Engine Bleeding air in the heater core

keel

Active Member

Aug 23, 2020

220

75

38

Seattle, Wa

Apr 2, 2026

#1

• Apr 2, 2026

• #1

Has anyone ever tried installing a bleeder on one of the heater core hoses? I can’t seem to get my heat to blow as hot as my other cars for whatever reason and I suspect it’s because there is air trapped in there.

Even with my car jacked up in the front the heater core is still not much lower than the radiator fill hole and the hoses coming off of it are also routed downward.

 

KRUISR

10 Year Member

Apr 16, 2015

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143

Apr 2, 2026

#2

• Apr 2, 2026

• #2

Year? Model? Mods? Pics?

I have only ever filled the rad, then started the car with the rad cap off and let if idle and warm up. Eventually the t-stat will open and coolant level in rad will drop. Then you will see coolant flow out of the rad tubes. Let this continue for a good 5 minutes or so keeping an eye on the coolant level in the rad. You don't want it to empty but you don't want it kept full - I would say about half full. The level could rise and fall over the 5 minutes and if you have added too much it will come out like a geyser so keep watching it and be ready to move.

After the 5 minutes of circulating I usually top up the rad and immediately put the cap on. You can then shut the car off and let it cool down. In a half hour to an hour check the overflow tank and fill it up to the appropriate level.

I have NEVER had issue using this method on any non-pressure tank coolant system. I do this with the vehicle sitting on level ground (I have never jacked up the front of the vehicle to make the rad cap the highest point).

 

Last edited: Apr 2, 2026

nicholase

I lubed and pushed, until it was all the way in

May 21, 2024

628

1,122

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New York

Apr 3, 2026

#3

• Apr 3, 2026

• #3

I've never jacked the front up either. The way it's outlined above is all you have to do.

I'd look at your blend door and cable.

 

Reactions: General karthief

keel

Active Member

Aug 23, 2020

220

75

38

Seattle, Wa

Apr 3, 2026

#4

• Apr 3, 2026

• #4

Alright I'll check the blend door too.

Cooling system is all OEM stuff and the heat still blows warm I just like it to be real toasty like it is on my Ranger. Maybe my expectations are too high?

 

AeroCoupe

lube between the nut and the face. I know my lubes

Founding Member

Oct 28, 2001

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Claremore, OK

Apr 3, 2026

#5

• Apr 3, 2026

• #5

So what temperature thermostat do you have in the car? If it is OEM it should be a 192 deg and that is plenty to get hot air in the cabin.

 

keel

Active Member

Aug 23, 2020

220

75

38

Seattle, Wa

Apr 3, 2026

#6

• Apr 3, 2026

• #6

Honestly I can’t remember off the top of my head the exact temperature but I got an OE replacement from Oreilly autoparts a couple years ago so it’s probably a 192 degree.

 

Reactions: AeroCoupe

keel

Active Member

Aug 23, 2020

220

75

38

Seattle, Wa

Apr 10, 2026

#7

• Apr 10, 2026

• #7

I checked the blend door by taking off the glovebox and moving the lever around by hand and it looks like I'm getting full travel with the climate control knob. I think I can rule out the blend door without opening up the heater box since that seems like a massive pain.

I'm going to install a little bleeder junction in one of the heater hoses and report back with results since I'm curious and I have extra hoses.

 

Reactions: nicholase

nicholase

I lubed and pushed, until it was all the way in

May 21, 2024

628

1,122

103

New York

Apr 11, 2026

#8

• Apr 11, 2026

• #8

Yeah, if the door actuates all the way then it's probably not the problem. Not sure how you tested it, but I would turn it all the way hot and mark the position of the blend door lever with something. Then take the cable off the little clip and see if it goes farther. Swing the blend door lever back and forth by hand and make sure it feels and sounds like it's opening and closing all the way.

When you have the hoses off to install your bleeder, blow through the core and see if it seems clogged. That could definitely cause a low circulation / low heat problem. There should be no resistance to blowing through it.

 

AeroCoupe

lube between the nut and the face. I know my lubes

Founding Member

Oct 28, 2001

5,842

3,972

183

Claremore, OK

Apr 11, 2026

#9

• Apr 11, 2026

• #9

If he can get down in the engine bay and blow on the heater core tubes that will sell on Only Fans....

 

Reactions: General karthief, keel, nicholase and 2 others

keel

Active Member

Aug 23, 2020

220

75

38

Seattle, Wa

Apr 11, 2026

#10

• Apr 11, 2026

• #10

Okay here was my solution:



When I cut the hose open almost no coolant came out which indicated to me that there was a lot of air in there. Bled the cooling system again after installation and the heat blows much hotter now.

I think it would have worked even better if I put the bleeder on the outlet hose instead of the inlet hose but the shape of the hoses made it a lot more convenient to use the inlet. Might mess around with it some more in the future to move the bleeder to the outlet but I'm pretty happy with the results.

 

Reactions: gkomo

limp

wrap a little cheese around it and its a done

5 Year Member

Oct 4, 2020

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Florida

Apr 23, 2026

#11

• Apr 23, 2026

• #11

A friend from a Radiator shop " many years ago" used to remove the Outlet side from the heater core to bleed problematic cooling systems that did not want to bleed ....

 

Reactions: keel