Heater not working

[JulieC]

My heat stopped working last week in my 2005 Grand Prix. We changed the thermostat and everything worked fine. Yesterday I noticed the temperature was running higher than normal (1 line past halfway) but the heat was working. Now the temperature is still running at that same mark but the heat does not blow out cold.

When I changed the thermostat, I added a little coolant to the overflow because I thought it was low (couldn't see the marks on it). For 2 days I could smell antifreeze when I got out of the vehicle but now it has no smell and the level in the overflow is back to where it always stays.

Any suggestions on what to try next? I saw a post that said to flush the heater core. I'm not sure how to do that. The whole system may need to be flushed as I have never flushed it and it has about 100,000 miles on it. Someone told me it could be the sending unit but I can't find any information about a part like that on this car.

Any help or suggestions would be appreciated. Thanks!

[bps02gtp]

there is no such thing as a sending unit unless they are refering to a water pump. that or your coolant elbows could be leaking but it is unlikely with low mileage. who knows double check

there is whats called a reverse flush on your heater core. sometimes they get a little clogged. theres 2 hoses. take them both off and use a hose to push water through both ways gently until you get an even flow in both directions. you should notice that the flow starts off a little slow and then gets fast. if it does then it was slightly clogged. and yes at a 100k miles you want to put some fresh anti freeze in there so just do a complete flush and you should be good to go.

if that doesnt work then you have an issue with your "blend actuator" i think is what its called where you control the temperature of your air coming through from hot to cold.

[JulieC]

Thanks for the quick reply. So if I do a complete flush, will that flush out the heater core? Or do I also need to do the reverse flush you mentioned?

[TheOtherNick]

A complete flush will also do the heater core, is your coolant full and bled? with no leaks?

[JulieC]

My coolant is full but I didn't know if it was bled. When we changed the thermostat, we had to add a small amount to it. The heat was working perfectly for about a week though.

We went out and tested and both hoses are warm from the radiator. What we found is that the hoses going to the heater core are both cold. By revving up the engine to about 3,000 the heat does come out warm so I think you are absolutely right about the heater core being blocked.

I'm about to go get what I need for a radiator flush and also some extra hose for flushing the core in case the flush doesn't break through the blockage.

I'll let you know how it turns out.

Thanks for the great advice!

[JulieC]

Flushed the system today and we had to run it through for about 15 minutes but it must have taken care of the blockage because the heat is running hot again and the hoses going to the heater core are hot again.

We found a leak after we turned it off at the heater hose fitting or elbow beside the alternator. You could hear it hissing. Ordered the 2 fittings and we are going to change them out when they get here.

Thanks for all the help on this.

[bps02gtp]

yeah the coolant elbows are common for going bad. they're cheap. i believe that is what you're referring to anyway.

[JulieC]

That's the ones. They are $1.84 for the set of them so I can't complain about that. It looks like they are pretty easy to change out too. We didn't notice it until we heard the hissing when we were running the engine with water and the flush in there. It doesn't hiss with the coolant in the system.

[midrange]

When you did the flush, did you replace the dexcool with the yellow, green coolant?

[Egg]

There is actually a sending unit, in fact Im pretty sure there are 2 of them.

[bps02gtp]

A sending unit for coolant? 2 of them? What r the names and where r they located?

[JulieC]

We went with the Dexcool again. The heat is still hot. The parts should be in today to change the elbows.

[Egg]

Im sorry I meant there is one sending unit (located under the thermostat housing, behind the crossover exhaust pipe). But it sends out 2 signals-1 to the gauge, and one to the PCM, making a stop at the ECT.