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Unread 01-13-2009, 11:57 AM   #1
242forme
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1977 CJ5 
 
Join Date: Jul 2006
Location: Williams Bay, Wisconsin
Posts: 131
1996 Grand Cherokee 4.0 No Heat / Overcooling

I have a 1996 Zj with a 4.0. 257,000 miles

I have only lukewarm heat from the vents.

The engine temp used to run at a hair below 210. It has always ran at this temp since I got it with 40,000 miles on it. I didn't remember ever changing the thermostat, so I decided to try that. Replaced it with a 195 thermostat from Napa...then the running temp was noticeably lower, about 4 thicknesses of the needle below 210. Picked up another 195 thermostat, this time from the dealer. Same result, lower running temp, and heat temp the same.

The radiator was replaced 2 years ago. The heater core was replaced when I changed out the evaporator core last fall. It had heat last winter.....

I can hear the blend door moving when switching from cold to hot on the temp selector on the dial. And the output of the heater changes from cold to warm.

I'm thinking maybe the heater core may be plugged...but then why the lower running temp? When I changed the thermostats they were seated correctly in the recessed area of the block.

I don't know what to try next...anyone have any ideas?


Last edited by 242forme; 10-18-2009 at 07:41 AM..
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Unread 01-13-2009, 05:25 PM   #2
elmer_fud
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1995 ZJ 
 
Join Date: Jan 2008
Location: colorado
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with the engine on and hot grab the heater hoses and see if they are hot. If not, turn the engine off, remove one and see if any fluid flows out when the engine is running. If not, then repeat this with the other hose.

If nothing comes out of either hose, or it is a slow flow, I would check the water pump. If the flow is good, but the hoses are cold after running for a while, I would say it is a cloged core or hose.
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95 ZJ, 5.2 V8,160,000 miles
Colorado Jeep Club member Pi
Quote:
Originally Posted by Speedycat View Post
I am not one to be changing lanes at 70 mph on a lifted truck on 33's, but since I am in Miami, I have to be prepared for the continuous influx of new drivers whose previous ride was a bicycle with wooden wheels.
Quote:
Originally Posted by FPKites View Post
badger, badger, badger, badger, badger, badger, badger, badger, badger, badger, badger, Mushroom!!! :D
Quote:
Originally Posted by ZeeJay1997 View Post
Or just tie a 12 lb fish to a one foot pipe.
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Unread 01-17-2009, 12:57 AM   #3
242forme
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Location: Williams Bay, Wisconsin
Posts: 131
I checked the heater hoses when it was warmed up and running, and they're hot enough where one is just able to keep a grip on the hoses, any hotter and one wouldn't be able to maintain a grip on them.

Today I removed the heater hoses and used a garden hose to flush through the heater core...water flowed through with no problem.

I also removed the dash and heater box and opened it up to look for anything that would cause lower heat temps. I checked the seal around the heater core to ensure that all the incoming air is forced through the core, and that was fine.

I'm at a loss here....everything seems fine with the heating system...but it puts out lukewarm heat.....It just seems the engine doesn't run as hot as it use to....I don't know what to try next
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Unread 01-17-2009, 01:56 PM   #4
elmer_fud
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1995 ZJ 
 
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Location: colorado
Posts: 2,457
check the fan and the temperature blend door (I don't remember the name)
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Brian
95 ZJ, 5.2 V8,160,000 miles
Colorado Jeep Club member Pi
Quote:
Originally Posted by Speedycat View Post
I am not one to be changing lanes at 70 mph on a lifted truck on 33's, but since I am in Miami, I have to be prepared for the continuous influx of new drivers whose previous ride was a bicycle with wooden wheels.
Quote:
Originally Posted by FPKites View Post
badger, badger, badger, badger, badger, badger, badger, badger, badger, badger, badger, Mushroom!!! :D
Quote:
Originally Posted by ZeeJay1997 View Post
Or just tie a 12 lb fish to a one foot pipe.
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Unread 01-17-2009, 04:01 PM   #5
242forme
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Location: Williams Bay, Wisconsin
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I checked both when I pulled the dash and heater box out.

What I did do was wire the door shut at the top of the heater box, which closes off the top of the box where it draws air from outside, and when it's closed on top, it's open on the side, behind the dash. Now the heater draws its air from inside, and it made a BIG difference, but not so much when it gets down to 20 degrees out!

I thought about using recirculation on the heater control, but the way it's set up is that only works on Ac, not on heat. When recirculation is selected, the outside air is blocked off, and air is drawn from behind the dash..BUT..the blend door also closes off to the heater core, and only allows air to travel through the evaporator

Last edited by 242forme; 10-17-2009 at 12:28 AM..
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Unread 10-17-2009, 12:21 AM   #6
242forme
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It's been a while since I posted to this thread. It's been getting down into the 30's lately and I really would like my heater to have the temp output that it should.

If I run the heater, even if it's 60 degrees out, the air from the heater is lukewarm!!

