It's been a tense few weeks since I lasted posted the thread about my W124 overheating. Since then I had replaced the thermostat, radiator cap, and just recently, the A/C aux fan switch.

That would pretty much cover every major component in the cooling system (water pump, temp sensor, radiator, and expansion tank were replaced within the last 6 months).

SO WHAT gives?????!!!!!!

Well, I suddenly remembered that even though temps remained nominal, even while 104 outside, the coolant would still boil over...the radiator cap would rattle while coolant spilled over...

WAIT A MINUTE...THE RADIATOR CAP RATTLES???

I had taken that cap off dozens of times to refill the tank with water and coolant, but NEVER TURNED THE CAP ALL THE WAY CLOSED!!!!

So this afternoon, I turned it fully clockwise until it seated firmly, and guess what???

NO OVERHEATING...AND NO SPILLED COOLANT!!! By the way it's 101 today, and the A/C was chugging at full tilt!

I told my wife about it excitedly, who just glared at me like I was some idiot...okay, I was some idiot!

Anyway, I dodged the blown head gasket paranoia for at least a little while...maybe I'd better save up for the inevitable, for when it DOES happen down the road...

Thanks to all who helped. I now know more about the cooling system than I ever cared to!

Maybe I can stop starting threads on the tech forum for awhile and go play in the what-cool-parts-I-can-add-to-the-car forum...

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car

I can feel your delight from where we are ...

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... Kerry

126 tailed by a 203, 129 leading the pack.

YOU MORON!! LOL!!!

Haha, just playing. Glad it was an easy fix!!

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2006 E350 w/ 155k miles (Daily Driver)

Previous:
1993 300E 3.2L Sedan w/ close to about 300k miles
2003 E500 Brilliant Silver (Had 217k miles when totalled!)
1989 300E with 289,000 miles (had for <1 yr while in HI)
03 CLK 500 cabrio (Mom's)
2006 C230k (Dad's)
1999 S420 (Mom's/Dad's)
2000 C230k Sport sedans
2001 CLK320 Cabrio (Mom's)
1995 C280 My First Mercedes-Benz... (155k miles. EXCEPTIONAL AUTOMOBILE. Was Very hard to let go of!)

but wait, 101 is still a bit high!! the aux. fan
should engage at 90 to bring the temp. down
to normal (80).

No, 100 they should kick on.....
?

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2006 E350 w/ 155k miles (Daily Driver)

Previous:
1993 300E 3.2L Sedan w/ close to about 300k miles
2003 E500 Brilliant Silver (Had 217k miles when totalled!)
1989 300E with 289,000 miles (had for <1 yr while in HI)
03 CLK 500 cabrio (Mom's)
2006 C230k (Dad's)
1999 S420 (Mom's/Dad's)
2000 C230k Sport sedans
2001 CLK320 Cabrio (Mom's)
1995 C280 My First Mercedes-Benz... (155k miles. EXCEPTIONAL AUTOMOBILE. Was Very hard to let go of!)

Joel:
In Texas in the summertime, 101 is the AIR temp. (Fahren.)!

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The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)

Sorry for the confusion...101 F was the outside temperature.

The engine temps hover at around 85-87C. When it's really hot outside, it climbs to 90-95C, and then the aux fans kick in, (seems like at around 97C), and the temperature goes back down to around 85-87C.

80C seems a bit cool for normal engine operation...

__________________
2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car