Purging air from the cooling system

TL;DR Some like it hot

I think I didn't cover the week-end in the Vosges and Black Forest at all but might have explained the cooling issue already. 

Anyway, I got the car back on a Friday, and it was overheating a bit and dripping coolant from under the nose cone on the next day. What happened is that the cooling fan fuse had blown with the crash and was duly replaced and tested before I got the car back. That new fuse died rather quickly, which led the engine getting up to 105°C in some queues due to roadworks at the highest point of the Black Forest. Weather was not even great or remotely warm.

The blown fuse resulted in some pressure buildup in the cooling system. Which should have been released by the 1.1 bar valve in the expansion tank cap. But is wasn't.  Instead, it was released from the hose connected to the top of the radiator, due to a faulty hose clamp.

So here I was with a pair of commercial jetliner mechanics, a classic Mini specialist and a hot and dripping Caterham. I couldn't guess on the spot all I told you here above, all I knew is that the front end was new, with a fan that could be faulty, or have a bad wiring, and a hose that clearly had an issue.

I let the car cooldown, and all was good as long as we were driving, I just had to stop the engine when we stopped.

After lunch at an enjoyable Italian place, we took a look at the coolant leak and tried to re-fit the hose clamp, with very little confidence that it would help much. It really needed to be replaced, so I called the day and told the others that I would go straight back to my friend's rather than continue driving in the Black Forest. We were already mid-afternoon and we all went back together.

I drove very calmly at first, then decided that the engine was warm and driving at highway speed wouldn't pose any issue with the natural flow of air in the radiator. So I pushed on a bit, and we were greeted with blue coolant on the windshield, through the hood louvers, and all over the hood as well. "Very nice", not only you have to choose a windshield wiper fluid you like the taste of, apparently the same goes for the coolant as well. Too bad I didn't think about 'locking' the dashcam footage.

As I did spot a car dealership in a village we just crossed, we went back to see that they were not opened on Saturday afternoons. Until they were, when the boss and one employee came by just for some nice pleasant work (by the look of it) while we were looking around the parking lot. That's how we met Sven Quade, owner of Autohaus Quade in Kandern. He did me a solid by replacing the faulty hose clamp, literally saving my week-end. We really felt the passion and love for his work, he's a former Lotus Elise driver too. He went as far as cleaning my windshield, I cannot thank him enough. I tried to send him some whiskey (they have a brilliant bar in the showroom), but Amazon.de couldn't let me confirm my age. Come on Amazon, my account is old enough to drink, how old do you think I am ?  

So we came back to our starting point, and I made troubleshooting the Caterham the highest priority for the evening while the others were checking out the 3 épis hillclimb stands around in the village.

Although the expansion tank was full when hot, I topped up my coolant with the bottle I had the genius idea to bring with us in France, I assume it's basic precaution to bring the only specific consumable along such a shakedown after a rebuild.

Checking out the cooling fan connection, relay and finally the fuse with a multimeter confirmed it was only a blown fuse. I was just in time at the local Leclerc grocery store (10 minutes or so before they close the doors), and got a variety pack of micro fuses, as well as a assortment of hose clamps. I knew Leclerc was my best bet as it's where we get our groceries from when on holiday.

I nice couple let met skip the queue (I didn't ask for anything), and came to talk a bit on the parking lot, the gentleman was there with his Fiat Barchetta;  I also talk with a father and a kid while replacing the fuse; and to thank my karma I offered a can of Red Bull I had in the map pocket to a guy who was asking for change and was bluntly shunned by most people.

The car was back to 100% operational with no leak but the life expectancy of the new fuse was still unknown, it had to come from something else. I was lucky that it was just bad luck, the new fuse is still there and well 3000km later.

I will spare you the details of the next day in the Vosges, we had more Caterham, it was all the better. We indulged in a switcharoo in the end, where my GF took my 170S with my friend's wife, I jumped in Guillaume's 165 with him;  and his dad took the wheel of the mighty "275 Kompressor" with my friend. It was fun to see that we had to touch the rev limiter on each gear with the 165 to be able to keep up with the 170S pulling along on its torque in "eco mode".

That makes for a very long story on how and why my car spat so much coolant in the weeks and thousands of kilometers that followed. The level got rather low one evening and the engine reached 100°C while not doing much out of the ordinary. It usually sits nicely at 85°C where the thermostat opens, and sometimes gets close to 90°C when pushing hard. Something was definitely off. 

On the next day I came back from work very gently to manage the heat and topped the coolant up.

I added 1 and 1 and came to the conclusion that the hose clamp story probably got me some (or a lot of?) air in the system.

So I opened the filling cap, got the engine to working temperature (85°C+) until the radiator was hot, with the cabin heater fully open too and opened the top plug of the radiator. As I didn't remove it fully, I got bubbles for a least a minute. I tightened it down, gave some revs', opened the plug again and only released a few more bubbles. I closed everything, got the nose cone and hood back, and didn't observe any significant coolant outbursts in the following days; including a 4 hours drive on Sunday morning.

The fact that the expansion tank was full when hot despite the leak was the telltale sign I should have recognized that there was air in there, and that I did needed to purge the cooling system asap.