My engine temp gauge(when engine is fully warmed up) now sits at just above the line before 210, which by estimation is about 185. I removed the radiator cap the other day, and started it when it was cold. I let it run for 20 minutes after warming up. It's like the engine never gets hot enough. Didn't get a bunch of steamy coolant vapor when the t-stat first opened. I even had a thermometer with a probe placed 4 inches into the radiator fill opening. When the t-stat first opened it read a steady climb in temp untill it got to 160, then dropped to 135, and never changed for the entire 20 minutes that I let it run.

I'm gonna pick up a non contact thermometer so I can take a reading on the t-stat housing when it's fully warmed up, but I'm willing to bet it'll read lower than it's suppose to.

Everything that I can think of leads me back to t-stat, but the last 1 that I put in was a Mopar 195

I searched here & elsewhere, found a few posts with problems close to what I have, but of course they never had any follow ups as to what caused their problem

Last edited by 242forme; 10-17-2009 at 12:32 AM..
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Unread 10-17-2009, 10:46 AM   #7
92rslt1
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It must be common because mines the same way... not very cold ac even after its re-filled and luke warm heat.. let me know if you do find anything out. mine runs at 210 and i replaced the water pump and still no change.
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Unread 10-18-2009, 06:48 AM   #8
ZJWally
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1995 ZJ 
 
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got the same thing goin in my 95 ZJ. Hot heater hoses, luke warm heat......full fluid level, no overheating, actually seems to run on the cool side......hope someone finds something on this.
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Unread 10-18-2009, 07:07 AM   #9
NXT-LVL
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Do you get good air flow through the vents?
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Unread 10-18-2009, 07:09 AM   #10
242forme
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Well I used an infared thermometer and took readings off of the t-stat housing with the engine fully warmed up........just as I thought, my engine temp gauge is correct. It never gets any hotter than 185. I took readings on the heater hoses and they are around 150-160

So both 195 t-stats I installed are bad?

I took readings on my wife's WJ to see what temps I would find. When it's warmed up it stays right at 210 on the t-stat housing and the heater hoses are around 180 (this Jeeps heat is like a dragon!!)
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Unread 10-18-2009, 07:48 AM   #11
NXT-LVL
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Well I used an infared thermometer and took readings off of the t-stat housing with the engine fully warmed up........just as I thought, my engine temp gauge is correct. It never gets any hotter than 185. I took readings on the heater hoses and they are around 150-160

Which hoses are you referring to? Radiator upper and lower, or heater core in and out?
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Unread 10-18-2009, 08:17 AM   #12
242forme
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Heater core in and out
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Unread 10-24-2009, 11:03 AM   #13
ZJWally
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i get good air flow. When im going down the road, its seems pretty warm....when i idle at a light with the blower on high, its not very hot at all....but if i turn the blower down to the middle, it seems to stay hot.
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Unread 10-24-2009, 11:37 AM   #14
ZeeJay1997
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Check for a 16 lb radiator cap.

From FSM:
A quick test to determine if the pump is working is
to check if the heater warms properly. A defective
water pump will not be able to circulate heated coolant
through the long heater hose to the heater core.

AND

INSPECTING FOR INLET RESTRICTIONS
Inadequate heater performance may be caused by
a metal casting restriction in the water pump heater
hose inlet.
DO NOT WASTE reusable coolant. If solution is
clean, drain the coolant into a clean container for
reuse.
WARNING: DO NOT LOOSEN THE RADIATOR
DRAIN**** WITH THE SYSTEM HOT AND UNDER
PRESSURE. SERIOUS BURNS FROM THE COOLANT
CAN OCCUR.
(1) Drain sufficient coolant from the radiator to
decrease the level below the water pump heater hose
inlet.
(2) Remove the heater hose.
(3) Inspect the inlet for metal casting flash or
other restrictions.
NOTE: Remove the pump from the engine before
removing restriction to prevent contamination of
the coolant with debris. Refer to Water Pump
Removal in this group.

AND

Do not change a
thermostat for lack of heat as indicated by the
instrument panel gauge or heater performance
unless a DTC number 17 is present.

AND

LOW COOLANT LEVEL-AERATION
If the coolant level in radiator drops below top of
radiator core tubes, air will enter cooling system.
Low coolant level can cause thermostat pellet to be
suspended in air instead of coolant. This will cause
thermostat to open later, which in turn causes higher
coolant temperature. Air trapped in cooling system
also reduces amount of coolant circulating in heater
core resulting in low heat output.
DEAERATION
As the engine operates, any air trapped in cooling
system gathers under the radiator cap. The next time
the engine is operated, thermal expansion of coolant
will push any trapped air past radiator cap into the
coolant reserve/overflow tank. Here it escapes to the
atmosphere into the tank. When the engine cools
down the coolant, it will be drawn from the reserve/
overflow tank into the radiator to replace any
removed air.

AND

Position thermostat in groove with arrow and
air bleed hole on outer flange pointing up.
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Unread 10-24-2009, 01:40 PM   #15
Thelt
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Join Date: Jan 2006
Location: Lenoir, NC
Posts: 604
I have been having the same issue. I finally got time to flush out the heater core and change the thermostat. The one I pulled out was 180 degree. I put a 195 degree one back in. It gets very hot now. Flushing the heater core probably did not hurt but I think the thermostat was the culprit.
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