Coolant dissapears then reappears in expansion tank

[Kjetil1Z]

When engine is cold the coolant level is correct. When engine is warm all coolant dissapears from reservoir. When opening the cap the coolant reappears in the reservoir.

 

2.0 tdi BMM 

 

Any ideas?

Edited 18 June, 2019 by Kjetil1Z

[pikpilot]

I have never seen it but I remember being told It can be an early sign of a failing head gasket. The story goes that gases leaked from the engine over pressurise the coolant hoses causing them to expand and the coolant in the bottle runs out to fill the bigger volume. When the cap is opened and the pressure is released, the hoses relax and the coolant is forced back into the bottle.

How low does the coolant go, as seen on the side of the bottle?

 

[MikeTheThinker]

Just now, pikpilot said:

It can be an early sign of a failing head gasket

 

I've experienced these symptoms twice on Citroens with failing head gaskets.

 

[Kjetil1Z]

Ok,

 

Thanks guys.

 

Others also says that it may be head gasket, but also crack in engine head or trouble with EGR cooler.

 

Anyway, I did some testing today.

 

At cold engine (3-4 hours after last drive) I filled to a bit under max in reservoir. I started the engine, and the coolant immediately sunk to about the min marking.

 

Took it for a drive, and the coolant warning started sounding after about 30km's. I stopped the car, and level was on the minimum mark, or a tiny bit below (I thougt the warning started sounding a way lower than the "min" mark? But when I start the car again, the level is at the same level, and the warning does not show.

 

I opened the reservoir and the reservoir fills way above the "max" mark. Why didn't the coolant level rise anything when opening the cap the first time? I guess the pressure let go somewhere (head gasket)?

Edited 20 June, 2019 by Kjetil1Z

[MikeTheThinker]

Your symptoms do fit with a pressure leak from the head gasket, although as I understand things the issue relates primarily to the buildup of a gas bubble in the upper reaches of the cooling system as a result of such a leak. 

 

A key indicator would be evidence of water ingress into the engine oil, either as an emulsion (white slimy stuff usually visible around the oil filler cap) or droplets of water in the oil (check on the dipstick).

 

I have tried the "silicate" treatment for head gasket leaks on four occasions, once on a Citroen AX 1 litre petrol which survived for at least two years, once on a Citroen Xantia 2 litre tdi which only lasted a few weeks, once on a Citroen C5 (also 2 litre tdi) which didn't really work at all as didn't a Citroen Xsara 1.6 petrol.  I would think the results on an Octy diesel motor would follow my Citroen diesel experiences because of the much higher compression ratios of modern diesel motors.

 

If the problem is a gasket leak the longer you leave it the more expensive it will be to fix and localised leaks of combustion gases often lead to distortion of the cylinder head - curable only by removal and skimming.

 

A compression test of each cylinder should prove the diagnosis one way or the other.

[pikpilot]

Yes it could be the EGR cooler but less likely. Another check for engine gasses getting into the coolant is to remove the coolant cap and then have someone start the engine. Be prepared for a spray of coolant if a bad leak.  Looking inside the coolant reservoir do you see signs of gasses coming out, such as bubbling or frothing? 

[Kjetil1Z]

4 hours ago, StickyMicky said:

Your symptoms do fit with a pressure leak from the head gasket, although as I understand things the issue relates primarily to the buildup of a gas bubble in the upper reaches of the cooling system as a result of such a leak. 

 

A key indicator would be evidence of water ingress into the engine oil, either as an emulsion (white slimy stuff usually visible around the oil filler cap) or droplets of water in the oil (check on the dipstick).

 

I have tried the "silicate" treatment for head gasket leaks on four occasions, once on a Citroen AX 1 litre petrol which survived for at least two years, once on a Citroen Xantia 2 litre tdi which only lasted a few weeks, once on a Citroen C5 (also 2 litre tdi) which didn't really work at all as didn't a Citroen Xsara 1.6 petrol.  I would think the results on an Octy diesel motor would follow my Citroen diesel experiences because of the much higher compression ratios of modern diesel motors.

 

If the problem is a gasket leak the longer you leave it the more expensive it will be to fix and localised leaks of combustion gases often lead to distortion of the cylinder head - curable only by removal and skimming.

