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Unread 08-23-2014, 02:34 PM   #1
Nightmares
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99 Not Getting Up To Normal Temps With Heater

Only had my Jeep a few months, but I'm starting to notice something weird with the heater. I wouldn't have called it chilly the other morning, but with my 1 & 2 year old daughters in the backseat I decided I'd kick the heater on while taking them to daycare. I turned it on as I pulled out of my neighborhood, and the temp gauge hadn't moved from cold. After about a half hour, I noticed the heater wasn't blowing hot, just barely warm, and my temp gauge was sitting at maybe 140-150. I turned the heat off and about 10 minutes later it was sitting about 210 (where it normally runs at). I then kicked the heater on and had full heat.

My first thought was a failsafe thermostat, so I went ahead and swapped that out. Now this morning same situation. I kicked the heater on before it warmed up, and after running some errands before heading to work (drove about 45 minutes) the heater was barely warm and I was running at most 150 degrees. Shut the heater off and it got up to 210, turned the heater on and it blew full heat, but after about 10 minutes I noticed it was cooling off again till it got down to about 180 and I had mildly warm heat.

Before the cold weather hits, I'd like to figure this out. What would be my next step?

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Unread 08-25-2014, 05:44 AM   #2
coopdc78
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Obviously the first step is to make sure your coolant level is correct. Need to know what engine you have. The 4.7 has the Allen key at the top of the top radiator hose to bleed out air. Is you haven't tried that yet that would be my first step.
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Unread 08-25-2014, 06:28 AM   #3
RyanXVII
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I have a 99 Grand cherokee limited as well, just got it last month and found out a lot about the vehicle. Make sure you google the infamous "blend door issues", this could exactly be why you're not getting the heat you want. you'll want to look into the cheaper method of fixing instead of spending $1500 per 50,000 kilometers because the stock blend doors are poorly designed and will constantly fail over a short time. while you're at it, check out the recirculation door to make sure it's functioning and not obstructing any air or anything. Also another thing is look into how to run the diagnostic to get error codes, it can help tell you if there's any issues. I'd explain it further but im about to go to work, google what i've mentioned and i'm sure you'll figure it all out. if not i can help later when i get home
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Unread 08-25-2014, 06:55 AM   #4
coopdc78
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Yes but if it's not getting up to normal operating temps I'd start with the coolant level first. Blend doors have nothing to do with why it only gets up to 140 degrees
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Unread 08-25-2014, 07:03 AM   #5
doityourselfMM
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Checked the OPs profile - says 4.0.

Yes, insure coolant level is 'full'. I hate to say it but I don't know what could be affecting the temp other than the thermostat. If the water pump had issues, the temps would run hotter. Have you tried installing a Mopar thermostat?
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Unread 08-25-2014, 08:12 AM   #6
Nightmares
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It's the 4.0 and when i did the thermostat i topped it off with coolant. It happened again this morning, except this time i let it get up too normal temp right below the 210. I kicked the heat on and had full heat for about 10 minutes. It cooled down to the 150 mark and i had barely warm air, turned the heater off and it ran back to 210.

The blend door shouldn't be causing the engine to cool off, so I'm at a loss. The only thing i can think of is a sensor. I know a few weeks ago at my work we had a tj that would overheat when only the ac was turned on, wound up being a sensor, but mines not having that problem as i can run the ac all day without issues.

I did not use a mopar thermostat, just the standard 195 degree from my work's parts warehouse.
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Unread 08-25-2014, 09:42 AM   #7
doityourselfMM
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The sensor doesn't control the thermostat. If the heat was always coming out hot, once the vehicle was warmed up, and only the temp gauge was reading low, then I would think it could be a sensor. But since the heater temps are erratic AND the gauge seems to follow the erratic temps, I still go back to the thermostat. I might be overlooking something, but I don't know what else is 'common' to the heater temps and the gauge, other than the coolant temp.

Once my coolant temp reaches 210, I can run the heater on high fan and any coolant temp change is negligable on the gauge.

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Originally Posted by Nightmares View Post
It's the 4.0 and when i did the thermostat i topped it off with coolant. It happened again this morning, except this time i let it get up too normal temp right below the 210. I kicked the heat on and had full heat for about 10 minutes. It cooled down to the 150 mark and i had barely warm air, turned the heater off and it ran back to 210.

