I know this topic has been discussed many a time on the forum, but perhaps now we can get to the bottom of the sometimes typical overheating problems associated with 124s and 103 engines.

Here's the story...

In May 2001 the original plastic thermostat housing cracked and all the coolant was lost. Mechanic replaced housing with a new [aluminum?] one, and refilled the cooling system. Before this the engine would run at 80 C all year (except when using A/C, it ran hotter). Since then, my engine has been running around 90-100 all year, even during the single-digit winters. The water pump was replaced about 8 years (120K miles) ago, but I can't imagine that's the problem, as the temp. change happened after the t'stat housing incident.

I'm going to flush and renew the coolant in the next week or two. Does anyone have a way they flush the system to remove particulate matter? Also, has anyone tried Red Line Water Wetter? I'd like to try it, but will not if it can have any corrosive or otherwise damaging effects on the engine or cooling system components.

Please share your war stories about overheating engine problems!

 

Check the fluid clutch for the main (beltdriven) fan. If the the silicon oil inside lost its properties the fan runs to slow and the coolant temp is rising into the 90-100+ in slow traffic or going slow uphill. The clutch is easily to exchange and if all the rest os okay the engine temp goes back to normal 80+ and w/ A/C maybe 5 degrees higher.
If you push the fan to turn by hand when the engine is hot (BUT NOT RUNNING), the fan should not turn anywhere close to an angle of 90degrees.
To cjange the clutch loosen the fan cawl. Then you need a steel rod of like 1/4'' diameter ~1 foot long and angled 90 degree at the end for 1/2 '' to prevent the fan from turning when you remove the center nut (allen screw) 5 or 6mm.

 

I replaced the viscous clutch last year. I will try turning the fan when the engine is hot (but obviously not running).

 

My mechanic told me that when the antifreeze boils over, it hardens inside the radiator tubes. This is probably what happened when the problem began in May 2001.

 

I bought a Prestone flush kit from my local Autozone for about $10 I think (5 years ago). It comes with a T that you splice inline with your heater hose. The T has a connection for a garden hose on it, so you just hook up the garden hose, remove the radiator cap and flush until it runs clear. If you suspect calcium buildup inside the radiator or block you can flush the system using citric acid diluted in water. This procedure is covered on the following page:

http://users.vnet.net/w123d/w123d/flush.htm

It is for a 123 car but will do well with yours. Also, 8 years on a water pump may be pushing it, but changing it requires removal of a number of other components, including the belt tensioner...

I have found that the lowest (not lower) radiator hose seems to be the best for draining the cooling system.

-D