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Old 04-18-2002, 03:14 AM
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Operating temp for the 603

My car consistently runs at an absolutely normal 83dC in good weather, no ac.

Well today it was around 100dF outside, give or take a few. I had the AC on full and on the highway crusing around 85mph for an hour, the temp stayed a hair under 100dC.

I didnt think this was too drastic, so I kept crusing at a good clip. When I took off from a dead stop (full throttle) and got back up to my crusing speed the temp went to about 105dC but cooled back down to around 97 after driving.

Same happens if I floor it to pass someone, it creeps up to 105 or 107 then regulates back to ~97 in a minute or two.

Are these temperatures normal in extreme heat with the AC on? I didn't drive this car at all last summer so I cant tell you how it behaved a year ago.

I just dont want to post here in a few months that I need a new head..

PS: The temp stays at about 90dC if I cruise below 80, but that just isn't the way I drive
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Old 04-18-2002, 08:15 AM
Registered Diesel Burner
Join Date: Aug 2001
Location: Northern Virginia
Posts: 2,911
Well, I can only provide observations from my '87 300D.

It has run consistently right on 80C during all the cold/cool/lukewarm weather. The past couple of days outside temperatures have been in the 90s here, yesterday 95F. In stop-and-go rush hour, the temperature crept up to maybe 83-85C at one point. The auxiliary fan would kick in, I presume because of some AC data point rather than a high temperature reason.

At some times moving along, the temperature gauge actually fell below 80C - can't figure that out.

I don't know if my thermostat is original or some aftermarket (lower temp spec) unit, but if the gauge is accurate then I'm pretty happy running at 80C.

As a complete guess on my part, I don't think MB temperature gauges are necessarily all that accurate. Yours sitting at 85C may actually be running the same temp as my car with my gauge showing 80C. But I'd say the relative change you are seeing under hot & AC conditions is something I'm not seeing.

If I were to make a wild guess - I'd say maybe its time for that citrus treatment in your cooling system that people discuss here. It sounds like there might be a slight limitation in your cooling capability.

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Old 04-18-2002, 10:17 AM
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Join Date: Jun 2000
Location: Plano, TX
Posts: 2,513
Turbodiesel - that's just about exactly the way my 1987 wagon has behaved for years. I'm in Texas, so hot weather is quite the norm down here. I find it will run about 95C in hot weather if the engine is working hard. Either high speed, or for me, a collection of bicycles on the roof rack. Accelerating or climbing a hill will take it a bit above 100C - but it cools right back down upon easing up a bit. Around town it generally stays in the range of 85-90. I've never seen the coolant temperature rise above 105C. Good thing - the Klima relay will shut down your air conditioning when the temperature reaches 115C.

Both the radiator and thermostat on my car are relatively new, so I believe this is the way it's expected to behave.
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Old 04-18-2002, 10:22 AM
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Location: NorCal
Posts: 442

Your cooling system is performing as intended - no worries.

'04 ML500 - 53k, Inspiration Edition, Desert Silver
'11 Audi A4 Avant - Brilliant Black
'87 300SDL sold
'99 C280 Sport sold
'85 190E 2.3 sold
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Old 04-18-2002, 10:24 AM
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Location: Western, PA
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Mine does exactly the same thing. My question, having grown up in Monmouth County, NJ, is, where are you able to sustain these high speeds for that lenght of time!!??:p
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Old 04-18-2002, 02:19 PM
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Thanks for the help guys, I guess I will leave it alone until the temp gets hotter or I see something wrong.

The parkway is very lax these days, almost no troopers around. Hell, the same with most of the roads I travel, 287, 295, 42, AC Expressway. 85 is around normal left-lane traffic.
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Old 04-18-2002, 09:18 PM
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My 300 here in FL. runs about 85c in normal city and highway. At sustained high speed 85+ for hours with the AC and temps in the 90's it will run about 90-95C When I take an off ramp or have to slow for traffic it will climb to about 100c but drop back to 90 as soon as I get back to speed. The only time I ever saw it go over say about 105c and boil some water out of the overflow tank was last summer when I had a bad pressure cap. I would say yours is normal.
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Old 04-20-2002, 05:22 PM
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Join Date: Aug 2001
Location: Evansville, Indiana
Posts: 8,150
The cooling fan visco clutch locks up at about 100C (spec is 105, I think), so you should hear it cut in -- makes quite a roar. You can also check it by opening the hood when the temp guage is near 105 and having someone shut the engine off -- fan should stop in less than half a turn.

