Volvo 850 T5
Replaced coolant temp sensor and coolant, approx 50/50 glycol/deionised water.

Next days commute (4 miles) noticed car takes longer to warm up, needle reaches 3 o clock pos and sits there, used to take about 10 mins but took 20.

Did a longer journey today at higher speeds 15 miles and needle reaches steady state but never got over 4 o clock. Air coming out of vents does not feel as hot.
If car is left stationary needle will reach 3 o clock and fan keeps it there so i dont think the cts is faulty.

Surely a coolant change cannot account for this, afaik it was the original stuff that is 20 yrs old. Thermostat was not touched.

Should i be concerned?

I will get IR thermometer to measure coolant temp.

[Edited on 22/3/15 by 02GF74]

Air lock in heater hose is my guess

Air lock

Hmmmmm.... need to read manual. I thought itd be self bleeding and just filled via the expansion tank.

No special steps mentioned in manual.

Dont airlocks cause overheating?

[Edited on 22/3/15 by 02GF74]

RTFM is good place to start

Been pondering over this, thermostat stuck open would cause this, change of coolant being coincidental?

Take the feed pipe to the heater matrix at highest point possible, release pipe clip and partially remove pipe till coolant emerges.