I bought a BMW E46 330Ci (M54 3.0L Engine) that was not properly maintained. It was leaking coolant and sputtering white smoke and water from the engine (didn't sound smooth). Coolant pipes were also broken.

I pulled the engine out, and replaced all the seals and gaskets and coolant pipes. I sent the engine head to a machine shop which pressure tested the intake and exhaust ports and said they were okay, and then skimmed the head.

I checked the block with a straight edge and feeler for any warping and it was within tolerances.

I put the engine back together and then back in the car. The engine feels really smooth and powerful, no more sputtering from the exhaust. The first few days, there was a strong odor (my guess is previous coolant in the exhaust system). I've driven the car for about 2 weeks now, there is still a noticeable odour, although nowhere near as much as before. The coolant level has dropped from max to min (I topped up once as well).

Torquing the head bolts were very difficult on an engine stand (didn't have a very long breaker bar either), and a few bolts, the 2nd torque angle I might have applied 70-80 degrees instead of exactly 90 degrees.

Here is a photo of the block after cleaning it, just before putting the head back on:

Engine Block

My next action is to do a leak down test. If I see bubbles in the cooling system, will this confirm that my head repair was not done correctly? Where could I have gone wrong in the repair?

Is there any other tests I can do before having to pull the head off again?

Edit: Photos of the spark plug (cylinder 1 & 3, both look the same) and the expansion tank cap. Would a half broken expansion tank cause coolant loss? There is no visible white powder stains near or under the expansion tank.

enter image description here

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  • Did you use new head bolts? Commented Aug 26, 2019 at 1:13
  • Since topping up has the coolant level stayed constant? It might have been an air bubble coming out.
    – Solar Mike
    Commented Aug 26, 2019 at 3:48
  • @Pᴀᴜʟsᴛᴇʀ2 of course, and oiled bolts as well.
    – tgun926
    Commented Aug 26, 2019 at 4:05
  • @SolarMike I thought that as well initially, but after topping up and a 30min drive, coolant level had dropped again. When I open the radiator cap after overnight, I can still hear pressure being released.
    – tgun926
    Commented Aug 26, 2019 at 4:06
  • The cooling system is a pressurized system and depending what ambient pressure is can still show signs of pressure after overnight cooling, so having the sound of pressure release after overnight cooling is not always a sign of a head gasket issue. Conduct a proper pressure test to find out.
    – Solar Mike
    Commented Aug 26, 2019 at 4:10

1 Answer 1


You can pull out the plugs and pressurize the cooling system overnight. If any problem occurred during assembly you might find coolant in one of the cylinders. Best to check with borescope, if not available let someone crank the engine watch for moisture coming out.

Another good method is to use TK head tester. It's a liquid that changes color when it comes to contact with combustion gasses (chemical reaction). Simply place it over the coolant expansion bottle by your radiator and idle the engine.

You can also pressurize the cooling system to the max operating pressure stated on your water bottle cap. Run the engine and monitor the gauge (pressure drops when fan comes on), if the pressure goes over the max relief pressure (usually 1 - 1.2 Bar) you got a problem. Be careful that you don't have any air in the system using this method.

These engines should ideally be filled using vacuum purge refill tool (under the assistance of compressed air), if not available bleeder plugs should be opened while filling.

Torque should alright, on many occasions I haven't went to full 90 and never had any issue.

If you experience any oil and water mixing (now or in the future) check your engine oil cooler (bolted to oil filter housing) they have a thin oil channels that tend to corrode over time, some people tend to misdiagnose it with a faulty cylinder head gasket. Also check you don't have minor oil leak like from your rocker cover or your vacuum pump in the back of the engine seeping on your exhaust (they do create unpleasant smell). PCV valves tend to go and burn smoke, check that out.

If all good I suggest you drive it and see how you get on. You might simply still have something small still in your exhaust.


  • Can you elaborate the first test? Do you mean run the engine to operating temp, turn it off, pull out plugs then check the cylinder the next morning? Or something more sophisticated using compressed air to pressurize the coolant expansion tank?
    – tgun926
    Commented Aug 26, 2019 at 6:48
  • Which plugs are you pulling out to pressurize the cooling system? Normally cooling systems are pressurized with a cooling system tester from the radiator cap position...
    – Solar Mike
    Commented Aug 26, 2019 at 7:10
  • I haven't got a cooling system pressure tester, so I was planning on pressurising it by running the engine to operating temp. Would this work?
    – tgun926
    Commented Aug 26, 2019 at 7:20
  • @tgun926 well, it has not so far... That is why there are cooling system pressure testers that will pressurize the system for 4, 6 or more hours to find long term leaks such as the one you have not found yet...
    – Solar Mike
    Commented Aug 26, 2019 at 8:08
  • Can you post a link to the tool you're referring to? Is it the one which looks like a hand pump which you screw onto the expansion/radiator tank?
    – tgun926
    Commented Aug 26, 2019 at 9:10

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