If it won't lock up, replace the visco clutch to prevent overheating.

I've not had the 300D long enough to see what the temp guage does in the heat -- repalced the thermostat last fall when it got cool. The 300 TE does exactly what your's does, although it tends to stay at 100 in heavy traffic with the AC on -- have a new visco clutch but haven't installed it yet.

1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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Old 04-21-2002, 06:28 PM
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Location: USA
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It sounds to me like your car is OK, but on the "high" side of normal temps. As long as it never gets over 110C, or consistently over 105C (i.e., not passing someone), I wouldn't lose any sleep. Check the fan clutch like Peter said. If yours is original (metal fan blade) it's probably due for replacement, ot at least a good cleaning. A lot of gunk builds up on the face and can keep the flat, diamond-shaped bimetallic spring from "engaging" the clutch at 105C (or whatever temp it engages at - I can't remember right now.) If you clean it, DO NOT remove the spring! Just use solvent, rags, a toothbrush, compressed air, etc as long as it doesn't deform the spring. Otherwise you'll be buying a new fan clutch for $250+.

Now, if your car runs hot at idle, with the A/C on, on a hot day (100F)... say 105-110C... your radiator is highly suspect. The car really should stay under 100C under those conditions. The radiators in the 124/126 OM603 diesels have a nasty tendency to plug internally such that they flow fine but do not transfer heat. A new radiator made my car go from constant 100-110C temps to refusing to budge over 95-100C. (Well, before my head replacement anyway, but that's a different story...)

Anyway, relax, your temps sound normal for being bloody hot outside...

Dave M.
Boise, ID

1997 E420 - 154kmi (Bugeyes)
1994 E420 - 143kmi (Blondie)
1993 500E - 193kmi (Lollipop)
1992 400E - 188kmi (Stinky Dirty)
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Old 07-07-2002, 09:35 PM
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Join Date: Dec 2000
Location: Fairfax County, Virginia
Posts: 856

I am late getting to your post on temps in you 300SDL ... we may have crossed messages in another post, too.

My 350SDL's temp has always been very steady at 82-85C in normal ops including high speeds with a/c off - it had always warmed up a bit in traffic, but NEVER above 100C ... I recently swapped the viscous clutch and replaced waterpump. It then ran very warm (in comparison to previous) ... in my opinion, yours is running too hot.

I later replaced the viscous clutch again AND the thermostat ... ran JUST LIKE IT HAD ALWAYS RUN! Back down to 82-85C in normal ops - rock solid! And, it appears to get up to operating temp much faster than before.

I think the tstat was bad and the system is now performing normally.

Does your temp "wander?" Mine did with tstat bad, but does not with new one.
George Stephenson
1991 350 SDL (200K and she ain't bent, yet)
former 2002 E320 4Matic Wagon - good car
former 1985 300 CD - great car
former 1981 300 TD - good car
former 1972 280 SEL - not so good car
a couple of those diesel Rabbits ...40-45 mpg
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Old 07-07-2002, 10:50 PM
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These days most of my driving is is NJ north and south- a new part of my sales territory. So I believe we have been experiencing the same weather and road conditions.

The temp on my 2.5 turbo periodically creeps into the triple digits as well with a new thermastat, radiator, and hoses. So, like most who have replyed thus far, I will encourage you to try youre best to believe your car is opperating within acceptible peramaters. One thing you might want to check is if both your auxillary fans are opperating. One of mine busted while the other was fine. Obviously this inhibits proper cooling. To do this turn on your defrost, wait for a few minutes and see if both fans go on simultaneously. See you on the road
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Old 07-08-2002, 10:16 AM
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Location: NorCal
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Aux Fans


Just a note to inform you that the '87 300 SDL has a single auxilliary fan.

'04 ML500 - 53k, Inspiration Edition, Desert Silver
'11 Audi A4 Avant - Brilliant Black
'87 300SDL sold
'99 C280 Sport sold
'85 190E 2.3 sold
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