Omega Owners Forum
Omega Help Area => Omega General Help => Topic started by: Ian_D on 08 July 2008, 01:49:32
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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? :-/
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it runs on a pressureised system fella never take cap off when warm and running lucky you didnt get burnt bud !! :o
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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' :y :y :y
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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.
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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!
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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!)
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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! :o
Learn something new everyday! :y
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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!
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water will release expanding air bubbles when boiling, under pressure the air can not expand, so no boiling.
hows that? :-/
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Sorry for the physics lesson!
But your now seeing the effect of what you were taught all those years ago :y
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! ;D
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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!
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Sorry for the physics lesson!
But your now seeing the effect of what you were taught all those years ago :y
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! ;D
considering his past exp. tho. i wonder if maybe oilcooler is increasing pressure more than he is used to, sludge???? what you think???
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Sorry for the physics lesson!
But your now seeing the effect of what you were taught all those years ago :y
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! ;D
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!
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Sorry for the physics lesson!
But your now seeing the effect of what you were taught all those years ago :y
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! ;D
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
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wo cocked that up, why did it not boil over on previos occassions, is what i dont understand?
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wo cocked that up, why did it not boil over on previos occassions, is what i dont understand?
Strange isnt it eh?
Unless it wasn't quite as hot last few times Ive opened it?
I will open juist after I get back home tonight, see if it boils again! ;D
Question...
Useing the above theroy, why doesn't a bottle of coke get hot when you let the pressure out?
Say you have a bottle of pop at 20 deg and its at 30psi... When you undo the cap, the pressure drops to 14.7, that would mean that the temp would rise to 40.8 deg? Or have I got this wrong? :-/
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water will release expanding air bubbles when boiling, under pressure the air can not expand, so no boiling or in this case bubbling.
hows that? :-/
this prob. applys more to the can of pop ;D
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No, you have not got it wrong......the heat in reality will be pretty quickly dissipated and hence is not really noticed.
In the case of an engine cooling system though its at the point where the water is almost boiling so what you see is a phase change from liquid to gas which is pretty violent.
What might have happened before is that the cap was removed a period of time after stopping and given the cooling system has a small leak, the pressures may have already equalised.
Many possible explanations
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bubbles/steam=expansion
under pressurse=no expansion. hence no steam/bubbles????
learning more on here than at school, probably koz i was over the fields on me bike ;D
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wo cocked that up, why did it not boil over on previos occassions, is what i dont understand?
Strange isnt it eh?
Unless it wasn't quite as hot last few times Ive opened it?
I will open juist after I get back home tonight, see if it boils again! ;D
Question...
Useing the above theroy, why doesn't a bottle of coke get hot when you let the pressure out?
Say you have a bottle of pop at 20 deg and its at 30psi... When you undo the cap, the pressure drops to 14.7, that would mean that the temp would rise to 40.8 deg? Or have I got this wrong? :-/
Totally different ... in coke the CO2 (Carbon Dioxide) is in solution with the liquid and held there by pressure, when you take the cap off it comes out of solution as bubbles .. there is no heat transfer whatsoever.
The water v pressure is to do with boiling point of water .. which is higher under pressure and lower with reduced presure ... try making a cup of tea on a mountain .. tastes crap as the water is not hot enough.
The whole point of pressurising a cooling sysetm is to raise the boiling point in order to reduce evaporation losses, when you take the pressure away the water boils .. instantly
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I know im going off track now, but if I got a bottle water, pressurised it to say 50psi, then heated it up to 50 degress... what would happen when I released the pressure? would it get hotter still? MS Excel says 170.0680272 degrees??? :-/
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Nothing at all would happen ... if it was 100 cc of water at 0 C when you started.. and you heated it to 50 C .. you have added 50 * 100 = 5000 calories .. it would remain at 50 C.
If you added 10000 calories you would heat it to 100 C and it would be on the edge of boiling, nothing else would happen .. it would remain at 100 C.
If you added 12000 calories it would now try to boil at 100 C as each the added calories would boil off water at the rate of 600 calories /gram ( the latent heat of vapourisation). As the bottle is pressurised this doesn't happen .. and the temperature of the water would continue to rise by 20 degrees so the water would sit at 120C.
As soon as you release the pressure the evaporation takes place instantaneously ... 2000 calories excess at 600 cals/gram , so 3.33 cc of water instantly turn to steam at 120 C ...
3.33 cc of water is about 7.5 litres of water vapour (22.4 l/mol) ....
So when it goes .. it goes !! If you want 7.5 litres of superheated steam attacking you .. try the experiment !!! But have an ambulance nearby !!
(The above is somewhat simplified as the pressure in the bottle will change as well .. but I'm trying to give an idea .. not a calculation .. ) :)
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Nothing at all would happen ... if it was 100 cc of water at 0 C when you started.. and you heated it to 50 C .. you have added 50 * 100 = 5000 calories .. it would remain at 50 C.
If you added 10000 calories you would heat it to 100 C and it would be on the edge of boiling, nothing else would happen .. it would remain at 100 C.
If you added 12000 calories it would now try to boil at 100 C as each the added calories would boil off water at the rate of 600 calories /gram ( the latent heat of vapourisation). As the bottle is pressurised this doesn't happen .. and the temperature of the water would continue to rise by 20 degrees so the water would sit at 120C.
As soon as you release the pressure the evaporation takes place instantaneously ... 2000 calories excess at 600 cals/gram , so 3.33 cc of water instantly turn to steam at 120 C ...
3.33 cc of water is about 7.5 litres of water vapour (22.4 l/mol) ....
So when it goes .. it goes !! If you want 7.5 litres of superheated steam attacking you .. try the experiment !!! But have an ambulance nearby !!
(The above is somewhat simplified as the pressure in the bottle will change as well .. but I'm trying to give an idea .. not a calculation .. ) :)
My head's beginning to hurt! :-? All far too long ago, as said I can only remember s=ut + ......... ;D ;D :y
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The moving water (past the sensor) could well have been at 96 degrees, but the metal its cooling could be over 100 degrees. Remove the pressure which is preventing it boiling and low behold..
Anyone ever done a Science experiment at school? Making milk boil at room temperature...just add a vaccuum!
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I know im going off track now, but if I got a bottle water, pressurised it to say 50psi, then heated it up to 50 degress... what would happen when I released the pressure? would it get hotter still? MS Excel says 170.0680272 degrees??? :-/
still or sparkling?;D
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lol, I love this site, girlies weren't allowed to do physics at my school (yeah I'm ancient and my school was even more so) so I'm learning a lot too lol.
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I was made to do a BSc Chemistry and I hated it!! Did it as part of my first job in order to get a pay rise and some prospects. Absoulutly detested it!!! Managed a 2:1 so not all bad.... just cannot be doing with it!!!
Phamacology was much better :y :y :y Although the chemistry helped lots :-[
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lol, I love this site, girlies weren't allowed to do physics at my school (yeah I'm ancient and my school was even more so) so I'm learning a lot too lol.
Something else you said that I agree with.... ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D
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lol, I love this site, girlies weren't allowed to do physics at my school (yeah I'm ancient and my school was even more so) so I'm learning a lot too lol.
Something else you said that I agree with.... ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D
You will be in the dog house...... ;D ;D ;D