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[Ian_D]

Today, I nipped round to a mate’s house (about 1/2 mile away from mine) to pick some bits up, and then went tesco to check tyre pressures (about another 1.5 miles)...

While I was doing the tyres, I thought I would top up the coolant level. (now, the car is leaking coolant very slowly, maybe a litre every hundred miles or so, I 'think' its either the oil cooler or thermostat gasket. The ‘Check Coolant’ had been flickering on and off for the past day or two, so I assume that was just lowish, and not empty otherwise it would be on all the time.)

So, I opened bonnet, and slowly opened the cap (have done it many times before when engines been up to temp, and never had a problem)... HOWEVER, the level in the tank rose, and then started spitting coolant out, so I quickly tightened the cap up, and left it!

Drove home (about 1 mile), taking it easy, and watching the temp, which was between 94-96 all the way home.

Got home, and opened the cap again... it spat a little bit of water out... BUT, I could hear the water boiling inside the engine block??? I put the ignition on to see what the temp was, and it was around 96-97 ish.

Any ideas on this?

I know its never sounded like a kettle boiling up before?  :-/

[markey mark]

it runs on a pressureised system fella never take cap off when warm and running lucky you didnt get burnt bud !!

[Andy B]

....
 I put the ignition on to see what the temp was, and it was around 96-97 ish. ......

Your actual engine temp could've been anything but what the gauge said. If it had boiled up a bit & lost water, the temp sensor could've been high & dry, and so giving a very false reading.
As said, not a good idea remove the cap from a hot engine as the water will boil at a lower pressure ie when it's now at atmospheric. Check the level when 'kalt'      

[feeutfo]

 the boiling you can hear, sounds the exact same noise i had after changing the coolant and the system was still bleeding itself.(still air in the system) probably from when you opened it the first time at tescos, esp if it "boiled" over, the only thing i find unusual about your post is that you say you have opened the cap while hot before and not had a problem!
 Its frouned upon on here koz it can block your system and clog your matrix but i had a slow leak and could not find it so used bars leaks, leak stoped! I guess never use more than 1 bottle. If its a bad leak tho, nfg.
Way up the risks i suppose.:-/


edited, just re read, i would not say yours is a slow leak! so would not use bars, i was topping up once a month doing 40 miles a day.

[Marks DTM Calib]

Its doing what it should.

Remember your physics (Boyles law!):

P1 x T1 = P2 x T2

If

P1= atmospheric pressure (consider it constant in this case)
T1= atmospheric temperature (consider it constant in this case)
P2 = The coolant pressure
T2 = The coolant temperature

You lowered the pressure in the system by opening it and hence the temperature of the water went up and it boiled!  

[Ian_D]

I understand about the boiling point been higher than 100 deg if its pressurised.  Just seems strange the way it was boiling up.

I know you shouldn't really open the tank when engines hot due to steam burns etc, but I have done it a fair few times with the Omega, must admit, the engine wasn't running this time when I removed the cap. (past few times, its been running. Maybe that’s why I’ve never had any problems?)

Does antifreeze increase the boiling point? That’s the only other thing I can think of, as there will be less anti freeze in it now as I have just added water last few top-ups (Need to buy some antifreeze anyway to protect corrosion etc!)

[Ian_D]

Its doing what it should.

Remember your physics (Boyles law!):

P1 x T1 = P2 x T2

If

P1= atmospheric pressure (consider it constant in this case)
T1= atmospheric temperature (consider it constant in this case)
P2 = The coolant pressure
T2 = The coolant temperature

You lowered the pressure in the system by opening it and hence the temperature of the water went up and it boiled!  

Really?? Didnt know that the water temp could actaully rise when the pressure is reduced!  

Learn something new everyday!  

[Marks DTM Calib]

So, consider the following for your car...

If

T2 = 95 degC (as you describe)
P2 = 18 psi (about the limit of the pressure relief valve in the expansion cap)

So we get a constant of 95x18=1710

You then suddenly lower the pressure to 14.7 psi when you open the cap (approx atmospheric pressure at sea level note this varies!)

1710/14.7 = 116deg C!

Hence it boils!

[feeutfo]

water will release expanding air bubbles when boiling, under pressure the air can not expand, so no boiling.
hows that? :-/

[Marks DTM Calib]

Sorry for the physics lesson!

But your now seeing the effect of what you were taught all those years ago  

If they had demonstrted it to you I suspect 99% of people would appreciate the theory more (adn remember it) but sadly, its probably against health and safety!  

[Marks DTM Calib]

water will release expanding air bubbles when boiling, under pressure the air can not expand, so no boiling.
hows that? :-/

Not really the case, the air would most likely have been displaced by the churning through the engine and the water pump.

The bubbles are steam!

[feeutfo]

Sorry for the physics lesson!

But your now seeing the effect of what you were taught all those years ago  

If they had demonstrted it to you I suspect 99% of people would appreciate the theory more (adn remember it) but sadly, its probably against health and safety!  

considering his past exp. tho. i wonder if maybe oilcooler is increasing pressure more than he is used to, sludge? what you think???

[Marks DTM Calib]

Sorry for the physics lesson!

But your now seeing the effect of what you were taught all those years ago  

If they had demonstrted it to you I suspect 99% of people would appreciate the theory more (adn remember it) but sadly, its probably against health and safety!  

considering his past exp. tho. i wonder if maybe oilcooler is increasing pressure more than he is used to, sludge? what you think???

The pressure is limited by the cap safety valve, you might get air drawn into the system when it cools down via any coolant leak but, this will be displaced to the reservoir pretty quickly.

Its just the simple rules of physics, it will happen on any car with a pressurised setup!

[feeutfo]

Sorry for the physics lesson!

But your now seeing the effect of what you were taught all those years ago  

If they had demonstrted it to you I suspect 99% of people would appreciate the theory more (adn remember it) but sadly, its probably against health and safety!  

considering his past exp. tho. i wonder if maybe oilcooler is increasing pressure more than he is used to, sludge? what you think???

The pressure is limited by the cap safety valve, you might get air drawn into the system when it cools down via any coolant leak but, this will be displaced to the reservoir pretty quickly.

Its just the simple rules of physics, it will happen on any car with a pressurised setup!

i understand, i just dont unerdtand why its so much worse than his previous expperience tho. suprised he s not had it bubble over before i mean, sorry to keep on


fixed oops

[feeutfo]

wo cocked that up, why did it not boil over on previos occassions, is what i dont understand?