Heater Core Flush

[Mel0]

So my heat is weak at best and I'm wondering if anyone knows of a good write-up to flush the core or if there may be any known simple fix for this.

 

[PacificBlue2005]

I have the same...weak heat on idle, a little more at higher rpm or under load. Temperature gauge reflects the same, so I am going to replace my t-stat tomorrow. I'm thinking it is stuck open.

Anyone know if the 80 in-lb torque setting is the same for the OEM replacement? I only ask because the original inlet housing is metal, and the replacement is plastic with metal inserts. I don't want to break a brand new $42 part.

UPDATED: never mind, I am an idiot. The original part is plastic as well, I must be thinking of my Tundra.

 

[Mel0]

Should the cold/hot air dial make any clicking noises when turned? It does have some resistance when turning from hot to cold or cold to hot and makes 2-3 clicks when doing so. The valve at the firewall is moving with the cable but I'm not sure where the little arm attached to the cable should be in either mode. When set on cold it is almost horizontal to the left and on heat is almost vertical.

 

[PacificBlue2005]

I have the same...weak heat on idle, a little more at higher rpm or under load. Temperature gauge reflects the same, so I am going to replace my t-stat tomorrow. I'm thinking it is stuck open.

UPDATE: replacing the t-stat did the trick. I didn't realize the cooling system has a heater bypass circuit, that allows you to get heat before the t-stat opens. With it stuck open, the engine takes forever to get to temperature to give off heat. What is old is new again I guess, since my 1966 Ford Galaxie 500 with a 390 cubic inch V-8 has this same heater setup.

 

[Mel0]

As it's getting colder, I finally realized that the heat vents for the back seat are pushing out HOT air but I don't seem to get even half that heat up front. Do the front and back vents work off of the same heat source/core? Is this an issue with the vent doors not opening properly? The cold/hot knob is difficult to turn and makes a "clicks" while doing so, which doesnt seem right to me...

Thanks all

 

[Dutch-Runner '99]

As it's getting colder, I finally realized that the heat vents for the back seat are pushing out HOT air but I don't seem to get even half that heat up front. Do the front and back vents work off of the same heat source/core? Is this an issue with the vent doors not opening properly? The cold/hot knob is difficult to turn and makes a "clicks" while doing so, which doesnt seem right to me...

Thanks all

The front and rear hear both work in the same way, they both receive coolant from the engine, the only difference is that the rear gets its air from under the front/passenger seat, so its only recirculating air and isn't bringing in fresh air from outside. So as the passenger compartment heats up the rear heater will also always be receiving warmer air to heat up and pump to the back seats where as your front heater may be getting cold air to heat up from the 'fresh air' setting.

My thoughts: If your rear heater is heating up just fine and your front isn't then your front heater core could have a blockage in it or your temp control knob isn't turning all the way to 'full open' to allow the warm coolant in.

 

[jmildoc]

The front and rear hear both work in the same way, they both receive coolant from the engine, the only difference is that the rear gets its air from under the front/passenger seat, so its only recirculating air and isn't bringing in fresh air from outside. So as the passenger compartment heats up the rear heater will also always be receiving warmer air to heat up and pump to the back seats where as your front heater may be getting cold air to heat up from the 'fresh air' setting.

My thoughts: If your rear heater is heating up just fine and your front isn't then your front heater core could have a blockage in it or your temp control knob isn't turning all the way to 'full open' to allow the warm coolant in.

that's not entirely correct, the rear heater has its own heater core, so it does suck in air from the passenger compartment but it gets coolant from the front and brings it to its own heater core and then blows it out. so your rear heat can be hot while your front heat isnt, they are separate.

 

[Dutch-Runner '99]

that's not entirely correct, the rear heater has its own heater core, so it does suck in air from the passenger compartment but it gets coolant from the front and brings it to its own heater core and then blows it out. so your rear heat can be hot while your front heat isnt, they are separate.

