M117 engine cooling system - Supplementary cooling fan? - PeachParts Mercedes-Benz Forum

JeffreyNMemphis · #1 04-20-2009, 07:10 PM

Hello Friends,

I have the 1973 280SEL 4.5 with the M117 motor. At what temperature should the supplementary cooling fan in front of the radiator kick on? The fan comes on, but after the car is getting toward the top of the temp gauge. I was sitting in traffic for 30 minutes and was getting anxious watching the temperature rise. Has anyone here added a manual switch for times like being stuck in traffic on a hot day?

Also, the maintenance manual describes a procedure for flushing the cooling system t0 remove calcium deposits. When I looked in my radiator I saw some calcium and the hoses have calcium deposits at the edges. What is the correct stuff to de-calcify the cooling system? I use white vinegar on my coffee pot. Is that new stuff called CLR bad for engines?

Thanks for you thoughts...

Tomguy · #2 04-20-2009, 07:30 PM

It's SUPPOSED to kick on @ 212. There's a line on the temp gauge where it should go on. My 4.5 idles in traffic at the mark or a little above for 175°F on 90° days - and it has 3.5L heads and cams which make it hotter. Your radiator may be corroded badly, your engine block is probably full of gunk, and you may need a new thermostat. But you sure need a new aux fan switch - the 212° (100°C) switch. Mine kicks on at 212° and I also rigged a switch to turn it on manually if I want.

http://catalog.peachparts.com/ShopByVehicle.epc?q=1972-Mercedes--benz---80sel-Cooling--System&yearid=1972%40%401972&makeid=63%40%40MERCEDES%2DBENZ%40%4063%40%40MERCEDES%2DBENZ%40%40X&modelid=16108%3AMBC%7C10000010%3AED%7C10000064%3AEB%7C1596%40%40280SEL&catid=240909%40%40Cooling+System&subcatid=241005@@Auxiliary+Fan+Switch&mode=PA

Arthur Dalton · #3 04-20-2009, 07:31 PM

Mnat guys run a cabin toggle switch by bridging the a/c reciever/drier for manual fan..................

JeffreyNMemphis · #4 04-20-2009, 08:20 PM

What do I use to flush and remove the calcium and gunk?

Tomguy · #5 04-20-2009, 09:05 PM

Honestly you can do a citric acid flush but that doesnt always work. My cooling became the most optimal when I pretty much power-washed off the inside of the block when I did the heads, and I had the radiator installed I bought off of a fellow forum-goer that was pre-boiled and de-scaled.

You may just be best off removing the radiator and having it boiled or just re-cored to be honest.

JeffreyNMemphis · #6 04-20-2009, 10:59 PM

I just got home from a spirited 40 mile evening drive. The temp didn't get above normal which looks like the 175 line plus about 5 degrees. The next line about 175 is 212 degrees? On a hot day like today, idling in traffic for 30 minutes put it above that next mark (212?). I don't like that. I am going to do something before summer gets here.

68_280SE · #7 04-21-2009, 08:24 AM

It could also be a bad fan clutch.

berfinroy · #8 04-21-2009, 08:59 AM

My Service Manual (page 83-12/3) says that the auxiliary fan comes on at 97 deg. C, which I believe equates to 206.5 F. A tyical source of trouble with a fan that doesn't come on at all is the RELAY, which on the 4.5s is located at the top right of the ECU, (firewall on 3.5s) which is located just to the left front of the radiator. Like all of these old reays, the points therein can get glazed over with contaminants resulting in no electrical contact.
To test the relay, turn on the ignition and ground out the thermo switch (3.5s and earlier have a "saftey switch" that opens the fan curcuit when the hood is up. It's a button that is pushed in by the hood itself. Find it and push it in as part of the test).These relays are expensive to replace but easy to repair. Carefully pry off the aluminum cover, clean the contact points with 600 or so wet/dry paper, pop the cover back on and you should be ready to go.

JeffreyNMemphis · #9 04-21-2009, 09:38 AM

Thank you very much for contributing your experience!

My fan turns on, but it seems to turn on after the notch above 175 on my temp gauge. If the relay was bad, it would not come on at all. The temp switch may be failing... If it is switching above 100C.

Does anyone what would be the best chemical solution to flush the cooling system with to remove hard water calcium stuff? Can I use something like CLR (calcium, lime and rust dissolver)??? I don't want to damage anything by using something too strong.

79Mercy · #10 04-21-2009, 10:44 AM

MB designed the fan to come on if the AC freon gets to the certain temp and if the motor reaches 100C. I wouldn't worry about 100C but if the temp continue to rise to like 115C then i'd start to worry. Once the fan turns on the temps shouldn't rise to much.

250 Coupe · #11 04-26-2009, 06:44 PM

Quote:

Originally Posted by JeffreyNMemphis

Thank you very much for contributing your experience!

My fan turns on, but it seems to turn on after the notch above 175 on my temp gauge. If the relay was bad, it would not come on at all. The temp switch may be failing... If it is switching above 100C.

Does anyone what would be the best chemical solution to flush the cooling system with to remove hard water calcium stuff? Can I use something like CLR (calcium, lime and rust dissolver)??? I don't want to damage anything by using something too strong.

You can buy radiator flush at any autoparts store but it's been my experience that they don't work. Check around for a radiator shop in your area and ask about a flush and fill.

Michael