95 Ram 1500 Heater problems

I am having problems with heat in my Ram 1500. I have read through the posts on the site and have some ideas, but none of the posts seem to quite fit my situation. So .. here goes:

1. On cold start engine temperature comes up normally and normal heat is available.

2. After engine reaches normal operating temperature, a short while later heat seems to no longer be available. If I put on recirc there is just a trace of heat.

3. Top radiator hose is hot and bottom radiator house is warm. Seems like thermostat is opening up and coolant is flowing through radiator. Temperature gauge is in normal range and moves up and down - seeming to indicate that thermostat is opening and closing OK.

4. Passenger side hose to heater core is hot. Driver side hose from heater core is warm or cool. Opened up flush fitting once and got fluid out. Tried again some time later and did not get any fluid out. Seems like this might indicate a clogged heater core, but how do you explain the initial abundance of heat?

5. Fluid level in radiator and overflow tank are normal.

Since I get really good heat initially I have been assuming heater core is not blocked. However, once thermostat opens up and coolant has a parallel path through the radiator, the flow through the heater core seems to be little or nothing.

Questions:

1. Is there some kind of valve or thermostat on the heater core loop that might be open initially but then failing closed when heated?

2. Does the main radiator thermostat control flow through the heater core?

3. Could this all be happening due to vacuum loss once engine is heated up?

Will be most happy to see your replies!

Thanks.

OC

Sounds like the thermostat is initially closed & opens correctly but doesn't "throttle" the coolant temperature and on it's way to sticking open all the time.
I'd install a new thermostat.

Sounds like the thermostat is initially closed & opens correctly but doesn't "throttle" the coolant temperature and on it's way to sticking open all the time.
I'd install a new thermostat.

Thanks for the feedback. I had pretty much given up on this BB since I didn't hear from anyone.

I did resolve the problem. Turns out there must have been some air in the system. I parked the truck with the radiator cap uphill and left the engine run with the radiator cap off until it was hot. After doing that the heater has been working perfectly.

This was all a bit puzzling since the fluid was drained and flushed prior to last year's heating season and the heater worked fine last Winter. No signs of external fluid leaks or fluid loss through internal leakage and burning. So - how did the air get in?

At any rate the problem seems to be solved for now.:wink:

Thanks for the update.
I thought about the air purge but the heat was there initially.
The coolant overflow line doesn't have a clamp on mine so I guess air could be drawn through those connections when the engine cools off and draws from the overflow tank.