Coolant Issue

[tomwilliams]

Hi folks,

I've got myself a 1.8tsi Ibiza Cupra. Owned it since around last October.

Over time I've noticed something odd happening in the Expansion Tank.

I first noticed the coolant level started to gradually drop over a few weeks, to the point it got a few CM under the min point, thought nothing of it as I couldn't see any drips or wetness and topped it back up to the max point. I then checked it a few days later and same again, it had dropped below min.

Decided to get it up to temp and took the expansion cap off, and lots of coolant flooded into the tank and went well above the max mark, so almost seems as though the coolant that was disappearing before, was getting lost somewhere? I'm not overly aware of how the cooling system works, so not entirely sure on what could be going on. When it floods back in, you can turn the car off and it'll go back below the min mark.

My main idea was an airlock in the system somewhere, so I've had the car up to temp and put the AC on full to see if it would push it out, and gave some of the pipes a squeeze, but the issue still seems to be standing.

Any ideas on what could be going on? Any input is greatly appreciated, thanks!

 

[Crossthreaded]

As you profess to not knowing much about how cooling systems work I'm reluctant to criticize you for removing the coolant tank cap when the system is "hot". Modern cooling systems are pressurized which allows them to run hotter (remember your school lessons? increasing pressure raises the boiling point of water) - However you have probably been very lucky not to scald yourself! Please don't remove coolant caps on hot cooling systems. The coolant can be ejected at high pressure and cover you in a "nice" spray of scalding coolant. I personally witnessed an apprentice doing this, the water went up higher than the open bonnet (which quite effectively deflected it all over him) and he had to go to the burns unit in the local hospital! Always let the system cool until you can comfortably hold your hand on the radiator.

Ok, now I've got that out the way. The effect you describe in your second paragraph would seem to indicate an air lock. You'll often see this effect when bleeding the cooling system during a change of coolant (typically every 5 years if you are using an OAT coolant) However this is not what you're doing so you need to ask where the coolant is going (you say you are topping up the level so it must be going somewhere) Try parking it on a dry clean surface, or slide a tarp or some clean cardboard under the engine and run it for a while. If it's leaking you will get some indications on the ground you can then see. If there are no obvious external leaks then it's possible you have the start of a head gasket problem. So with the engine cold take the coolant cap off - so the system can't pressurize - and run the engine up to somewhere near normal temp all the while watching the coolant in the expansion tank. If the head gasket is blowing you may well see a steady stream of bubbles surfacing in the tank.

If you get nowhere with this many garages now a days will have a chemical gas checker for exactly this purpose. It's a syringe with a chemical in it into which coolant is introduced. If exhaust gas residue is present a colour change takes place. It's a very quick check and shouldn't take long so shouldn't cost much.

I can think of other horrible reasons, but let's not go there just yet. Anyway, if you don't have much knowledge of these things you aren't going to benefit from it anyway.

So good luck with it all, let's just hope it turns out to be something simple and cheap to fix. Good luck.

 

[andycupra]

i would remove the cap when cold, , leave car running and get it up to temperature so the coolant is fully circulating and leave it running for a little while with the cap off (good idea to leave yourself a reminder) this 'should' allow any air trapped in the system to get out and complete a full purge as systems are 'self purging'.
Then leave it to cool down with the CAP OFF. This is important because you want the system to be at neutral pressure when cold and under pressure when hot. If the cap is removed when hot, it releases pressure, and if you replace the cap when still hot the system is not under pressure when hot and then when its cools it will end up being negative pressure. - pipes/joins may then allow air into the system.

then check level and top up to guide lines. mid way when cold. - will likely be over max when hot, this is normal - but not so much so there is no room in the expansion tank.
Then see if you continue to get issues. this might solve it, but if not then you need to look into where it is leaking from.