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Weak uneven heat, '95 XJ, heater core flush?

R

robhurlburt

NAXJA Forum User
Location
lexington,ky
i heard this is the place with all the smart people :wave:

The heat in my XJ is pretty poor, and inconsistant between vents. the floor is borderline useless.

Would a heater core flush fix this? If so, any good DIYs? If not, what would?

-center defrost good and hot, outsides mildly warm
-center vent good, outside vents mildly warm
-feet, just blows air

thanks!
 
Usually the first place I would start is checking to make sure the valve that opens up the heater hoses and fully opening and your hoses appear to be moving alot of heat with the heater on max. If the upper hose is way hotter than the lower hose then usually that is because there is a blockage.

A lot of people have mixed opions about cleaning the core, but I cleaned out my heater core with a 50/50 mix of clr and water and it brought it right back to life. By doing this I disconnected the core from the hoses and just took a random old pip and a funnel and just poored it in and let it sit for an hour came back flushed it out really well. Finally I have :flame: and heat works great.
 
Radiator CLEANER. Prestone, Zerex, others make it. You want the stuff that you put in the coolant system and drive for 3-6 hours, not the 15 minute crap. Some people have run the radiator cleaner for as long as a week, but no guarantees on what that might do. You can do the 3-6 hours of driving over multiple days, so maybe it doesn't matter.

You could have issues with the vacuum system/vacuum motors. Test the vacuum system.

And don't forget ktwalker01's recommendation and check the coolant control valve to make sure it is opening/closing fully.
 
ktwalker01 said:
Usually the first place I would start is checking to make sure the valve that opens up the heater hoses and fully opening and your hoses appear to be moving alot of heat with the heater on max..
Click to expand...

how do i check this?

joe_peters said:
Radiator CLEANER. Prestone, Zerex, others make it. You want the stuff that you put in the coolant system and drive for 3-6 hours, not the 15 minute crap. Some people have run the radiator cleaner for as long as a week, but no guarantees on what that might do. You can do the 3-6 hours of driving over multiple days, so maybe it doesn't matter.

You could have issues with the vacuum system/vacuum motors. Test the vacuum system.

And don't forget ktwalker01's recommendation and check the coolant control valve to make sure it is opening/closing fully.
Click to expand...

how do i test the vacuum system? I'll try the cleaner

Sorry, this is my first XJ, still learning.
 
If you want to see if the heater core is plugged, check the return line from the core. You can test by either monitoring how hot the input and return lines for the core get, or you can unhook them from their respective supply/return points and run water through it.

I had to gently flush mine with a pressure washer last year to remove build-up due to coolants being mixed without my knowledge. If you use a pressurized source, be careful to know blow-out the core. Some will probably say this procedure is bad. I say it depends on the condition of the heater core and how much common sense you have.
 
robhurlburt said:
how do i check this?

Method one: purchase a vacuum pump and apply vacuum to the coolant control valve and observe the movement of the little arm in response to the application and release of vacuum--that is assuming that the valve itself isn't clogged/broken internally. Poor man's vacuum pump--buy some appropriate sized vacuum hose at the parts store, locate the vacuum port on the intake manifold, use the hose to apply vacuum to the valve and release the vacuum by pulling the hose off the valve.



how do i test the vacuum system? I'll try the cleaner

A vacuum gauge comes in handy here. Hook up the gauge to the vacuum port on the intake manifold, and measure the available vacuum at idle. Note the inches of vacuum. Next, move to the vacuum reservoir behind the front bumper, passenger's side, and measure the vacuum there and compare it to the manifold reading. Inspect the vacuum line(s) where they pass under/behind the battery, that is a common place for the hard lines to break. Move back along the vacuum line towards the firewall and measure where ever you can "T" in and compare the readings. You are simply looking for a loss of vacuum that would indicate broken/split lines.

Sorry, this is my first XJ, still learning.
Click to expand...
 
robhurlburt said:
OK, the top hose going into it was warm, the bottom was HOT.
Click to expand...

The hose that runs from the thermostat housing to the coolant control valve/firewall is the heater core inlet; the hose that runs to the water pump is the heater core outlet.

The outlet hose should be slightly cooler than the inlet hose.
 
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