I'm really stumped on this truck. Should the heater core always have flow, or only when the thermostat opens?

The truck never warms up. I replaced thermostat today from ford, went for a 15 mile drive. Heater and radiator hoses felt warm. AE scan said the oil temp was 178 deg. I don't know about the coolant temp due to a broken temp sensor. After being parked for a few minutes it cooled back off to the touch. I have no heat and have checked the heater door for debris and pens. I took the heater core hoses off and flushed water through it, no blockage. With it running I don't have flow through the heater hoses while they are disconnected and motor is running. Is my water pump shot? If it is them why is the motor cool? It seemed like the thermostat wasn't long enough to close up the hole at the bottom of the water pump. I measured it before installation and it seemed short, but looks like the one that came out.

What am I missing, please help me!

The truck is a stock 97 f350 plow truck. Not my 99 pictured and in my sig.

 

Has it done this since you had the truck? There are two different thermostates for our trucks. The 97 should have the long stat.

 

96 & 97 should take the long stem thermostat, 94 & 95 take the short stem. Are you sure that you have the correct stat? The water pump should pull the water from the block threw the heater core to the water pump. I have had the heater core get an air lock and could get no heat, although thaat was in an IDI.

 

Yes it has done this since I bought it earlier this fall. I thought it was supposed to have the long thermostat, and I'm pretty sure I got the long one today, it's motorcraft part number rt-1201 f6tz-8575

 

I took of both heater hoses at the core and had no flow from either hose.
I'm hoping someone can verify the part number on the stat. Its definitely longer then most I've come across, but when I checked the depth with a caliper it still seemed short.

 

According to the part number in the stickys, that is the right one. I am interested to what others have to say. On another note, your temp gauge does not work?

 

That sounds like a too-short necked thermostat. The one that came out might have been a replacement that was also the wrong one. I suppose if you're really curious, you could boil the thermostat in a pan of water, then carefully (use a tongs or something), while it's still hot and open, drop it into place in the water pump and see if the lower disc closes the bypass hole.

Then again, if both heater hoses are warm, and you still have no heat, the problem must be in the core or the HVAC box. Try this - take the glove box out, and the RABS computer and the cover over the heater core. Put the cover back on with just a couple screws. Drive around to heat up the engine, then pull the cover off the heater core and see if the core itself it warm.

If your water pump were bad, your engine would overheat.

 

i would also recommend pitting in a international 203 tstat

richard

 

Do you have a control valve in the hose to the heater core? This is often installed to give colder AC temps.

My truck had the wrong thermostat installed when I bought it form the previous owner. When I bought the replacement pump they gave me (and I installed) the wrong thermostat. I don't remember long or short, but I had to thumb wrestle with parts house desk jockey to keep looking at different year trucks until we found the other length. I now have steady temp gauge readings and a toasty heater.