Classic Expansion tank cracked wide open!

As stated, my tank popped at a seam and of course gushed coolant everywhere. Scrounging around the shop at work I made a bypass for the tank and made it the 25 mile drive home.

My question is can I drive it without the tank and cap until I can source a new tank or should I park it?

I would be tempted to park it without a pressure cap. it's there for a reason

Rubberknees said:

I would be tempted to park it without a pressure cap. it's there for a reason

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I was kinda thinking the same thing. I think I have a spare on the dormant 93'.

Pressure increases the boiling point of water, look inside your kettle when it gets close to the boil then imagine it's your engine

kermit_rr said:

Pressure increases the boiling point of water, look inside your kettle when it gets closer to the boil then engine it's your engine

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Huh?

In a decent running cooling system does the pressure cap continually bleed off pressure or does it function as an emergency measure?

It is an emergency relief valve normally at about 12 - 15 psi,
water boils at 100c a lot of engines stats open at 95c but by pressurizing it raises the boil point to say 110c, so with no cap it will boil
The l322 stats open at 105c so above boiling point, but not when its under pressure.

Western Slope Rover said:

Huh?

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Auto correct at it's best again

As long your not driving in the Himalayas where water will boil at low temps ,at sea level driving with no cap is fine as long as you don't seriously labor the engine ,and the cooling fan works. slow moving traffic ..But if uv a head gasket problem you will overheat ,blowing water out .Iv done it lots of times just had to top the water up now and then .....

dubbleRR said:

As long your not driving in the Himalayas where water will boil at low temps ,at sea level driving with no cap is fine as long as you don't seriously labor the engine ,and the cooling fan works. slow moving traffic ..But if uv a head gasket problem you will overheat ,blowing water out .Iv done it lots of times just had to top the water up now and then .....

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But I was driving with a closed loop with no cap. So, basically it was under pressure the whole time.....

It is merely a thought experiment now because the tank on the 93' was good and it has been transplanted.

Western Slope Rover said:

In a decent running cooling system does the pressure cap continually bleed off pressure or does it function as an emergency measure?

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It will increase in pressure as the water expands and then should have no further increase in pressure once at temperature. If you release the pressure once at temp then it shouldn't repressurise - if it does that may be a gasket leaking into the coolant or something is causing an overheat. With no cap you're open to atmosphere so it will slowly evaporate but probably OK for short journeys. As Brian says, it pressurises the system slightly allowing hotter running (better emissions, hence the BMW electronic devil-stats) but essentially it is a saftey valve.