[W126 Coupe] Engine Temperature of a 1989 560 SEC

[Dick Spellman]

If the engine temperature climbs as you describe it's typically one or more of the following that need to be checked and replaced:

If mileage is over 100-120k then it's:

1. Viscous fan clutch.  This is the most common reason for climb in temp in stop n go.  Your 120 C is a bit high unless you are at high elevations or in the desert southwest.

2. Electric aux fan.  Juice it with 12 vdc to see if it works and then test AC relay and engine manifold temp sensor to see that the two fan speeds works as advertised.

3. Thermostat.  You'll see erratic behavior when this sticks closed on a cold start (temp gauge will show a fast rise then it drops back to 82 or so), or it sticks open (runs cooler than 82 or so and eventually gets to norm)  Anyway if miles are 100-120k miles I'd replace it.

4. Coolant pressure cap.  If you notice mystery coolant loss you might start here or proceed to 5.

5. Radiator.  If it has not been cared for and wrong coolant added etc it will be tired at 100-120k miles.  Easily tested with an IR meter to check for hot spots, cool spots on the heat exchange surface.  You can also use an IR meter at the tstat housing to confirm it's working.

Check the mbcoupes archives for lot's of additional information and testing of the viscous fan clutch which is what I would suspect is your problem if it's never been done and your mileage is 100-120k or more.  Don't buy Truktek.  I've been using Behr but recently heard Sachs might be better because of a negative change in manufacturing quality at Behr.  All I have experience with are Truktek (tried twice & they are consistently junk) and Behr (done 3 or 4 and they are good out of the box) so others will need to chime in on Sachs.

Regards,

Dick
not a mechanic but have been playing with MB's for a few years now and picked up all info from members of this and other sites
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