Engine overheating - How to assess damage?

Hi guys,

I have a 2001 manual 330Ci which I use for track days and always repair myself.

Yesterday I was cruising on the motorway on my way to a track when I heard a strange sound (similar to an old steam engine) choo-choo-choo-choo... Also similar to a exhaust gasket failing. Then I realised the temperature needle was half way to the red. So I stopped immediately on the hard shoulder, opened the bonnet and carefully opened the expansion tank cap.

It was completely empty, and when I tried to top it up, I realised all the coolant was coming off the radiator drain plug at the bottom.

Then I called the recovery truck, and I was towed back home. A couple of hours after that, I started the engine to see what was the outcome. It started without problems and sounded OK, but there was loads of burnt oil smoke coming off the exhaust.

I am planing to do whatever repair it takes by myself, but I have no idea where to start. Before disassembling the whole engine and change the headgasket or send the head to skim, I need to understand what's wrong with it.

Anyone can point me to a good tutorial or manual to do such job?

Thanks guys!

Things I would do:
- compression test
- leak-down test
- cooling system pressure test
- inspect oil for signs of coolant
- inspect coolant for signs of oil

Originally Posted by BaliDawg

Things I would do:
- compression test
- leak-down test
- cooling system pressure test
- inspect oil for signs of coolant
- inspect coolant for signs of oil

Thanks for your answer!

Any tips on how to do the first three? And what would indicate a positive or negative on any of those tests?

Originally Posted by osdecar

Thanks for your answer!

Any tips on how to do the first three? And what would indicate a positive or negative on any of those tests?

Google and youtube can answer that better than I.

Originally Posted by osdecar

Hi guys,

I have a 2001 manual 330Ci which I use for track days and always repair myself.

I am planing to do whatever repair it takes by myself, but I have no idea where to start. Before disassembling the whole engine and change the headgasket or send the head to skim, I need to understand what's wrong with it.

Anyone can point me to a good tutorial or manual to do such job?

These comments are pretty inconsistent with one another, but whatever.

Search on the compression test process as suggested. I would do it with the engine warm. Pressure readings for each piston should be reasonably close with one another, and probably between 175 - 190 psi (don't know what that is in Bar). Please post your readings here.

Since you shut it down before temp hit red and did not continue to drive, you have a good chance of avoiding damage. The fact that it starts and runs without codes is another good sign.

Thank you all for your answers

Originally Posted by Effduration

These comments are pretty inconsistent with one another, but whatever.

Well, I've owned the car for a bit more than a year, and I have repaired/upgraded myself everything that has gone wrong so far, with a bit of patience and internet research.

The engine has been very reliable all this time, so never touched it. Never touched an engine before, in fact. But there's always a first time for everything right?

Originally Posted by Effduration

Search on the compression test process as suggested. I would do it with the engine warm. Pressure readings for each piston should be reasonably close with one another, and probably between 175 - 190 psi (don't know what that is in Bar). Please post your readings here.

Since you shut it down before temp hit red and did not continue to drive, you have a good chance of avoiding damage. The fact that it starts and runs without codes is another good sign.

I have already ordered the drain plug that came loose, and I will top up the coolant as soon as I receive it. I will post here any possible engine code (the EML was on when all this happened) and I will let you know compression values and will check for bubbles in the expansion tank.

A guy has suggested checking the cylinder walls with an endoscope. Is this worth it at all? Are those cheap ebay endoscopes any good?

As balidawg effduration has suggested here.Compression testing at the very least and its cheaper.Even if you do have a scope,would you know what to look for?.
I would say compression test and if the numbers are good just fill with coolant, bleed and test drive gently watching the temp guage see if it holds and maintains level.That would be the cheapest and most practical way without investing in a lot of tools.