OM603 running temps?

[BodhiBenz1987]

I'm really sorry if this question's been done a million times ... I used the search and found some info, but wanted to check to make sure I know the right answer specific to my car.

On my way home from a road trip, I have to cross the Nittany Mts., which is a pretty good climb. My car (87 300D) generally runs at just above 80c, sometimes up to 90 (this seems to be consistent in winter and summer times). While I was hiking up the steepest, roughest part of the drive, it was rolling just above 3,000 rpms and sounded pretty good, but the temp climbed somewhat quickly to 100, maybe even a little higher. It gradually dropped back to a little above 80 once we hit the downhill again and stayed there. I would assume this is normal when the engine is under a heavy load, such as climbing a mountain, but I never want to assume TOO much, so I thought I'd ask. I have heard all the cracked head horror stories on the 603. I have been warned many times to immediately back off if this car starts to overheat. ... is there a specific temp at which I should ease off a little? I don't really want to find out by pushing it until I see smoke billowing out of the front!

I hope I don't ask too many questions, esp. ones that have already been done before. But you guys give me great answers, and I have learned a ton from this forum. A year ago I couldn't have told you a thing about cars, and between this group, my mechanics and my dad, I'm approaching competancy. Hopefully someday I will have enough knowledge to "give back" to the Mercedes community instead of just asking 5 million Qs.

[Hatterasguy]

Yep that sounds normal, what were the outside temps?

The electric fans don't come on to 105C, but I would say 110C is the upper limit. If it gets close to or above that back off and cool it down.

[BodhiBenz1987]

Originally Posted by Hatterasguy

Yep that sounds normal, what were the outside temps?

About 50F, I would say. It may have been a little warmer than that (the outside temp guage display is busticated, so I'm going by what banks and car dealerships along the routes had flashing on their LCD signs!).

[Brian Carlton]

Every 603 will exhibit the behaviour that you describe. Some of the better ones, with a very good cooling system (excellent radiator) will top out at 100°C. Mine has been observed to hit 105°C. on a very long (5 mile) upgrade in 80°F. ambients.

If your radiator is not all that terrific, it could climb above 105°C. under continuous load. But, not a problem. That's why you have the gauge. If the temp. reaches 105°C., just lift your right foot and climb the mountain at at 2000 rpm at 45 mph. The temperature will immediately stabilize and will probably start back down.

The fan clutch should be fully engaged at 100°C. This normally holds the temperatures below 105°C. if the clutch is functioning properly.

If the temp climbs above 105°C., the electric fan should kick in and assist.

[peragro]

I live in the middle of the Sierra mountain range in CA, thus I get lots of experience with some pretty steep grades. There are lots of places where I'll be going 50 or so up a hill and the temp gauge is reading a little above 100. This last year I changed out the coolant and flushed the system and cleaned out the "between the fins" area of the radiator - lots of really fine dirt in there... . I saw lower around town and cruising on the level highways temps, but the same temps as before the change out on some of the steep grades. It now reads a little above 80 for normal operating temp.

Something weird did happen the other day though, maybe someone can shed some light. Heading up the Cajon grade the other day, pretty steep (don't know the exact grade) for about 20 miles or so at around 60-65 MPH. Shortly before the top the low coolant light comes on. I pulled over as soon as possible, a little past the summit on the downhill grade. Temps never went beyone 105-110 according to the gauge. By the time I popped the hood and looked I had a full reservoir of fluid. Everything else looked fine and temps read a little over 80. I closed the hood and drove the 100 miles home. Any thoughts on what happened? I'm not leaking any coolant (since the H2O pump replacement, anyway) and I don't have any pressure in top hose prior to starting in the morning.

[BobK]

How about the float in the tank switched on because of the grade? and maybe you were just low enough on coolant with the tilt on the tank?