Weird: Coolant Level vs Pressure

6270 Views 19 Replies 9 Participants Last post by Dilksie, Jan 3, 2011

Gringo_el_Bingo

Discussion Starter · Dec 17, 2010

Evenin' all!

Was in my mates Bora today ('00 plate, 115bhp, SE, PD engine) and the "STOP CHECK COOLANT LEVELS" alarm came on.

We pulled over, looked at the coolant level and it was still visable in the bottle, but well below the minimum level. He opened the bottle, which was obviously pressured, as it made that "whooshing" sound as the pressure was released.

Weirdly, the coolant level then rose to the level between min and max, and when the engine was restarted, the warning lights were gone, and it drove fine.

Could anyone shed some light on this please? It this common? Or some sort of epic-fail-in-the-making?!

Any and all suggestions greatfully recieved.

Ta,

******.

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sootpig

· #2 · Dec 17, 2010

its a pressurised system, as the coolant gets hot, it expands, and the coolant loop is under pressure, releasing this pressure (shouldn't be done while the coolant is hot) will cause the reservoir level to rise, but there is still not enough coolant in the system.

wait for the engine to cool (a couple of hours) then top up the reservoir with water.

its perfectly normal for the coolant to rise when you release the pressure, which is exactly why you should alow the engine to cool, before doing so. Hot coolant, under pressure, spitting all over you will hurt, alot.

Rustynuts

· #3 · Dec 17, 2010

Bearing in mind the winter temperatures we're having right now, and the fact that people are generally topping up with water and diluting the coolant, I'd suggest getting some VW G12++ coolant and topping up with that instead. No point diluting the stuff and getting a freeze up.

Gringo_el_Bingo

Discussion Starter · #4 · Dec 17, 2010

Hey. Thanks for the swift reply!

That all makes perfect sense, but the only thing that's confusing me is that surely every time that you run the car the natural build up of pressure would force the coolant level below the point that the sensor trips the alert...

The distance between min & max on the Bora coolant bottle is quite small, and the level it ends up as after running the engine for 10 minutes is further below the min than the distance between the 2 levels (if that makes sense!).

Or are you saying that we need to put more coolant in (once the system is cold) to ensure that when the pressure increases it doesn't force the coolant below the line that trips the alert? Even if this is slightly above the max-line?

The other thing that I should have mentioned is that this is not an isolated incident, and has happened on a few occasions over the last few months. But if this is normal, then I guess a top up of coolant should fix the problem...

Am I also correct in assuming that if there were a leak in the coolant system somewhere, then the pressure would not be able to build up, so we definately don't have to worry about that?

Sorry for being thick, but it takes me a while to get my head around anything that's ever been assembled with a spanner!

Ta,

******.

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madman

· #5 · Dec 17, 2010

no...because when the coolant is at the correct level cold, it will expand above the cold level when it gets hot. Thats why it has an expansion bottle to accomodate this.

Gringo_el_Bingo

Discussion Starter · #6 · Dec 17, 2010

Hmmm... now I'm really confused. If the heat of the engine etc makes the coolant expand (and therefore rise in the expansion bottle), why is it dropping and setting off the sensor?

sootpig

· #7 · Dec 17, 2010

maybe some air in the system...? undo the reservoir cap, stick the cabin heater on full, and squeeze the top and bottom radiator pipes (with the engine running). that should remove any air locks...

The coolant level will rise slightly when its at temperature, but because its pressurised, it shouldn't rise by much. If it does exceed the maximum mark, you'll hear hissing and spitting noises, when going around corners. Nothing to worry about, its just coolant venting out on the reservoir.

madman

· #8 · Dec 17, 2010

because you have a leak?

Gringo_el_Bingo

Discussion Starter · #9 · Dec 17, 2010

@ sootpig: thanks bud, I'll give that a try tomorrow.

@madman: so the fact that it's still pressurised doesn't mean that the system is airtight? Perhaps you're thinking that the leak is slower than the build up of pressure, therefore there could still be a leak and pressure at the same time? (Albeit at a lower pressure than it would be if there were no leak...)

madman

· #10 · Dec 17, 2010

dunno mate top it up and monitor the level. Leaks are not common[

]

Dilksie

· #11 · Dec 18, 2010

I've had this before on another car and it was due to a failed head gasket (gone between cylinder and water jacket) pressurising the system and pushing the fluid down. Get a garage to do a sniff check to confirm

Engimaneer

· #12 · Dec 18, 2010

dunno mate top it up and monitor the level. Leaks are not common

Yes they are....

