That would be an incorrect conclusion. The figure of "80" indicates that this temperature is the point where the 'stat just begins to open. In reality, depending on many other variables, the system will operate between 80C.and 94C. At the point of 94C., the 'stat is fully open and the cooling system is operating at it's maximum capacity. Of course, as the coolant temperature climbs above 94C., the capacity is also increased, so it's a bit self-regulating once the 'stat is not in equation.

The purpose of the thermostat is to "enforce" a minimum temperature. Considering that an 80 degree thermostat only begins to open at 80 degrees, and does not fully open until 94 degrees, the expectation of an 80 degree operating temperature is completely unreasonable.

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When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

I believe this is mostly due to the fact our Mercedes have actual working temperature gauges that, when all is working properly, give quite accurate readings of engine/coolant temperature; whereas just about any newer car you'll drive has nothing more than an idiot light with a needle. I'm glad Mercedes installed a working gauge rather than a dummy, I like to know that my car is running at a given temp under given cirumstances.

Actually, the OP would be better with an idiot light, unfortunately. When that gauge swings up to 110°C., he behaves like a scared rabbit. The engine is fine..........the coolant is fine.............HE is not.

I think this thread should help ease his fears a bit. Your point about cooling system capacities and the thermostat's function is a good one. I have always noticed my 606 can swing between 85c-100c quite easily if it's hot out and the AC is running, but it doesn't seem to surpass 100c no matter what I do or what the ambient temps are. It just goes to show how well Mercedes did infact engineer our cooling systems and engines. 100c is an efficient and safe temp and you really have to try hard to get most of these rigs to exceed 100-110c once that thermostat is fully open. It just tends to freak people out when they see that gauge actually move, rather than sit "harmlessly" in the middle of the temp range as it does on most cars.

First of all thanks for all the input......

Bottom line though... I agree running at 105 C to 110C or 230F may not kill the motor if incidental and gets to cool off say on a down hill run afterward. However clearly the system is taxed if it is continuously running above 100C – 105C, and sure is not the way it should be running all day. Add some extra hills and yes I’m getting concerned (Please drop the idiot inferences suggesting we play ostrich lol).

See.. my goal in these hot environments is to have the motor running in a manner that when I hit a good grade I have the capacity start well below 100C & to run upwards or over 100C….not start there!

Mercedes did install “Tropical Climate” set ups for other markets needing it to keep these jobs running in the 80C to 95C range…yes even with the AC on. Apparently not in the US Market 603 years.

So in summary what I am searching for is a way to keep the motor cooler during these scorching months here in the South West Desert (as in other regions) where hot and dry is really hot and clearly not incidental (Yea I too have read the “bulletins” that say its ok to run it almost to the Red Zone but not in my car I don’t)

Anyway I have to agree with Hunter here and work to get these temps down by helping the cooling system out with steps like taking the trans cooling function out of the circuit and handling it differently, etc. And that it is important to remember that at high mileage there is more friction / heat being generated by older parts (even rebuilt).

Spoke with the folks at the MB Classic Center in Irvine today who agreed & shared several ideas and suggested I swing by tomorrow. I’ll share their thoughts with y’all asap.

Thanks...Rob

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1986 300SDL 440,xxx

That solution might be a good one for you. I am not aware of anyone else trying it for this vehicle and would be very curious as to what you determine if you implement it.

Please bookmark this thread and return to it if you to make that modification.

Good information, useful to think of the thermostat operation that way.

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Chief

1991 350SD

I agree that those temperatures won't damage your new head, but they are still higher than they should be for an OM603 with a properly sorted cooling system.

I've posted my temperature data here. Hopefully some others will post and we can all learn what "normal" is.

Brian: If my memory serves me correctly you have had 2-3 OM603s. What did your temp gauge read when you were hyper-miling at 62 mph? Yes I know your recent mileage thread was with an OM617, but I'm going to assume you drove the SDLs the same way.

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1987 300TD 309, xxx 2.8.2014 10,000 mile OCI


Be careful of the toes you step on today, as they may be connected to the ass you have to kiss tomorrow. anonymous

“Be who you are and say what you feel, because those who mind don’t matter, and those who matter won’t mind.” Dr. Seuss

The 80 SL/SLC uses a 75C thermostat. It use to state it in the listing when looking up the part. now doesn`t show it.

Maybe this thermostat will help.

Charlie

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there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works

A lower-rated thermostat is never the solution to an overheating condition, real or imagined.

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When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

A lower rated thermostat will buy time until the engine reaches temperatures that make the driver uncomfortable.

With all due respect....

1) Why the condescending comments...I mean "really". Please give a direct answer why they seem to be required!

2) Why does MB and many other mfgs offer a 80*C & an 85*C thermostat versions for the 603 if it aint gonna mean a hill of beans in the end? Furthermore "Tropical Cooling" systems for arid climate markets with 70*C & 75* thermostats. And ya we understand optimum combustion, smog control, fuel economy etc. Please explain!

P.S. I think it would be safe to say we'd all love a brand spanking new factory motor and cooling system if dropped in our lap at no charge.

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1986 300SDL 440,xxx

Kindly review the three posts that I have made in this thread (while trying to help you at no charge) and let me know what you find to be condescending.

Then help me understand how a fully actuated 75* thermostat promotes cooling any better than a fully actuated 80* thermostat. Presumably, both would allow for the exact same degree of coolant flow to the radiator above 94*. So, if the two thermostats perform exactly the same at the upper end, how is is a lower-rated thermostat going to reduce a 100* coolant temp any better than the higher rated one? 100* is outside the range of regulation for either thermostat.

What is your coolant/water ratio?

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When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

I don't think tango was condescending, but Brian Carlton certainly seems to be at times.

That said, around here I think you have to take the good with the bad.

Some of the guys are crusty (and, in fact, are quite proud of it), but they know their stuff.

I think the crustiness must come from a lifetime of keeping old diesel Benzes running. It'll probably happen to me sooner or later.

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Lots of diesel W126s in the past
Current: 1991 Toyota 4Runner with an OM603