Lukewarm Heater

[qualicas]

The heater just started to blow lukewarm air about a couple of weeks ago. Previous to that it was fine. The temp gauge goes up quickly to just under 200. Just like always. I replaced the water pump and thermostat about a year ago just for preventive maintenance. Today I went out and grabbed the top rad hose and I could hold it for a while. That would tell me it isn't getting up to temp yet the temp gauge says it is. Also, I notice when I come to idle the truck the air from the heater gets even cooler than when driving. All this would lead me to think it might be a faulty thermostat. I have never had to add coolant, well a couple of years ago I added a litre! Any other ideas?

[8.1HD/ALLISON]

Try backflushing the heater core first. If coolant temp is just under 200 shouldn't be thermostat issue. Should be 2 small hoses that hook to the water pump leading up to firewall. Remove these hoses at the waterpump and flush water back and forth between the two with a hose till it runs clear for a while. Hook back up, top off with coolant and give it a try.

[qualicas]

Well, I'm getting heat now! I back flushed the heater core. Easiest job ever. I just undid the hoses at the fire wall and ran a tap water both ways and blew it out with air. Didn't look like anything much came out but got lost of heat on the way home so I'm happy. Lets see how it will be in the next few days. We are having a snow storm. Highways closed and people stranded all over. Temp supposed to go down to about -29C. (-20F)

Thanks 8.1HD