My c4 is playing games I don't like

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Cutac
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My c4 is playing games I don't like

Post by Cutac »

Hello,

I've got a problem with my VTi c4. 1.4, 2011, 120000 kilometers, oil consumption is 1L per 10000 kilometers.
The story goes like this. I've changed coolant last October and all was fine until August. Suddenly, coolant level dropped by 1 cm in the expansion reservoir. It stayed like that for a month, and then on Saturday I checked it, it was still 1 cm off, but on Sunday it was at the bottom of the reservoir. I topped it up, checked for leaks(there were none) and put a new expansion cap on. It was fine until today, in the time between Sunday and today it dropped by 1-2 centimeters. Still no leaks, coolant is crystal clear, and so is the oil cap.
Engine should be fine since I can drive it at 189 kph on the flat road(was like that since the beginning).

As the driver, I've noticed no changes in the car behaviour. I drive it mostly in a calm manner, usually fifth gear and speeds between 80 and 120 kph. Every now and then I give it the beans for 20 minutes just to keep everything in order. I've been driving it the same way for the last 7 years, all servicing was done on short schedule so that everything would be in the best condition possible.

With that said, where the hell does my coolant go?
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Fake Concern
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Re: My c4 is playing games I don't like

Post by Fake Concern »

When the coolant was going from my VTS with no visible leaks, it turned out to be the water pump.
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white exec
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Re: My c4 is playing games I don't like

Post by white exec »

If your expansion tank (coolant reservoir) has an expansion/overflow drain tube, temporarily fit a shorter one leading into a small bottle to see whether anything is being thrown out there.
Causes could be an air-lock/pocket in the cooling system (= localised boiling and coolant throw-out), a misbehaving thermostat (how's the gauge?), or a poorly sealing pressure cap. A leaking heater matrix in the cabin is another possibility - is it dry in there?
Any steam or white smoke from the exhaust? That would be coolant getting into one of the bores (= head gasket) and being burned.
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Cutac
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Re: My c4 is playing games I don't like

Post by Cutac »

Water pump had been replaced at 60000 km.

Interior is bone dry, I've also checked visually what I could and heating system seems to be spot on.
Exhaust seems fine.
Thing is that coolant loss is not constant. Level literally goes down over night. In the last month I'd check it every time I would be driving and it was fine until today. That's what's puzzling me and that's why it's hard to find the cause of loss.
It also doesn't matter how much I drive it. I did 600 km in two days and all was fine, but in the last week I drove it twice and did 15 km each time and it lost coolant.

Temp gauge is fine. I use Torque Pro and it's always between 85 and 100°C, mostly it sits at ~92°C
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white exec
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Re: My c4 is playing games I don't like

Post by white exec »

Our XM does something similar when it comes to coolant level, on a cooling system which behaves perfectly in all other respects.

1. If coolant is topped up (cold engine) to the specified level in the header tank, and the car taken for just one journey, coolant will be expelled (header tank overflow pipe), and by the next morning the level will have fallen to 4cm below specified level*.
2. If topped up, this will repeat ad infinitum.
3. If left at the dropped level, it will drop no further, irrespective of number of journeys or driving conditions.

On this car, at least, the 13.2 litre coolant volume is obviously capable of producing a significant rise in header tank level as it gets up to working temperature - even if at first thought you might not expect that. On putting the data into an online calculator for expansion, 13.2 litres of water expands by just over 530ml as temp goes from 20 to 110ºC. That's a significant proportion of the XM's header tank.

Crucial thing is does the level on yours continue to drop after it has reached its low level? If it carries on falling, there must be ongoing loss. If not, then maybe not an issue. Is a low level warning being triggered?

* On ours, there's a level marker in the tank, and book says level should be 20mm above it. Fill it to 20mm below, and it stays there pretty much for ever.
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Cutac
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Re: My c4 is playing games I don't like

Post by Cutac »

I did the calculation and for 1.4 VTi it would expand by 400ml(more or less, depending on the coolant capacity).
That's quite a lot given that the expansion reservoir capacity is around 300 ml, but from max to the cap, I reckon it's about 150ml of capacity.

Even if that was the cause, why didn't it happen before, in previous 5 years of ownership?

Regarding the level decline...
First time it dropped by 1 cm, stayed that way for a month, dropped to the bottom of the reservoir, I then topped it up, and it stayed topped up for a month until now when it's dropped by 1 cm again.
I've topped it up now and will be monitoring it.

It's weird that it won't drop in a month no matter what the driving regime is, but then randomly drops a bit.
If it was a leak then it surely would have to be steadily declining.
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white exec
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Re: My c4 is playing games I don't like

Post by white exec »

Air lock somewhere in the system? Maybe air being drawn in under certain conditions?
Some cars have a very specific cooling system bleeding procedure - unsure about your 1.4 VTi.
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Cutac
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Re: My c4 is playing games I don't like

Post by Cutac »

I'll try to bleed it again to see what will happen.
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Cutac
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Re: My c4 is playing games I don't like

Post by Cutac »

It's went down a centimeter, and still no visible leaks.
I'm thinking of adding UV dye to the coolant.
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EDC5
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Re: My c4 is playing games I don't like

Post by EDC5 »

UV dye sounds interesting.

Perhaps it is a crack in one of the plastics of the cooling system that only opens up under certain circumstances. If the leak was small enough, then the water could run onto the block and evaporate without leaving puddle.
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Cutac
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Re: My c4 is playing games I don't like

Post by Cutac »

That's probably the problem.
It's lost approximately 20-30 mL in the last 800 kilometers.
It's losing it very slowly and sometimes not at all. I don't think I'd be able to find the leak without a dye or the crack getting bigger.
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Re: My c4 is playing games I don't like

Post by EDC5 »

I had a similar problem on my old Ford Focus 1.6. The thermostat housing would only leak above a certain temperature, so motorways were fine, but city / hard driving caused some water to escape.

Luckily I spotted what looked like limescale on the engine block below the housing, which lead me to run a finger under it and sure enough it was wet!
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white exec
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Re: My c4 is playing games I don't like

Post by white exec »

What I was asking above was: if you let it drop to a low level (but still visible) in the header tank/reservoir, does it continue to fall, or does it stabilise that that point?

Also a bit puzzled by your saying the reservoir has a capacity of only 300ml (is that right?), but expansion can be 400ml. That doesn't sound correct, and would give you a nearly-always empty reservoir. Something not right here.

Is this the expansion tank you have? What diameter is it?
C4 1.4 VTi header tank.JPG
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Cutac
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Re: My c4 is playing games I don't like

Post by Cutac »

Expansion tank is 2L in capacity, I don't know where I got 300ml from.
I think level does continue to lower since at one point it was at the very bottom of the reservoir.

It's tricky to find the leak since I don't know when it'll happen and I can't look for it every time I drive the car. That's why I'm thinking of adding a dye or Liqui Moly Radiator Stop Leak.
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white exec
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Re: My c4 is playing games I don't like

Post by white exec »

And the level? Does it stabilise or continue to fall?