Who's running +100 C at high speed on hot days?
 

Maybe I'm asking more from the car than I should be, but when it hits 95+ deg F out here, I can't make more than 70 mph without the water temps climbing towards 110 deg C.

Everything's in tune; valves adjusted, tires inflated, EGR's "fixed", new thermostat & fan clutch, flushed the coolant, cleaned the radiator.. but I'm still running hot at high speed. The car's always done it too, so it's nothing new but..

I like going fast :D

So I'm thinking about buying a 500SEL radiator and mounting the oil cooler under the bumper (I had AN fittings TIG-ed onto the oil cooler years back, so it'd be easy to move).

The V-8 radiators are thicker and about 15% more cooling area. If I can run 70 mph at 100 C, then that should mean I could run 80 (speed of traffic on I-210) at 100C with the new radiator.

Thoughts?

Something isn't right. The only time it should get to 100*c+ is with the A/C on in very slow traffic.

70mph with 95*F air temp should not cause overheating.

Sounds like your radiator is clogged. How old is it?

You should be able to run pretty much WOT and not get above 100C.

Yup, my 300D used to do that (up to about 105C) until I replaced the radiator. With the new radiator, I can't get it above about 95C.

you say you cleaned the radiator... do you mean you took it out and physically pressurewashed it from the fan side to clear ALL the debris from it? cause if you didn't, you did not clean it well enough. also after you have pressurewashed it for debris, you need to soak it in some good bug dissolving detergent and rinse well.

next be sure you acid flush the entire cooling system. with some good rinses in between... follow the procedure described here. be sure and degrease well first, and rinse well after the degrease from the block drain twice at least...
next verify you have a NEW GERMAN 76°C thermostat. NEXT verify your water pump impeller has not disintegrated...

You should also update to the later plastic fan and smaller pump pulley.

Replace the radiator cap. Do you have coolant leaks? Heater smell funny?

old cars like these
 

have often at some time in their past been run with straight water for a summer. While it will work for a summer it causes so much rist in the block that it is hard to get them clean enough a few years later to cool properly. And lots of thermostats aren't very accurate or stick part way open.
And then that thing about water pumps disintegrating - once took one apart (off an old international harvester school bus) that had almost no trace of the impeller blades left... just rusted away.... I'm guessing it was run on straight water or very old antifreeze with no rust inhibitors left in it.

on another note, I just got through pulling the block in my 85 parts car... and thought I'd pull the VP and WP... the impellers had a coating on them like teflon... is this normal? the replacement WP I bought for my SD was plain steel. do the OE WP's have teflon or some kind of paint on their impeller blades?

Could just be hardened slime or oil.

no, it was a very clean block, and the impeller was pristine as well as the rest of the block. (I couldn't believe how clean the water chambers were, the volute of the WP was shiney!) I am sure there was a factory coating on this thing. I will take a pic tomorrow sometime.

Buy a new radiator.

I did a new water pump about 4 years ago, never ran straight water, and there weren't any of the telltale rust stains. The thermostat was a new Behr, radiator cap replaced a couple years back but there's no leaks.

What diameter is the smaller water pump/fan pulley?

Radiator scaling/clogging sounds like it's the most likely at this point. It looks like it might be original.

Thanks guys!

Wow, original radiator?? Change it before it leaves you stranded.

WOW!! Original Radiator on an 82.. Too Cool.. or Too Hot.. LOL.. Couldn't resist. Let us know what happens when you replace the radiator. Good Luck.