapped air can be expelled into it.

Thanks gents:

The tank is from one of those mentioned: its a late model Nissan tank. There is a bleed nipple at the top of the tank and a drop down tube inside.

So slightly lower is good. Is 3.5" lower too much?

--Thanks, Chris

Bottom of drop down tube must be at or above the level of the highest point in the system.

Thanks BT! But I checked my wife's Toyota (my Jetta TDI uses the pressurized system) and found that the bottom of the drop down tube is about halfway down the radiator. The top of the bottle is parallel with the radiator.

For those of you who actually dismantled the bike to remove the engine, where is the header tank in relation to the radiator (above, below, etc)?

--Thanks, Chris

Chris - these guys are referring to a PRESSURISED system, which needs the bottle at the highest point in the system for the air to be purged (air rises, it separates in the bottle, coolant goes back into the cooling system).

An overflow system - like the one you have - doesn't need the bottle to be at the highest point. I'm glad you checked your wife's car, because that's the way you should be mounting the bottle you have. Mouting it 3.5" below the rad cap IS FINE!

The bleed valve is to allow air to escape quickly as the bottle fills with the expanded coolant. It would be a good idea to put a long, small bore hose on this and route it towards the ground thereby ensuring any escaping coolant goes straight under the car (but away from tyres!).

Please trust me on this - I helped design and develop cooling systems when I worked at Ford.