• Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

Is my radiator cooling too much?

Jeepguy03

Jeepguy03

NAXJA Forum User
Location
Connecticut
2000 XJ 4.0L, 130k miles.

Two years ago, my jeep was running hot. I replaced all the cooling system components including a new CSF 3 row radiator. Keep in mind that the previous owner removed the A/C system, so there is no condenser in front of the radiator. I also flushed the cooling system with prestone.

The new system has been great. On a hot summer day, I can floor the jeep on a long hill and the temp will spike to 211*, then immediately go back down to 200*. It runs 195*-205* pretty consistently according to scan gauge for most of the year.

The ambient temp outside right now is 12*. Lately, my jeep has been taking longer to warm up. When the thermostat opens, the temp drops back down to 185* then steadily climbs back up. The heat also sucks in this Jeep, and it has since I bought it. I've flushed the heater core twice, which seems to help a little each time. The heat is never really HOT. The hoses are hot to the touch, and the blend door is working. I can tell its working cause I can hear it moving if I have the radio off, and I can feel the temp difference in the air coming from the vents.

If I go on a long highway drive, the heat comes out decently warm. It just seems to take awhile for it to get to that point.

My previous 2000 could keep the cab warm with the windows down the heat was so hot. Is there any strong cleaner I could use on the heater core? Last time I did it the water came out clear but I feel like it still might be clogged. I also feel my Thermostat is working because the temps will fluctuate accordingly.
 
Last edited:
Did you backflush the heater core?

Your standard 195 degree thermostat STARTS to open at 195 degrees.

Now, in COLD weather you may have to put a restriction in front of part of the radiator to get things a little warmer--think BIG TRUCKS with the covers over the radiators in winter.
 
joe_peters said:
Did you backflush the heater core?

Your standard 195 degree thermostat STARTS to open at 195 degrees.

Now, in COLD weather you may have to put a restriction in front of part of the radiator to get things a little warmer--think BIG TRUCKS with the covers over the radiators in winter.
Click to expand...

Hmm, got to thinking here, does the heater core supply come from the radiator directly or the head after the engine has heated it back up? I know it bypasses the T-stat!!!!
 
Ecomike said:
Hmm, got to thinking here, does the heater core supply come from the radiator directly or the head after the engine has heated it back up? I know it bypasses the T-stat!!!!
Click to expand...

Out of the block via the WP through the heater core and then returns to the WP lower side.
 
joe_peters said:
Out of the block via the WP through the heater core and then returns to the WP lower side.
Click to expand...

Then it bypasses the T-stat, and radiator if / when the T-stat is closed.

Just clicked, thanks. I had forgotten how the outlet plumbing looked, pump itself. I rarely replace water pumps. Been lucky.
 
OP, have you checked the fresh air damper door near the passanger side door, under the dash? Is letting outside air in?
 
Ecomike said:
Hmm, got to thinking here, does the heater core supply come from the radiator directly or the head after the engine has heated it back up? I know it bypasses the T-stat!!!!
Click to expand...

Right, coolant constantly bypasses the T-stat. The heater core supply comes from the head. Water pump pushes coolant through the block.

I didn't think there was such thing as "cooling too much" (other than installing a 185 or 165* T-stat), but I'm curious about this "issue". I over-hauled my cooling system recently & haven't noticed my e-fan operating since. Although, per dash gauge, my operating temps are always at ~200 (a dash under 210). Before the over-haul, the rig would over-heat consistently, & the gauge would show it.

I don't have complaints on the heat, as last winter I consistently had oily fog/film limiting my view, which led to eliminating the HC & then I had NO heat. The heat is good, but from what I remember, it used to be HOT.

Could it be the system is cooling too efficiently?

Jeepkid, what do you mean when you flush the HC it's helped a bit? It puts out more heat??
 
joe_peters said:
Out of the block via the WP through the heater core and then returns to the WP lower side.
Click to expand...

wait.. what?

coolantsystemflow-1.jpg


Pic's a bit deceiving, but I know one heater hose connects to the T-stat housing & the other on a pipe from the WP
 
The opening in the housing is beside the thermostat, not behind it.

tstatheaterbypass.jpg


Here's the side that attaches to the head, the big hole is for the tstat, the small oval is for the heater supply.

