Topic: E46 overheating

At CMP for testing,  and car is overheating after 10 minutes on track. History: it overheated at the spring race, took it home had compression and leak down tests done on the engine and pressure test on the cooling system.  No issues found. Replaced the expansion tank.  Only overheats when racing, can idle for an hour with no issues.
Any thoughts or ideas welcome, otherwise our weekend is over.

Re: E46 overheating

Has the car ever run on track without it overheating, or is this new behavior?

Compression test only tells you that you have a good seal at the rings and valves. Pressure test on the cooling system will only tell you that there are no coolant leaks, it doesn't tell you how much flow you are getting.

You are getting enough coolant flow to handle the heat load generated when idling. When you run on track, you need more coolant flow to overcome the additional heat load.

Bad water pump, collapsed/blocked heater hose, partially plugged radiator, limited air flow path in/out of the radiator spring to mind. We had a radiator that got partially plugged and exhibited that exact behavior (ok at idle but too hot when running on track). We diagnosed it with an infrared thermometer pointed at the radiator surface, we saw different temperatures across the face of the rad (cooler where it was plugged because no hot water from the engine was getting to that part).

We swapped radiators and the problem went away.

Do you have any spares with you? The above items should be easy to replace and check (if you have any). If you have a blockage internal to the engine, not so much.

We Audi Be Faster
'85 Audi Coupe G(in &) T(onic)

Re: E46 overheating

We ran barber this winter without problems, and spring CMP started fine, but the expansion tank cracked so had to replace. It hasn't tracked without overheating since.

Re: E46 overheating

Sorry to say you probably are jobbed.  We did this dance with our E46 after it cracked its expansion tank.  Blown head gasket.

1990 RX7 "Mazdarita" 
1994 Jaguar XJ12 (Winner C-Class 2013 Sears Pointless)
1964 Sunbeam Imp (IOE 2013 Sears Pointless)
1980 Rover SD1 (I Got Screwed 2014 Return of Lemonites) (Sold -> Houston.  Gone and forgotten)

Re: E46 overheating

Simple check for other than cooling system overheating issue.  Get it hot but not overheating.  Pull in.  Since you have a pressure cap on your overflow (actually expansion tank), put on a welding glove and take it off while running. After the shit settles down (about 3 minutes) watch for bubbles or oily bits in the expansion tank.  ANY bubbles (almost always tiny) and the headgasket is blown.

Re: E46 overheating

Agree that bubbles in the radiator is a sure sign of a head gasket. But you don't need to go on the track or open a hot radiator. Just take a piece of cardboard and stick it tight to the radiator in front of the fan. Take the cap off the radiator. Start the car and heat it up. Watch the water temp and watch for bubbles in the radiator. If the car won't heat above 210 sitting at idle with the radiator covered with cardboard then have someone sit in the car and up RPMs to 1500 - 2000 for ten minutes or until temp gets to about 220 - 225. No bubbles, probably not a head gasket.

Not sure what year the car is but the newer years of that gen have an overheat tattle tail on the head. Look for a circular piece of stamped metal about the size of a dime flat on the head at one of the corners. If that piece exists and is curled or deformed then you have a head gasket and a warped head. Don't waste you time and money replacing the head gasket until you take the head to the machine shop.

Re: E46 overheating

^ this is all fine and dandy but we went through the exact same symptoms with our Lemons E46 after a cracked expansion tank.  Wasted a couple races after everything checked out "fine". Blown head gasket.

1990 RX7 "Mazdarita" 
1994 Jaguar XJ12 (Winner C-Class 2013 Sears Pointless)
1964 Sunbeam Imp (IOE 2013 Sears Pointless)
1980 Rover SD1 (I Got Screwed 2014 Return of Lemonites) (Sold -> Houston.  Gone and forgotten)

Re: E46 overheating

Honestly pull the head, check to see if it's straight.  If straight have machine shop clean it up then stud the head for cheap insurance.  Leave stock rev limiter on it to prevent over rev's

Re: E46 overheating

When you replaced the expansion tank, did you bleed the cooling system using the process recommended by bmw?  Before pulling the head, I’d try to bleed it again.