Ok I never thought that in would have to ask this question but I guess I am. My 87 300d still has the #14 head, and has 148,xxx miles. The car will not run over 80c, the only day it went over was when we had ambient temps of 98 and the ac was on and I was was in heavy stop and go traffic. Even with these conditions, the needle just barley lifted off 80c and was still almost touching it. The few days that it has been below 60 ambient, the car runs just a tiny bit under 80c.
At the moment I find this fine bc I have huge fears of the car overheating, but I am concerned about it being to low for winter months. My 92 300d always ran between 90-95c, and that is what I'm kind of comparing to.
Please correct me if these are ok temps for it to be running. And I would like to know what others om603 cars are running at?

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1987 300D(Erma)- #14 head, 193k
2003 TDI Beetle sold
1985 300sd sold
1987 300D(Ursala)- #14 head, 157k when sold
1987 300D(Wilbur)- #14head, 356,000+miles, sold after 7 days of owning it.
1992mercedes 300d- totaled and in a junk yard somewhere..
1983 mercedes 300sd- scrapped
1980 mercedes 300sd first mercedes diesel-sold

Sounds Perfect

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Greg
2012 S350 BlueTEC 4Matic
2007 ML 320 CDI
2007 Leisure Travel Serenity
2006 Sprinter 432k
2005 E320 CDI
1998 SLK230 (teal)
1998 SLK230 (silver)
1996 E300D 99k, 30k on WVO
Previous:
1983 240D, on WVO
1982 300D, on WVO
1983 300CD, on WVO
1986 300SDL 237k, 25k on WVO (Deerslayer)
1991 350SDL 249k, 56k on WVO - Retired to a car spa in Phoenix
1983 380 SEC w/603 diesel, 8k on WVO
1996 E300D 351k, 177k on WVO

You're fine, that's how my fathers wagon runs.

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Allen Kroliczek
Oak Grove Autosport | Oak Grove Autosport
01 G500, 82 300TD, quite a few more.....

I run in between 80 and 85. I need to check the fan clutch... but it's not too hot so I dont really give it much thought. Don't go nuts staring at the temp gauge... just give it a glance at the same time you check your speed. You ARE watching your speed right?

I usually have to make sure I'm not going too slow

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08 R320 CDI current

Past
95 E420
87 300D Turbo 5spd
90 300TE
83 300SD
85 300TD
92 400E
85 190D

Jeremy checked some senders and found similar resistance vs temp response. Gauges on the other hand have more variance. What you see as 80*C could register as 85*C on someone else's gauge. There are other things to consider as well such as how long it takes to get to operating temperature, and how much the gauge fluctuates in normal driving.

FWIW mine runs at 85-90*C. Goes to 95*C when the AC strains or I charge uphill. I suspect my clutch isn't the healthiest either.

Sixto
87 300D

Mine is an OM606 but thought I'd mention this.

I just replaced my 85C thermsotat with an 80C as the temp guage tended to hover between 85C(minimum) and 95C. It just seemed too hot for the longer term.

Now it hovers between 80C and 85C. The car really does run smoother at this temp.

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1995 E300 Diesel

Ok thanks, Im glad that it's normal. And yes I'm still in that stage when I watch the gauge more than the speed. Which will eventually get me in trouble, bc this car creeps up in speed on me all the time. For some reason she likes to run 75-80 instead of 70, and that's not ok with 65mph speed limits...

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1987 300D(Erma)- #14 head, 193k
2003 TDI Beetle sold
1985 300sd sold
1987 300D(Ursala)- #14 head, 157k when sold
1987 300D(Wilbur)- #14head, 356,000+miles, sold after 7 days of owning it.
1992mercedes 300d- totaled and in a junk yard somewhere..
1983 mercedes 300sd- scrapped
1980 mercedes 300sd first mercedes diesel-sold