The blend door shouldn't be causing the engine to cool off, so I'm at a loss. The only thing i can think of is a sensor. I know a few weeks ago at my work we had a tj that would overheat when only the ac was turned on, wound up being a sensor, but mines not having that problem as i can run the ac all day without issues.

I did not use a mopar thermostat, just the standard 195 degree from my work's parts warehouse.
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Unread 08-25-2014, 10:00 AM   #8
Nightmares
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Well I'll go ahead and see what I can find with a different thermostat then. I wasn't having any issues with it aside from the heater with the old one, so I figured it was a failsafe thermostat that when it fails it stays open to prevent overheating. The thermostat I installed was not a failsafe, and I'm having the exact same problem so that's why I'm hesitant towards replacing it again, but I'm not sure what else it could be. I'll also go ahead and do a full coolant flush tonight at my work and update with results in the morning.
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Unread 08-25-2014, 10:19 AM   #9
scparrish
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I have been fighting this same battle for a while. I keep replacing thermostats. There is nothing else in the system that can make it run too cool.
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Unread 08-25-2014, 10:55 AM   #10
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have you flushed the entire system, with a flush chemical and replaced with the correct coolant mixed with distilled water ?

I'm at a loss after looking through your thread,
For the "not getting up to temp" side of things, have you made sure your E-fan is working properly, these things have frequent "fan control relay" issues. Maybe fan stuck on full speed as soon as the JEEP turns over....???
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Unread 08-25-2014, 01:08 PM   #11
86cj74.2L
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Quote:
Originally Posted by wsar10
have you flushed the entire system, with a flush chemical and replaced with the correct coolant mixed with distilled water ? I'm at a loss after looking through your thread, For the "not getting up to temp" side of things, have you made sure your E-fan is working properly, these things have frequent "fan control relay" issues. Maybe fan stuck on full speed as soon as the JEEP turns over....???
I was going to suggest the cooling fan or fans too.

Also what does the inside of the t-stat housing look like?
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Unread 08-25-2014, 01:12 PM   #12
scparrish
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I know for me I replaced the thermostat housing a couple times. In the winter I unplug the electric fan and remove the mechanical fan, so no fans. The electric fan is brand new as well as the fan control relay. It's my wife's vehicle and she is unhappy every winter.

What flush is recommended for the 4.0? I have some flush that I used on my powerstroke I may try.
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Unread 08-25-2014, 01:56 PM   #13
Nightmares
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Quote:
Originally Posted by wsar10 View Post
have you flushed the entire system, with a flush chemical and replaced with the correct coolant mixed with distilled water ?

I'm at a loss after looking through your thread,
For the "not getting up to temp" side of things, have you made sure your E-fan is working properly, these things have frequent "fan control relay" issues. Maybe fan stuck on full speed as soon as the JEEP turns over....???
I have not flushed the system yet, the Jeep had a full service done with receipts about a month before I bought it that included oil, trans, power steering, brakes, and a coolant flush (I know because my work did the work on it). I plan on flushing it out tonight though.

I have not thought of the fans yet, however I'm not sure if it would be related to that either. I don't know a TON about Jeeps, but I am mechanically inclined. The thing that's stumping me is it's ONLY when I turn the heater on. I can run with the AC all day and run with the whole system off and sit at about 210, but as soon as I kick the heat on the engine cools down to about 150. I'll take a look at the fans tonight.

Quote:
Originally Posted by 86cj74.2L View Post
I was going to suggest the cooling fan or fans too.

Also what does the inside of the t-stat housing look like?
I didn't notice anything abnormal about the housing when I did it last week. The seal on it actually peel right off with the housing which leads me to believe it was done recently before I purchased it, however I see nothing on the receipt from when we did the flush for the previous owner. Maybe they did it themselves?
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Unread 08-25-2014, 02:12 PM   #14
HavasuRat
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Im guessing...maybe heater core is plugged. Pull hoses from therm housing and pump housing and push some water through the therm housing hose to backflush core. Otherwise...check temp guage sending unit??
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Unread 08-25-2014, 02:26 PM   #15
scparrish
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The heater core isn't plugged if his heater setting is dissipating heat from the cooling system.
It sounds like the gauge is reading correctly also.

Maybe try a higher thermostat, cheap and easy to replace.
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