Originally Posted by ashedd

I know I know... there are many topics on the issue. I think my question is a bit unique, to me at least.

After today I have successfully driven 3 diesel MB's from Newport News Va. to my home in Indiana. TomTom takes your right through the appalachian mountains on this trip. Stunning scenery and it get's nice and cool out at the top.

The max grade that I saw via signs were 5% and 7%. The SD did the hills without breaking a sweat and the temp stayed a rock solid 60 degrees. The 190d parts car did the hills at maximum available power output(3rd gear, foot to the floor, 45-50 mph) and never broke the 60 degree mark.

Now we have the 300d with the om603. This car has power, lots of it. It loves the highway, as many of you know. I was charging hard the whole trip and never got below 70mph in the mountains. That means I was doing 70mph on the same grades the 190 was doing 45 wide open. But the 300d(Black Beauty) temp went from it's normal 65 degrees to 100 during the climbs. Pretty much anytime I put a significant load on the engine the temp would rise. It broke 100 once during the trip but NEVER hit the red mark(220 is it?). Once the load/hill was over with the temp would fall pretty quickly back to good ole 65.

So whats the deal? 2 out of 3 cars holds a constant temp and one of them has a aluminum head like the 603. Last week sometime I citric flushed the 300d's cooling system and replaced the thermostat with a new behr replacement. I also added the correct G-05 coolent.

So what needs replaced? Fan clutch? Water pump? Nothing?

I hope you can understand my reluctance in heating my #14 head unnecessarily.

Thanks

PS.

the black beauty has about 140K miles on it.