Vito 638 - 1999: Issue when starting hot

Hello!

Im having issues with my Vito when starting hot. I'll describe the problem first then give you a bit of background.

Its a Vito 110, 1999 model, 2.2 Diesel.

Its starts fine cold, but when it warms up I switch the ignition off, then when I try to turn it back on... nothing, there is no power at the switch.

The temp gauge goes up, then instantly drops again, then the engine oil light comes on. If I leave it for a while it will eventually start again. This depends on how long I have been driving it, after a long 1-2 hours drive, I've had to wait 4-5h hours, one time a couple of days.

You can see a video I made here:


I have the van running at normal operating temperature, then I switch off the ignition, then when I switch it back on again you can see the temperature gauge go up and back down again instantly, then the oil light switches on. When I try the ignition, nothing, no power at all. Then when I switch the ignition off you can see the speedo and rev counter flicker a bit.

I've just change the thermostat, housing and sensor. Before the dash would not go above 40, now it goes up to 80.

The first time this happened (didn't start hot) I noticed the coolant was very low, my fault for not checking it for a long time. I topped it up, it took quite alot, then the issue has stayed ever since.

I have good mechanical knowledge, around 10 years ago I worked as a motorbike mechanic, but Im a bit rusty these days. And electrics have never been my strong point.

Im guessing its a sensor issue. Not sure if I just need to get the fault codes read / cleared now I've changed the thermostat.

And is the sensor in the thermostat housing where the dash gets its reading from? If not then I guess I might need to replace the temperature sensor.

Thanks in advance for any help!
Matt