1979 300sd (w116)

Would a bad servo prevent the bleeding of all air from the cooling system.
I recently reported that my servo magically turned on after being dormant for a few years. Well its inoperable again.

My diesels temp gauge seems to be reading higher (hotter) than usual (195-205 deg F) when driving uphill or flooring the accelerator pedal on a flat stretch of highway, and this happened right after I replaced the coolant and thermostat. Not sure if I got all of the air out.

The temp gauge NEEDLE eventually does settle down to around 180-185 deg F when descending a hill or driving on a flat stretch of highway (the needle will sit right between the actual number 175).

I'm using the number 175 on my temp gauge as a reference to where the needle settles but keep in mind that the ACTUAL MARKING for 175 deg F is before you get to the number.

Not comfortable with this because I know from experience that my temp gauge is really sensitive and can register even the smallest coolant leak. I've looked around and haven't seen a drop of coolant. Will have to double check that.

I'm bleeding the air bubbles out by parking my car on an inclined driveway, removing the reservoir cap and running the engine for approximately 10 minutes. Since warm air is no longer coming out of the vents I feel that the coolant is not flowing thru the servo, thus preventing all of the air to be properly bled out.

Thinking about removing the servo and giving it a backwash to see what happens.

Replaced the fan clutch maybe 6 or 7 months ago
Using Zerex 05 concentrate and mixing it with distilled water (50/50).

Any advice on how to properly bleed the air out of the cooling system is greatly appreciated.

Rip it out and bypass it

You might want to test the small auxiliary water pump as they tend to seize up over time .

I made up a jumper and run it directly when bleeding out the Klima I HVAC system .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

+1 on the aux pump trick, just be sure to observe the polarity or it will run backwards.

Remember brown = negative on just about everything Mercedes

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The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

Question

Would a seized servo or Aux water pump cause the engine to run warmer or maybe even over heat? What is the proper way to bleed all of the air out of the cooling system and do all of the cooling system components (Servo, aux water pump, etc..) need to be in good repair to bleed the air out?

I don't see how a failed servo or failed aux pump would have any bearing on the main cooling system. If they trap air, who cares as long as the main cooling system is circulating water. If they "burp", you'll find air in the radiator which you can then bleed out. It's a non-issue.

If your cooling system is operating correctly, the temp gauge should be pretty well dead-center. 190-205˚ isn't out of line for pulling up a hill or hard acceleration. If the temp comes right back down, it isn't an item to worry about. Check your boost pressure. If the turbo is making low boost, you'll be running high EGT's.

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

I disagree, having owned several Klima I equipped cars, all were hot runners until I learned to properly burp them .

To each their own, just the thought of air in the water jacket makes me cringe, maybe because I live in the Desert.....

If the Evil Servo is dead, by pass it, I use a late 1970's vintage Dodge manual hot water valve as it's cheap and has the correct mis matching size hose barbs on it .

One simple way to avoid any air in the cooling system is to drill a tiny hole in the flat flange of the thermostat .

I don't think this is good policy but many newer engines come this way from the factory .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Thanks,

I will keep an eye on the needle and watch out for leaks.

Thanks, going to consider by-passing the Servo.

The main thing to remember is : this is the Chrysler Air Temp II system used under license .

There are several manufacturers still making the evil servo, I bought the alloy bodied one and it was fine, some of them leak even though new .

Pretty much any crud in the cooling system will cause the servo to jamb up sooner than later, red / brown coolant is a BIG red flag, if you see it, get busy cleaning and flushing NOW, doesn't matter if it's Summer, suffer the heat of proper flushing as the servo traps sediment, binds up or drags, causing the amplifier to burn out or the Bakelite servo housing to crack and leak out all the coolant whilst you're driving along.....

I hate this system greatly but once working it's wonderful, until the next time it fails .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better