Where is my coolant going?!

[Still Mulling]

Hi Folks. My 2010 Octavia vRS (facelift) has recently started drinking coolant. There is no apparent leak, the weather has not been overbearingly hot, much of my driving has been long, fast drives with good airflow (motorways), with some slower, hillier work around Exmoor for a long weekend just gone.

It's just been serviced/MOTd, and has been regularly maintained. The complete lack of leak evidence leads me to it being consumed at a higher rate than expected during use, but my knowledge starts to run out when hypothesising why that could be.

Any advice or other places/things around the engine bay to check would be greatly appreciated!

[Panamax]

You need an overnight pressure test with the engine cold (so that leaked coolant doesn't evaporate but leaves a trail instead).

I don't know the particular engine/car but typical invisible leaks include through the water pump shaft or from a hose connection "at the back of the engine".

[SteveKTMer]

I had a motorbike with a very small hole in the radiator, small enough that when it was hot it expanded and didn't leak, but when it cooled down, it cooled faster than the engine so the hole opened up whilst the pressure remained high enough to force out a little bit of coolant through the hole. In this case it left about 5ml on the floor each time it was ridden but in a car this could easily collect inside the under tray or in the chassis somewhere and evaporate when it's next used.

Kemptson radiators did a great job tracking it down, pressurising it to find the hole.

[Aunty Pasty]

Probably leaking a little from the thermostat housing.

[GreenV8S]

Still Mulling said:

recently started drinking coolant

How much? That will dictate how obvious any external leak would be. Any stains under the car after you leave it parked hot? Any unusual smells inside the car?

An overnight cold pressure test might leak enough to make any external leak more obvious.

A block test aka sniff test might reveal a small leak into the engine.

Coolant smells inside the car might indicate a leak in the heater matrix/plumbing.

[Huff]

How is the radiator constructed? Plastic endtanks swaged-on? such things can leak at the join, or have micro cracks develop on the plastic moulding lines, and if the rate is low enough (like the pinhole mentioned above) the evap rate is low enough you'll never see it, yet enough that you loose coolant at a noticeable rate.

its a common thing on certain BMW models. Ask me how I know.

Oh - and go over all the hose connectors, twistloc or clip style, ensure they are properly seated, and use a torch to look for cracks in the hose around/under.

After that it's flourescien and a torch ...

[markiii]

hole in the head leaking to the cylinder was where i found my coolant leak.

got through a ton of coolant but did a lovely job of steam cleaning the cylinder

[trickywoo]

Still Mulling said:

It's just been serviced

Did they change the coolant. If so they may not have bled it properly and the expansion tank level going down is it self bleeding.

[Skyrocket21]

Is it a diesel or petrol, the diesel could dictate some other factors, regarding the egr cooler or a blocked heater matrix, obviously either could be caused by a leak or the cylinder head, on the radiator check the bottom of the plastic with the metal crimps this can expand under heat, usually a build up of pink residue.

If it's a tdi this is what can happen, it's quite crazy but here goes,

The heater core / matrix becomes blocked, also the oil cooler housing too, this restricts the flow, you can check your return hose on the expansion bottle at 2,500 rpm or so for the flow back.

This in turn causes the egr cooler to boil and gas off the coolant, this will be evident through pressure build up and the radiator at the top left will be cool, until the gas is bled released.

This then causes the coolant to be pushed out of the expansion cap when it gets too hot, usually you would see the oil temperature rise rapidly on motorways going up hill, oil will keep climbing above 110 to 120c.

Plus this one: if it's been serviced, the other obvious one is the water pump leaking around the seals, this is behind the timing belt covers, look for any leaks obviously with the engine off!! if cover removed or just look at the bottom for anything.

When a DPF regen is happening the EGR is closed off, so the boiling in gas build up doesn't happen.

Probably worth trying a sniff test on the bottle to rule out, headgasket or egr cooler leaking if tdi.

The nightmare one would be a cracked head etc, should see puffs of white smoke, if a TDI this could be the regen happening on post injection!

Edited by Skyrocket21 on Friday 25th August 08:40

[Still Mulling]

Thanks Folks; appreciate the responses. It is the petrol, not diesel (sorry, should have been stated from the off).

In a twist, the engine management warning light came on yesterday while my wife was out with the kids. Kept an eye on temperatures and got the car home over 75 miles with no major issues other than the engine bay appearing to heat up very quickly (within minutes, her description).

My old ODB reader isn't compatible with newer apps, it seems (), so I'll be booking it into the garage. Sigh.

...

In news that I can neither confirm nor deny as related: anybody wanna buy a Race Blue Škoda?

[richhead]

Still Mulling said:

Thanks Folks; appreciate the responses. It is the petrol, not diesel (sorry, should have been stated from the off).

In a twist, the engine management warning light came on yesterday while my wife was out with the kids. Kept an eye on temperatures and got the car home over 75 miles with no major issues other than the engine bay appearing to heat up very quickly (within minutes, her description).

My old ODB reader isn't compatible with newer apps, it seems (), so I'll be booking it into the garage. Sigh.

...

In news that I can neither confirm nor deny as related: anybody wanna buy a Race Blue Škoda?

Oh dear, an obd reader, despite what most think, doesnt fix mechanical faults, how do you think cars were fixed before they existed, yes they have a use, but not for everything, you need a cooling system pressure tester, put it on , pressure the system and it you should be able to see a leak, if you cant, its going in the engine somewhere, dont forget it may be leeking from the heater, often inside the car.
Its most likely something stupid, like a pin hole in a radiator etc, often hard to see the trace of a leak, as some coolants dont leave a trace, but if under pressure, like it would be if the engine is hot, it is normaly spotable.
What ever you do dont use a radweld type fix, these can cause more problems than they cure.

[Still Mulling]

richhead said:

Oh dear, an obd reader, despite what most think, doesnt fix mechanical faults, how do you think cars were fixed before they existed, yes they have a use, but not for everything, you need a cooling system pressure tester, put it on , pressure the system and it you should be able to see a leak, if you cant, its going in the engine somewhere, dont forget it may be leeking from the heater, often inside the car.
Its most likely something stupid, like a pin hole in a radiator etc, often hard to see the trace of a leak, as some coolants dont leave a trace, but if under pressure, like it would be if the engine is hot, it is normaly spotable.
What ever you do dont use a radweld type fix, these can cause more problems than they cure.

I’m aware of what an ODB reader does. Clue’s in the name.

There was a split diaphragm which has now been fixed.