Coolant always flows through the engine, 100% of the time, it just doesnt always flow through the radiator
 
Last edited:
...& just thought of it. Per the picture, the inlet is on the bottom - upper on top, what would be the repercussions of swapping the Inlet/Outlet on the HC??

Could the HC possibly not absorb enough heat in this configuration?
 
Everything is about heat transfer, which always works from hot-to-cold. Coolant is colder than the engine so heat transfers to it (cooling the engine in the process). Air around the heater core is cooler than the coolant (hopefully) so heat from the coolant transfers to it. The HVAC controls set a blend door inside the dash that determines how much external air is directed through the heater core vs the AC evaporator, and also determines which of the dash vents the resulting air is directed to. OP has a 2000 so he doesn't have a control valve, but on earlier years that was another widget that would return coolant back to the water pump immediately and bypass the heater core (later models just rely on lack of airflow through the core to prevent cabin air from heating up).

Generally speaking the problems are with lack of coolant flow through the core (blockage) or with something in the blend door, or sometimes with the outlet selector, and sometimes with the engine.

Could the HC possibly not absorb enough heat in this configuration?
Click to expand...

Meant to address this. Not really about "absorb" as much as it is about transfer. The heater core is basically a figure-S tube with a bunch of thin fins, coolant heat transfers to the fins, and airflow through the fins provides warm air to the cabin. Coolant flow is driven by the water pump, so you get less flow at lower RPMs than you do at higher RPMs. Also when the thermostat opens, a bunch of relatively cold coolant enters the engine, and that gets drawn into the heater core. Otherwise the limitation is usually related to gunk buildup on the inside of the core that is restricting transfer from the coolant to the metal, or sometimes a problem with restricted airflow through the core (blend door failure). The heater core coolant circuit is pretty simple, especially in the later models that do not have a control valve.
 
Last edited:
jeepkid03 said:
2000 XJ 4.0L, 130k miles.


The ambient temp outside right now is 12*. Lately, my jeep has been taking longer to warm up. When the thermostat opens, the temp drops back down to 185* then steadily climbs back up. The heat also sucks in this Jeep, and it has since I bought it. I've flushed the heater core twice, which seems to help a little each time. The heat is never really HOT. The hoses are hot to the touch, and the blend door is working. I can tell its working cause I can hear it moving if I have the radio off, and I can feel the temp difference in the air coming from the vents.
Click to expand...
If the hoses are too freakin' hot to wrap your bare hand around, the flow through the heater core is OK. If you can hold them in your hand when the engine is warmed up, you need a new heater core.

X2 on replacing the thermostat. It should keep the engine at operating tempreature.

Sounds like your radiator is doing what it should. :)
 
ehall said:
Everything is about heat transfer, which always works from hot-to-cold. Coolant is colder than the engine so heat transfers to it (cooling the engine in the process). Air around the heater core is cooler than the coolant (hopefully) so heat from the coolant transfers to it. The HVAC controls set a blend door inside the dash that determines how much external air is directed through the heater core vs the AC evaporator, and also determines which of the dash vents the resulting air is directed to. OP has a 2000 so he doesn't have a control valve, but on earlier years that was another widget that would return coolant back to the water pump immediately and bypass the heater core (later models just rely on lack of airflow through the core to prevent cabin air from heating up).

Generally speaking the problems are with lack of coolant flow through the core (blockage) or with something in the blend door, or sometimes with the outlet selector, and sometimes with the engine.



Meant to address this. Not really about "absorb" as much as it is about transfer. The heater core is basically a figure-S tube with a bunch of thin fins, coolant heat transfers to the fins, and airflow through the fins provides warm air to the cabin. Coolant flow is driven by the water pump, so you get less flow at lower RPMs than you do at higher RPMs. Also when the thermostat opens, a bunch of relatively cold coolant enters the engine, and that gets drawn into the heater core. Otherwise the limitation is usually related to gunk buildup on the inside of the core that is restricting transfer from the coolant to the metal, or sometimes a problem with restricted airflow through the core (blend door failure). The heater core coolant circuit is pretty simple, especially in the later models that do not have a control valve.
Click to expand...

