I have bought a nissan micra expansion bottle;
I know very little about cooling systems but have found the expansion tank is not sealed, it is open at the vent to the right of the cap. There is
however a substantial restriction on the inlet.
Is this how expansion bottles normally work or does the micra have a different cooling system to my BMW engine?
Depends on how you intend to connect it.
Un pressurised expansion bottles are connected to the little overflow pipe on the radiator cap, as the water heats up and expands it gets pushed out
of the radiator tank into the bottle, normally there is a little standpipe or the connection is at the bottom so that as the cooling system cools down
and contracts the excess can be drawn back in again through the radiator cap. You need to have a radiator cap at the highest point with the overflow
connected to the bottle, if this isn't the radiator then the radiator needs a blank cap. This type normally has an unsealed plastic cap.
The pressurised type are tee'd into the cooling system and normally have at least two connections to allow circulation through the bottle to
assist with bleeding of trapped air, this type usually have radiator type cap. The air gap above the coolant level allows for expansion without any
coolant leaving the system.
Cheers
Davie
quote:
Originally posted by daviep
Depends on how you intend to connect it.
Un pressurised expansion bottles are connected to the little overflow pipe on the radiator cap, as the water heats up and expands it gets pushed out of the radiator tank into the bottle, normally there is a little standpipe or the connection is at the bottom so that as the cooling system cools down and contracts the excess can be drawn back in again through the radiator cap. You need to have a radiator cap at the highest point with the overflow connected to the bottle, if this isn't the radiator then the radiator needs a blank cap. This type normally has an unsealed plastic cap.
The pressurised type are tee'd into the cooling system and normally have at least two connections to allow circulation through the bottle to assist with bleeding of trapped air, this type usually have radiator type cap. The air gap above the coolant level allows for expansion without any coolant leaving the system.
Cheers
Davie
Lots of aluminium tanks online but would like one that I can see the level, any recommendations? I have two outlets on my cooling system as per
diagram below, do I want to connect both to expansion tank or blank one of them off?
VW spherical expansion tanks are well enough suited, I think they look OK, are easy to mount, the pipes point in sensible directions and most
importantly they are cheap 
Radiator Coolant Heater Overflow Expansion Tank Bottle Spare - Topran 103986755
Big connection on the bottom connects to the bottom hose ( tee in-between radiator and water pump )
Little connection connects to the top hose to allow any air to circulate to the bottle.
Cheers
Davie
quote:
Originally posted by daviep
VW spherical expansion tanks are well enough suited, I think they look OK, are easy to mount, the pipes point in sensible directions and most importantly they are cheap
Radiator Coolant Heater Overflow Expansion Tank Bottle Spare - Topran 103986755
Big connection on the bottom connects to the bottom hose ( tee in-between radiator and water pump )
Little connection connects to the top hose to allow any air to circulate to the bottle.
Cheers
Davie
That's exactly what I have on mine and it works just fine. Got it from the scrappy for next to nothing and I even matched the colour of the cap.
The thinner hose goes to the radiator cap overflow and the thicker one to the bottom of the cooling circuit. Easy to bleed just by taking the cap off
and squeezing the pipes.
Description
quote:
Originally posted by SteveWallace
That's exactly what I have on mine and it works just fine. Got it from the scrappy for next to nothing and I even matched the colour of the cap.
The thinner hose goes to the radiator cap overflow and the thicker one to the bottom of the cooling circuit. Easy to bleed just by taking the cap off and squeezing the pipes.
Description
Yes, the expansion bottle needs to be at the highest point. I made a bracket to position mine so that the water level was somewhere between the max and min lines on the bottle when the coolant system was full to the top. As already mentioned, this allows for expansion room without overflow. Incidentally, I also araldited a 'deflector shield' over the high pressure overflow on the expansion bottle as, left as it was, any overheating would have sent a jet of hot water straight onto the battery!