I think yall are worrying too much. We returned to TN from San Diego via Yuma and Phoenix in August a couple years ago. Our 85TD was towing a popup and we saw ambient temps as high as 114 . We ran interstate speeds with no engine temp issues. The only issue we had was above 112, the envirosafe refrigerant in the ac failed to condense and the AC completely stopped working. Windows went down and we kept driving. Once the temp dropped below 112 the ac came back on again.
You have a recent radiator, waterpump, and coolant. Assuming your thermostat is good, I would not remove it.
You will be fine.

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1985 300 TD 448K
1984 300 TD 278K

1983 240D euro 240k
1994 f-250 idi turbo 330K
1986 f-350 IDI
1987 F-350 IDI

1985 JD 1050 4wd
1965 IH 3660

Not sure why a non-turbo would be worse, other than perhaps the cooling system isn't as adequate. Does yours have an oil cooler?

As one data point, after changing to Evans Waterless Coolant in my 1984 300D, I was a bit concerned on it having a lower cooling limit, since 50/50 coolant works better when new, and straight water even better. The advantage of Waterless is that whatever it does new shouldn't degrade since it should never get corrosion. My son drove it over "The Grapevine" on I-5 South (Tehachapi Mtns, north of LA Basin) on a 110 F day. That is a steep climb for 10 miles, and I understand some manufacturers qualify their new coolant designs there. He said the dash gage hit 101 C right before the top, then dropped. Otherwise, it normally holds at 82 C. I recall about the same long ago with 50/50 coolant.

The coolant temperature will creep up slightly even before the T-stat goes wide-open. That is because for it to open more, the coolant must be hotter. Engineers term that "proportional droop" in control theory. But, from testing T-stats in hot-water, I recall they are full-open by 90 C. As the temperature rises further, the radiator can reject more heat, but the red-line of 120 C will come soon once full-open.

The easiest way to reduce the heat load, is to simply slow down from 65 mph to 40 mph and drive in the truck lane. It is only 10 miles to the top anyway. Ditto when pulling a trailer, where overheating and overstressing the transmission is more a concern than the engine. Otherwise, flushing hasn't made a noticeable difference on any of my vehicles over decades, but good to try. More commonly, the problem is a tiny leak to lose coolant. When replumbing, I use silicone heater hoses in all my cars, which lasts much longer.

I did have an overheating problem in my 1985 300D, both with Evans and with pure water (testing to fix the problem). The temperature would creep up to 100 C when idling at long stoplights in summer, but fine once driving. After trying many things over several years - 2 water pumps, removed w.p. housing to search for obstructions, several fans and clutches, flushed radiator, used radiator flushed w/ citric acid, and such, I finally tried a new radiator and no more problems. The prices dropped from $350 to $120, so I jumped on it. The old radiator had a thin film of orangish "metal mud" on top of the tubes. It brushed off easily, so don't know why the flushing and even running a long grill brush inside the top reservoir didn't loosen it. Could also be the new aluminum radiator cools better than the OE copper.

BTW, I recently fixed overheating in my 1996 Plymouth by flushing the radiator. A bunch of tiny dark particles was in the capture bucket. I suspect from having used DexCool long ago, then flushing and switching to green coolant. To be safe, I drove it a week on pure water w/ 1 lb citric acid, then flushed several times before green 50/50.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans

I'd replace the V-belts and thermostat as well. Transmission fluid recently changed? Check level. Engine oil - check level.


Tires at least good, aired up to 32 lbs. when cool. Check youvr spare for 32 lbs. of pressure too.

Watch your engine temperature. If it gets too high, cut the AC. When exiting the Interstate highway for a bresk or fuel, let engine idle a full 3+ minutes to let it cool down. If just getting fuel - let idle. It's hard on the engine starting and stopping it.

Turning the heater on max for 20 seconds or so is usually good for a noticable coolant temperature drop.

You just have to think holistically about how the system works, and where you can remove heat. Once you get past the obvious devices; fan, thermostat, misting, etc, you have to examine the rest of the system. Fresh oil is beneficial. So is a higher water concentration in the coolant mix; water dissipates heat better than most coolants sold.

Mum lives in Phoenix and I used to regularly drive, and ride there on my motorcycle, from LA to see her. The advice to do it at night is probably the best advice.

