Loosing coolant without leaks

[PixelPie]

For I while I have this strange issues.

 

- No visible leaks

- New radiator

- New water pump

- Problem still not solved

 

I think that may be a head gasket, but I can't find any coolant evidence in oil and vice versa.

 

I noticed some strange things. When the car is hot, coolant level is lower. If I remove the cap, coolant will be back. Sometimes I can drive 100km without coolant lost, and sometimes can lose half litter on 100km.

 

Just to mention, that last summer I overheated this car. I replaced the head gasket, radiator, and water pump. This car lost coolant before overheating also, but on much less level.

[RicardoM]

30 minutes ago, PixelPie said:

I noticed some strange things. When the car is hot, coolant level is lower. If I remove the cap, coolant will be back.

Replace the cap with a new one.

[PixelPie]

16 minutes ago, RicardoM said:

Replace the cap with a new one.

I think the cap is fine but I'm not an expert. Is pretty hard to open, so I guess sealing is good.

[RicardoM]

It is not about sealing. On the contrary. The cap has a pressure relief valve in it. It is in fact a safety valve used to control or limit the pressure in the cooling system.

[PixelPie]

14 hours ago, RicardoM said:

It is not about sealing. On the contrary. The cap has a pressure relief valve in it. It is in fact a safety valve used to control or limit the pressure in the cooling system.

I may don't explain well. My radiator doesn't have pressure cap. I was talking about a cap on the coolant reservoir tank. I think that cap doesn't have a pressure valve.

[Breezy_Pete]

Check to see if there is any pressure in the expansion tank first thing in the morning when the engine is completely cold. If there is, I would suspect a fire-ring head gasket leak.

[PixelPie]

2 minutes ago, Wino said:

Check to see if there is any pressure in the expansion tank first thing in the morning when the engine is completely cold. If there is, I would suspect a fire-ring head gasket leak.

I already opened cap in the morning on the cold engine few times. If I remember good, yes there is a little pressure... But I will do that tomorrow again to make sure.

[technics100]

Are you having to top the coolant up?  I had this on my A4 and it was leaking at the back of the block then evaporating off the engine.. 

[KenONeill]

@PixelPie - All modern cars have pressurised cooling systems; the pressure cap may be on the expansion vessel rather than the radiator header tank.

[PixelPie]

28 minutes ago, technics100 said:

Are you having to top the coolant up?  I had this on my A4 and it was leaking at the back of the block then evaporating off the engine.. 

When I fill to the top, I quickly lose coolant. When coolant is close to a minimum is more stable, but I still lose. After a long drive, it seems like I lost a lot of coolants, but if I immediately open reservoir cap after driving, coolant will be back almost on the normal level. Some guy tells me that this may be normal, because of pressure, but I'm not sure.

19 minutes ago, KenONeill said:

@PixelPie - All modern cars have pressurised cooling systems; the pressure cap may be on the expansion vessel rather than the radiator header tank.

Well, my car is far from modern  I never see pressure cap, I even made research on google and everything that I find was regular reservoir cap. If Skoda favorit from 1994 has a pressure cap, will be great if some of you guys can guide me.

[Papez]

22 hours ago, PixelPie said:

 

Well, my car is far from modern  I never see pressure cap, I even made research on google and everything that I find was regular reservoir cap. If Skoda favorit from 1994 has a pressure cap, will be great if some of you guys can guide me.

 

By "modern" is meant from second half of 20th century And Favorit has cap with integrated pressure valve, just look at it from bottom

 

Failed head gasket in early stages doesn't cause water leaking into oil in these engines, because they mostly fail around cylinder lining. 

I had very similar issue with my Felicia. Disappearing water, when I removed reservoir cap, water rushed out of it, but there was no water in oil. It was head gasket.

[myjalopy]

Oh dear. Just found this thread after posting a similar one just now. I'll check the cap for pressure/expanded tank in the morning.

Edited 3 March, 2018 by myjalopy