Overheating

If the temperature gauge told you it was hot and you kept driving, this is a problem. If the red light came on and you kept driving, this is a bigger problem. If steam came out of the engine, it's an even bigger problem. If the steam was black or blue, you're looking at an engine rebuild, because that means fuel or oil. If the steam was white, it's coolant, and you've got an issue with a leak. Find the leak (pressure test is easiest) and fix it. Then do a full cooling system pressurized flush cleaning.

Please note: I HIGHLY RECOMMEND you have the cylinder head removed and inspected for heat damage/warping. You can fix all the leaks you want, but if the head's damaged, you'll only have further overheating and driveability problems. Cylinder heads can sometimes be repaired, usually rebuilt, and always replaced, it's just a matter of cost.

I also suggest looking at your temperature gauge once in a while in the future, because all this was probably highly avoidable.

First, is the overflow bottle filled to the line where it is supposed to be???

Second, need to check that the thermostat isn't stuck shut... follow the big hose from the radiator to the thermostat housing, it should look like this..

http://cgi.ebay.com/ebaymotors/BMW-318-323-325-328-M3-Z3-Thermostat-Housing-1991-1999-_W0QQitemZ170216855929QQcmdZViewItem

remove the hoses, loosen the bolts on the bottom of the housing...remove it and you should see the thermostat.. it will look like this


http://www.autopartswarehouse.com/mmp/bmw~318i~thermostat~parts.html

Take it inside you house, put it in a pan with water covering it, put it on the stove over medium heat...add salt and pepper to taste... errrr I mean... just watch it as the water heats up, and see if it opens, if not replace it with a new one.

even if it opens, try putting the thermostat housing back on the car without the thermostat...hook the hoses up and and start the car, let it run and see if it still over heats, if so...maybe buy some radiator flush and use it per instructions on the bottle.

Also, make sure you are using coolant and not water... most people think coolant is so it won't freeze...and thats wrong, coolant will not freeze...however, it also won't get as hot as water does or as fast.

If none of that works... could be the water pump, most have a seep hole so they start leaking when they are going bad...notice any water dripping under the car anywhere?

Othyer than that, could be a blown head gasket, or a number of other things making the car run hot.... check everything in the order I showed.. it starts at the cheapest fix.

Good Luck!!