Coolant flow weak/nonexistent when cap is secure...

[NHMike]

in my never ending battle to get heat in my CJ7 , I decided to troubleshoot it again today. I have found that if the cap is on the coolant flow to the heater core is slow or non-existent. However if I crack the radiator cap flow seems normal. I have the Jeep runningand the pedal is pressed down so that the RPM's are up. Can anyone give me some insight as to what I could possibly need, hopefully its just a new radiator cap.

Thanks.

I've burped the system and the entire system is new, heater core, water pump and Thermostat are all new.

 

[Torxhead]

Interesting, it does sound like the heater core does have air in it. I have found that with having the radiator fill cap at the highest point on the cooling system, it does help with not having any air in the system issues. I have heard of guys filling the radiator with the Jeep on an upward slope and/or driving the vehicle up and down steep hills afterward.

 

[NHMike]

Interesting, it does sound like the heater core does have air in it. I have found that with having the radiator fill cap at the highest point on the cooling system, it does help with not having any air in the system issues. I have heard of guys filling the radiator with the Jeep on an upward slope and/or driving the vehicle up and down steep hills afterward.

When I take off the bottom hose, Coolant runs freely though. Of course, that's when the cap is cracked. When I close it back up, it slows and /or stops. This is while the motor is running and at high rpm's.

 

[Torxhead]

That might be O.K., but not sure. You should have at least a 195 deg. thermostat, if you have like a 160 deg. one it will affect heater temp. From what I have seen radiator caps do have a lot of work to do and do not last forever,

 

[SlowPocono]

How old are the heater hoses?
The only thing that the radiator cap changes is the pressure in the system.
Pressure cap.

There's a slight possibility that a deteriorating coolant hose has developed a sort of "flapper valve" inside that deforms and inhibits flow under pressure. This condition has been observed in diesel fuel systems.

That's a remote possibility, but it's becoming clear that this isn't an ordinary mystery.

 

[gert]

How old are the heater hoses?
The only thing that the radiator cap changes is the pressure in the system.
Pressure cap.

There's a slight possibility that a deteriorating coolant hose has developed a sort of "flapper valve" inside that deforms and inhibits flow under pressure. This condition has been observed in diesel fuel systems.

That's a remote possibility, but it's becoming clear that this isn't an ordinary mystery.

Ya your problem definitely is a mystery, did you change the radiator hoses to? I dont remember if you did or not, same thing with the heater hoses under suction the lower hose can collapse

 

[NHMike]

Hoses are not new, however, they weren't very old either.

It's getting pretty frustrating to say the least. I'm dumbfounded as to why it's not working.

 

[mtnwhlr]

Is the motor running at 190 and not over heating when you are driving it around? So the only issue you are having is little to no heat from your heater?

 

[SlowPocono]

Is the motor running at 190 and not over heating when you are driving it around? So the only issue you are having is little to no heat from your heater?

Apparently it's not just a lack of heat.

It's been said that there is very little flow of coolant through the core when the radiator cap is on, but it does circulate well with the cap off.

That's what I understand. Is that incorrect?

 

[mtnwhlr]

Apparently it's not just a lack of heat.

It's been said that there is very little flow of coolant through the core when the radiator cap is on, but it does circulate well with the cap off.

That's what I understand. Is that incorrect?

What I was trying to find out is is the motor over heating or running cold. If everything is normal with that then the coolant flow is fine and the problem is in the heating system. A lack of flow would cause the motor to over heat.

 

[NHMike]

Is the motor running at 190 and not over heating when you are driving it around? So the only issue you are having is little to no heat from your heater?

Unfortunately the temp Guage is inoperable, so I have no idea what the motor is running at. But it's been driving during the summer with no overheating.

 

[Posi]

Does the top hose get hot to the touch?

Did you open the heat gate while purging the system of air?

Is the heater cable in good working order?

 

[mtnwhlr]

Unfortunately the temp Guage is inoperable, so I have no idea what the motor is running at. But it's been driving during the summer with no overheating.

I think your problem is in the heating system in the dash. You need to make sure that when you pull the temp and air knobs that the are opening like they should and you are getting plenty of air comming in the cowl vent and down tru the system. It sounds to me like you have something not opening or a blockage in the air flow tru the system.