Can happen from the radiator, any of the connecting pipes, connections between pipes or within the engine itself.

For ages I had a similar problem of the car telling me the coolant was low when starting, but after two mins, if you re-started the engine the warning was gone. And the level never physically changed, it just displayed low at normal start up once a day, then throughout the rest of the day (even if not driven for hours) would be at what it was when I last renewed the system with fresh G12++.

One day it stopped doing this and has been fine for around 8 months.

djbuzz

· #13 · Dec 18, 2010

Also if your stop check coolant may come on because of the metal rod sensers in the tank getting crap on them, i stuck an allen key in mine and scrapped it up and down both sides to 'reveal fresh metal' and ive never had the warning back since and it was happening every other time i got into the car before.

Gringo_el_Bingo

Discussion Starter · #14 · Dec 18, 2010

@ djbuzz: I'm pretty sure it's not a problem with the sensor etc, as it only seems to trip the alarm when the coolant level is genuinely below the 'min' line. Might do the scrape thing anyway, though, just to keep things clean! Ta.

@ Engimaneer: Good to know leaks are a little more common. Cheers. Your problem sounds slightly different in that your levels never moved. The alert seems to be coming up legitimately, as the coolant level is dropping below 'min' under pressure.

@ Dilksie: I was hoping nobody was going to mention this. Boo. (I should add that I was going to buy this Bora off him in the next couple of months!) Sniff test it is, then. Cheers!

Geoff

· #15 · Dec 18, 2010

I've had this before on another car and it was due to a failed head gasket (gone between cylinder and water jacket) pressurising the system and pushing the fluid down. Get a garage to do a sniff check to confirm

Same problem here too, Head gasket.

Chris.

· #16 · Dec 18, 2010

Sounds like there could be a air lock in there.

madman

· #17 · Dec 18, 2010

dunno mate top it up and monitor the level. Leaks are not common

Click to expand...

Yes they are....

Can happen from the radiator, any of the connecting pipes, connections between pipes or within the engine itself.

For ages I had a similar problem of the car telling me the coolant was low when starting, but after two mins, if you re-started the engine the warning was gone. And the level never physically changed, it just displayed low at normal start up once a day, then throughout the rest of the day (even if not driven for hours) would be at what it was when I last renewed the system with fresh G12++.

One day it stopped doing this and has been fine for around 8 months.

Well if they are common...you dont hear much on here about them![:S]

Engimaneer

· #18 · Dec 19, 2010

I disagree with that, have seen many posts on here with people suspecting leaks, and then finding them. Or having issues that are pinpointed to coolant leaks after closer inspection.

Also, if you asked every car owner with a car over 7 years old, well over 70% will have experienced a coolant leak at some point as it is the rule of fluidics. Seals wear and pipes split over time, regardless of make. Radiators often develop leaks as they corrode or get damaged over time also.

Gringo_el_Bingo

Discussion Starter · #19 · Jan 2, 2011

maybe some air in the system...? undo the reservoir cap, stick the cabin heater on full, and squeeze the top and bottom radiator pipes (with the engine running). that should remove any air locks...

The coolant level will rise slightly when its at temperature, but because its pressurised, it shouldn't rise by much. If it does exceed the maximum mark, you'll hear hissing and spitting noises, when going around corners. Nothing to worry about, its just coolant venting out on the reservoir.

Just a quick update to finish the thread off (I hate reading threads where you never find out what the actual problem was!)

A few days ago we tried the above. Once we'd been squeezing the pipes for 10 minutes or so, we switched off the engine and the coolant level was quite low. This was because the air that had been in the system had been expelled through the open expansion bottle.

We topped up the level, and it's been fine ever since.

Massive thanks to all who suggested stuff!

Ta,

******.

Dilksie

· #20 · Jan 3, 2011

Glad you got it sorted and thanks for putting up your findings. I too hate it when you don't find out the actual cause of a problem. I'm sure your findings will help someone on here in the future.

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