hi guys

as title says, my temperature gauge has started going up very slow since i replace the rocker cover as i think i have cracked it in few places trying to take the old one out, only hair line cracks, that was why i didnt notice till i drove it for few days and saw quite abit of oil on the top of the rocker cover.

i am guessing either the coolant sensor or the thermostat is stuck open.

can anyone advise please?

many thanks guys 🙂 

also when it does finally get to the middle of the gauge and when i go downhill the temp on the gauge will slowly go down.

Yeah sounds like the thermostat is stuck open.

As MJNewton says, this would normally be the thermostat.  But if you want to, you can check the output of the ECT (engine coolant temperature) sensor by using Forscan to do an 'oscilloscope' trace of both the ECT and IAT (inlet air temperature from the TMAP sensor) without having started the engine.  They should both show the same (ambient) temperature.  For me, this did recently reveal a broken ECT that was reading about ten degrees too low.  Once the engine is running, the ECT should normally rise to about eighty-five degrees after only a few minutes.