I'm happy to report that the desert portion of this trip was an absolute success. They did as much of the driving as they could in the mornings and evenings. The hottest temperature they drove in was 108 degrees but they drove for more than ten hours at ambient temps between 100 and 104 without any trouble. It was only on a couple of grades that they turned off the a/c in addition to slowing down to reduce engine temp. Purely by luck, the weather ended up being cooler than it had been predicted to be in the weeks ahead of the trip.

From 200 feet elevation in the desert they have headed to the Sierras and just minutes ago crested the Kingsbury Grade at of 7,300 feet elevation. While a bit on the slower side, the 1975, W115 300D is, even at 46 years old, a capable vehicle that's an absolute pleasure to drive.

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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.”
― Brian P. Cleary, You Oughta Know By Now

Good to hear! Sounds like a memorable trip in a fine motorcar.

Very good! Impressed.

-H

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1976 Mercedes-Benz 300D, Colorado Beige / Mahogany
www.hmclever.com

Glad to learn all went well on the trip. Congrats! I think you knew, all along, there was nothing to worry about. I guess some folks on here (myself included) were thinking of the worst case scenarios and what could go wrong. More than likely, you were quite entertained by all the "Cassandra's" foretelling doom and gloom of your great car and the tragic end to the brave journey (lol). These automobiles are truly amazing and although my '83 240D is "nothin special", it continues to impress me every time I'm behind the wheel. Cheers to your great friends and great car!

The thing I kept from y'all is that the driver is my 17 year old daughter and the passenger is her 17 year old best friend. They started planning this road trip when they were 13 years old. As her mom, I put countless hours into replacing anything on the car that was remotely questionable. Even though I have a Gen II Cummins tow vehicle and a car trailer at the ready, I really want the trip to go well for them as well as not wanting to have to go make a rescue many hundreds of miles away. They are now 1,900 miles into the trip and they just spent the afternoon, outside of Portland, visiting with the generous man who owned the car from 1999 to 2016. When she turns 18 I'll transfer the car's title into my daughter's name but I'll always be her indentured mechanic and curator of the car's preservation.

This thread gave me some great ideas that I incorporated for extra peace of mind and I appreciate everyone's participation. I kept the driver's demographic identity vague because I thought I might get beat up on if I divulged that a kid, and a girl at that, was going to be behind the wheel.

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Like a fine M. Night Shyamalan movie, the unexpected twist at the end of the story was perfect. I have the 1968 version of your car, and hope that my daughter shows interest in it when she is of driving age. Well done.

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1968 220D, w115, /8, OM615, Automatic transmission.
My 1987 300TD wagon was sold and my 2003 W210 E320 wagon was totaled (sheds tear).

Touche, indeed! Excellent plot twist! Beautiful car. Had "we" seen that, first, I'm sure many fears would have been allayed. Wonderful story, especially the visit with the PO, and a great "cast of characters" (including the vintage Benz). The car looks new. No doubt it's mechanically as well as cosmetically "tip top". My hat's off to you, your daughter and her best friend. This saga would have made a great documentary (as would so many of the stories and experiences on this forum). Cheers, to all!!

Great story. Congratulations to your daughter and her friend. A good tip about turning on the heater if the car starts to over heat. The heater core acts as an additional small radiator. While the passengers will feel the extra heat for a short time, it will help to drop the engine temperature.

Terrible advice, DON"T DO THIS! The thermostat is a bypass type, which means when fully closed, all the coolant is forced to stay in the engine circuit, and when fully open, all the coolant is forced to go through the radiator. Remove the t-stat, and now the coolant decides on its own which way to go. It may decide to stop going through the radiator, and then you overheat. By pure luck, no one in the group has suffered this terrible fate.


LEAVE THE THERMOSTAT INSTALLED, and think about carrying a spare as well as a spare radiator cap. Test new thermostats before installing, it is possible to get a bad thermostat right out of the box new.

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Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC

This a direct quote from post #10 on page #1 of this thread, with the added link. "Samebeef" is a spammer account.

http://www.peachparts.com/shopforum/4176712-post10.html

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- Greg -
1973 220D, The Prodigal Benz
1974 240D