Overheating

Iv had a search and found nothing like what my 300 tdi dedender is doing when going down motorway it starts overheating heaters still blowing warm only goes 3/4 up gauge doesnt go into red after having heaters on it goes back down to normal also does this when towing everything is running fine have cleaned out the radiator did a 2 hour drive like this and no problems other than gauge saying its overheating
Any help wouldbe appreciated thanks

Have you been in water or deep mud recently??? check the radiator isnt blocked

Have checked the radiator it was blocked but i washed it out and its still doing it
Thanks for the reply