Appreciate the info. I understand the purpose/functions/process of the combined components working in the cooling system. When I say "absorb", I meant the Heater Core metal/fins absorb the heat from the coolant, in turn, transferring heat - which then is blended (or not) with outside air, via the blend door, & driven out, via the blower, through the selected vents, via the appropriate blend door & selector.

97+ do not have the control valve.

To clarify, in my case (& what I think Jeepkid's), the system & components are fresh. I began with a 6 hour chemical flush, then bypassed leaky heater core. Totally flushed out block & head, & even blew out any water with compressed air. I then replaced - water pump, T-stat, T-stat housing, upper/lower hoses, clutch fan, & belt. Heater core, A/C evaporator, & heater hoses were done a month or so later. Brand new components, fresh 50% distilled water & 50% extended life coolant, re-circulator blend door works & air flow from outlets change accordingly with the selector. All done within the past 6 months.

So, what you think could be happening is a restriction in the core? Like I said, I have good heat, Jeepkid bringing it up made me curious as to what could explain lesser than HOT air being generated. Also, in my case, aux fan has not operated since my overhaul.

Or if another factor I've wondered about - which would be a better heater core material, copper or brass??
 
Hey don't forget to park on a steep hill, nose up, left front fender highest (rad cap), heater on. I had weird cooling issues until I figured out how to bleed the air.
 
Ecomike said:
OP, have you checked the fresh air damper door near the passanger side door, under the dash? Is letting outside air in?
Click to expand...


How would I go about checking this? Where is it located under the dash? Can I view it without ripping the whole dash out? I have a FSM for my 2000 but I must have missed it, I only saw a diagram showing the blend door.

Sorry for the late response, classes just started up again so I have been busy.

When I bought the Jeep, it had no heat. Within a month of owning it, the jeep suddenly overheated. It had a clogged radiator. I replaced the entire cooling system and flushed it out with that Prestone stuff. I had luke warm heat.

Halfway through winter, I couldn't take it anymore and had my friend's shop flush the heater core. After they did that, the heat was much better, but still not hot. I flushed it myself last winter using the prestone, and a little bit of crap came out, but not too much. It helped a little but the heat is still not hot, and takes awhile to warm up, even though the temp is at 210*.

I currently have cardboard blocking half my radiator (in front of the mechanical fan). It helps the heat warm up a slight bit faster, and the engine temps appear to not have changed at all. I've only done this for a few days and its been about 10* out every day this week.

My friend has a 2000 XJ with about the same mileage, same engine, etc. His heat is much hotter than mine.

I heard White vinegar is great at cleaning limescale. Should I try running some of that through the core? Its supposed to be not as damaging as CLR.

The thermostat is also a factory 195* from the Jeep dealer.
 
Last edited:
Same issue as you until I blew it out with compressed air and water. Several cycles. Water and cleaner alone did not work for me. Only gave me warm air, now its hot. i believe the PO used some of that rad leak stuff and completely gunked up everything including the core.
 
Just for info. I have had a heater hose seperate inside and partially block the flow into the heater core.

I have the same heater issues as described here on our 97XJ & I have 2 new heater hoses, a new 195* Stant thermostat ready to install when this midwest weather improves.
 
Tomorrow I will let the heater core soak in white vinegar. How long should I let it soak? I could do overnight if needed. Also, how would I find the fresh air damper?
 
jeepkid03 said:
Tomorrow I will let the heater core soak in white vinegar. How long should I let it soak? I could do overnight if needed. Also, how would I find the fresh air damper?
Click to expand...


4-8 hours soak should do it. If it is real cold go for the overnight or 8 hours. The damper door, if it is the same as older jeeps, is near the passenger side door and dash corner, under the dash at the bottom. It is about 4"x4" and very obvious looking. Even more obvious when it moves for selection changes from max A/C to vent! On mine I can see the blower wheel when it opens.
 
You must log in or register to reply here.

Similar threads

V
High temp woes
2
Replies
21
Views
391
Vitzaa
V
Jeepmedic46
Heater core
2
Replies
32
Views
4K
RCP Phx
R
R
Fan not turning on when hot- fan works!
Replies
2
Views
2K
JMA_2001XJ
J
X
Replacing my entire cooling system
2
Replies
23
Views
4K
RCP Phx
R
S
Issues flushing dirty coolant
2
Replies
29
Views
4K
fenns7
F
Back
Top