W123 Running Hot With AC

[PunkJr]

Hello all
I have recently acquired a 230e from my Great Uncle. It is a one owner completely original car in fantastic condition however I've recently had to replace the compressor. Without the air conditioner running, the car runs at around 83 degrees centigrade however when I put the air conditioner on it runs may be around 90 to 100° sometimes a whisker above at highway speeds.

The electric fan cuts in at around one hundred degrees but I've heard that some people will wire it to run all of the time when the AC is on. The temp seems to run high on hotter days at highway speeds (maybe up to 105 when it is around 44 degrees C) but never gets up to the red. Even on a mild day around 30 degrees the temp will run around 90 degrees on the highway . Should I be concerned about this? I think the thermostat is fine as it maintains the right temperature without the aircon running, and I've just replaced the coolant with genuine Merc blue. I don't think there is any air locks in the system.

Any advice would be appreciated .

 

[grober]

What you are descibing is a system that is running close to its thermal dissipation load capability. This could be down to a performance problem with the engine cooling system- water pump,engine radiator interior passages choked, engine fan [viscous coupling?] or with the extra cooling for the aircon kicking in too late fan thermal switch, choked A/C radiator cooling fins, restricted airflow-- OR the overall system design is simply marginal for the fairly arduous conditions its being subjected too. First thing to check is that the main engine radiator is working ok- a remote ir thermometer gun is usefull in identifying any cool spots in the radiator where its choked and no heat exchange is taking place. [ poor cooling performance in older cars is often down to part choked radiators] They can sometimes be back flushed but usually recoring the radiator or total replacement is the answer- not forgetting to change thatmost basic component -the radiator pressure cap

 

[PunkJr]

Thank you Grober. I had thought about the cap - there is a sticker on radiator that says "Use only 120 cap" (or something like that) and I notice that my genuine cap is 100. I will try this first - I had gone to buy a 120 MB cap but it seems MB only do a 140 now so finding a 120 is proving more difficult than I thought. I have been keeping an eye on the electric fan and it does kick in at around 100-105 deg however I figured that it would not affect the cooling a great deal at say 100 km/h highway speed, more so at lower town speeds (?). Maybe after 35 years a new radiator is also due, but I want to follow the diagnostic steps as you've outlined. My Uncle has looked after this car well but he is 93 years old and has been using his local mechanic for recent repairs and and I am unable to get service/maintenance records.