Okay, dumb question time. If one wanted an accurate (okay somewhat accurate) temperature reading with a surface-mount thermocouple, where would one mount this thermocouple. I have had good luck measuring liquid temps in pipes with surface application and proper insulation in both the lab and in the car, but I don't know if the oil cooler line would be the best place to check the temperature. Any suggestions??

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That sounds normal to me. Temps up to 110C in summer up a major grade are not abnormal, as long as the needle isn't creeping towards 120C (the red zone). On a side note, there is a separate temp cutout for the AC besides the KLIMA. The gray 3-prong switch on the head coolant outlet triggers the electric fan on high at 105C, and kills the AC at 120C (on the SDL). Perhaps this switch needs replacement (about $35). I'm assuming your electric fan is engaging on high at 105C... this switch is almost always dead after 15+ years, I've had to replace it on every Mercedes I've owned (gas and diesel both!) that use this 3-prong switch. (Gassers have a 105/115 and the W124 uses a 105/128 for some weird reason.)




Odd. What oil are you using? Switch to Mobil-1 5W-40 if you're not already using it. Mercedes never did entirely cure this problem, so even with new lifters it may pop up at times. Is your oil pressure 1.5bar or higher at hot idle?




The problem is more that you have R134a than lack of airflow. Tinted windows can help a lot (or V-Kool, if you want to block heat without dark tint). A reverse conversion to R-12 would help but would NOT be cheap or easy. A SPAL fan may not help except at idle, and may actually pull less CFM on the freeway - not sure. You'd need a 150A alternator upgrade to feed that puppy. You can't hear the stock fan clutch roar, in my experience. To test it, get the temps at 105C on the dash gauge, pop the hood, and kill the engine. The fan should come to a stop immediately or turn maybe 1 revolution. Compare this to a cool/warm engine (under 95C), where the fan will freewheel for many turns when you kill the engine. The older OM617 fans/clutches made a LOT more noise and were easy to test by ear, not so with the 603, especially if you have the updated plastic fan from the 606.

You're so right. I'll fix the original post.

Thanks,
Sixto
95 S420
87 300SDL

It hasn't occurred to me that the SDL can and should be driven this way

Thanks for bringing up coolant temp vs oil temp. That makes perfect sense.

Sixto
95 S420
87 300SDL

To gsxr's questions:

- The wiring diagram shows the coolant temp sensor going into pin 12 of the Klima socket. Is there a feed to the PBU as well?

- The fan works on high and low as it should as far as my ears can tell.

- Mobil 1 15W-50 for the last 12K miles except for 3K on Delo 400 after turbo and IP work a few K miles ago.

- Oil pressure drops to 2 bar at hot idle. I don't think I've seen the pointer drop below 2 bar. The gauge jumps to 2 bar when glowing, then to 0 when cranking, then climbs to 3 bar a couple of seconds after catching.

- I didn't know the SPAL had such an appetite.

- The clutch fan stops in less than a quarter turn.

- I'll have to check if the fan is metal or plastic but I'm pretty sure it's metal.

Thanks,
Sixto
95 S420
87 300SDL

- Now I'm not sure about the AC sensor. I thought there was a feed to the PBU but maybe it goes to the KLIMA first. Easy to test - short out that 3rd pin and see if it kills the AC.

- Mobil 1 15W-50 is good stuff. I'd switch to the 5W-40 in the future if you can, Mall-Wart has it for $19.xx/5qts now. I'd pretend you don't hear the lifter, since you're probably not going to be able to fix it. Oil pressure sounds great.

- I think the SPAL pulls something like 20-25A, and the stock 70A unit is already weak. The alternator upgrade is relatively easy, and about $100-$125 total cost. I wouldn't do a SPAL install without it.

- The clutch fan is working perfectly if it stops in less than a quarter turn when hot. If you added silicone, it's probably the metal version.

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Dave
Boise, ID
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If you have an OM603, I'd mount an internal probe in the #1 port, using the existing hole. I ran a 1/8" NPT tap in a few turns past initial resistance, this worked great. Not sure why you'd want an external surface mount unless you have a 617 and don't want to drill...

Over the Grapevine, I can maintain 80mph in my 116 (Modified 617.950) with the A/C on and temperature stays around 185°F all the way.

With the increased boost pressure, fuel and camshaft timing modifications, the engine pulls very well and I don't have to keep it "on the floor" to make the grade.

On our last trip to Lucerne Valley, we drove the 116 between 80 and 110 mph all the way there and back, whenever traffic permitted. We recorded our worst ever fuel economy of 22.4mpg.

No matter what we do to this car, it never dips below 22 mpg.

If I drive it 60-65mph religiously and stay out of the Turbo, I can get 35mpg.

Very pleased with the overall performance...Bert

I have a half-dozen type K surface mount thermocouples lying around, is why. I don't have a probe-type and am not interested enough to want to spend the money for one.

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Keep everything as simple as possible-but no simpler--Albert Einstein