I know I've asked variations of this question before, but I can never really get straight what appropriate running temps are. I have an OM603 with what I assume is the #14, so I worry very much about a cracked head:
Today it was about 85F ambient temperature as I was driving to work. The drive is a bit uphill but hardly a mountain, and it has three or four stoplights, which are ALWAYS red when I get to them. Toward my destination I noticed the engine temp reached almost 100 and stayed there ... I stopped for a coffee, when I started up again it went right back up to 98 or so. I let it idle for a while when I got to work an it dropped a couple degrees, maybe.
This car usually runs at about 85, 80 when its cooler outside. It does go up to 100 pretty much everytime I drive up Nittany Mountains (about once every two months), but that's a big mountain and I expect it.

Is it normal for my car to get so hot on a normal, slightly uphill drive when it's 85-90F outside?

Again, sorry to be repetative in my question-asking ...

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1987 300D, arctic white/palomino--314,000 miles
1978 240D 4-speed, Euro Delivery, light ivory/bamboo--370,000 miles
2005 Jeep Liberty CRD Limited, light khaki/slate--140,000 miles
2018 Chevy Cruze diesel, 6-speed manual, satin steel metallic/kalahari--19,000 miles
1982 Peugeot 505 diesel, 4-speed manual, blue/blue, 130,000 miles
1995 S320, black/parchment--34,000 miles (Dad's car)

With the A/C on going up hills and stop and go traffic 100c is a high normal when idling. Do you have the Aux fan, and does it work if so? I would think that is a bit high though. How long since you replaced the thermostat ? Or, maybe the radiator needs cleaned from the outside, fins. Behind my aux fan was dirt, twigs, grass, and bird feathers. Or, maybe the radiator needs flushed. Or, worst case, replaced. Or, maybe your water pump is shot. Any coolant leaks? I would start with the easiest and cheapest first. Keeping the cooling system straight is no waste of time.

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1984 300D Turbo Sedan (Hilda) 272,115 miles.....
Anthracite Gray/Palamino Leather, I am 3rd owner

2001 Dodge Stratus (Silver) (wifes) 55814 miles...

1982 280TE Wagon Astral Silver Metallic/
Anthracite Velour
260,512 miles (Eva)

1969 230 Sedan Olive Green/Black MBTex
4 Speed Manual
84,213 miles ????
Haus Frau


2004 Boreem Ninja Pocket Bike
Highly Modified 49cc (Ling Ling)

Einigkeit und Recht und Freiheit

first off, don't take advise from anyone that has no experience with the OM603 engine in either a 124 or 126 chassis. These cars run hotter than the ones with OM617 engines. this has been said by gsxr also, and there were sugestions in one thread that the best thing a owner of one of these engines can do is put a nice big therm gauge on the dash!
see thread: 1987 300TDT Overheats on long hills


It's a fact of life that the cooling systems are different between the 603 and other diesels made prior. There is a fuel heater for one thing. And I think the radiator is a bit undersized, and there's the under pan that might affect airflow across the rad fins, I dunno. Are you running a 1.4 bar cap?
I use Redline Water Wetter, I have a new radiator and a new water pump and a #14 head and mine runs about the same as yours under similar conditions.
Just take it easy and there shouldn't be a problem. (knock on wood!

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

I'm new to this all, so bear with me ... what does this mean?

__________________
1987 300D, arctic white/palomino--314,000 miles
1978 240D 4-speed, Euro Delivery, light ivory/bamboo--370,000 miles
2005 Jeep Liberty CRD Limited, light khaki/slate--140,000 miles
2018 Chevy Cruze diesel, 6-speed manual, satin steel metallic/kalahari--19,000 miles
1982 Peugeot 505 diesel, 4-speed manual, blue/blue, 130,000 miles
1995 S320, black/parchment--34,000 miles (Dad's car)

look at your radiator cap, it should have 140 stamped on it, indicating 140 millibars or 1.4 bars
Also called atmospheres, millibars are another unit of measure for pressure.
To convert from bars to psi multiply by 14.7 therefore 1.4 bars = 20.5 psi
Earlier diesels used 1.0 bar pressure caps, then the turbo diesels went to 1.2 bar finally the 603 went to a 1.4 bar cap. Higher system pressure allows the coolant to reach higher temperature without boiling.

