its starting to get warmer here and im already seeing 100C temps.

i know ppl have said fan clutch, and i plan on replacing it because when i shut off hot (110C) i can easily spin fan by hand. I guess it should be locked to engine at that temp. so i will replace. new water pump, tstat.

but the damn thing will run 110C on hot days cruising at 80 mph. Seems like that would be far more air than the fan could ever pull. Ive flushed hell out of system, running G5 coolant. Ive had rad out of car and thoroughly flushed it/back flushed it/sideways flushed it/ect... water pours out of it just as fast as it goes in. Its clean, but does have 286k miles on it.

guess i should start with fan clutch and work from there but why would it still overheat on highway ?

this heat is causing the D2 to vaporize at the billet wvo valve, so when i run for a long time on wvo then try to switch back to D2 it stalls until the cold D2 comes in. problem only happens from mid april to mid oct.

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Paul
Benz-less
I need an SDL !

the gauge could also be faulty. have you measured the head temp with an infared thermometer?

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1981 300SD 512k OM603

Are you willing to spend 3 hours work with a decent (but not 100%) chance of lowering the temps by 10°C?

I wonder what Bryan has up his sleeve but in the mean time I'll say what I think about this.
Just because water flows in and out of the rad doesn't mean its ok. If the tubes in the rad get a layer of crud built on them over time, as happens in a radiator, the thermal transfer capability diminishes until the heat builds up in the block and you have overheating. If the radiator is over 10 years old, just replace it. Remember, you are gambling with the aluminum head on a 603 engine and it is well known for its tendency to warp or crack (or both) if overheated. A new rad is a LOT less than a replacement head.
DDH

er, well, I re-read the post where you admit the rad has 268K on it, right? GET RID OF IT!!!!!!!

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

I added viscous fluid to the fan and it seemed to help marginally. I drive up steep mountain grades in the Arizona desert and have seen about 105 max with air on. Check my posts back in '05.

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Dan
1981 240D
1987 300D Turbo
1973 220
Das Beste Oder Nichts

I am...sigh...knuckles still bruised from the blower motor replacement but Im persistant, and I want this car to make it thru the summer.

Rad is $$. Hate to replace a good 1, but I hear what your saying. Must be some way to flush out the crud, like I said best I could tell it was clean. I'll shoot it with the IR thermometer, see if theres any cool spots.

__________________
Paul
Benz-less
I need an SDL !

I am certain either it has scale (which CAN be reduced using citric acid flush) or the plastic necks are ready to crack and leak.
There are flushing machines that attach to a cooling system and run a while to gradually filter the acid out of the system, I never used one but have done citric flushes on engines with cast iron heads. I would not want to do that on my 603 (aluminum head), I replaced the original radiator at 250K because it was running hot. On my second car (a lien sale) the PO had already overheated the engine and the head cracked that's why the car was only $475 That radiator went promptly into the waste can.
What you have to realize is the 603 is a hot running engine, there is very little margin for error. I ran an '87 300D without the AC condenser and could see a lower running temp while going uphill.
I also use and recommend going to the 606 fan upgrade (plastic 8 blades instead of the metal what- 5 blades? fan)
In addition, you can buy a lower cost thermoclutch for the later fan, it fits in the same way but the screws are different so if you do go that route be sure to pick up the right screws from the dealer.

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

read this post:
Fan clutch issue 603????

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

read this too!
1987 300TDT Overheats on long hills

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

gsxr's excellent words on that subject:
1987 300TDT Overheats on long hills

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

more of gsxr's wordds on this too
1987 300TDT Overheats on long hills

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

Yep, rad is big $$ and you might be able to get away without a replacement if you do the following:

1) Remove the radiator from the vehicle

2) Purchase some industrial "condenser cleaner". Put the radiator on a flat surface and brush the condenser cleaner into the fins...........forcing the cleaner through the fins until it drips though on the opposite side. Let the cleaner do the work for a couple of hours.

3) Get an air compressor or a pressure washer and blow the fins clear of all debris and residual condenser cleaner. If you're using a pressure washer, be extra careful not to bend the fins with it.

4) Thoroughly flush the fins with water.

When done, pick up the radiator and hold it up to the sun. Look through the fins and see if the debris has been eliminated...........should be a clear view right between each air passage. If you have that............reinstall it into the vehicle. My bet is that you get 10C. from that effort. It seems that nobody is willing to make the effort and the default is a new radiator. Your decision.

thanks guys, i will do a bit more troubleshooting, make sure aux fan does come on (i think it does), ect...

is there anyway to descale the rad once I remove it? i hate to run citric thru whole system, that stuff eats heater cores and heads...i donno, maybe i need it.

yeh between gsxr and brian, all these problems are discussed in detail. if we ever meet 1st rounds on me!

__________________
Paul
Benz-less
I need an SDL !

Remember, I originally asked you...........before providing the solution..........if you would spend the time required. You agreed.

I expect you to follow through with your agreement and do the work. I want to see the results of that work and how much the temperature drops from thoroughly cleaning the radiator's air passages.

im gonna work up to the rad removal, try some easier stuff 1st but im probably headed that direction.

i know the fan clutch is toast, so i guess it will go like this :

1. check the 3 pin and aux fan operation
2. RR fan clutch (was gonna keep metal fan, unless you guys tell me 9 blade plastic is vastly superior?)
3. remove rad and clean it per brian.

dont worry, i wont just replace the rad, i will 1st try 2 clean it. $338 is worth a few hrs time. my exp with that sort of thing is i usually eff up the fins cleaning them. will let you know.

__________________
Paul
Benz-less
I need an SDL !