I replaced my water pump a few months ago and ever since I have had fluctuating temps. The new pump is a bosch from pepboys and had a shroud on the impeller and the old unit did not, I also noticed the new one was harder to turn than the old one but that is to be expected. My temp used to set right around 188-194 and now driving down the interstate at 70 I get swings from 188-222 today. It would go up pretty fast and come back down to around 200-205 or so but I cant help but theink its the new pump. I may try a new radiator cap too but what does everyone think?

--- Update to the previous post...

The old pump worked great but I did a coolant flush and it leaked from the weep hole afterwards and is the reason it was replaced. The o-ring was also flat but I dont believe it leaked, if I were to put a new o-ring on it would it fix the leak from the weep hole? The bearing and impeller feel tight and spin freely.

This coolant hasnt been in 3000 miles yet and the coolant before that was in about 15k or so but im not sure about the coolant that was in it when I got it, it may have been in for 200k and 8 years?

...yep. It is not always your fault, per se. I just had to replace my radiator. Did a new t-stat radiator cap, and new coolant. I have not driven it on the highway yet, so I dunno if the temps are swinging still. If they are, a fan clutch, temp. sensor and headgasket are the only things left that it could be.

This coolant hasnt been in 3000 miles yet and the coolant before that was in about 15k or so but im not sure about the coolant that was in it when I got it, it may have been in for 200k and 8 years?

Something is going on if the water pump is rather new and built up that junk? Plain weird if the coolant is not all that old and now depositing junk on the water pump...

...yep. It is not always your fault, per se..

Never is...