Loss of coolant

[TehRin]

Hi all,

I've noticed a loss of coolant (around 3 litres as that's how much I've topped it up). After checking under the car though apart from the wet undertray/driveway there are no signs of leaking! The only leak I have found is from a crack in the top of the expansion tank, just enough for air/coolant to bubble through. As you can imagine I lost heat from the heaters etc but I can't imagine the expansion tank being the issue as it's the highest point, unless it's boiling over - is that possible though, to loose that much coolant through a fine crack in the top of the tank?

I have had the undertray off and crawled underneath the car however I couldn't see much obvious so I may have to remove the front bumper and inspect the radiator.

Thanks

[LarJammer]

A cracked tank can absolutely be the cause of a massive leak. The system is usually under pressure so will escape from any hole, regardless of whether it is up high or not.

If in doubt get a pressure test carried out which will show any leaks.

[GreenV8S]

TehRin said:

is that possible though, to loose that much coolant through a fine crack in the top of the tank?

That's like asking whether it's possible for a pan of water to boil dry. Yes, if you keep it hot enough for long enough.

[paintman]

TehRin said:

Hi all,

I've noticed a loss of coolant (around 3 litres as that's how much I've topped it up). After checking under the car though apart from the wet undertray/driveway there are no signs of leaking! The only leak I have found is from a crack in the top of the expansion tank, just enough for air/coolant to bubble through. As you can imagine I lost heat from the heaters etc but I can't imagine the expansion tank being the issue as it's the highest point, unless it's boiling over - is that possible though, to loose that much coolant through a fine crack in the top of the tank?

I have had the undertray off and crawled underneath the car however I couldn't see much obvious so I may have to remove the front bumper and inspect the radiator.

Thanks

Yes. Until you deal with that you're wasting your time doing anything else.

[B'stard Child]

What car has a bearing on it

I have a BMW E38 that runs at 118 deg C at normal operating temp - this is fine as system is sealed and as a result pressurised to surpress the boiling point - they are quite prone to header tank issues - at over 100 deg C and without system pressurised due to tank failure you lose a lot of water fairly quickly

[TehRin]

I'll start off by changing the expansion tank!

It's a Volvo S40 T5 and I've read that can up to 104 Degrees "normally".


I just took it for a small spirited(ish) drive, with small bubbles escaping however no notable loss of coolant. But I guess as there's a crack in the top of the tank it's due a change regardless.

[Andy 308GTB]

I was losing a similar amount of coolant in my wreck of a MK1 Focus recently. I tracked it down to a hard plastic pipe that had split down a seam. It was invisible to the naked eye.
It was only when I wiped down all the visible hoses and got the car up to temperature that I could see the coolant bubbling out.
£12 spent on eBay and that problem was fixed.

The other give away was the dried coolant splattered over the exhaust manifold heat shield. But I had ignored that because it could have happened at anytime over the last 16 years. A clean engine bay can really help diagnose problems.