Hi Tan, Well, the good news is, your auxiliary fan switch still works - this part is often dead after 10+ years (at least it has been on every W124 owned by my family.) That also means your dash gauge is probably accurate. So you are either not getting coolant flow, or the radiator is not doing it's job properly. Since the radiator outlet is cold, my guess is you have a lack of coolant flow? I'd think if the radiator was bad, it wouldn't happen suddenly, and the outlet would be hot.
You can test the t-stat in a pot of hot water, it should visibly open fully by ~94°C, before the water is boiling. No pressure is needed to make the t-stat open. I'd pull the water pump and replace it. I suspect the impeller could be separated from the shaft - not likely, but I'm fresh out of other ideas. I'd get a rebuilt pump from the dealer (or OE from Rusty), that was the most economical option the last time I checked. Please keep us updated, I'm curious what the root cause is. :-) -Dave M. > ------------------------------ > Date: Wed, 28 Dec 2005 08:45:33 -0800 (PST) > From: Tan Qu <[EMAIL PROTECTED]> > Subject: [MBZ] SOS - '87 190Dt Overheat! > > > Yesterday I noticed our 190Dt started to overheat. > Outside temp was around 60F's but the coolant temp > shot up to 120C degrees. The auxillary fans came on > but the temp still won't come down. Last night I > inspected the belt drive system, replaced the fan > clutch with a good used one and also the belt. Rest of > the belt drive parts are fairly new. Also replaced the > thermostat with a god used one. But the car still > overheats. Temp stayed around 118c. The coolant > overflow tank is clean with no oil trace. The upper > radiator hose was not pressurized when the car cooled > down. One thing I noticed was throughout whole time I > was testing the car the lower radiator hose was cold. > It seems to me the coolant did not get circulated > through the radiator at all. I want to suspect the > thermostat was the culprit but the one I just put in > was a known good one, actually came off the same car > when I did preventative maintenance. > > Any possibility that the water pump could be bad (put > in about 80k miles ago)? What usually happens when the > water pump goes out? Also how does the thermostat work > exactly? I understand the the bimetal parts expand at > the different rate when the coolant temp rises but > what exactly open the valves? Does the expansion rate > difference of the bi-metal opens the valve or the > pressure in the coolant system (applied by the water > pump) push open the valve? > > Any troubleshooting ideas are greatly appreciated. > > > Tan
