E39 M5 after repair knowledge needed

[fatmansv8]

Hi everyone I just had my car back after repairs. I had the thermostat and coolant temperature sensor switch replaced. The symptoms were temperature needle on the gauge never reached half way it ran 1/8th of a inch above the blue. On motorway journeys however the needle would shoot off the scale past the red but the car was not overheating there was no smell of overheating nor steam coming out in fact the car would run normally ,but when I switched the engine off and back on again the needle would read normal just over the blue again.So I put the problem to you guy's on this forum and it was advised I changed the thermostat and coolant temperature sensor switch. So did that yesterday along with the diff seals and rocker cover gaskets. But after I picked the car up the temperature needle is still just above the blue I took it back to the garage and was told it may be a gauge calibration issues and they could recalibrate the gauge. They did notice that the when the engine is turned onto accessories mode the needle shot over to the red and then back to just over the blue. Do I have a gauge problem or is there something else.
Sorry for the length of post but replacement of all the diff seals and rocker cover gaskets and thermostat and coolant sensor switch cost me £881. I need to know do I send the car back or get the gauge replaced.
Thanks for reading through FatmansV8

[fatmansv8]

Hi 😡angrydog where are the 2 sensors located I can ask which one they replaced at the moment all I know is they replaced a coolant temperature sensor. He did say the old thermostat was jammed shut and definitely needed replacing. You know I've never used the obc ever so do I press the button on the end of the stalk 6 or seven times until the temperature reading appears. I'm sorry I'm bit of a caveman about car's angrydog.
Thanks Fatmansv8

[fatmansv8]

If did notice soot in the exhaust tips where there was non before I handed the car in Hmmm.

[fatmansv8]

I did notice soot in the exhaust tips where there was non before. Hmm

[fatmansv8]

Hi everyone a quick update for you guy's. I took the car out after cleaning the exhaust tips off all the soot. A few things I noticed the warm up indicators went off alot quicker within a couple of miles whereas before they began switching off after 20 miles or so. So I guess that's good news. The problem with the gauge needle going off the scale on the motorway didn't happen over a 45 mile round trip, so I guess that's good news to. The needle did reach half way for a while then reverted back to the dot between blue and halfway.There is no soot in the exhaust tips also good news. I reported back to the garage as suggested by you guys I had the other sensor replaced at cost of the part only no labour. They then plugged into the ecu and left engine running their computer was showing engine running at 81 C to 83 C which is normal right? even though the needle was inbetween the dot above the blue and centre. So a big thank you for all your advice you have been a massive help and a big thank you to pistonheads for this forum.
Yours greatfully Fatmansv8

[fatmansv8]

Hi guy's as you know I have just replaced the thermostat and both coolant sensor's. The warm up lights 🚥 go out alot quicker now but the the gauge is still reading between the blue and 1st dot on the gauge. I took the car back and had a diagnosis done via the OBC it showed it running at between 81°C & 83° C. Do I need to change the gauge guy's or is further work required. Thanks
Fatmansv8

[fatmansv8]

Hi thanks Depthoar will give it a bash will try out the live data.thanks Fatmansv8