NEED HELP, OVERHEATING!!!
 

So. This weekend while on a long trip and while stuck in traffic, I noticed steam rising from under the hood and my temp gauge on full red. After a long ordeal I finally got home. I assumed it was due to a failed thermostat so swapped it out with a OEM part, fired it up and went for a test around the block. Temp gauge went to full red again:mad: So now I'm stumped because I checked for leaks from radiator, hoses, water pump, thermostat housing, and found 0. Also something strange is that the car seems to accept only a very little amount of 50/50 coolant, not even half a gallon before full. other points to mention are I checked radiator fan for functionality and found it operational. I checked relays too and found them operational. And lastly, I swapped the stock radiator for an E36 M3 full aluminum model, and the expansion tank too. I have be running EXTREMELY well on this setup for at least 8 months. Even on the longest of trips, say 100 miles, the temp gauge never exceeded the mid point. Any suggestions are much appreciated. I would really prefer to fix this myself then sending to a mechanic to be robbed.

Sounds like either a clogged radiator or a water pump. Check for even temperature from top to bottom on the radiator. I believe these are cross-flow radiators. If so, you want to make sure the bottom of the radiator is roughly the same temp as the top. If the top is hot and the bottom only warm, that would indicate the bottom rows are clogged. If you're not getting much heat anywhere, I would suspect water pump.

Yeah. After a few test drives and sitting idle for some time, even with the temp gauge on max red the radiator was cold. But the engine block was hot. But i do remember that while i was filling the radiator after replacing the thermostat i spilled some coolant the radiator and when i came back after the first test ride i saw it steaming from that spot where the coolant spilled. So thats definetely and indicator of heat but the sides and top if the radiator where cold.

Definitely sounds like a circulation problem in the cooling system Did you fully bleed the cooling system? Possibly an air lock situation, or bad water pump.

Yea I did a bleed and nothing came out. I ordered a new water pump and its coming in tomorrow so hopefully this is the fix. Either way ill post the results.

I think that you might only be draining and filling the radiator. If you were to drain it out of the block the rest would come out.

Good luck. I think water pump too. I'm not sure how they fail (maybe broken fins), but if you rev the car up the water pump RPM's will increase thus trying harder to circulate. Could be an interesting test. I wouldn't move the car or let it go past half way on the gauge though.

Interesting point. But to drain the radiator I disconnected the 2 main hoses that connect to the thermostat. So all the fluid from the radiator AND block should have poured out. But there was only a small amount, like less then HALF a gallon. Also the new pump I ordered has a metal impeller so should be good for quite some time.

Only way to drain the block is remove the coolant plugs located right above the oil pan, you will find small plugs that completely drain the block for winter storage without antifreeze in the cooling system.

Sounds like you have a vapor lock in the block. You need to read the tutorial on filling the rad on a BMW. It has to be done a certain way and if not you will have issues like you are experiencing. It takes a while to do it correct and get all the air out of the system.

Hmm, maybe so. Well I got the new water pump on today pretty easily. But the fun started on the start up. This car used to never run at mid heat on the gauge. It was always at just above cold even after long trips. I managed to get a gallon and a half of 50/50 anti freeze in this time, but right away when I started it up the gauge went quick to mid point and stayed there. So I went on a test run and pretty quickly the top radiator hose blew and coolant was spewed all over. tightened up the hose (which at no point during this fix did I loosen). got back home and noticed a steady stream of steam rising from that right side of the radiator. so im thinking either the radiated heat is burning off the coolant that leaked there, or I have a hole in the radiator. But until now I have a new thermostat and a new water pump, but am still no closer to a solution. Also I think some of you are under the impression I am with an M44 stock little radiator. This is not the case, I have an M3 radiator so filling and bleeding procedure may be different.

Ok, let's get a few things in order...

Your Temp should be TDC (top dead center) when at proper operating temp. If your temp never rose to that level, your thermostat was bad and stuck open. So when your car is now actually getting up to temp, it's not overheating, it is finally getting up to temp.

It does now sound like you have cleared the vapor lock from your block when you opened up and replaced the water pump. Regardless of whether you are running a 6 cyl or 4 cyl radiator, proper cooling system bleeding is required to ensure no bubbles remain... See this DIY -

http://www.318ti.org/forum/showthread.php?t=27983

Why you blew the top radiator hose and why you may have a tank leak are most likely separate topics...