 

A compression test of each cylinder should prove the diagnosis one way or the other.

 

Thanks for the input. There are no signs of water in the oil. 

 

I will take it to a shop to do a comp test as fast as possible.

 

5 hours ago, pikpilot said:

Yes it could be the EGR cooler but less likely. Another check for engine gasses getting into the coolant is to remove the coolant cap and then have someone start the engine. Be prepared for a spray of coolant if a bad leak.  Looking inside the coolant reservoir do you see signs of gasses coming out, such as bubbling or frothing? 

 

Thanks for the input. As far as I can se, everything looks normal inside the reservoir.

 

 

 

[dilksie]

Definitely head gasket, had this on a Passat TDi. Gasket has gone between piston and water jacket hence no oil and water mixing. Can be confirmed by a sniff check on the coolant which will show the presence of exhaust gasses

[Kjetil1Z]

2 hours ago, dilksie said:

Definitely head gasket, had this on a Passat TDi. Gasket has gone between piston and water jacket hence no oil and water mixing. Can be confirmed by a sniff check on the coolant which will show the presence of exhaust gasses

 

Thanks.

 

I bought a sniff test set earlier today, so I guess it will show something.

[J.R.]

Well played, I wanted to advise thatbut did not have the time.

[Kjetil1Z]

Took a sniff test now, and it did not indicate HC in the coolant.

[RicardoM]

On 20/06/2019 at 18:21, StickyMicky said:

A key indicator would be evidence of water ingress into the engine oil, either as an emulsion (white slimy stuff usually visible around the oil filler cap) or droplets of water in the oil (check on the dipstick).

Not quite. There are many ways a head gasket can fail.

31 minutes ago, Kjetil1Z said:

Took a sniff test now, and it did not indicate HC in the coolant.

Inconclusive. Those kits are usually a waste of time and money. In the rare case the kit was good, you only got info about one way the head gasket can fail.

[Kjetil1Z]

37 minutes ago, RicardoM said:

Not quite. There are many ways a head gasket can fail.

Inconclusive. Those kits are usually a waste of time and money. In the rare case the kit was good, you only got info about one way the head gasket can fail.

Thanks. Nice diagram.

 

Yeah, they do not show all ways, but in this case most people point to compression leak to coolant. Thats why I did try this. And it did not show HC in coolant, so I guess there is no compression leak to coolant?

 

I have no misfire or rough idle, no smoking, no coolant in oil, and no oil in coolant. Also no visible coolant leak (need to check this more). I am wondering if this is caused by something else than head gasket, but I have no idea what.

 

When driving, the coolant dissapears from reservoir. When the alarm goes of, I open the cap to let air out, and the coolant fills up the reservoir to over "min" mark again, and I can drive 20-30 km's before the same happens. I am loosing some coolant every time, so I eventually have to refill.

 

Edited 23 June, 2019 by Kjetil1Z

[RicardoM]

Can you borrow a known good coolant reservoir cap?

Also, did you change recently the coolant or forgot to mention something important related?

 

Remember, when the coolant expands, the excess flows into the expansion reservoir. When it cools, a vacuum is formed that allows atmospheric pressure to push the fluid back into the system. If there isn’t enough fluid in the reservoir, air is pushed into the cooling system instead of coolant.

Edited 23 June, 2019 by RicardoM

[J.R.]

Fill the reservoir slowly when the engine is cold after an overnight stop, run the engine at fast idle with cap off in case of any airleaks, top up again if needed, refit cap.

 

Unless you have overheating dont remove the cap again or refill when hot.

[Kjetil1Z]

Thanks for all input.

 

Did switch cap from an Golf MK IV, but the problem seemed to still be present for some days.

 

But now suddenly, I have drove the car for about 300km's and there has been no warnings for low coolant, and the level is ok.

 

I don't know if it in fact was the cap, or if there was some air pockets etc. Where those air pockets came from are unknown for me.

 

I will just drive it, and see what happens.

 

Thanks so far!

Edited 28 June, 2019 by Kjetil1Z

[Guest]

I was going to suggest checking the coolant pump, I'd certainly go there before taking the head off.

[Kjetil1Z]

Hi,

 

A late update on this. It turned out to be the head gasket. It completely blew on 405 000 KM. I ended ut with scrapping the car.