After a nice, long (and cold) winter came a warm summer... with it some cooling system woes. Most of my cooling system has been replaced in the last 5,000km so this posed a real puzzle as to what was really happening to the car. Here I will go through the list of things to check when your M70 is overheating and what you can do to rectify the problem. For me the problem ended up being a super simple one, a blown fuse.

First thing you can check is the fuses (for me it was the last thing I checked LOL). The fuses you need to check are #25 (30A) and #29 (7.5A). Those are the ones for the air con system and your auxilary fan. Chances are if your auxilary fan isn't moving, its because one of these fuses is blown.

Here is a picture of a fuse box cover for my 1991 850i (it may be a little different for US spec cars).

This is the fuse that was blown (in spot with no fuse). In this picture you can also see that all of my fuses have been replaced to the new style of fuses vs the ones that the BMW came with originally. The wire fuses are a poor design and have a tendency to loose contact points a lot quicker and/or blow then the new style ones. I advise all BMW owners to do this.

This was the 30A fuse that was blown, replaced it with a new one and voila! Everything was back to normal and the car was getting the proper cooling.

If your fuses are fine and the car is still having overheating issues chances are its one of the other components of your cooling system. Here is a list of things you can check:

• Make sure your cars coolant is bled properly and has no air bubbles in it. (Go on a slanted hill, start the car and blast the heaters - then go to the front and open the bleeder screw - its a messy job have rags and stuff)
• Has your thermostat been replced in the last 100,000km, if not get a new one - its a cheap peace of mind
• Replace fan clutch and fan (the fans like to disenegrate and explode = expensive repairs to the hood - the both are cheap anyways, relatively)
• Replace all the belts and pulleys/shock absorbers
• If all the above didn't help, its most likely a bad water pump or auxiliary water pump