Hi People

just brought my 2004(54) Astra MK5 17CDTi Metalic Green 43k

been looking at Astra's for months and this was the first green one i have seen plus its was in great condition - full service history 1 prev owner - only downside is the tax ends in sept so that when i may hit my first problem

just really looking for some advice on upkeep

best oil?
recommened changes?
Tests i should make?

also the tempreture display inside the car seems to always sit at 31c is there a way to refresh this? or do i need to wipe or test the sensor for this? where is it located?

any other information would be great