need help guys, my c180 is lately has been having its temperature gauge rises everytime i hit the freeway especially in roads with elevation changes. the temperature drops when i descend or back on a level road. the situation is more severe with the ac on.

i've fixed and replaced

- visco fan
- auxiliary fan relays it's running normal now
- radiator cap

this problem happens at around the same time i had my oil changed.
does engine oils have expiry dates?

coolant level is good everytime i check, it doesnt diminish so i think the head must not have warped, and the engine runs smooth.
normally the car's temp would go to about 100 and then dropped back to around 90 after the auxuliary fans kicked in. but now it just stays at 100 or above (when climbing)

check the thermostat.

it is propably half open...

thx for the reply, i'll go have it checked tomorrow.
have u any idea how much a thermostat costs?