Overheated at 38-degree outside temp, new radiator
 

My car has not overheated before last night but to be clear I have only been driving it for a couple of weeks so far. We were moving slowly in a neighborhood looking at Christmas lights behind a row of vehicles and after only 5-mins my car started rising into the red. I turned the heater on and left and as soon as I started moving it cooled off so it wasn't warm for very long. I have had it out on much warmer days in traffic with no problems. I also just had a new radiator put in.

A few hours prior to the overheating I had my exhaust repaired with new muffler and pipes. It had a huge hole in it before this. Is there any way that putting on a new exhaust could have caused the car to run hot? I realize there would still be a problem somewhere but this just perplexed me. I am guessing it's coincidence and that I may just need a thermostat but all opinions are welcome. Anything else to consider?

My car has done this as well (73 280 w114). when driving in stop and go traffic, the needle would rise and fall with stops and starts. Sometimes hot enough to trigger the 100c electric fan.

I flushed the radiator and replaced the thermostat and the temp has been running steady ever since at right about the 9 o'clock position. Little cooler on the highway, little warmer in traffic.

So maybe you need a new thermostat is all. I believe it's common practice to replace it after rebuilding/replacing a radiator.

What car are you driving?

I updated my sig with car info, sorry thought I did when I signed up. I thinkmtheynfailed to top up the coolant when they did the radiator or I have a slow leak somewhere because my coolant was low and triggered the heating up. I didn't suspect this because the radiator was new and I hadn't noted any coolant leaks but always pays to start with the obvious I guess. My thermostat seems to be buried under three pressure lines so that turned me off from replacing it on my own but hopefully I can keep an eye on the coolant and figure out if there is a leak or not.

I have been thinking of adding an electric fan, car didn't have one fitted, couldn't hurt!

Still not seeing your car info.

My first guess is that it was just air trapped in the system when the radiator was replaced. And under normal driving, this low coolant was not a huge issue.

Like you said, keep an eye on the coolant and temps now that you added more. If its still a problem, consider t-stat, etc. There is even a chance that the temperature sensor is bad and giving a false reading.

Check the electrical connections on the temp gauge sender. If they were working on the exhaust, it's possible they dorked something up: misconnected, melted/cut a wire, etc.

An IR-gauge may help tell if your temp gauge is accurate or not.

Car info not showing up in posts, but profile says '62 220SE.

I would suspect an air bubble or bad T stat. have to burp them after a new radiator is put in :)
Takes practice on these ol gals

Hi, it shows my car info as saved in my sig but just not on the posts, I'll check into it more, but my car is a 1962 220se W111 coupe. Took it out for long test yesterday and I am suspecting it was just an air pocket from the replacement radiator, she acted normal and kept her cool in standing traffic and a couple of idling tests I did. I'm still gonna have a closer look at the underside to verify nothing was damaged with the exhaust replacement.