I never understand why people go through all the hard stuff/expensive stuff then not add another £50-£70 on some decent gauges. I don't trust my temperature gauge as far as I can throw it thus have my own plumbed in. Does the fan kick in at all? Radiator functioning properly? system fully bled (don't know if it is self bleeding or not)? Sticky stat? Decent mix of antifreeze to water is often overlooked.