Help on troubleshooting this one.
94 C280, 126,000 miles

Temperature
-Freeway driving .................80-90 C.
-Street driving night ............80-90 C.
-Street driving hot day ........100-120 C.
-Noticed when driving and temp went high, I go to the freeway and temp will come down @ 85 C in a minute.
-While temp was high and coolant boiling out of the reservoir, the fan turn ON at temp @ 110 C and not even a
minute to lower down the temp.

My theories are the ff.
-Not the radiator because the temp goes down at freeway speed.
-Could be the temp sensor that latch the fan is now at the high temp range.
-Could it be the fan has a ON time set or it is not meant really to cool the radiator.
-Thermostat might not be opening all the way, low water pump pressure at low RPM weak force to
circulate the coolant.
-Might not be the water pump cause it is temp is comes down.

I was ready to replace the water pump but I thought off asking for second opinion from this forum.
I'll appreciate if we can eliminate the above possibilities or give me some opinion where to start.

Thanks guys.......
-

 

Most probebly the thermostat.
not to hard to fix,
I wouldnt worry to much bout those temps tho, my one goes up and down all over the show. just as long as your not loosing water out of your overflow and having to top it up i personally wouldnt be to worried.
maby check your fan fuses to..
hope that helps

 

thanks, ill check it out in the morning..Or better off ill get a new thermostat and put it in

ill update afterwards

 

the upper radiator hose is soft and no pressure inside?

water will not boil above 100C if got pressure. and therefore won't increase the temp rapidly.

maybe your cyl head gasket is leaking air to cooling system.

 

......Didn't get a chance to work on the car right away.... but today I got some thermostat and installed it....poured 50/50 and did a lot of city driving.
Even parked it let it run..the temperature stayed around 90 C....that was great..
Good advise guys.......thanks a lot.

This forum is a great community...

 

Sweet, glad it all worked out for you, and i didnt give bad advise :-)

 

The way I see it.......there is no bad advise.....all of them have use....sleepwalker advise gave me a chill.
Its not because it was wrong....it is because it's possible and if that was the case I said to myself

Holy s***, look like it will be a @#$%^ and &$#$ .... I'll be spending or working on this car for a longs time.

Just kidding.....I went with the easiest one.............Thanks guys.

 

because you mention "boiling".