Freightliner classic no heat

Mine will get heat if it’s idled up to 1300 +, that tells the impeller is slipping.

 

Got everything back to normal. After replacing waterpump, I thought I might need thermostats, but I just had some air pockets, topped it, ran with cap off and vent in top pipe open, till it ran clear no bubbles.So it definitely was only the waterpump impeller slipping, funny thing is, it never got hot, Guage May have been inaccurate, as I ran it almost a couple gallons low more than a few times.A stuck open thermostat will also cause a loss of heat at idle. Usually corresponding lower temps also, if guage is correct. Then with a higher idle, engine gets hotter. Heat works, I used to drive old city Trucks, They must have hadbad or no thermostats, always had to get moving to make heaters work. Lol

 

I've had bad thermostats in my current truck 3 years now.

When it gets cold. Sso does the heater. Need a cover to block the radiator to get any warm coolant

 

I drove a couple hrs, stopped for coffee, left it at high idle w/ fan on,came out, no heat!! I’ve got a pinhole in reservoir tsnk, might be the problem. But I think heat should still work, even without pressure, as long as it’s circulating . I think I’ll change thermostats, tomorrow. They were in my last Truck for a few months,back in 2008, I put them in this Truck about 4 yrs ago, one of them must be sticking open.This goofy stuff bothers Me. Usually how head gasket symptoms start.

 

Update, fixed the pin holes in tank, ran it with cap tight, thought all was well. Found it’s pushing coolant out of overflow, cracked head or blown gasket. Trucks in for an O.H. now.

 

I drive a 2000 Freightliner the heater has a new pour when it's off after that I turned it on and it blows hot for a few seconds and then blows cold. I know the thermostats are good my engine temperature at highway speed just above 150. But when I sit and idle it's 180 but either way it blows hot air for a few seconds then blows cold air I can't figure it out.

 

That’s what mine was doing at an idle. When I idled it way up, it got heat. Waterpump was new. Problem was a cracked head. If your coolant levels staying good. Not disappearing, or going out the overflow, You may have a thermostat stuck open, or an impeller slipping on waterpump. It should run a little warmer than 150, on highway. If guage is accurate, I’d say 1 of the 2 thermostats may be stuck open.