I don't see where the difference is between what you and I said

 

[nevada]

drain all the coolant.
get a chemical cooling system flush. maybe even several bottles.

add the flush(some systems will take 2 bottles), top off with water. run the engine until the system is full.
go for a 10-15 minute drive.

let it cool, drain the system. refill with water, and possibly another bottle of flush, if its really bad.
repeat the above.

I try to run a water cycle TWO times after adding the flush, to make sure everything gets removed. then refill with the proper antifreeze mix.

 

[RussToy]

As it's getting colder, I finally realized that the heat vents for the back seat are pushing out HOT air but I don't seem to get even half that heat up front. Do the front and back vents work off of the same heat source/core? Is this an issue with the vent doors not opening properly? The cold/hot knob is difficult to turn and makes a "clicks" while doing so, which doesnt seem right to me...

Thanks all

I have a 2000 with a dial. Mine turn nice and smooth with no clicking. So this might not have anything to do with your heater core. If it was me...I'd take a look behind your dash and make sure everything is working properly before I started spending money.

Good luck...

 

[Mel0]

I'll start by pulling the dash cluster off and check out what the resistance is with the hot/cold knob first. But wouldn't the "doors" be operated by the vent selector knob??? Anyone know if I'll even be able to access the "door or doors"? Also, I noticed there are two lines that look like ac lines headed underneath the passenger seat so it seems like there would be a secondary core for the rear heat. However, those are connected after the valve(?) or whatever it might be that is under the hood at the firewall. That valve appears to fully open and close. I don't know, I'm confused as to what does what and where the heat could be getting stopped up....

thanks all

 

[nevada]

I'll start by pulling the dash cluster off and check out what the resistance is with the hot/cold knob first. But wouldn't the "doors" be operated by the vent selector knob??? Anyone know if I'll even be able to access the "door or doors"? Also, I noticed there are two lines that look like ac lines headed underneath the passenger seat so it seems like there would be a secondary core for the rear heat. However, those are connected after the valve(?) or whatever it might be that is under the hood at the firewall. That valve appears to fully open and close. I don't know, I'm confused as to what does what and where the heat could be getting stopped up....

thanks all

yes, the rear heat has its own core.

before you start tearing anything apart, check the hoses going to the heater core.

get the rig up to temp, put it as hot as it goes, and the fan on high.
check the heat coming out of the vents, make sure its as warm as its going to get.

then open the hood, and find the 2 heater hoses going into the firewall. carefully grab each one. they should both be HOT. if one is significantly cooler than the other, the restriction is in the core itself.

sometimes you can just reverse the two hoses, to run the water in the other direction to clear it up. but usually, its needs to have a flush done, as I suggested above.

there are also places that will do a pressurized flush, with a machine. but, I would attempt to do it myself with the chemical treatment first.

 

[Brian757]

yes, the rear heat has its own core.

before you start tearing anything apart, check the hoses going to the heater core.

get the rig up to temp, put it as hot as it goes, and the fan on high.
check the heat coming out of the vents, make sure its as warm as its going to get.

then open the hood, and find the 2 heater hoses going into the firewall. carefully grab each one. they should both be HOT. if one is significantly cooler than the other, the restriction is in the core itself.

sometimes you can just reverse the two hoses, to run the water in the other direction to clear it up. but usually, its needs to have a flush done, as I suggested above.

there are also places that will do a pressurized flush, with a machine. but, I would attempt to do it myself with the chemical treatment first.

I just did a heater core flush on my girls Passat. I used a hose and sprayed into one of the lines that run into the firewall, and ran the other line into a bucket. I monitored all of the particulate coming out of the heater core. And then ended up using Prestone heater core flush. It worked well. Her heat is back to normal. But yes, Nevada is all correct. Feel both lines to see if one is hot, and one is not. Usually a good sign of a bad clog.

I was recommended to use Drano, but I'm not trying to beat up the heater core. I was also told to use a pressure washer to spray into the heater core, again, another idea I passed up, because I don't want to hurt the heater core.

