Little to no heat

[hksdrift240]

I've got a 95 nissan 240 5spd with about 164k miles on it. Its starting to get cold here so i need heat, but i found out i dont have any. The temp gauge reads in the middle. I thought it could be the thermostat, so i replaced it...it seemed to help a little, but not like it should. I let it run after replacing the thermostat, and after it ran for like 10-15 mins, I took it down the road (at this point, the radiator was full, and the cap was on) and came back and let it idle for about 5 mins and the temp gauge started going up and got almost to the H mark and the heat actually felt like it should. I cut the engine off cause it kept getting closer to the H, and when I started it back up, the temp droped back down to normal, and that nice heat left too. I felt of the 2 hoses going to the heater core and both were really warm, but not to the point you couldn't touch them. It almost seems that the engine itself isn't warming up enough. I dont really know what to do at this point. I thought about reverse flushing the heater core, but seeing how it put out really good heat when the engine temp went up, It seems like its ok.

[rickgerhardt]

I have delt with this problem before. First off, the reason your temp gauge went to hot is because it had an air pocket in the system. These engines are terrible for that with all the small coolant lines running through the intake and throttle body. Usually if you just drive it down the road for a few min then shut it off and let it cool then take off the rad cap you will see its not actually full anymore. Just top it off and you will be good to go. Anyway, what temp thermostat did you put in it? What brand? Those heater core lines should be hot once the engine has been running for a little bit. Ger your coolant toped off first then check it again. Are the heater core hoses both the temp? Its possible your heater control valve could be stuck or broken. If the core was clogged the bottom hose will be significantly cooler. Hope this helps, LMK.

[hksdrift240]

Im pretty sure its a 170 degree thermostat...i dont remember the brand though, however, it was the exact same thermostat as the old one. The coolant is topped off. I checked it this morning before I drove it and a few hours after I drove it today and it was still right at the top. Those two hoses feel the same temp, and they feel the same temp as the top radiator hose. What I find weird though is that when the temp gauge went up, the heat got hotter, and when it came back down, the heat got cooler. It only did it that one time. Also, one of the recent days that was in the 70s, i turned the heat on after driving it, and it was good.
Modified by hksdrift240 at 8:05 PM 10/18/2009

[Patarach]

your saying the heater isnt working correct?

My guess is that you either have scale in the heater core or heater lines

or

you have a bunch of crap clogging up the actual surface of your heater core

or

the linkage that moves the temperature selector is bent or something

BTW cars have thermostats to both warm up faster and to stay at operating temperature, for example a car with no thermostat would overheat after time bc coolant is flowing through the rad to quickly and it has no time to cool down.

[rickgerhardt]

I disagree with the heater core being clogged. The bottom hose would be cooler. Its possible that it could be a faulty thermostat thats stuck open. Are the radiator hoses too hot to touch? or just warm. Can you hear your "door" open when you switch it to heat? It is still possible that the heater control valve is broken. Happend to me on a jeep once, the valve broke off and wedged itself in the line, not allowing much coolant to flow through the heater core.

[Patarach]

I didn't say that the heater core was clogged, at least not completely. I said it might have scale deposits in it, which is probably unlikely bc scale usually forms on hotter parts of the cooling system but the large amount of surface area in the core, and the size of the passages make it possible. Scale insulates to the amount of 1/16 of an inch of scale has the same insulating effect as 4" of cast iron, and any covering of the interior fin structure of the core would cause the heater core to not put off as much heat as it should. Although I doubt this is your problem, it is a possibility.

Modified by Patarach at 10:24 PM 10/18/2009
Modified by Patarach at 10:28 PM 10/18/2009

[hksdrift240]

I think it could be that valve that lets coolant come in through the heater core because when I got home today, I tried to open and close it, but the little arm only moved maybe a quarter inch....maybe. Then, I changed the interior temp setting from hot to cold, and it was still blowing heat, even after I turned the a/c on with it on the cold setting even though my a/c doesn't work the best, but I remember it did actually get cool a few weeks ago. Or i guess it could be the temp door in the dash...but I dont know how to check that.

[rickgerhardt]

First thing I would do is pull the heater control valve off and look inside it. Mine looked like it was functioning properly but the only way you could tell it was broke was looking inside it. If you pull it off and move the hinge back and forth you will know. Its pretty self explanitory how it works. If thats not your problem then its gotta be your "door". When you move it from hot to cold can you hear it actually opening and closing? It should make a dull "thud" kind of sound when the door hits the walls. Hope this helps

[hksdrift240]

I guess moving the arm on that control valve did something, because I have good heat now. I drove it down the road, and the heat kept warming up. The only thing is when you slide the interior temp control knob from hot to cold, it still puts out the same temp heat.

[rickgerhardt]

Huh. Sounds like you def have a problem with your controls. If it was me, now that its workin, I would leave it. lol Then in the summer switch that heater control valve off manually so its not circulating through the heater core.