Hi guys I am new to the site I just want to share with you some important information that I have learnt over the last few days and the importance of using a digital thermometer when bleeding the coolant system. This is a bit of a long one but please bear with me.

For the last few months i have had to bleed the coolant  system far too many times for one reason or the other.
 In the first month of owning the car I had to change the coolant cap as it fell apart.
The thermostat as it was sticking.
There was a small amount of gunk in the system so I used washing detergent to clean and flush  it with the hose pipe to ensure that there was no blockage etc…
I must add that there was no oil or any signs of a blown head gasket at this point but I did wonder if the head was cracked as this would cause the pressure in the system.

During one of my weekly checks  I noticed that  the coolant had magically disappearing without a trace.
Even though I had bled the system according to the manual.

 I found out that the coolant was being forced out of the overflow when I was driving.

So this time I decided to do it differently.
Now I read in a post on here that you shouldn’t trust the coolant temp gauge on the dash and that you should use a digital thermometer in the expansion tank.

So that’s what I did
 I was shocked to see that when the gauge on the dash was reading 88 c  (operating temperature) the thermostat was only reading 70 c at the expansion tank.
I also found out that if you let the engine idle with the blowers on it simply  took way to long to get up too temp and I mean like at least 2 hours.

I believe that this was because of  trapped air in the system which needed to be forced out,
 letting it idle just wasn’t doing the job.

So when it got to 70c I gave it a little throttle and  it got up to temp quicker.
And  a huge amount of coolant was thrown out of the expansion tank.
 I left it idle until the coolant settled.

During the procedure I could see the coolant raising and falling above the max mark.
  When all the air was forced out of the system the coolant level dropped  to where it should be I then let it idle for 15 mins with the heaters on full.
I switched the engine off and let it cool down.
After an hour I started the car and repeated the procedure this time the coolant did not go above the max line.
I repeated the procedure again and left it over night.

The next day I checked the coolant and it was low so I added half a litre and checked the system over.
 I found that there was a leak at the thermostat housing and the top radiator hose.
 So I repositioned the hose and put the clamp back on and ran the engine whilst checking for leaks.
 I then bled the system once more. 
Now usually this would be it and the job would be done but as I’ve been here before I went that extra step just to ensure that there was no more trapped air.
I do not recommend doing this part.

 Once up to temp with the cap off I  went through the revs making sure that the coolant did not spill out of the expansion tank because if it did it meant that there was still trapped air in the system. I even max reved  it for ten secs two or three times and the coolant did not go above the max mark so I know that there is no air in the system.

Now I know this is not the way to do it by the book however as an experienced mechanic I knew that the only way to get rid of the air lock  was to force it out.  Plus I didn’t have any other way.

I DO NOT RECOMMEND DOING THIS UNLESS YOU ARE WILLING TO AXCEPT THE RISKS INVOLVED AND OR ARE CONFIDENT/COMPETENT IN DOING SO.

[The Gonz]

Thanks, Paul.

Not a problem I've had with my 2009 1.6 CRDi, but I'm noting the symptoms just in case.

[PGN I30]

When I did mine I drained the system at the radiator drain plug and cap, removed a heater matrix hose, flushed with deionised water through the hose till it ran clear.
I then replaced the radiator drain plug and cap, filled with a funnel through the heater matrix hose, this filled the head and radiator then kept filling until the coolant constantly ran through the heater matrix and out at the bulkhead.
I then reconnected the heater matrix hose and topped off the coolant reservoir, the reservoir dropped slightly after around 3 runs, then was topped off and is now settled.
All done on a cold engine, I used to do it hot on my old car so the thermostat was open and the head cleared but would occasionally get an airlock in the heater matrix after filling which needed bleeding.

[BrendanP]

When renewing the coolant on my 2011 FD CRDi, I let the engine warm up to normal temperature, then released the pressure at the header tank, and then drained out as much coolant as would drain out through the drain plug in the bottom of the radiator. I then topped the coolant back up using deionised water. After that, I drove the car around for a few minutes, and did the same thing again, and kept repeating this until the water coming out was fairly clear. You can't drain all of the old coolant out but it's been diluted enough by fresh water so that it's not significant. finally, drain enough water out so that the correct amount of anti-freeze can be added. This seems to avoid getting air locks in the system. It's a bit tedious but avoids draining coolant out of areas that are hard to refill.