__________________
'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

Another note not mentioned for the 603 is that the aux fan is regulated by a thermo switch and the aux fan should come on at 105c.

My 87 300D will run hotter in the summer heat, and with AC on too. On the hottest days, I've never seen my temp guage go past 90c, but I've never climbed a mountain under those conditions either. Also make sure your clutch fan is not shot, give it a spin, there should be resistance and you cannot make it spin a full revolution on it's own by giving it a whirl with your finger (engine off of course) ....BB

DDH is right on the money.

If the member doesn't own a 603, ignore the advice.

Mine basically does the same thing as yours. On a warm day, it will climb right up close to 100°C. when doing 0-50 runs off succeeding stop lights, with normal acceleration.

However, it won't go above 100°C unless you are on a very long upgrade using very close to maximum continuous power. In such conditions, at 80°F. ambient, I have observed a maximum of 105°C. after five minutes of this uphill abuse at 70 mph.

Your thermostat is fine. If the temperature stays at 105°C. or less, the fan clutch is probably fine as well.

The only thing you can do, if you are very ambitious, is to pull the radiator and thoroughly clean all the fins. This is not an easy task and requires compressed air and/or a light duty pressure washer. It takes a couple of hours to do it right.

What ever you do, don't start spending a bunch of money to fix things that are not broke (now where did I hear that before?? ).

Thanks folks. As always, I greatly appreciate the peace of mind that comes with having a vague idea of what's going on. The cap is indeed 1.4 bar, and looks in good order. I did notice a slight menagerie of insect species collected in the radiator ... so I'll entertain the thought of planning a cleaning session. Add that to a list of 2+ hour jobs I need to do if I ever get a block of two hours with reasonable weather, the right tools and an area in which to carry out the procedure ...

__________________
1987 300D, arctic white/palomino--314,000 miles
1978 240D 4-speed, Euro Delivery, light ivory/bamboo--370,000 miles
2005 Jeep Liberty CRD Limited, light khaki/slate--140,000 miles
2018 Chevy Cruze diesel, 6-speed manual, satin steel metallic/kalahari--19,000 miles
1982 Peugeot 505 diesel, 4-speed manual, blue/blue, 130,000 miles
1995 S320, black/parchment--34,000 miles (Dad's car)

When I bought my '87 about 18 months ago I was curious about the temp gauge readings, they seemed high to me. I replaced the radiator (it was leaking slightly) and I had some engine work done, a new water pump and a new vac pump installed and new belt and idler pulley. It still ran the same temps. Then along came a thread on the subject and after the discussion died down I felt assurance that the car was normal in that respect. I still wish it ran as cool as my iron head turbo diesels though.

Another thing you may want to do is replace the fan thermo switch, the three terminal one. As busybenz raised earlier there is a lower temp one available from the later series diesels. gsxr recommends this "up-grade" (see below).
The reason I suggest replacing this switch, even if with the original type, is because they tend to fail after a few years because they carry the entire fan current (about 12A at least and more when they start). There was an idea which proposed adding a small relay to take the high current load off this switch, that is something I'd like to do when I get time.

quoting gsxr: 3) The electric fan high speed is only triggered by the 3-prong sender up at the water outlet on the cylinder head, near the upper radiator hose. The 603.960 switch is blue and rated 128/105, and costs about twice as much as the 603.961 switch (which is gray and rated 120/105). If you replace it, get the cheaper switch, which will also engage the AC safety shutoff at 120C instead of 128C, which IMO is ridiculously high.

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

I know that Dave likes to replace this switch.

However, if the engine never gets above 105°C. the switch never engages the fan. So, the fan can't do anyting for you.

My personal goal is to make damn sure the engine does not go over 105°C. So, if they made a switch that works at 100°C. I might consider a new one.

But, with the starting point for the fan at 105°C., why bother unless you need to run long upgrades at highway speed at 90-100°F. ambient temperatures.