Heat not hot at higher fan speed

[btah]

Hello, looking for a little advice/direction on a heat issue.

issue: Since it started to get cold up north I noticed my heat has not been working well. At low fan speed the heat comes out of the front vents at about 140 degrees F. As I turn the fan speed up it comes out cooler. By the time I get up to full fan speed it is still a little warm but it isn't going to cut it when the temps really drop. While sitting at idle it is cooler than when moving. I know a little bit of that is normal, but it gets much cooler than it should at idle.

All of the controls work. Wherever I direct the heat, it goes there. Floor/defrost work but the temp stays the same. The hot/cold dial (is it called the thermostat?) works as I can go from cold to hot and the temp changes. It just doesn't get real warm on higher fan speeds.

However, it does seem to get a little warmer when I put the fan in "max" mode. Not sure if that is a figmant of my imagination or not.

I flushed the heater core twice (just flushed with water, no cleaner). It seemed to make it a little warmer. The path seemed clear to me both times I flushed it. I can blow through it very easily and it doesn't seem to me like there is any restrictions. While flushing the core I noticed I had a small radiator leak. I replaced the radiator and thermostat and that hasn't help out.

One of the hoses going to the heater core is definitely warmer than the other one. The hoses are set up so that there is a larger diameter hose coming from the coolant reservoir that goes into a tee with smaller heater hose coming from one side of the tee to the heater core and the other side of the tee going to the engine (water pump?). The other heater hose from the core goes directly to the engine right next to the other hose. The hose that goes directly from the heater core to the engine is warmer than the other hose with the tee. It gets hot enough that I can't hold onto it for more than a few seconds.

I don't understand how the coolant is supposed to flow. Can someone explain that to me? Also, any ideas as to what I can look at next? The coolant I drained out on the radiator replace was the original coolant (10 years old). The truck has 65,000 miles. The coolant and everything else I looked at was very clean and I didn't get any chunks out anywhere.

it is a 2003, 4.7.

If you got this far, thanks.

 

[MegaMouseGW]

Kinda sounds like the heater core is getting clogged. Even though you way you can blow through the core even a small bit of clogging or deposits can have major effects. Either replace the heater core, take it too a shop that can do a complete flush with an acid to get rid of all deposits.

 

[btah]

I have read a lot about using CLR for a cleaner. Anyone have any experience with that? Any other products anyone have experience with? I don't mind trying something if it isn't going to trash the core. It is not bad enough for me to go after swapping out a core.

Also, it is definitely warmer when I use the "max" setting (although not as hot as it should be). Not sure why that would be, anyone?

 

[devans]

I did a complete system flush on my 02/4.7 two years ago using prestone and got better heat out of it. The following winter not so much. So I borrowed a buddies infra red thermometer and started checking hoses with the engine warmed up. What I found was the inlet and outlet temps for the heater core were different by around 50 degrees. That's huge. This was with the fan off BTW. I back flushed the heater core with water and got some crud out then once I was happy the core wasn't plugged I hooked a pump to the outlet hose and back flushed with that. This year same thing low heat. I too read somewhere that someone used CLR and I gave that a shot. Worked like a charm, I now have more heat than I know what to do with and for whatever reason the whole system heats up faster than it used to. It used to take around ten miles before I had decent heat, now I have it in two.
We'll see what happens next year.
If you use CLR be sure to dilute it. It says right on the label not to use it on aluminum, guess what the core is made of, and when you flush it to clean out the CLR do it for a long time.
Hope this helps.
Don

 

[btah]

Thanks for the reply. If you are still following this maybe you can give me a little more info. Did you dilute it 50/50? How long did you let it sit in the core before flushing it out?

 

[devans]

Yea, I'm still following. I won't post a reply and walk away like that. I looked at the label on the CLR jug and kind of fudged the numbers a bit. I was pretty nervous about the don't use on aluminum warning and as far as I know the heater core in my truck is original.
I think I used between 1/2 and 1 cup to a gallon or so of water, pumped it in through the outlet/top hose and into another bucket. I let it sit for about 4-5 minutes and hooked up a water hose and ran that for probably 5 minutes. You really want to make sure the CLR is out of there. I did this a couple of times.
I used a very small transfer pump to get the CLR solution into the core and to get the antifreeze in and the air out later. I only disconnected the heater hoses and didn't do a full blown antifreeze change out. You will need to clamp off the hoses on the engine side to keep from losing the antifreeze from the engine and radiator.
I have a writeup with pictures I did at a different site I could post here on this site if your interested. It shows the pump, which hose is which and the clamp setup I used.
There are some videos on youtube as well, I watched one by eric the car guy but he didn't get specific about diluting the clr and it appeared to me he used it straight. I'm not that brave.
Let me know and keeps us posted on your results.
Don

 

[MegaMouseGW]

Using CLR on aluminum straight is a no no. Dilute it pretty well. Like Devan said at least 1 cup per gallon of water.

 

[btah]

I thought I would try to avoid CLR since it is pretty clear that is is not made to be used on aluminum. At least I am trying to avoid it right now since winter is kicking in and if I trash the core I would rather do that in the spring. So, I flushed the hell out of the core again. I let a hose run through it for about 10 minutes. I then filled the core up with Prestone super flush and let that sit for about 4 hours and then flushed it with a hose for about another 10 minutes while periodically stopping the hose and blowing through it with compressed air.

The heat seems to be much better although I don't think it is back to what it should be. At low fan speed I was previously getting about 135 degree heat, now I am hitting 160. It still cools down to about 135 when I put the fan on high. Also, it cools off into the 120s when at idle. It is going to drop to zero this weekend so that will be a good test.

After doing a little more research I never ran across a strong product that is OK to use on aluminum. However, drano might fit the bill. I haven't found anything yet that says to not use it on aluminum.

Thanks again for your input.

 

[devans]

Hey I was nervous about CLR too but I'm glad I bit the bullet and did it. Your numbers sound about the same as I was getting before CLR. I haven't checked the actual temp coming out of the vents yet but as I said earlier the truck heats up much faster and I have more heat than I know what to do with.
Even my wife commented on it and she rarely rides in my truck.

 

[MegaMouseGW]

Hey I was nervous about CLR too but I'm glad I bit the bullet and did it. Your numbers sound about the same as I was getting before CLR. I haven't checked the actual temp coming out of the vents yet but as I said earlier the truck heats up much faster and I have more heat than I know what to do with.
Even my wife commented on it and she rarely rides in my truck.

My wife rarely rides in my truck also (says it is too loud for her taste), but she always says that it seems my AC is a ton colder than hers. Wonder why???

 

[devans]

My wife rarely rides in my truck also (says it is too loud for her taste), but she always says that it seems my AC is a ton colder than hers. Wonder why???

He,he,he. My wife likes the loud pipes on mine and she actually likes riding in it. Says she can see more in my truck (stock height) than her Nitro, but other than me driving to work the truck sits in the driveway a lot. Every so often I have to get hay for the critters or someone needs something big moved and she does a ride along. Her Nitro does get better milage so we take that out more often.
She told me the other day I need to learn how to use the temperature control knob. That made me chuckle.