e46 n42 head gasket

So, as I mentioned earlier I replaced my expansion tank due to it emptying itself at a rate of knots as I thought it was probably the well documented problem of a cracked expansion tank.

Unfortunately I could not see a crack in the old tank and upon refilling I found out what the real culprit was. When I started the engine with the expansion cap off I noticed that there were a lot of bubbles in the coolant, it was almost frothy. Furthermore, it didn't seem to matter how many times I ran the engine and bled the system there was always more air coming out.

I went for a drive and came back to find that there was coolant all down the outside of the expansion tank, just as there had been with the old tank.

I found that if I revved the car past 3000rpm at idle coolant would exit the tank via the expansion cap. The expansion cap of course is also a one-way valve so that coolant can exit if the pressure in the cooling system gets too high.

Having seen almost identical symptoms on a VW Polo, I decided the most logical conclusion was the head gasket. Everyone thinks about oil in the water or vice versa when it comes to head gasket failure. However, it is also possible for a gasket to blow between the cylinder and the cooling jacket. This lets exhaust gases into the cooling system, which subsequently pressurises it and forces coolant out of the expansion cap. It is also possible for it to go the other way and for coolant to be burnt in the cylinders, but this was not my problem.

Bizarrely, I wasn't experiencing any overheating and it seemed to leak more when the engine was started and stopped so I actually made it to my brothers in the South of France. This was a slightly nerve racking experience as the coolant light was permanently on. I simply stopped every couple of hours, let some air out, put some coolant in and then carried on.

I covered 1500 miles and used ten litres of coolant on that journey.

I didn't have an in-car heater for most of it either, so it wasn't the most comfortable of journeys!

I have always fancied a 6 cylinder engine and with a newborn around I didn't want to be faffing around with a head gasket change, so I decided to use this as an excuse. I sold my trusty 318i touring for a e46 330i touring.

So it was a fond-farewell to our trusty 318i SE ...

And I warm welcome to our new 330i M Sport:

e46 n42 Bottom Hose Confusion

So I was about a week away from visiting my brother in the South of France when I got in my touring to find the coolant light was on. I lift the bonnet and unscrew the expansion cap to discover an empty header tank.

It had been a slight loss of coolant over time since I got the car which I hadn't been able to trace so I just put it down to that, filled it up and forgot about. A couple of short journeys later she was empty again.

There was a lot of coolant on the outside of the expansion tank so I assumed I had fallen victim to the well known cracked expansion tank issue. I ordered up a replacement expansion tank and fitted it.

However, when I filled it back up with coolant my original top and bottom hoses leaked, it seems the o-rings that seal them don't like to be disturbed. Unfortunately BMW don't sell them separately and you have to fork out for the full pipe. I am sure I could've found o-rings to fit, but I was in a rush as I was about to drive to France so I wanted a permanent reliable solution.

However, getting the pipes from BMW was harder than expected, the BMW diagrams are not 100% clear and the car differs quite a lot from the six cylinders. I needed to replace the top hose and the pipe which attaches to the middle of the expansion tank.

So, originally the technician ordered completely the wrong pipe. I had to take pictures to get him to believe me that it was the wrong part. So I will try and describe the problem as best I can just in case it helps someone else:

The problem is this parts diagram which I've taken from realoem.com (the dealer's was identical) ... According to this diagram the large pipe (no 4) that runs underneath the radiator from the thermostat/water pump attaches to the middle of the expansion tank:

I thought the pipe was incredibly expensive when I ordered it (even for BMW) because the pipe I actually wanted is this one (no 7):

No 7 runs from the middle of the expansion tank to the heater matrix and is quite short, and has one of BMW's plastic attachments at one end and a jubilee clip at the other...

However, the dealer looked at the first picture first and it took quite alot of too-ing and fro-ing to get the correct pipe.

The large pipe actually attached to the bottom of plastic bracket that holds the expansion tank to the radiator (no10):

This is a different set up to the six cylinders which don't have anything going into the bottom of that bracket. You can see in this picture that there is a connector for a pipe sticking out of the bracket, this is where that long bottom hose attaches...

Hopefully that makes sense and saves somebody some time with the dealer! Unfortunately, after all that, the car still had a serious cooling problem... check my next post to find out why.