Coolant lose

[paul]

Gave my car a bit of a caning yesterday the oil temp didn't get too high and the water temp didn't go over 90 degrees but when i stopped it i could hear the coolant boiling in the header tank then noticed the pressure was pumping it out through the overflow.HELP.


Paul

[tryphon]

That sounds normal. You should always let the car cool down before switching off by not pushing it for the last mile or so.
Even better practice when you switch it off leave it there for a minute or so then start it up again to allow the water and oil to recirculate though the engine and spread the temperature evenly. Repeate one or two times to allow everything to cool down gently and avoid hot spots.

[colin artus]

Or fit an electric waterpump, switched or on a delay, so you can circulate the coolant for a minute or so after stopping the engine.




Colin

[Swamprat33]

Hi Paul, I also was out playing in the sunshine yesterday. I was told that this behaviour is normal and to ensure I let the car idle for a minute or so before shutting down.

Just remember to check the water levels before the next session.

Hope to see you round MK some time soon.

Cheers

Tim

[guy mayers]

Try checking the pressure rating on the radiator cap. If it is below 13lbs it may allow any steam in the system to blow past or it could just have a bit of grit jamming it slightly open allowing fliud loss? Try replacing it with a highr rated one.

[paul]

Thanks chaps,
I drove really gentle for about 6 miles stopped at work to show some work mates who wanted to see my car.It pumped some out then after about 10 mins i drove slowly home when i stopped it released some more.It must have done it more times than that cause before i left it was topped up and when i refilled it today it needed 3 litres of coolant,best check that cap.Thanks again.

Paul

[tryphon]

Now that's less normal. I would check the head gasket...

[Sando]

Try a new cap first though !

If you say the temp is normal whan driving and it is only boiling when stopped, then the higher rated preasure cap should stop it boiling up. - I found a standard Peugeot cap at halfords with a higher rating. There was a thread (quite a few actually) about this if you do a search.

cheers
Rob:cool:

[Marmott]

I do not ever see the problem of bubbling or boiling in the expansion tank, or of the need to slow down for the last couple of miles, good practice though that may be .
In competition your on the limit till you cross the line, the car is then held stationary whilst your time cards are marked. This can take 5/6 mins, at the worst time for heat
No luxury of a cool down period , or even of a slow down lap.
I am talking of rallying
If its bubbling and boiling in the expansion tank , something is not right, it needs investigating.
The only time I saw this was when the porosity in the head broke down, it would be the same for head gasket , possible faulty cap.
Looking at the worst case , I hope yours isnt, it appears a common problem to have porosity in the heads, the are not the best quality in the Alfa V6, most are weldable.
Best of luck

[tryphon]

It's quite normal for boiling to occur, however this only happens when the engine is switched off, in normal circomstancies.

The good practice is to allow the boiling to occur and then restart in order to take away the hotspots that could:
1) Stress components which are no longer cooled
2) Burn the oil into a thicker form and that will gradually create deposits in the oil ways.

In rallying you normally don't switch your engine off in control stops. And these engines are rebuilt frequently anyway ;)

[paul]

The caps only rated at 13 lbs so i'll change that,i took the oil filler cap of and had feel around i found no gunk so hopefully it's just the pressure cap.Thanks.

Paul

[paul]

Good news it's sorted,
Looks like it was just a massive airlock it was that big when the thermostat opened the pipes to the rad were cavitating and banging together (wondered what that noise was).Anyway i bled the system and i looks like the head gaskets are ok as well so i had a lucky escape so i'm well happy.

Paul

[Arthur]

Paul,

Can be a bugger, this marginal cooling lark. If I ever get mine completely sorted, I'll post and tell the world exactly how. In the meatntime...

The guys have covered everything, pretty much, but really do watch the "airlock" thing. These engines (and pipework layouts) are notoriously difficult to bleed correctly, and airlocking will do exactly as you describe. I have to disconnect top hoses to be sure, and usually run the engine lightly to temperature a couple of times, give the hoses a good mashing by hand, then let it cool and check hoses again.

Meantime, I tend when coming in from high-speed, to kick the heater onto high speed full-blow for a few minutes. Every little helps, and the "heat soak" as you shut down can be high, despite the 7+ litres coolant volume in the engine. (No airlocks, you'll get some thermo-syphon - with airlocks, you won't get anything).

best of luck
Arthur.

[Marmott]

If you continue to get problems please call me , there is no need for you to have a marginal installation, if it is ,something is not right,
Although rallying ,I am not in the market to rebuild my engine each year, that is one benefit of the Alfa V6 , its strong.
Rallying does emphasise the cooling requirements , so if its right for competition it will be ok on the road, mine certainly does both well.
Bleeding the engine throught the standard bleed on the top on the thermo housing , and one above the top hose on the rad is sufficient.
Capacity, of the rad, and position of the expansion bottle is important, both are very easy solutions.

[chris.richard]

position of the expansion bottle is important,

Can you expand ( ;) ) on that Gary - in case I've done it wrong?

[Arthur]

Guys, Radiator caps and pressure ratings.

I keep seeing references to "check the pressure rating" of your cap. Fact is, water doesn't boil until it gets to 100 degrees C. With anti-freeze, and/or the usual mess of deposits, the boiling point will be above 100, rather than below. Until you hit the "witching temperature" the system will only see vapour pressure, which is at most a couple of psi. Soon as you hit boiling point, you'll see - sod all more than this. To lift a 13 psi cap (1.8 bar absolute, more or less, absolute being atmospheric of 1 bar (15 psi) plus the 13 psi of the rad cap) will require a temperature of 117 degrees. To lift a 25 psi cap (2.66 bar abs) will require a temperature of 129.5 degreesC.

Unless you are actually seeing those temperatures, then rad cap pressure doesn't matter a jot until you switch off.

More important is the seal of the cap. Provided that's tight, no probs. If you have a head gasket gone, then you could certainly see raised temperatures, but even so, its doubtful you'd let it get that high without stopping to cool down. More likely is gas leak to cooling water spaces, which could cause water sytem pressure increase independent of temperature, but I've never seen one this bad - usually the water goes out the cylinders.

Last problem is heat-soak at quick stop from working hard. Now here it is actually possible to see those kinds of temperatures, at a time when the ignition is normally off, so the gauge doesn't read, or the temp sensor is somewhere other than on a head, in which case it may not actually register the true temperature, but the cap still blows. And is the sole reason for using the 13 or 25 psi caps in most common use.

As for water blowing out when the cap is removed - often its an airlock. Doesn't have to be a big one, and most sytems will have bubbles here and there, or a small free space in a radiator, etc. This air will be at the same pressure as the system (couple of psi vapour pressure normally is all) (re Dalton's law of partial pressures, it will be a touch higher than the same system filled solely with water and water vapour) but as soon as you lift the cap, the AIR expands, and pushes hot steaming WATER out. This is NOT "boiling over", it's an entirely normal occurrence. "Boiling Over" entails a Vesuvius-like expulsion of instantaneously vapourising water, and an immense steam cloud. I speak as one who used such a flow as a nasal spray, and thanks to the NHS for the absence of scarring.
You probably know what I mean. But if you have a big airlock, you could certainly see half the contents of your cooling system discharged all over your boots. If it stays liquid, albeit steaming somewhat, its probably not over 100 degrees. Ergo not overheating. If it flashes off, then it was bloody hot, and doubtless the steam cloud will impress.

Hope this helps.
Arthur. (Oh yes, those numbers came from my Steam tables (Thermodynamic and Transport properties of Fluids) - doesn't everyone have a copy.......?)