My 1975 300D will be driven through the desert in about a week with temperatures expected to reach between 110 to 115 degrees farenheit. The car is running great and I've recently gone through it in preparation for this trip. The water pump is new, radiator is fairly new (about 15K miles since it was replaced) and I'm running distilled water/Zerex G05 at 60/40 plus Water Wetter. The coolant temperature keeps between 175 to 185 in 90 degree ambient temps. It's currently fitted with a Sanden 508 clone a/c compressor that's blowing ice cold. I'm going to fill the tires with nitrogen.

Does anyone have experience driving a naturally aspirated OM617 in 110+ degree temperatures? How do these cars do in extreme heat? I don't foresee any hill climbs at these high temperatures, is it reasonable to expect the engine cooling to be adequate or would it be wise to rig up a radiator misting system?

Watching this thread, my experience stops in the high 90's which was no problem in a 220, 240 and 300.

Idling and long extended hill climbs are the stressors.

What weight oil are you running?

Good luck!!!

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

I run Delo 15W-40 in it. I thought of going with 20W-50 but I don't have a local source and the car always ha good oil pressure.

Having driven through that kind of heat my advice is don't. Plan your trip to drive at night. if you absolutely have to drive during the day in 110 to 115° heat, prepare for a breakdown. Bring water, ice, umbrellas for shade, multiple cell phones with fully charged batteries, AAA card. Think about the people you're going to have in the car with you. Can they handle sitting in the sun in 115° for 2 hours while they wait for a tow truck? This is the type of weather that kills. Depending on your age and the health you are taking a big risk here in a car that hasn't experienced this kind of weather before. Please take this seriously. Extreme heat kills more people than hurricanes tornadoes blizzards, etc combined. Plan for the car breaking down in the worst of it.

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CENSORED due to not family friendly words

tjts1, thank you, sage advice. I won't be going on the trip and the two travelers are healthy and accustomed to heat training. They'll be well prepared and will do most all of the driving before and after the heat of the day. I have tried to talk them out of this leg of their trip to no avail. My job is to prepaid the car as best I can and be available with my tow vehicle and car trailer if their 200 mile AAA tow isn't going to be enough. Where we live we see a handful of days over 105 degrees each year and have had a couple reach 112. While I was working on the car two weeks ago it was 107 one of the days. I just haven't driven it much on the hottest of days to get a feel for how it might preform.

First of all, plan on the trip taking a longer time than expected. Figure on a cruising speed of 65-75 MPH. Don't think you are going to be running at 75+ MPH down the road. Don't believe that hogwash of, "Well, these cars are designed for the Autobahn and they run all day at 200 KPH" because that is B.S.. The gasser Benz'es will do that but not the diesels.

Drive by the temp gauge. You'll quickly discover the speed the car runs best. As the temp rises, slow down until it stabilizes.

Carry extra WATER in the boot, NOT coolant. Ya can't drink antifreeze/coolant.

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“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
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Hope this isn't horribly off-point... but, it's reasonably hot & humid here in New Orleans. Our little OM617 group which was fairly active from 06-14 found after a lot of testing/flushing/new parts etc., that tossing the engine thermostat out the window worked pretty well here with folks seldom hitting 100C in 100+F and very humid conditions.
Of course, keeping radiators (and, condensers) free of debris and a good fan clutch is quite helpful as well. We also opted for the Maradyne 142K Low-Profile (225 watt) High CFM/Static Pressure aux fan. Not exactly the purest approaches... but, compromise occasionally has some benefits.

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'84 300D (211k) *New*... (Wife's)
'85 300TD (174K) 10th Year... (Mine)
'96 F-350 7.3L Dually (149K) Since New
'85 300D (156K) ~~~Wrecked~~~ Damn it! (parts)
'84 300D (176k) ~~~Wrecked~~~ Damn it! (parts)

Thank you for this highly practical advice. Six gallons of bottled water plus one gallon of coolant premix are being packed in addition to a cooler with additional water and drinks for the two high temperature days of the trip.

Do you mean running without a thermostat whatsoever? If so, how much did you see that reducing operating temperatures? Thanks

There is no NA diesel that likes heat, they will however run but they'll be slow and down on power compared to cooler days. If driving in high heat brings engine temperature creep then slow down, and don't expect the AC to be able to handle the situation in the worst of the day.

My recommendation is to start the drive early in the morning or late in the day (after 2/3). The 9-3 (or 10-2) window is the worst time to go and the most stressful. And if it's a long day of driving I would start very early if possible, before daybreak.

As others have said, prepare..not just for your own breakdown but in case there's been an accident that brings traffic to a standstill.

Steve

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Steve A
92 W140 OM603
97 VW Jetta TDI
90 Passat variant TDI 6 speed MT
94 Chevy K1500 6.5TD
05 E320 CDI
+ others

Are you talking be about going to Death Valley.. high dessert? I’d advise to go early in the morning. There are very steep hills there .. the hwy will go from sea level straight up to 5k feet that really bog the car down. You’ll be running the heater a lot. And then there’s that part where your in the bum **** middle of nowhere.

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1993 e300
1995 e320
1994 e320
2006 s500 4matic
2004 Jeep wj overland
2001 Ducati 748
2004 Honda shadow aero

YES, No Thermostat. About a 10-12C drop on average. All other measures for free air/coolant flow should be followed (not counting the Maradyne aux fan). My experience is that these vehicles @ 40+ plus years old are very ambient temperature sensitive and any restriction in heat transfer is deleterious to one's enjoyment. Put it back in later... or, not.

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'84 300D (211k) *New*... (Wife's)
'85 300TD (174K) 10th Year... (Mine)
'96 F-350 7.3L Dually (149K) Since New
'85 300D (156K) ~~~Wrecked~~~ Damn it! (parts)
'84 300D (176k) ~~~Wrecked~~~ Damn it! (parts)

So, lemme see if I've got this right: You're LENDING your 45+ year old car to a couple friends for the purpose of them driving it through, possibly, some of the WORST conditions/weather the car has ever experienced. Is that it, in a nut shell?
A couple other questions, just off the top of my head: Are you mad at your car? Do you want to get rid of your car? Are you mad at your friends? Do you wanna get rid of your friends? And, finally, why are you doing this?
Bottom line, IMHO, never lend your car to friends (if you like your car and want to keep your friends). Even under the BEST of circumstances, this sounds like a very bad idea. This situation seems even worse than that. No one will take care of/drive your car the way you do and the way your car is accustomed to.

Brutishly Honest! On Point! Thoughtful.. and, Entertaining!

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'84 300D (211k) *New*... (Wife's)
'85 300TD (174K) 10th Year... (Mine)
'96 F-350 7.3L Dually (149K) Since New
'85 300D (156K) ~~~Wrecked~~~ Damn it! (parts)
'84 300D (176k) ~~~Wrecked~~~ Damn it! (parts)

I can agree with this...even the best of friends manage to do something wrong...like when I had new seats in my Jetta tdi and a friend in the passenger seat dripped burger juice on it...and then looked at me and said, "what?" like nothing had happened....

If you're set on doing this then be prepared when the car comes back on a rolloff.

Steve

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Steve A
92 W140 OM603
97 VW Jetta TDI
90 Passat variant TDI 6 speed MT
94 Chevy K1500 6.5TD
05 E320 CDI
+ others