Thermostat Overheating, Radiator Cool

[ADarkDividedGem]

I was driving my 2007 Berlingo on the motorway and noticed my temperature rising above 95 degrees. When I pulled over I saw my radiator was loosing coolant. This happened before but I just added radiator sealant and it worked fine in blocking the hole. However, when I tried to refill this time with radiator sealant I noticed the hole was too big for the sealant.

I managed to drive it home one mile at a time. During this time the multiple start stops killed my battery. I managed to replace the battery and got it home.

I replaced the radiator with one from AutoDoc and bled the coolant until I got laminar flow from the small hole next to the brake fluid reservoir, as shown on the Haynes video.

The coolant does seem to cycle since I put in a 1 litre of yellow coolant first followed by 3 litres of clear coolant. The reservoir then turned from clear to yellow. 

However, after a quick drive the thermostat still goes above 95 degrees yet the radiator seems cool to touch. The cooling fan does kick in but the radiator doesn't need cooling.

Does the thermostat need replacing?

[evdama]

Or theres a big amount of air still in the system.
Mine took a couple of weeks to stabilise after a coolant change

[ADarkDividedGem]

Oh good catch. I went to the van today and noticed the coolant reservoir was empty after being full yesterday. There was no noticeable leak, so I used 1.5 litres to fill it back up. I drove it for the same amount of time yesterday, and there was no sudden increase in temperature.

Thanks again, I was preparing for the worst.

[evdama]

We call it a resevoir but the manufacturer terms it as an "air separator" .
Perhaps its doing its job.
Id still keep a close eye on it though.
Perhaps a quick visit to the bleed valves too.

[ADarkDividedGem]

Yeah, will do, the "air separator" didn't seem to lose as much coolant today.

Although when I went to open the bleed valve, some air was released, but no coolant came out. Is that normal when the engine is cold, or does it only happen when it's hot?

[evdama]

I did mine with the motor running so the system was pressurised.
Gets painful as the temp increases though.
Not sure what engine you have but mine has another valve at the back
It got more air out but its a pita to access.
ET would be the only creature to find it easy.

Another issue with the b9 (cant remember about the M series) is that the resevoir is not above the top of the engine so that theres no gravity feeding the coolant in.
To get a good initial system fill you either have to buy an automatic filling stack or unbolt the reservoir and perch it on a rolled up anorak to get some gravity or you end up with massive air pockets.
It might apply to yours too.
Youll get there in the end

[Mark604]

As evdama said, "Mine took a couple of weeks to stabilise after a coolant change." - patience is a virtue. Regular checks, keep an eye on it and eventually it'll settle down rather than being able to do one thing and it's 100% cured every time in five minutes.