heat problems

[skiles76]

I just bought my truck and had to replace the thermostat right away but the overheating was under control now just recently the truck started to run real hot but the heater puts out almost no heat. The heater used to be unbearable hot. Also when i let the truck idle the engine temp. drops quickly.
Any Ideas?

Thanks Alot

 

[plschick]

I just bought my truck and had to replace the thermostat right away but the overheating was under control now just recently the truck started to run real hot but the heater puts out almost no heat. The heater used to be unbearable hot. Also when i let the truck idle the engine temp. drops quickly.
Any Ideas?

Thanks Alot

I don't know if you still have the problem, the date being in January. Sounds to me like the coolant isn't flowing, broken water pump= no heat in cab, coolant not moving fast enough to cool under load conditions, at idle however thermocycling takes over ( hot water rises circulating the coolant enough to cool without heavy load). Another possibility is during the thermostat change some junk broke off plugging some lines or passages. Did the thermostat get put in backwards? Not opening.