2007 S600, bought a couple of weeks ago. I fixed a bad radar sensor so now my Distronic works. Fixed the headlamp washer door. But one persistent issue has been the intake air temp (charge air temp). It's typically about 190 F. I can watch it with the MB II scan tool I bought for it. I replaced the intercooler pump. The old one was definitely bad, but the temps have not come down any.

I checked fuse 116 in the rear SAM, and swapped relay Q with one of the others. No joy. I'm about out of ideas. Anyone have any more bright ideas? It's getting warmer by the day, and this is going to get serious before long. I really want to get it fixed.

 

You need to bleed the cooling circuit, or install an overflow tank like detailed here:
https://mbworld.org/forums/m275-v12-...reservoir.html

I had temps similar to yours until I installed the overflow tank and allowed the air to escape, now I'm at 100F-120F.

 

Yep. The system needs a good bleeding. This is one of the hardest systems to bleed

 

Well, silly me. I owe you guys a beer.

I guess it was naive of me to assume there was actually coolant in the system. I put over a liter of water in that sucker before I got even a drop coolant running from the bleed fittings into the tubes I had run down into the filler neck. Yes, I know it's not actually bled yet... but at least it's full, or as much so as I can get it right now, and despite the outside temp being about 15-20 degrees hotter than yesterday I was seeing IAT about 60 lower. Ambient was 92, IAT ranged from the mid-120s up; the highest I saw was 156. It was normally around 132-135, even after a nice little 45-100 MPH pull.

The more I read about the low temp circuit, the more I am in agreement that it's a poor design. I'm sure the designer figured that if the temps stayed within the norm, AND the cap was in good shape, no water would be lost to expansion through the pressure cap. The problem is, that fails to take into account conditions outside the norm. If the cap isn't in perfect working order, or the temps get elevated due to, say, a non-functional pump, everything goes downhill very quickly. In my humble opinion, a properly designed system works when everything is right -- and when as many things go wrong as you can think of. When the system is not performing, it should alert the user. This system does none of the above. There's no expansion tank "just in case"; there's no coolant monitoring, there's no monitoring of the pump to verify that it's running. A DTC for high charge temp is the only indication of what's going on, and the driver won't even know about it.

OK, end of rant. It's like a different car now. Full power under all conditions, including start-stop after a couple of "enthusiastic" short runs. Acceleration was impressive before, it's even better now. And I love the way the S600 does it -- no drama, no roaring or jerking, just an ultra-smooth jump to light speed. I'll see about getting it properly bled and making sure the coolant mix is up to snuff (since I just diluted it with a liter of water), I'm sure it will only get better.

 

Just to follow up... a few days ago, I installed a Wilwood remote reservoir as an expansion tank for the IC circuit. I also installed a new regular radiator cap, to allow it to suck coolant back in as it cools down. All good, but... today, I opened up the cap and found it was low buy a couple inches. I'm guessing I have a leak somewhere. Between this and the effing ABS pump issue, I'm just about done with this car. I had deep reservations about buying a 2007, but it seemed near perfect during the test drive. I am now seriously questioning the wisdom of buying this thing. For certain I'm about at the end of my wrench turning patience.