'02 330Ci: Check coolant light + heater + temp gauge, no codes thrown

[psuwayne]

Hi all -- I drive an '02 330Ci (with Dinan Signature S package) and about 2 years ago my "coolant light" came on again. I'd seen it twice in the past and it always accompanied a fault code that indicated a bad thermostat, which I replaced both times. But this time, no code (And no discernible fluctuation in the engine temp gauge). I checked the coolant level, which was just fine. So I kept driving it hoping to eventually get a code that would indicate the problem. What I noticed was a pattern...

I'd start the car in the morning and start driving. The coolant light would be off and after 3-4 minutes, the engine temp would rise up to the middle position and hold. 5-7 minutes later, the coolant light would come on (in the winter, I also noticed that the coolant light coming on would coincide with the heat starting to come out of the vents. Sometimes when the light goes off, the heat stops as well). After a short while, the light would go off, only to return several minutes later. This would continue on and off as I drove (toggling maybe 4-5 times in a 1 hour drive). Still, no codes are thrown. Eventually I chalked it up to just a bad sensor, although I would have expected a bad sensor to throw a code?? This morning I was driving and the same pattern was happening, only today when the light went off at one point, the hot air from the vents was replaced by cold air. I noticed the engine temp gauge shot up almost to the red zone for about 20 seconds, then came back down to normal and the heat started blowing again. I got to work 40 minutes later with no further issues and checked for codes. There were no codes related to the thermostat or cooling system (just a couple O2 sensor codes and a code for functional check purge valve). I'm completely stumped at this point. The car is almost 16 years old and has 155K miles on it, so I'm not big on the idea of taking it to the dealer and spending big $$ to get it looked at only to have them tell me they have no idea and start swapping parts hoping to find a cure. Anyone here have any ideas I might be able to try myself? Thanks very much!

[02Pilot]

What are you reading the fault codes with? If you're using a generic OBD2 reader you may very well be missing existing BMW-specific faults.

[shadowpuck]

i'd also want to know the state of the whole cooling system - at 155k it's at least at its second replacement by now.

[bmwdirtracer]

Yep: Radiator, expansion tank, coolant level sensor, plastic water manifold, cap, water pump, thermostat, the two plastic pipes under the intake manifold, every hose, and the sensor in the lower rad hose; and a fan clutch. Then vacuum-fill the system with BMW blue coolant and distilled water.

Some of our supporting vendors have "packages" to redo the entire cooling system. Try ECS Tuning and FCP Euro. Buy OEM or OE parts only. If you have any doubts, give us a link and we'll check.

You need to understand that the E46/M54 does not give anymore warning than you have already had. If you continue driving it without immediately attending to the 16 year old cooling system, the engine will go pop in a very expensive way. You have air in the system, which means you have, at best, a coolant leak. At worst, a blown head gasket, which means a warped head and threads torn out of the engine block.