M104 high water temp

[FLYGEEZER]

My 174,000 mile E320 started running hot in traffic & highway speeds (107c & above) This and other forums & sources led me to an operational check of the fan clutch by heating up the engine to above 107c and check the fan for engagement by attempting to turn the fan with the engine off. Did that, and found the fan disengaged. A rush to judgement promped me to orded a new fan clutch. After the installation the engine continued to run hot. Then the thought process ramped up and I came to the conclusion that the fan clutch was operating normally. The "heat sensor" on the face of the clutch reads the heat off the radiator to engage. Well dummy me.......If the radiator is cold & the engine is hot (where the temp. is taken from) the clutch ain't gonna engage and IS NOT the problem. If the engine is Hot & the radiator is cold, then it's a blockage as in a thermostat not opening or opening late & closing early. Removed & replaced the thermostat with a new Behr < $ 20 and the o'heat went away. Easy job, Put the car on an uphill incline to keep the radiator above the level of the expansion tank to prevent antifreeze loss, remove the 3 Ten mm bolts, remove gooseneck , pry out "O" ring with an awl or something with a sharp point, lift out thermostat and install the new one with a new "O" ring in the same position with the weep hole at 12 o'clock or toward the rear of the engine. You will lose only about a cup & a half of anti'freeze, no need to drain the rad. After it's all back together, remove the pressure cap from the expansion tank, squeeze & release the top rad hose several times to "burp" the air out (if any) add fluid, if needed, after running at idle for 5-10 minutes Put the pressure cap on & ride. Recheck fluid level, put the tools away & have a beer. I put a wad of paper towels to soak up the fluid loss on top of the water pump. NOT a drop hit the driveway! Do the thermostat first!!!! it will be a lot cheaper that a fan clutch. They are $ 226.00 at the stealership. Good luck & happy motoring.

[oldsinner111]

nice write up.I had to buy my inverted star sockets at Sears,mine has these bolts.