Plastic tank

[Jan Wulfsberg]

My –84 x-flow has a plastic tank connected via a hose to the filler neck on top of the thermostat housing. I suppose its purpose is to collect steam if the water should boil and condense it in to water. What is the point of collecting this water in a tank and not just letting the steam flow trough a hose that ends under the car? Can I get rid of the tank all together to get a tidier engine compartment? confused.gif

 

For a fresh Seven owner in Norway, this forum is a fantastic source of information. thumbsup.gif

 

Wulf (Viking) id=red> cool.gif

[Big Brother]

Jan,

The tank is there to collect "expanded" water when the engine is hot. Once the engine cools the coolant in the bottle "should" be suched back into the engine.(this is why you have a "bead" type valve in the outer rim of your thermostat)

 

Neat Idea - but not very reliable in practice!

 

I have heard many stories of people driving their cars hard (Trackdays), then having lunch and not checking the coolant before venturing back out onto the track and cooking their engines sad.gif

 

An alternative is to plumb in a "sealed" type expansion tank.

This seems to be the recognised way of curing overheating crossflows.

 

 

Steve

www.Se7en-Up.co.uk id=limegreen>

 

[Jan Wulfsberg]

Steve!

 

Having checked the filler cap there is no “ "bead" type valve” just a spring loaded plate that can let out pressure. There is no way the cooling system can suck back water if the pressure sinks.

 

Still confused.gif

 

Wulf (Viking) id=red> cool.gif

[Baby Bucket]

Jan,

 

Welcome to Blatchat !! It seems that you have a catch tank for water that bypasses the radiator cap that sits on top of the engine.

 

You can replace this cap with a sealed (but not sprung) cap that allows water to escape to an expansion tank AND return (i.e. the tank is under pressure). The expansion tank is fitted with a sprung pressure cap (to prevent explosions !!)

 

I have had this fitted to my 1.6 x/flow.

 

Hope this helps

 

Peter

[Big Brother]

Jan,

Normally the filler cap will have a small brass centre piece. This will be on the lowest surface and can be pulled out/down by about 1mm.

It allows coolant to be drawn "through" the spring loaded pressure plate, back into the engine when there is a negative pressure.(suction)

The bead type valve is fitted to the outer edge of the thermostat - not the filer cap.

 

Steve

www.Se7en-Up.co.uk id=limegreen>

 

[Old Septimus]

I have used an expansion tank for > 10 years and it works fine. Whenever I check the level in the swirlpot it is always up to brim. Most (if not all) bayonet rad caps have an air return valve in the centre of the spring loaded valve plate otherwise when the hot water contracts after you turn off the engine a partial vacuum is created and the hoses collapse. If you then insert a rubber washer on the inside of the bayonet cap to make an airtight seal and run the overflow hose into a container with some water in it, it will suck water rather than air back into the system when it cools. The expansion tank can sit low on the lower frame tubes as the system seems to suck uphill quite happily and my tank is a discarded 2 litre container that held screen washer fluid. It doesn't seem to mind getting hot. Make sure that the expansion tank itself has a small venting hole to atmosphere if the hose is a tight fit into the cap.