Coolant levels after new thermostat

[AudiAK]

Hi All,

So I finally got the chance to fit a new thermostat after my 2.0TFSI was suffering from the usual temperature drop at motorway speeds.

For some reason I found it very easy to do (once the alternator was off) and glad I didn't let my garage do it as it took 1.5 hours as opposed to the 3 hours quoted and as long as you had the right tools it was a doddle.

I also decided to fit a new expansion tank has mine was badly stained and the entire tank was literally bleached red.

Once all fitted back together I decided to let the car to get hot with the tank cap off and then also let it idle to temp. Inspected everything and no leaks but I noticed a dribble below the expansion tank (it looks like its an overflow around the cap hole?). It dropped close to low a few times and topped it back up to max.

Took it for a run up the motorway and glad the car now gets up to temp fine, but when I got back I noticed that the coolant level was again between max and min but more near minimum.

I couldn't really see the level before (as the expansion tank was heavily stained) but is this normal behaviour or is something wrong?

TIA

 

[joinerman]

Top it up and monitor it for a few days

 

[csaby1973]

Coolant level should be checked whith cold engine before start it up.

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[AlpineCab]

Switch on heating to full but with air con off (ie Econ mode), plus some models have a bleed screw near the back of the bay to help bleed out any airlocks. Might be an idea to change the filler cap too if that was not provided with the new expansion tank fitted.

 

[AlpineCab]

The level can on occasions take a few goes to steady, as any airlocks bleed out, but as the other poster says, should be checked as somewhere between min/max when cold. Which may exceed max level when hot.

 

[AudiAK]

Thanks all. I've heard of coolant levels rising (when up to temp) but never knew it would drop.

Anyway this morning I opened the bonnet (car was cold) to find that the coolant was higher than the max mark (yesterday night it was near the low mark after a drive).

Fished some coolant out and left it on the max. Will monitor it but don't think it has any leaks.

 

[Charlie Farley]

When you replaced those bits and refilled you would have most likely developed a small air pocket somewhere even with the expansion cap off, normally it is around the heater matrix that air pockets occur.
With topping up etc and any air venting itself out of the system the coolant level will have dropped and then you topped it up again hence why it is now higher due to hot water expansion in the system.
After a few days just check to ensure it's halfway when hot, that way its allows for expansion when hot and cooling.

 

[AudiAK]

So just an update. I've let it run for a few days and it seems to run fine and get up to temperature ok.

However it seems to be dumping some coolant somewhere. I noticed a puddle under the car (directly below the thermostat housing but there is a opening there on the undertray too so that is the exit point for fluid collected in the tray itself).

I have checked the thermostat and connecting pipes visually. There doesn't seem to be any sign of a fresh leak there. The only place where I see a potential coolant leak is directly below the expansion tank (where there is an overflow hole around the cap). The expansion tank is new and so is the cap. However they are not genuine parts. Could these be potential culprits?

 

[AudiAK]

So I got to the bottom of the coolant loss. The brand new thermostat was leaking - the plastic was slightly warped from new.

I swapped it for another and its now not leaking. However, when I fill the coolant to the max level I am finding it leaks out of the overflow when it warms up and then settles midway between min and max (basically the seam of the expansion tank). Is that where coolant should sit when low and is the max marker for when its hot?

Asking an basic question here I know but previously my expansion tank was heavily pigmented so it was like it was painted pink (could never see the coolant level).