Heater Core Bypass; Air Trapped in Heater Core?

[my12by60]

I am thinking of doing a heater core bypass since my heat does not work anyway. One of the little motors has failed and the blends doors don't move properly to route airflow past the heater core.

I am still trying to solve a problem with my coolant temperature rising in hot weather. I am wondering if I have some air trapped in the heater core. If yes, wouldn't this air just be released through normal bleeding procedures?

I have the Lisle funnel and have used it. Of course, when I do the bleeding, I can't turn on the heater because of the failed blend door motor. Does the inability to put the system into heat mode have any impact on the ability to bleed air from the system? Or does the second generation Q have a continuous flow of coolant through the heater core whether the heat is turned or off?

If bypassing the heater core has no possibility of eliminating any air trapped in the heater core, then I won't waste any time on the bypass as I have no signs of a heater core leak.

[Q451990]

I'm not sure, but my understanding of the heater setup, is that the core is always hot - but just bypassed by the air dampers/doors. If that's the case, I'm not sure why the FSM tells you to set it at max hot during bleeding though.

[my12by60]

My 1998 Durango works the same way. The hot coolant is always flowing through the core. When heat is selected at the dash, then the airflow is redirected over the core via a blend door shift to produce heat at the vents. If this is the same with the Q, then I agree that the FSM makes no sense as selecting heat at the dash has no bearing on coolant flow. Maybe somebody else will chime in an explain why the FSM says what is says.

[ZiprHead]

As far as I can tell, there is a heater control valve that controls the amount of hot coolant going into the heater core. If that is stuck closed, you won't get coolant into the system and won't be able to purge the air from the system.

[my12by60]

If that is the way the heater control valve works, and the valve is stuck closed, then it seems like it would not matter if air was trapped in the heater core or not. This is because the circulating coolant loop would exclude passage through the heater core. Any air in the heater core coolant is isolated from the circulating coolant. So once air was purged from the circulating coolant, the coolant should be able to do its job even though an air pocket may exist in the heater core. Does that make sense or do you disagree?

[ZiprHead]

If the valve is stuck closed, I don't believe air in the core would matter. You could try manually opening the valve. I believe it's right by the firewall before going into the core on this vehicle but I could be wrong about the location. It would be somewhere in the inlet hose path.

As far as your blend door system malfunctioning, there is an onboard heater control diagnostic function built into the system. How to use it is in the FSM.

[my12by60]

I already used the diagnostic and it said that the blend door motor had failed along with another of the motors that controls the system. The system produces cold ac but no heat. The motor that lets you control the temperature of the ac also does not work. So it blows very cold air and our only adjustment capability is to vary the fan speed. This works ok for us since we are in Phoenix and don't need heat and the ac control that we do have is good enough vs. true thermostatic control. Of course, it would be nice if the system was fully operational, but tearing the dash out to get at those small motors is too much work and cost vs. the benefit.

The more important problem that I have been trying to solve is the creep up of the coolant temperature during hot weather with either sustained driving at freeway speeds or climbing hills. So based on our discussion, I think I can eliminate air in the coolant as the possible source of the problem since I have used the Lisle air bleeding funnel.

[ZiprHead]

From reading your other posts about your problem, I'm wondering if your radiator is partially clogged.

[my12by60]

I guess that is possible, but I don't think that is the source of the problem. The prior owner had the original radiator replaced in Sept 2013. She provided the receipt, which included replacement of hoses and thermostat at the same time.

[ZiprHead]

Okay, I seem to remember that from the original post.

I did a quick google and found this.:

"Ramsey Mesyef, ASE Certified Mechanic turned grad student...
Written Jan 5, 2016
First make sure your thermostat is working, that is a much more common problem than a radiator being blocked.

If you're sure your thermostat is working (either by carefully feeling the coolant hose coming out of it to confirm it is hot or going so far as to remove it completely as a test if it's easily accessible), then carefully see if the hose leaving the radiator is warm.

If your radiator is partially blocked and causing coolant to go through it more slowly than it should, the symptoms should be variable with outside temperature and vehicle speed (whereas with a thermostat it should be pretty much the same under all conditions). For example, it will be hotter sitting in traffic than at highway speed.

What is more common than an internally blocked radiator (though of course that does happen) is an externally blocked radiator where road debris and dried bugs are preventing air from passing through it and hampering its ability to cool things down. Visually inspect both the front and the back. If dirty, ou can literally take a garden hose to it and should notice a differnece immediately (if it is your problem). Even if it is not visibly dirty, make sure the air from the fan is passing through it to the engine side. And while we're on the topic of fans, make sure yours is working. That's also a much more common problem than an internally blocked radiator.

Again, seriously, be careful, the components will be hot."

Also this one came up.:

"Joe La Garbo, 30 years experience as an Automotive Technician. Employed at All Transmissions.
Written Jan 2, 2016
In the trade we use a in fared thermometer laser pointer and shoot it at different parts of the radiator to see how much the temperatures vary. If the temperatures vary by 30-50 degrees and the thermostat is working, chances are it's restricted. Without this you can also check it with the palm of your hand. First after the engine is warmed up shut it off and feel the upper and lower radiator hoses to see if the temperatures vary. If restricted chances are the upper hose will be very hot to the touch while the lower will be just warm. Once again that is if the thermostat is functioning properly. Also if you have access to different parts of the radiator core itself (the finned middle portion) feel it with your hand in different locations to feel for temperature variations. Be careful however because if you have an electric fan it can come on even with the car off. If temperatures vary, you can try to power flush or reverse flush the cooling system, but your best bet is to replace the radiator or have it boiled out by a Radiator repair shop, because at this point flushing is usually only a temporary fix. Without the year, make, model and engine size of your vehicle it's hard to give you a more accurate answer. But be sure your cooling system isn't leaking, thermostat is working and the electric fan(s) come on (if the car uses one). Good luck and hope this helps."

Other good tips here. https://www.quora.com/How-do-I-know-if- ... ng-coolant

[my12by60]

Ok. Thanks. I will check a few more things as suggested in the information you provided. This has been a stubborn problem to diagnose.