Coolant consumption conundrum - non MB

[fabes]

It's not an MB but my daughter's otherwise perfect for her, Pug 207
2012, FSH (yup!) and a basic but adequate cheap to run (and insure) 1.4 8v petrol
It's used for very local short journeys mainly

It uses coolant.
Nothing for the first 4 months we've had it but since early December when she took it to Reading (50 miles or so) which it did with no issues apparently, the coolant tank was nigh on empty.
No leaks visible on the drive when sat there for days

Since then I have filled it twice and put it into the local garage I use for the daughters cars 3 weeks ago

They did put a new thermostat housing when we got it (picked up on the service it was due when we bought it)
Garage pressure tested it and there was no leak.
They then ran it in their yard, going through 3 heat / cool down cycles with no drop in the expansion tank level
Didn't charge me as it took none of their time and it seemingly didn't need anything.
Air lock or bubble was suspected that cleared itself and nothing since (it has been used for short journeys since)

I took it out for a short trip today, it was almost up to temp when I got back, and guess what....
Coolant down to half way from halfway.
Car fine in all other aspects.

Coolant isn't entirely clean now so is the head gasket the next or most likely cause?
Any advice appreciated before I phone the garage on Monday to discuss

Cheers

 

[mercmancdi]

If no water in oil it might be worth getting a drop of fluorescent dye to add to system in case there’s a small leak you can’t find before starting to go down route of head gasket. In a small leak even at thermostat housing or hose if cars at temperature the water is dried out more or less by the time you open bonnet. I would have expected a bit of overheating or a misfire if head gasket was away I’m not convinced you don’t have a leak , if only happened on long runs then that when the stat will have opened , if it’s a small enough leak it will probably evaporate on side of engine before it gets a chance to drip onto the ground.

 

[mercmancdi]

If no water in oil it might be worth getting a drop of fluorescent dye to add to system in case there’s a small leak you can’t find before starting to go down route of head gasket. In a small leak even at thermostat housing or hose if cars at temperature the water is dried out more or less by the time you open bonnet. I would have expected a bit of overheating or a misfire if head gasket was away I’m not convinced you don’t have a leak , if only happened on long runs then that when the stat will have opened , if it’s a small enough leak it will probably evaporate on side of engine before it gets a chance to drip onto the ground.

Also meant to add is heater blowing hot air ok and worth feeling as far as you can up in at footwell high up at sides for any damp in case you have leak at heater pipe etc up in there.

 

[fabes]

Cheers

Heater is working fine.
My thoughts are also it's when the thermostat fully opens - it does take a while to get up to temp. Not forever, but longer than I am used to in our other cars.

Will have a feel around for a leak, but fluorescent liquid next step can be discussed with with the garage then as I don't really want to go spending wads on a head gasket job.

Would have thought them putting positive air pressure into the system for 15 mins would have 'found' a leak.

Any other thoughts anyone?

 

[Trickythemerc]

Sniff test for exhaust gasses in the coolant, or early signs of water pump failure with coolant being thrown by the pump pulley. Has the pressure cap been checked ?

 

[FiveAlive]

I once had a radiator that leaked when warm - not hot, and not cold. I only found it when I started the car from cold and drove it for a short journey and then parked, which isn't something I would normally do (I had picked it up from a service and taken it back to my office car park, a journey of less than two miles). Fortunately the car park had a slight slope and as I walked around the front there was quite a puddle/stream emerging from underneath. I immediately drove home carefully so as not to be stranded without coolant but by the time I got home it had fully warmed up and the leak had stopped.

I guess flourescent dye would have enabled me to track it down if I hadn't chanced upon it.

 

[tonysmb]

Any staining on the radiator fins where coolant has evaporated? Expansion tank cap? Have any hoses been replaced at a recent service, or old ones splitting around the clamp area.

When you say the coolant looks dirty, what do you mean, oily?

 

[Smiley]

The most common cause of slow coolant loss is a failing water pump; slight leak out of the drain hole and water evaporates on the hot engine. Not much evidence. But that should show up on a pressure test. If it is not that then, as has been said, it is time to sniff for gases in the coolant.

 

[grober]

https://www.honestjohn.co.uk/forum/post/index.htm?t=106120