1999 Other Jeep Models Heating Issues

SWATAZ

MEMBER
1999 JEEP
6 CYL
4WD
AUTOMATIC
98,000 MILES

I have a 1999 Jeep Grand Cherokee Laredo and suddenly, I have diminished heat in my vehicle.

Here's what I already know:

Even with a good 10 minute warm-up and a 10 mile drive, the heat never quite gets hot enough, even when fully cranked. In fact, anything less than fully cranked was not doing the trick.

Some things to note:

* Temp gauge was in the normal range
* No coolant smell or leakage inside the vehicle
* No fogging of windows
* 4-month-old cooling system including radiator, hoses, water pump and thermostat.
* Heater hoses leading to the core are warm to hot to the touch.
* Heat seems to be marginally warmer when I rev the engine.

I have read the symptoms of a heater core failure and they almost invariably involve the coolant leak and smell, both of which I lack.

Could my thermostat have gone bad already? Is my core possibly clogged?

Any clues?

Thanks!

3 Replies

BMRFIXIT

MECHANIC
19,053 POSTS

Since the temp gauge in the norm range
I would say the thermostat is good
and since no overheating and no leak of coolant
I would say its the heater core
and its operation
lets begin by checking the coolant level and adjust if needed
then let it worm up and check the heater core hoses under hood
they both should be hot
if not check the heater valve and its operation and vacuum line
you may have a faulty heater valve

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Friday, January 25th, 2008 AT 6:17 PM

SWATAZ

MEMBER
11 POSTS

Since the temp gauge in the norm range
I would say the thermostat is good
and since no overheating and no leak of coolant
I would say its the heater core
and its operation
lets begin by checking the coolant level and adjust if needed
then let it worm up and check the heater core hoses under hood
they both should be hot
if not check the heater valve and its operation and vacuum line
you may have a faulty heater valve[/quote:d122f192bd]

Thanks for the very quick response.

As mentioned, the hoses to and from are hot, and if there is a heater valve with a 1999 JGC, I am not aware of it. Before asking you folks, there seemed to be conflicting opinions whether the 99-04 JGCs even have one.

Would it be somewhere on the heater hoses that go between the core and the water pump and the thermostat housing? If so, where would I look?

The coolant level is almost to the top when I take off the cap, so I am fairly confident it is ok. Should there be coolant all the way to the tip-top? It is visible as a shallow pool when I take the cap off, so again I think I am ok there too.

Can the core plug up randomly like that? A shift in sediment, debris, etc?

Thanks again.

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Friday, January 25th, 2008 AT 6:48 PM

BMRFIXIT

MECHANIC
19,053 POSTS

Since the temp gauge in the norm range
I would say the thermostat is good
and since no overheating and no leak of coolant
I would say its the heater core
and its operation
lets begin by checking the coolant level and adjust if needed
then let it worm up and check the heater core hoses under hood
they both should be hot
if not check the heater valve and its operation and vacuum line
you may have a faulty heater valve[/quote:d4ccb22173]

Thanks for the very quick response.

As mentioned, the hoses to and from are hot, and if there is a heater valve with a 1999 JGC, I am not aware of it. Before asking you folks, there seemed to be conflicting opinions whether the 99-04 JGCs even have one.

Would it be somewhere on the heater hoses that go between the core and the water pump and the thermostat housing? If so, where would I look?

The coolant level is almost to the top when I take off the cap, so I am fairly confident it is ok. Should there be coolant all the way to the tip-top? It is visible as a shallow pool when I take the cap off, so again I think I am ok there too.

Can the core plug up randomly like that? A shift in sediment, debris, etc?

Thanks again.[/Quote:d4ccb22173]

Well if you don’t have any valves on the heater hoses between the engine and the firewall then what you have is a blend door and motor in /on the HVAC
located
behind glove box, between heater box and fire wall, temp. Blend doors do break and do require removing dash and heater box, the drivers motor can be replaced without removing dash.

So check the motor first

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Saturday, January 26th, 2008 AT 1:47 PM