Hey guys 1st time post and 1st time Volvo owner, 1994 960 2.9L, anyways I finally got the opportunity to change out the radiator since it had a leak and I had to top off once a week then gotten worse to 3-4 times a week.
My mechanic swapped it for me with no problem, at least to what I can see from, but I failed to drive the car for a few miles before he left, since it was dark already. Turns out after 2 or so miles the temp gauge starts to increase drastically, however, when I stop at a light it goes back down to the center of the gauge like normal. Once I accelerate goes back up while all this is happening the fan is turned on, something I've never heard from my old radiator unless the car's been on for a good amount of time.
My mechanic says it may be a sensor and/or water pump. I had an old VW passat that the water pump went bad on it but it didn't do the same, as soon as I cranked the car up for 20 seconds the needle would go all the way up. So I want to throw that thought away but keeping it in mind. I just need some assistance to led me the right way. Any help would be highly appreciate it!!! Love forums like this because we can share both good and bad experiences but unfortunately we sometimes share bad ones more than good one

 

Did he replace the thermostat?
Sounds like a bad thermostat to me.

 

Sorry to omit some information, we removed the thermostat, according to him it's not really needed for warm weather, and in North Carolina it's pretty warm. That's what he said at least made sense but don't know if it's entirely true. Thanks for the reply

 

Totally wrong you need one. I would get one in there ASAP.

When you do not have one and drive at a faster rate of speed to coolant is flowing to fast through the radiator and cannot be cooled. That will cause it to overheat.