Plz help I have a 6.0 diesel and will crank but will not start I used some starting fluid and fires right up and will run and start agine but as soon as it cools down it back to not starting what can it be I have replaced fuel filters and relays

Diesel engine *COLD START* problem: The sole purpose of the glow plugs is to aid in starting a COLD Diesel engine .. Since the engine is starting ok after it warms up - Strongly suspect the glow plugs are NOT operating correctly - after engine 'cold soak' (parked overnight) - the COLD start problem returns .. The BEST thing to do is have a *professional scan test* performed so glow plug operation can be checked - also a functional test can be performed using same professional quality scan tool. ▪️https://repairpal.com/repair-shops▪️