I just replaced the thermostat and radiator fluid. My heater blows air but not hot air. Any ideas what it might be?

Well, if it worked correctly before you got in there then you probably need to purge all the air out of the cooling system.

It would be wise to create a signature describing your vehicle so readers know what you're working on.

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2004 Ranger FX4 Level II, 5R55E, Sonic Blue Pearl

Proudly JAP/RICE free since March 2000

I have a 91 ranger w/ the 3.0 V6. The heater did not work before I replaced the thermostat. I'm the 2nd owner and I know that majority of everything is factory. I did purge the lines, I checked the fuses. How can I check the heater core w/out removing it? Or can I?

With the heater control setting in a heating position, temp slider on hot and the fan on high, one line leading into the heater core should be hot (warm engine, of course) and the other one should be cool. If both heater hoses are hot, your blend door (mechanical, operated by dash temp lever) is not allowing air to blow over the heater core; if neither line is warm/hot, then you have a flow problem in the core.

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2004 Ranger FX4 Level II, 5R55E, Sonic Blue Pearl

Proudly JAP/RICE free since March 2000

I will try this and let you know what happens. Thanks for the info.

NP, I hope it helps.

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2004 Ranger FX4 Level II, 5R55E, Sonic Blue Pearl

Proudly JAP/RICE free since March 2000

So I checked the heater lines. One cold one hot. The blend door seems to be working properly. The only thing I think it could be is the heater core is shot. Or the heater coil is bad. any other ideas?

Turn heater off, turn fan off. Slide temp to cold. Thoroughly warm up engine and feel heater lines. Two hot heater hoses = coolant flowing through heater core. Not to say that it not adequate flow, but does confirm the blend door operation. Should this be the case, I'd think about checking the heater core for plugging. No mention is made of what the coolant looked like before you changed it (assuming that's what happened) or what it ever looked like in the past, but neglected cooling systems develop crud that restricts/plugs things.

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2004 Ranger FX4 Level II, 5R55E, Sonic Blue Pearl

Proudly JAP/RICE free since March 2000