Cooling problem

[Sidaries]

This will be quite difficult to describe, but I try. So I have an interesting and annoying cooling problem.
The major symptom was that I realized, that the coolant level is decreasing in the coolant bottle. When I checked where it could be I saw that it went out through the ?overflow pipe?. The car works well, no overheat or any problem happening, only that I always have to refill the water (about 1dl/100km, which is quite a lot). What is strange is that the water level is way beyond the maximum sign and any time I stopped with the car and checked the level, it was never over the max. When cold, it is even lower than the min. sign sometimes. When I checked the water it was clean.
I have only one idea, which is that maybe the bottle cap is not closing properly, but I am not sure. Any ideas?

The three pictures I add is the following. One is with the water level when cold, one when the water is hot and the pipe, where the water goes out.

[Jonathan]

If those two lines are your cold and hot, min and max levels, then this is fine. If coolant is being lost as it gets hot and is expanding, I would think your reservoir cap is not relieving at the 15 psi it is supposed to, but instead it is letting out pressure lower than that. If the system does not keep itself pressurized, the boiling point changes of the coolant and what should have stayed as a liquid, may flash out your overflow. A new cap is fairly inexpensive all things considered and may very well solve your problems. If you cannot get one from a DMC franchise or vendor based on where you are, most any other cap that fits correctly will work as they are not generally that unique (i.e. they all are set to do the same thing).

[WelmoedJ]

+1

For your car's sake I hope that by referring to the coolant as "water" you do not mention it to be real (fresh) water.
Although a majority of the cooling system is aluminium, water is not intended to be the coolant.

Use either the prescribed type of coolant, or the modern G12+ (by VAG).
The prescribed coolants protect your engine, also in winter against freezing.

[Sidaries]

+1

For your car's sake I hope that by referring to the coolant as "water" you do not mention it to be real (fresh) water.
Although a majority of the cooling system is aluminium, water is not intended to be the coolant.

Use either the prescribed type of coolant, or the modern G12+ (by VAG).
The prescribed coolants protect your engine, also in winter against freezing.

No. Of course it is not regular water. :)
Then I think I will try a new cap and see what is happening.

[Jonathan]

As Welmoed mentioned, the system is not intended for plain old water (distilled or otherwise). Two reasons: boiling point and corrosive tendencies.

Pure water is going to boil at 100 deg C at atmospheric pressure. It boils at a slightly higher temperature at 15 psi. When you mix in the recommended percentage of coolant, you are increasing the boiling point as well. This is a good thing. You want your coolant to stay as a fluid and not a gas. If you have the 50/50 mix, you can keep your coolant at even a few more degrees hotter and it will not boil.

The pure water part is a trade-off. If you take all the impurities out of it, it becomes corrosive. Not quite as corrosive say as caustic or sulfuric acid, but more so than water with impurities in it like what comes out of your tap at home. The trade-off part is that if you have a bunch of impurities in your water/coolant, it is going to be left behind in your cooling system. Of course, the 'suspended' solids in the coolant can settle out, but of more concern are the 'dissolved' solids. Hardness for example, from Calcium and Magnesium. If your system does get a bit too hot or over-pressurized and the fluid does flash out to steam and down your overflow tube, generally when a fluid boils, the pure liquid only goes out as steam and not the minerals. They get left behind because they don't get carried out (although if it barfs out a bunch of coolant it will for sure take some of the minerals with it). But if down in your system it has boiled off, what is left behind is similar to what is at the bottom of your kettle for making tea.

You can see how important having each of these aspects in check is. If the concentration isn't right, your boiling point is not as designed. If the cap isn't relieving correctly, it doesn't maintain the <15 psi pressure of the system. You could still have other issues like an otterstat not working or fans that don't come on, but the easiest and first step is to make sure the correct volume and concentration of coolant is in the system. And then go from there.

[Rich]

...... the coolant level is decreasing in the coolant bottle. .
I have only one idea, which is that maybe the bottle cap is not closing properly, but I am not sure.

Perform a pressure test on the cap. Or replace it with a new cap, as you plan.

Also, very important, pressure test the cooling system at 15psi (normal driving pressure) with engine cold, to verify that the cooling system has no leaks. A car repair shop can do both of these tests for you easily. The fittings for the cap are not special on a D.

A pressure test is the only method for testing. Coolant can leak in places you cannot easily inspect in a D. So if you see no leak there can still be a leak....somewhere.

[Sidaries]

At last I found a solution. Obviously it was a small thing.
At first I changed the bottle cap, but it did not help. Maybe it became a bit better, but the water still came out. Then we measured the height of the inner side of the new cap and the height of the bottle's neck and the neck was almost 1 mm longer. So we put a rubber ring into the bottle and then put on the cap. Now it is working as it should be.
So it seems the bottle had some factory error, but with this ring it is ok. Now I have to make a pressure test to be sure, but since the fix no water came out.
Thanks for the suggestions.

19791

[Ron]

$.02

You should use the adapters and application chart in the pressure tester kit to figure out the right cap to use....

If you don't do something like find an alternate method to pressure up the system and see where that cap releases pressure while installed, you are really asking for it!