In the summer my 85 300SD is running right on or a little below 100 c. At what temp. will these cars steam at? Some people say its fine to run at this temp. some say not should I be concerned?

According to the owner's manual, steam will happen at about 125C if everything is in working order. Mine runs 100C when warmed up at pretty much all times. I've been running it in this condition for about 30,000 miles.

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.

100 c is what both of ours run since we replaced (and re-replaced) the thermostats. It's been over a year, and they both seem to be happy and well-adjusted to their new temp. Should be fine.

I run a cooler thermostat my temps stay a 80c

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1999 w140, quit voting to old, and to old to fight, a god damned veteran

If your coolant ratio is correct there shouldn't be a problem running 100C but I would take out your thermostat and test for when it opens in a pot of water on the stove. It should say on the thermostat what temperature it is supposed to open at. My 190 was running at 101C almost constantly so I flushed the coolant and checked the thermostat and sure enough, it was opening at 96C instead of 85C. I got a new one from my mechanic then installed it and have been running around 90C ever since.

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Current: 1975 450SEL, 83 300D, 88 Yugo GVX, 90 300D OM603 swap, 91 F150 4.6 4v swap, 93 190E Sportline LE 3.0L M104 swap, 93 190E Sportline LE Megasquirt, 03 Sprinter, 06 E500 4Matic wagon.

I agree, both my cars (87 300TD w/OM603 and 98 E300DT w/OM606) both reach operating temperature at 80 c and pretty much hold there. I have occasional brief excursions to 90-95 depending on load and ambient.

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The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

100°C would be what I would expect to see climbing a hill at 60% to 70% throttle opening with the A/C on.

This is an acceptable temperature under these conditions.

My Dad's W126 runs 175°F to 182°F on the highway at cruise and only sees 212°F (100°C) under heavy loads and then the temps drop right back down when he lets up on the throttle.

He is running the stock MBZ plastic/Aluminum radiator, FWIW...

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Did you just pass my 740 at 200 kmh in a 300SD?????

1978 300SD 'Phil' - 1,315,853 Miles And Counting - 1, 317,885 as of 12/27/2012 - 1,333,000 as of 05/10/2013, 1,337,850 as of July 15, 2013, 1,339,000 as of August 13, 2013



100,000 miles since June 2005 Overhaul - Sold January 25th, 2014 After 1,344,246 Miles & 20 Years of Ownership

No issue as far as I am concerned on an all cast iron engine. It may be even superior to running at eighty degrees. Also the temperature reading circuit may be a little off calibration probably as is as old as the car.

Basically if you never boil over I would leave it alone.

Just something I have noticed over the years, people seem to pin point all the problems of higher temperature to either the water pump or thermostat..... While people always over look the simpler things....the radiator cap and fan clutch.....the springs on radiator caps wear out and the seal cracks.....the fan clutch throws its oil and doesn't lock up at the right temperature.....

Finally I also believe that if your running the original radiator, people should consider replacing it after 30 years....specially now that most are become NLA.....we forget that there is a transmission cooler at the bottom of the radiator....all the sediment falls to the bottom of the radiator, thus its harder to cool the transmission thus over heating and causing temperature raise....and if the transmission cooler leaks, then it can kill the transmission.....just a few observations...

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Good points, when it comes to cooling, airflow, airflow, airflow, airflow....

I cannot force my ratty old W116 over 180°F (with 71°C thermostat) even going up the grapevine, in 100°F ambient temps at 75% throttle with the A/C on, so I don't know how I could work the motor any harder than that....

To the OP:

Confirm what your gauge is telling you, then report back to the forum....Robert

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Did you just pass my 740 at 200 kmh in a 300SD?????

1978 300SD 'Phil' - 1,315,853 Miles And Counting - 1, 317,885 as of 12/27/2012 - 1,333,000 as of 05/10/2013, 1,337,850 as of July 15, 2013, 1,339,000 as of August 13, 2013



100,000 miles since June 2005 Overhaul - Sold January 25th, 2014 After 1,344,246 Miles & 20 Years of Ownership

One more point that people also forget about, is to flush out your heater core....when ever someone does a coolant change, they never open the mono valve and drain out what's in there...on the newer Mercedes there is also a screen on the mono valve that gets clogged.

Granted I have the evil servo unit, but my cars coolant was very clean and bright....then I removed the heater hoses, I literally had the hose hooked up for a half n hour before clean water started following.



This I also believe can contaminant your coolant and cause temperature rise.

And also remember a good tip, if you start seeing a temperature raise....turn the heater on!

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Very good points!!!!!

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Did you just pass my 740 at 200 kmh in a 300SD?????

1978 300SD 'Phil' - 1,315,853 Miles And Counting - 1, 317,885 as of 12/27/2012 - 1,333,000 as of 05/10/2013, 1,337,850 as of July 15, 2013, 1,339,000 as of August 13, 2013



100,000 miles since June 2005 Overhaul - Sold January 25th, 2014 After 1,344,246 Miles & 20 Years of Ownership

No you should not,given that you dont see 110C under load.
cast iron is very tolerable but if your coolant is weak (old,dirty or bad % mixture)
it can boil.

if its steady 100C I would try to burp cooling system to be sure and leave it alone....


.

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w126 500SEC gen II euro, powered by OM617 turbo stolen from 84 300SD 2.88 diff,EGR blinded
next wish/project: w114 coupe OM603 powered

I think there is some variation in thermostats, and many of them will put the car's operating temperature around 100 C. To the folks with cooler running cars, what kind of mpg are you getting? I get about 24-26 flogging it hard, and up to 30 if I'm easy on it.

I ask because I used to have an old Lincoln in which I ran 'stats from 160 to 180 F, and I lost a couple mpg with the cooler one. I also lost hot heat in the coldest part of winter, which is what prompted me to switch back to the hotter one.

__________________
Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.

Just something I have noticed over the years, people seem to pin point all the problems of higher temperature to either the water pump or thermostat..... While people always over look the simpler things....the radiator cap and fan clutch.....the springs on radiator caps wear out and the seal cracks.....the fan clutch throws its oil and doesn't lock up at the right temperature.....


Can't let this one go. The radiator cap has nothing to do with coolant temp. it only increases the boiling point of the coolant.