Car – coolant loss mystery

2019 Peugeot 5008 1.5 diesel

Wife set off for work yesterday and within 15 mins the temp gauge started going up and then back down several times and a temp warning  on the dash.
she came home and I checked the coolant bottle and it was totally empty.

I put 1.5 litres in last night and ran the car but the level in the bottle kept dropping as it ticked over on the drive.
I realise it will take some coolant to refill the system but my concern is that there is absolutely no sign of a leak. Floor, underatray all dry. Oil Dipstick looks normal.  Carpets inside are dry.

I’ve had the AA out this morning to take a look and he has done a pressure test and found no leak and the car isn’t showing any faults so he’s topped the bottle up to max and said run the car and keep an eye on it. If it drops take it to a garage.

so my wife used it for the short school run and is saying the level has remained at max. I’m at work so I plan to run it tonight and see how it goes .

my underlying concern is where did the original coolant go.

is it possible for the car to use a little coolant and I’ve just not noticed the level dropping over time?

any other suggestions? Am i best getting  a garage look at it?

I put 1.5 litres in last night and ran the car but the level in the bottle kept dropping as it ticked over on the drive.

If the system was completely empty is there a chance that the 1.5l has ended up refilling the pipework leaving the reservoir empty?

The coolant tank cap may not be holding pressure so coolant is escaping through the cap, but I would have thought there would be signs of it there?

Some cars lose coolant over time in my experience, through vapour escaping from the joints. Also, if there’s any pockets of air the expansion tank can quickly empty. I’d just keep an eye on it over time.

Cracked heat exchanger? I had similar with oil entering the coolant. Have a look at the oil filler cap for signs of contamination. Hopefully not as it’ll be expensive.

What’s changed recently? Service, repair, etc?

Check the oil level, has it risen suspiciously?

Otherwise, bottle of coolant in the boot and monitor levels for the next few days

@timba no change. Car is serviced. Did several hundred  miles last week at half term without issue. Oil level is fine.
it actually ran ok the night before this started because the wife was out in it for an hour.

@mashr absolutely so AA have topped it up now and I’ll watch it but my concern is around it disappearing in the first place. Seems odd.  Maybe i just have t noticed but I’m not used to coolant just disappearing.

good suggestion to stick  a bottle in the car 👍🏻

good suggestion to stick  a bottle in the car 👍🏻

But make sure it’s coolant and not just water.

Have a look around the thermostat housing, they can have tiny cracks which only open up when the car gets hot.

its pretty easy for a car to slurp up most its coolent with a very small leak and go un-noticed, then boil a bunch more off when it overheats – I put 4l into a ford KA once, and after it bled itself properly it hardly dropped over the next 6 months.

There’s a a whole pile of things it could be other then a regular leak. Leaks into combustion chambers are easily found – the AA should have done a sniff test on the expansion bottle to check for signs of combustion products (its a chemical test that changes colour when it comes into contact with exhaust gasses). You could do a sniff test yourself: halfords or any motor factor will have the kits.

Its  diesel: so potentially exhaust gas cooler – you might see steam from the exhaust, or if its combined oil/egr/water heat exchanger then potentially water in the oil.

Radiator cores and the ends caps are made of cheese and are particularly vulnerable but also hidden away behind trim, air con radiators and intercoolers.

Broken heater matrix? Check under your floor mats – any signs of damp and does that dampness taste ridiculously sweet?

I had something similar it was a bad radiator cap, change the radiator cap and top up the coolant that’s pretty cheap to try. If it’s still disappearing it’s something more serious and you might be best taking to garage with diagnostics they can tell from coolant if it’s head gasket or pressurise system and find leaks.

Thanks.
i’ll run it tonight , get it up to temp and see if it behaves.

Make sure you are refilling with proper mixed coolant, not water.

It can go a number of places:

• Header tank cap not sealing – will only be leaking when hot/pressurised, unlikely to have lost so much this way
• Water pump leaking, very common, can be hard to spot as its often hidden under a big pulley
• Leaking pipes everywhere
• Radiator holed
• Oil/Water intermix from a heat exchanger – check your oil
• Exhaust gas cooler
• Heater matrix in the cabin
• Oil water intermix from the head gasket
• Water into comubstion chamber from head gasket.
• Core plug leaking

You may on a cursory look assume that ‘theres no leaks’ but its amazing how well it can hide itself, tucked under a manifold or dribbling down onto an undertray and slowly dripping out into the airflow as you drive. You needit up on a ramp, trays off and with a good, thorough visual inspection with a lamp before deducing ‘theres no leaks’.

You can buy a small bottle of UV dye that you chuck in the coolant header tank, drive it around for a few days then have a look (in the dark) with a uv torch. That’s how I found a very small leak at a hose joint on my Freelander.

you’re fine to top up coolant with water this time of year to get you home. Its worth getting it re-mixed with some coolant before the winter comes, but no damage will be caused with water in the system – its probably safer than mixing coolant colours

The only time I’ve had coolant loss and overheating was because the head gasket had blown.

On that engine, given that there’s no other obvious leaks, there’s a good chance its the EGR cooler assembly starting to leak.

Most coolant will evaporate off initially, then it’ll start dripping onto the starter motor, so the actual leak has to get pretty bad before it’ll drip on to the ground.

And it’s a horrendous thing to change.

That particular engine in the Volvo V40 was prone to cracking the engine block in half, and the first sign was unexplained coolant loss. Please get it thoroughly checked out.

I’ve had the AA out this morning to take a look and he has done a pressure test and found no leak

I assume you ran the engine to hot before testing, otherwise it could be a crack thats contracted when the engine has cooled.

That particular engine in the Volvo V40 was prone to cracking the engine block in half

Yep see above

@andy8442 Are you sure it’s the same engine? Isn’t that issue related to older Volvos on a 1.6 engine?

I’m asking because  I don’t know. Not heard of this issue until I’ve read these comments.

AA report (I wasn’t there when he attended)…

Member states vehicle loosing coolant and had to top up. Coolant level OK on arrival. No visual signs of leakPressure test coolant system – all ok, no pressure drop. Cap okRan vehicle up to pressure, coolant circulating ok, fans working ok. Advise member to keep eye on coolant level, if coolant level drops take straight to garage. Engine Oil Level Ok. Coolant Level Ok.

Have a look around the thermostat housing, they can have tiny cracks which only open up when the car gets hot.

Something like this. I had similar on s car a while ago. It was a crack that would only open up with pressure AND heat. Can’t remember which bit, though.

Yours isnt really old enough for this to happen but my ’04 Hdi Pug Partner was losing coolant recently and I couldn’t find from where. I let it ‘develop’ which then showed itself as a knackered (screeching) waterpump bearings. Changed the timing belt, idlers and water pump.