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Discussion Starter #1
My '99 is blowing nice cold air on the driver's side and HOT air on the passenger's side. After reading the forum I dismantled the duovalve, cleaned everything up, lubricated and reassembled (a very easy job). Unfortunately, I still have the very same problem. Is it time to replace the whole duovalve assembly ($137.74 at AutohausAZ) or could there be another problem?

MDBenzguy (MDBenzgirl's husband)
 

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I relented and purchased a new duovalve. Before I install it, how much coolant can I expect to loose during the process?

MDBenzguy (MDBenzgirl's husband)
 

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i have the same problem but im blowing cold on driver side and warm on passenger side. imma about to try and clean mine. let me know if the new one fixes the problem. and u wont loose a lot of coolant. i had the plastic T break on me and it was a mess because i was driving like that for a while intili notice my car smoking from coolant everywhere, but i caught it before it overheated. just have sum towels just to catch it
 

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Update... The dealership sold me the wrong part for the duovalve. At first I was miffed but in desperation, I tried the A/C one last time before ordering one online. (BTW, I noticed AutohausAZ.com lists the wrong part for a 1999 SLK.) Lo and behold, the A/C was working great and both passenger and driver sides were blowing nice, cold air that could be adjusted. I suspect the cleaned duovalve needed a little jiggling to get it operating. It's been a few days now, and everything seems to be operating smoothly! That's almost US$300 I saved!
 

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oo wow thats good.. what did u do? i took mine apart, it had a little corrision on it and rust on the medal things with the spring on it. i got some of it off. Did u take the whole thing a part , like to see the medal coils too?
 

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I followed the instructions found in the forum. Once you take out the plungers, pry the silver plate off and the brass valves will be underneath it. I rinsed them off with water and put everything back, lubricating the plungers. All in all, it was about a 15 minute job. Good luck!
 

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Today my valve decided to stick again. Eventually it worked fine but I think I might need to take it apart again and give it a more thorough cleaning. I noticed a little bit of corrosion on the plungers the first time and I didn't clean them thoroughly enough because I feared damaging them. I will try a tad more elbow grease next time.
 

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If there is corrosion, spend some of that money you saved, on new coolant!!!! - will save you heaps in the long run

Oberoi
 

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New coolant is tops on my list. We have an auto hoppy shop for DIY'ers close buy and can rent a bay for $6/hour which includes fluid disposal. Since this is a new purchase, I like to change all the fluids and filters at one time since I don't know the habits of the previous owner. I'm gathering everything together and I hope to be able to get it done this week or next. Now that you brought it up, is there a commercially available coolant I could use or does it have to be MB?
 

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Now that you brought it up, is there a commercially available coolant I could use or does it have to be MB?
Congratulations on your work to date - really impressed with how many stealerships you are sending to the wall!!!

The Benz coolant is pretty cheap ($12 here) and frankly worth the money to be sure (zerex have an equiv. in USA apparently - Zerex G05)

The Benz stuff is blue/green and will stay crystal clear for at least 3 yrs

The important thing is not to mix coolants if you are not sure what has been used - flush with water a few times to get all the old stuff out (just by undoing the red plug below the radiator - no need to undo the plug on the block necessarily if you run it after each refill - get it hot enough for thermostat to open a bit)

If you are really picky, use distilled or de-ionised water (supermarket- cheap) for the last flush and refill

This job is easy enough to do at home - you'd save the cost of the fluid in hoist fees!! (just don't let the dog drink the old coolant!)

Oberoi
 

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Discussion Starter #11
I took apart the valve yet again. I wiped evrything down thoroughly, to include the cylinder bore where the small pistons move and also where the brass valves seat. I then lubricated everything with silicone spray. So far, it's working like a champ. So far, I've spend a total of US $16.50 on getting my little SLK running like a champ. I will be replacing all my fluids and filters next week and hope to have it in tip-top shape. I get great satisfaction sticking it to the "stealership" whenever I can!
 

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Use only the genuine Benz fluid or Zerex G05 (Zerex makes the MB fluid). The Zerex costs about half the MB price if you buy the undiluted type. The color is NOT green in the USA, but a yellow-orange color. Using distilled water is essential - you don't want to add all the crappy minerals and chlorine in tap water into your radiator.

Distilled water only cost about $1/gallon at any supermarket, so buy 4 or 5 gallons and flush the system 2 or 3 times with the distilled water as well. Then pour the undiluted Zerex or MB fluid equivalent to half of the system capacity into the radiator and fill up with distilled water. You will notice that it takes less than half the capacity of the distilled water, since there would still have been water left in the engine passages and the heater core. That is why you want to use the undiluted version of the fluid, since the remaining water would just dilute the fluid further.
 

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Discussion Starter #13
Cleaned the duovalve and everything was working great for a couple of weeks. I finally got around to changing out most of the fluids and filters today. Coolant (Zerex G05), oil & filter, manual trans, air filter, cabin filter, fuel filter, and spark plugs. Everything was great and then the duovalve stopped working again! I think it was used to the old coolant. I'll try cleaning and lubricating it again but I think I eventually may have to bite the bullet and buy a new valve. :-(
 
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