Strange Cooling loss !!
 

Please bear with me a little with this tale. I have had the car now since 2017 and carried out a fair amount of work to get it to be a nice reliable car. I have never had a loss of coolant, and I check all the fluid levels once a week.

About 3 weeks ago, my wife and I set off very early one morning to go and see her mother (130 mile journey). I had gone only a mile or so when I got the low coolant level alarm up. I drove the car back onto the drive and had a look, and it was at the low level. As we were in a hurry, we transferred everything into the wifes car and left. When we came back the next day, I had a look under the car and there appeared to be a coolant patch under the front near side.

I refilled the bottle to the correct level and started the car - no leak visible. Ran around the block a few times - no leak visible. Did this for a week. No loss of coolant and no leak visible. Bought some coolant dye and put it in - no leak visible and no loss of coolant.

I have been running it for short journeys now for a couple of weeks and no loss of coolant. What the heck ??

If I could see a leak (or had one) I could fix it, but at the moment I'm afraid to do a long journey in case it goes again for some reason.

If it wasn't for the alarm coming up, I would have thought it was just an abberation of mine.

Am I missing something obvious that may have happened?

Thanks

The nearside leak location?
Was it radiator, engine block or bulkhead position, approximately.

Momentarily stuck thermostat causing overflow? Having traveled just a mile, it is possible!

In a recent video, I show how I use my Sealey brake bleeder to mimic cooling system pressure whilst the engine is off to make leak detection easier on a stationary car.
It's worth it's money as a brake bleeder just on its own but having the ability to test cooling systems too makes it a worthwhile investment.

Also see this thread whilst although a D5 shows that tiny leaks in the system can be found.

The patch on the ground was nearside of the car where I usually park. When I got underneath to have a look round, I could see no leaks at all from anywhere on the system, even with the dye in.

I hadn't thought of that. Where does the water come out when it overpressurises ? If its the bottle, I would have expected to see the patch on the ground on the off side.

Haaaaa....... just watched your video. I was looking at pressurising kits, but didn't realise the Sealey Unit (which I have) would fit on the water bottle. This will be my next step. More dye and some pressure should confirm it one way or the other.

Thank you all for the replies.

Has anyone been at the radiator drain screw, broke it and done a creative repair?

I'll have a look when I get under - another good thought. Thanks!

Bit wet where I am today, but I have just been out to try and pressurise the cooling system using the Sealey brake bleeding kit as mentioned by Simon and his Youtube Video. I cannot get any pressure! I put the kit onto the brake fluid resevoir and voilá, pressure.

So while I have not lost anymore fluid from the system since the initial loss a few weeks ago, there is obviously a problem as I cannot get pressure on the system.

Any ideas where I should start looking? The bottle above the water line looks fine without any cracks. Anything cracked or damaged below the waterline should be leaking fluid and I would see a loss on the resevoir - but no.

So, I'm a bit stumped.

Cracks on the expansion bottle can be so fine you would have difficulty seeing them with the bare Mk1 eyeball & the usual suspect area is I believe, around the base of the threads of the filler cap?

The cooling system capacity is 8 litres versus less than a litre for the braking system so takes much longer to build pressure.
It would need to be a pretty disastrous leak to not allow any pressure to build and any coolant leak would be constant as you try to build pressure.

Basically, persevere with the Sealey.