 

[Mel0]

The inlet line is a bit warmer than the outlet line for both of the heater cores so I think that may be a contributing factor. But I think my main issue is with the blend doors since the knob doesn't turn to hot or cold without clicking and much resistance. Anyone ever had this sort of issue? I read through Skids thread and he oiled up some pivots points somewhere on the unit below the glove box so I'll give that a try...

 

[reelamin]

Adding to old thread to help others as I am having same issue now.

My heater started putting out less heat and basically was barely putting out any heat. I just recently dumped in some Blue Devil (Two months ago) due to blowing a radiator up and possible head gasket issue. Two days ago I checked the hose temps...and no question the T-Stat was stuck open 156 or so on top and 84 on bottom...120 going into the top heater hose.

Yesterday I put in a new T-Stat and there was some definite slimy looking build up on the bottom lip of the old T-stat. I have never seen anything like that before, and it just washed right off with the hose. (Now I realize I should have taken a pic.) I'm thinking it was from the Blue Devil...not sure...but having flushed the system with cleaner and water before the Blue Devil....antifreeze does not cause it.

The heater worked great yesterday sitting in the driveway and for about the first 20 miles today. Went right back to doing the same thing of no heat, barely any heat, then cooling off, rev engine by down shifting or taking off from stop and get a little heat back. Rear heater is putting out warm air constantly now where before only luke warm. Before the new T-stat it was also cooling off. Today I put the thermometer on the hoses and the new T-Stat is working fine....top 176 and bottom 156. Inlet to top heater core 156....outlet 123....with minimal heat output.

I think I have found my culprit. Flushing the top/main heater core is next. I will just flush it in the rig and catch what ever comes out.

 

[Mellemel]

Isn't this so GD annoying !!! I have had the same issues for over 2 years now ! Yes 2 years, Ok so I just replaced the rad and T-stat, it was nice and hot for a day, now it's doing the HOT then cold then HOT then cold routine again. FFS.

I flushed the heater core (front one) out so many times over this time period and even ran CLR thru it, I think that helped. The thing is it's nice and hot in summer when you don't need it and I thought I'd fixed it !! WHY ????????? When the winter rolls around it just doesn't wanna play.

I need to either replace the heater core, get a new OEM rad cap as I think the current original cap is allowing air to leak into the system still and do a system flush with some chemical stuff. I have burped and burped many times which has some effect but not for long.

I really really don't want to rip apart the dash to change the heater core, might have to though to get this prob fixed for good.

 

[thegipper]

Have you captured the flushed fluids that came out of the heater core to see how contaminated it was? I know you said you tried CLR (I've used it too on a heater core) but maybe a specific heater core flushing chemical is in order.

Try flushing it again, maybe its super plugged and needs a couple more tries with a good chemical cleaner. Be careful you don't apply too much pressure in the core or you will be replacing it when it bursts.

Good luck

 

[reelamin]

So I flushed my top heater core today and did not seem like I got much out of it. I just hooked up a garden hose to the inlet and outlet at the firewall. Used 10lb of compressed air to blow out the coolant (left container), then added a few quarts of water and blew it out (middle container) added in CLR let sit for 15min and blew it out (individual container). I just hooked the garden hose up and allowed low pressure to flush the system of CLR. CLR did absolutely nothing as far as remove any more material than the water did.

Temps are working great so far, but only took it on a few mile drive. I checked the temps at the valve, outlet pipe, vent, and defroster numerous times. Overall they were consistent with some slight fluctuations of a few degrees. Basically I ended up with the following temps at the vent and center defroster at idle/60mph.....125/145 and 105/115. The thing works great for now....will see if it keeps working so well.

 

[Mellemel]

You know what worked for me ? I reversed the heater core in and out hoses now I can't believe the heat output I have had today. Freaking awesome. If only I had done this 2 years ago !!:loco:

 

[thegipper]

Maybe they were backwards to begin with? Either way, glad it is working again.

Whenever I flush out a heater core, I always flush in both directions to help break loose any gunk that is in there.