engine oil temp is more important that coolant temp.
is you car getting up to temperature properly, i.e just short of 90 degrees when normal running or is the temp hovering around the 50-70 mark? if its not getting up to just short of 90 then your car isn't getting up to temperature, which won't be doing her any favours.
if she isn't your thermostat is definately dead which may well mean your radiator is also passed its best. have a check and run your finger down the edge of the rad when cold and see if its all soft and crumbly. if it is, it needs replacing.
I would check the fault codes if you can to see if its flagging up any dead lambdas. as they start to give up when cold you will find the car very hesitant although under full throttle the lambda is ignored and it will go normally.
that would be my first port of call anyway, lambdas don't always throw fault codes although software should tell you what the engine is reading from the lambda if not a multimeter should show it cycling its output voltage so you can have a look.
1999 156 1.8TS Sport Pack 3
2001 166 3.0 V6 24V Super
2003 156 GTA 3.2 V6 24V
2005 156 1.9 JTDM-Jet Sport
2008 159 1.9 JTDM Lusso
1997 GTV 2.0TS Lusso
2001 147 1.6TS Lusso