Radiator expansion bottle

[Dave Lane]

So the question is why add an expansion bottle
Well a few reasons ,
Extra coolant capacity .
If you use a see through bottle as I have then checking the coolant level is literally at a glance .
In some cases it can even tell you if your head gaskets on its way out .
Spotting coolant loss is easy .
Fitting one is fairly easy . The pressure cap stays on the rad as before and the bottle is non pressurised , my bottle looks like it has a pressure cap fitted but it has the centre relieve valve jammed open .
A pipe from the rad overflow outlet goes to the expansion bottle . Bottle is filled to one third full and as long as the pipe from the rad to the bottle is ALWAYS in the coolant it will work .
Heres how it works .
Original rad if filled to the brim . As the engine heats up the coolant expands and it goes into the bottle , on mine the rise is around one inch . As it cools down when switched off a vacuum is created and the coolant gets sucked back into the rad . for the first few times the level will drop , this is because the Imps rad has an air gap due to the top being at an angle . After a while this air is got rid of and the imp rad is now really full with no air pocket in the rad at all .
If theres a slight coolant leak - when cooling down the coolant in the bottle will still keep the rad full until the pipe is no longer in the coolant - again easy to spot .
Its better if the bottle is lower than the top of the rad .


Level when cold


Level when hot




Mounted using a couple rad mounting clips and bolts on a home made bracket . Bottle if from a Triumph Stag

[PMCG]

Nice Dave, how have you plumbed it in?

[John A. Ross]

One of my favourites, just looks like it belongs there, you can never tell it was an after thought. The coolant level marking are good as well Pat as it shows the height warm and cold

[PMCG]

One of my favourites, just looks like it belongs there, you can never tell it was an after thought. The coolant level marking are good as well Pat as it shows the height warm and cold

I can sort of guess how the thing gets plumbed in.

What I can't figure out is what the 2 spark plugs do. :)

[Dave Lane]

I can sort of guess how the thing gets plumbed in.

What I can't figure out is what the 2 spark plugs do. :)

Plugs are just spares , its an old 60s spare plug holder

[MartinSullivan]

Is the pipe on the neck of the bottle just to atmosphere, and the connection from the radiator overflow goes to the connection at the bottom of the bottle? Definitely a worth while mod - I know what Im going hunting for next

[John A. Ross]

MArtin

Yes it is a non pressurised cap on top of the rad and the take off from the collar.

Looks great there doesnt' it, not sure my shiny aluminium one would look as cool as that.


/ John

[MartinSullivan]

MArtin

Yes it is a non pressurised cap on top of the rad and the take off from the collar.

it looks fantastic and provides a very useful service.

im pretty sure Dave runs with the pressurised cap at the radiator and the non pressurised on the bottle - it allows the system to fill every nook and cranny of the radiator.

i would like more details on the “plumbing” as the Stag bottles I’ve seen have a port on the neck and one at the bottom of the bottle like the one shown

[Dave Lane]

it looks fantastic and provides a very useful service.

im pretty sure Dave runs with the pressurised cap at the radiator and the non pressurised on the bottle - it allows the system to fill every nook and cranny of the radiator.

i would like more details on the “plumbing” as the Stag bottles I’ve seen have a port on the neck and one at the bottom of the bottle like the one shown

Rad pipe goes to the bottom one , the one on the neck is just an overflow as can be seen in the second picture , correct the pressure cap is on the rad as normal , i used another pressure cap on the bottle but the centre valve in the middle of the main seal is jammed open

[MartinSullivan]

Cheers Dave - that’s what I thought , but just wanted to check , thanks for the confirmation

[PMCG]

Rad pipe goes to the bottom one , the one on the neck is just an overflow as can be seen in the second picture , correct the pressure cap is on the rad as normal , i used another pressure cap on the bottle but the centre valve in the middle of the main seal is jammed open

How does that work then, assuming the bottom of the expansion tank hose is connected to the overflow on the top radiator tank?

With the standard pressure cap on wouldn't the system have to get up to pressure where it was coming out the original overflow pipe (on outside of cap) on the radiator before it went into the expansion tank or maybe I've missed something?

[Dave Lane]

How does that work then, assuming the bottom of the expansion tank hose is connected to the overflow on the top radiator tank?

With the standard pressure cap on wouldn't the system have to get up to pressure where it was coming out the original overflow pipe (on outside of cap) on the radiator before it went into the expansion tank or maybe I've missed something?

Thats how it works , exactly as the Husky / van one did from the factory
Theres a small sprung valve in the caps centre , this opens as it cools and lets the coolant back into the rad

[PMCG]

Thats how it works , exactly as the Husky / van one did from the factory
Theres a small sprung valve in the caps centre , this opens as it cools and lets the coolant back into the rad

Call me thick but I'm still scratching head.

Is the cap on the radiator standard then?

I'd have thought not as the coolant would be stuck below the overflow until the pressure was high enough to blow the cap open so that it could escape.

Fit just any cap on the rad. with no stop then a pressure cap on the expansion tank should do it.

Have i got it or do I need to train my brain more?

I'm one of these annoying people that if I don't get it I just keep asking till I understand 100%.
I can be a real nuisance at seminars. ;)

[Dave Lane]

Call me thick but I'm still scratching head.

Is the cap on the radiator standard then?

I'd have thought not as the coolant would be stuck below the overflow until the pressure was high enough to blow the cap open so that it could escape.

Fit just any cap on the rad. with no stop then a pressure cap on the expansion tank should do it.

Have i got it or do I need to train my brain more?

I'm one of these annoying people that if I don't get it I just keep asking till I understand 100%.
I can be a real nuisance at seminars. ;)

Yep , totally standard radiator cap , 7lb short reach as normal , So it works like this - rad is full to the brim , engine heats up enough to move the cap so coolant goes into the expansion bottle , as the engine cools a small internal valve in the cap is sucked open letting coolant back into the rad . you can fit a blank cap on the rad and a pressure cap on the bottle , this works fine but means theres always an air gap in the top of the rad and of course the bottle is pressurised , either works well although sealing the rad with a blanking cap can be tricky as they only seal on the outer top edge which often isnt perfectly flat

[PMCG]

Yep , totally standard radiator cap , 7lb short reach as normal , So it works like this - rad is full to the brim , engine heats up enough to move the cap so coolant goes into the expansion bottle , as the engine cools a small internal valve in the cap is sucked open letting coolant back into the rad . you can fit a blank cap on the rad and a pressure cap on the bottle , this works fine but means theres always an air gap in the top of the rad and of course the bottle is pressurised , either works well although sealing the rad with a blanking cap can be tricky as they only seal on the outer top edge which often isnt perfectly flat

I've got it now, so the tank is filled to the brim and it's the expansion when it heats up that moves it into the expansion tank not the pressure.

I wouldn't have thought it would be able to get back from the tank to the radiator with the cap. Didn't know about the internal valve in the cap.