I recently swapped out a radiator and completely flushed the system. I had paid a shop to swap out the Dex-Cool last year but ended up with a nice greenish-orange blend instead. Turns out I didn't quite finish the job on my first try because I didn't backflush the heater core so I did that a few days later with the hose. I wanted to make sure to get the tap water out of the core before reconnecting it to the system so I used a shop-vac to blow it out, flushed it with distilled water then refilled it with coolant, bled the system and let it idle for 20 minutes and the engine sat at around 190 degrees so I thought I was all set. Until my wife drove it. She called me and said "it sounds like sloshing water when I drive away from a stop." If you look at the design of the heater core, the highest point is well above the outlet so it is essentially designed to trap air. Friggin' Brits. Last night I tried to bleed it again but only got a nice steady stream of coolant. So I started up the truck and figured I would try to force the air out. I revved the engine up a little, pinched the outlet hose shut with my finger to build up a little pressure in the heater core, then let go of the hose. As I was releasing it, I could feel air bubbles moving through the line. I did this repeatedly until I couldn't feel anymore bubbles flowing through the line. Of course, by then the hose was so hot I could barely touch it so it may have just been that I couldn't feel. I let it cool and then tried to bleed it through the srew but didn't seem to get any air out. Not sure if I got it all. It was blocked in the driveway and it was late so I didn't get a chance to drive it. It check it out tonight and see.

Has anyone else been through this? When you just flush the system, the heater core stays full so this isn't an issue but with a replacement it would be. I'm wondering if there is another way. Even if I don't hear any sloshing sounds I wonder if there still might be some air in there.

 

If properly bled, when engine is stone cold, not running, fill the coolant bottle until a steady stream of coolant is coming come the bleed screw then that is all that is needed. If done right, then let the engine warm up to operating temp with both heater set full hot, at idle you should then have warm to hot air, if not but you do get warm to hot air at a higher RPM, then you still have air trapped but even that should move to the recovery bottle after a couple of drives.

 

I had penty of heat at idle, but there was definitely air trapped in the heater core. When installed, there are several inches of heater core above the outlet pipe so air can definitely be trapped with the the fill and lift the reservoir technique. I did just that with the engine cold several times to no avail. Since I had blown out the coolant with air, the heater core needed to be completely filled somehow and there is no way to do that with gravity alone. I'll see if the pinch-and-surge technique did the trick.

 

Its the proper bleeding that works no pinching or any other stuff needed. Just follow the procedure to the T and that's it.

 

I completely disagree. If you are simply flushing and then refreshing the coolant then yes, it is fine because the heater core will always be full of coolant. The lines to the core are higher than the top of the core where they run along the top of the valve cover so there is no way that pulling the lower radiator hose will drain them. But if you have evacuated all of the fluid from the core, then there will always be air trapped in there when you fill it under gravity because of the location of the outlet on the side of the core in relation to the top. Now if the standard bleeding technique removes sufficient air from the system that it will eventually bleed the air out of the top of the core just through volume and pressure of the flowing coolant then yes it can be considered to work but after driving the thing around for maybe 10 miles it was still making sloshing sounds so I was a little concerned. The approach I used definitely removed at least some of the trapped air because I could feel it flowing through the hose, whether or not I needed to do it is up for debate. I just threw this out there in case anybody had replaced a heater core and had come up with a better way to get the air out.

 

I can only speak on using the method that Mike and 2001 have mentioned. It has worked for me. Though it took me about 3 bleeds to get all of the air out.

 

When you needed to bleed your cooling system, was it because of something you did in front of the engine like a thermostat or just a coolant flush? If you didn't remove all of the fluid from your heater core by blowing it out with air, then it stayed completely full and that part of the system didn't need to be bled. The only way for air to get out of there under gravity filling is for it to flow down through the fluid and that aint happening.

 

I have had the pleasure of changing at least 30 heater matrix on D II over the years and never had a problem with air being trapped in the top of the heater matrix. Simply because of the bleed process nothing special. I have never used any pinch method or anything like that. So no I am not talking about a simple drain and refill or a t-stat change and a fluid top off. There is no specific bleed procedure for a heater matrix dude you put it in and then bleed the entire system as (ONE) as a "WHOLE" .

 

if your that worried about it pull off both heater hose from the engine, fill one with coolant untill it comes out of the other and put them back on. Whatever air is in there will work it's self out.

 

Warning - no one agrees with this method of bleeding but...

Unclip the coolant tank and raise it up high.
Wedge rags under it to keep it high and steady.
Fill it with coolant up to the fill line
Keep the coolant cap off.
Start the rover.
Run the engine in Park at 1,200 RPM for about 8 minutes.

Then go to idle.
Turn off engine.

Fill the bottle to the fill line again.
Put the cap on.
Clip back into holder.

Done.