318 overheating in idle, now freeway
 

So after looking around for a long time, I finally bought a 318is a couple of weeks ago. It's a '92 with almost 180k miles, but in really nice shape and has been treated well. I really love the car, it's a lot of fun to drive and even the acceleration is better than I expected given the size of it's engine. The best thing: it's a manual! :)

Anyways, so two days ago I was dropping of a friend and we ended up talking for about 15 minutes in the car while the engine was idling, and suddenly I realized that the temperature gauge had gone way up and the warning light came on. I shut off the engine immediately and opened the hood, and I saw a little steam coming from the radiator cap. I left the hood open for another 10-15 minutes for the engine to cool down, and finally drove home (which wasn't far) without any problems. What surprised me though was that I couldn't hear the fan running -- I will have to get that checked out.

However, while driving home from work today I noticed that the temperature was going up again -- so far, the gauge usually had always been right in the center, now it was on the line between the center and the red. When traffic was slowing to a stop-and-go, the meter started inching closer to the red, and I was prepared to pull over to the right and stop, but as soon as traffic got lighter and I could drive faster, the meter went back to it's previous place (halfway to red).

Now this really surprised me -- if it's really just a broken fan, when I drive at freeway speeds in "cold" weather (about 65 F), shouldn't the temperature be fine?

The only thing I've done to the car since I bought it was getting an oil change (that was about 2 weeks ago). Unfortunately, I forgot to tell the mechanic what oil it was running, so he put in a different type (what he said was the manufacturer recommended one for this car). Note, this was at an independent garage that specializes in BMW and Mercedes, and the guy had over 15 years of experience (and excellent reviews online). Unfortunately I can't decipher the oil type on the receipt, I'll call the place tomorrow to find out, but I remember that it was mineral oil, while the previous owner said that only synthetic oil (15W50) had been used in the car for the past few years (there's still 2 bottles in the trunk).

Could this be at all related to the different oil? I do remember reading here that it's not good to switch the type. But I also thought that was only related to the seals. (BTW the mechanic said that the seals on this model aren't designed for synthetic oil and it may have caused some leaks. Actually, he showed me the underside of the car which was kinda oily, and told me to wash it off some time before the next oil change, so that next time he'd hopefully be able to find the leak).

Any ideas?

Sounds like a classic case of dead radiator fan(s). I'll bet if you put your AC on the temp would go down as it would trigger the second elec fan. Check the relay and wiring to the fan, you may have a thermostat trying to die, and of course check the coolant level. You mechanic sounds right on, take it to him for this he'll probably start in the same place. (also make sure the radiator isn't blocked by debris or some such nonsense)

So today after work I double-checked and actually, the fan is working! (Of course it was not running when the engine was shut down, as I had wrongly assumed after having seen several cars that have an electric fan that keeps on running even after the engine is shut down, if temperature is still high). Apologies for that.

Also, the auxiliary fan seemed to work just fine after I turned on the AC. Both fans running did seem to keep the temperature in control a little bit better, but when going uphill or in traffic, the gauge would still hit the third mark, although it did go back down to normal when going downhill.

So I'm ruling out the fans. However, I did notice some loss of coolant -- I checked it yesterday and filled it up to the mark, and today I had to refill again, quite a bit actually. Could this be a result of the overheating, or does it mean I have a leak there? Just in case, I checked the oil but couldn't see any signs of coolant in it.

My best guess right now is the waterpump, my last car (Toyota) had the same problem, and that's what it was there. I guess I'll just have to get it checked out at the garage ASAP.

I seem to recall a problem with the timing case gasket on the M42 engines. Could be serious. I'm sketchy on the details, run a search on this forum or on Google.

Just got back from the shop, they did a pressure test on the cooling system and it turned out I have a leaking radiator. There were at least two streams of coolant dripping out on the right hand side. I guess that'd explain why I seemed to be loosing so much of it (it was almost a quart a day).
I'm getting it replaced now, hope that'll solve the problem.

So I got a new radiator now. However, overheating still persists. It takes a little longer now, about 15-20 minutes on the freeway, but in after that (or after about 10 minutes in heavy traffic), the temperature needle starts heading for the 3/4 mark again.

Any other ideas what this could be? Is it completely impossible that this could be happening due to the different oil it's running now? I'm just asking because BEFORE the oil change, I did not have any overheating problems, and I even drove the car on a slightly longer trip than just to work.

I'd take it back to the shop since they didn't fix it (still has the problem), and give them a second chance to get it right. Possibly a thermostat, possibly the oil. Run OEM recommended oil ONLY regardless of mileage. Could still be fan relays, does it cool down w the ac on?

What's the latest on this? My car is having a similar issue.