1998 jeep cherikee. Very little heat. Heater core supply from thermostat housing is hot core return line is very cool. Coolant level is full. I do not see any flow control valves on heater hoses. What could be the problem.

There are several possible reasons why you may be experiencing cool or no heat in your 2002 Jeep Grand Cherokee Laredo after replacing the thermostat and bleeding the air out of the lines. Some possible causes could include:

1. A malfunctioning blend door or actuator: The blend door controls the mix of hot and cold air that is directed through the heating system. If the blend door or actuator is not functioning properly, it may cause a lack of heat.
2. A clogged heater core: The heater core is responsible for transferring heat from the engine to the cabin of the vehicle. If the heater core is clogged, it may not be able to transfer heat effectively, resulting in cool or no heat.
3. A faulty thermostat: If the thermostat was not properly installed or is not functioning correctly, it may cause the heating system to not work properly.
4. A problem with the water pump: The water pump is responsible for circulating coolant through the engine and heating system. If the water pump is not functioning properly, it may cause a lack of heat.

There a a couple of possibilities

1. The thermostat is stuck open. This can usually be veried by looking at the temp gauge. If it is not about half when after the engine has had enough time to fully warm up than I would suspect a bad thermostat.

2. the coolant level is too low. The highest point in the cooling system is the heater core. If the coolant level falls to low the heater core will not get enough hot coolant to function properly.

3, the heater core is plugged. Proper cooling system maintenance will remove much of the debris that ends up in the cooling system. If this service has been neglected this debris will settle in the heater core. Over time it will build up to the point that hot coolant can not flow through the entire heater core resulting in less than adequate or no heat.

4. The last possibility (and the least likely) is that you have a head gasket failure. The air that gets pushed into the cooling system will cause an air pocket in the heater core restricting the coolant from entering.

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Bad coolant flow. check for low coolant, also a thermostat could be restricting proper coolant flow. If coolant is full in the radiator than touch your upper radiator hose to see if it is hot. If their is proper coolant level and engine is warmed up to temp and radiator hose is cold replace your thermostat.

SOMEHOW I BELIEVE YOUR TWO INTAKE & RETURN HEATER HOSES THAT FEED THE HEATER CORE HAVE BEEN REVERSED. EITHER THAT OR a plugged heater core

the only way you should have to replace a heater core is if it leaks or gets plugged up. When motor is hot feel the two hoses that go to the heater core. one should be fairly hot and the other should be the same but if one is just warm then follow hose and locate a flow valve and check for operation. OPening and closing with control hot /cold knob. Check coolant level in radiator while cold as well as fill reservoir to full when cold. Also remove radiator cap when cold and warm truck and check for flow of coolant. if lower radiator hose is hot hot hot and upper hose is cool then thermostat may not be opening properly, or thermostat is stuck open not building heat. You didnt mention if truck was overheating?? If its not i'd check for the flow valve operation, if it is i'd make sure coolant levels are full and waterpump is working.

no heat is probably low coolant or bad thermostat,although you have fog and smell ! the heating and cooling systems are closed systems the only way the windows fog is the coolant is hot and steams inside the car due to some leak inside the heater core box. as well as the smell being present. Now it is possible that a little leak has occured where the coolant supply or return line connects to the heater core and is running into the car which is running onto the core and creating steam and smell. hopefully it is a easy clamp tighten fix for you.

Could be the heater bypass valve is stuck or the heater core is blocked.
I'd check the heater core first.You may have trapped air in the cooling system or the heater core may be partially plugged up. Engine coolant is delivered to the heater core through two heater hoses. With the engine idling at normal operating temperature, set the temperature control knob in the full hot position, the mode control switch knob in the floor heat position, and the blower motor switch knob in the highest speed position. Using a test thermometer, check the temperature of the air being discharged at the HVAC housing floor outlets.
Temperature Reference
Ambient Air Temperature 15.5° C (60° F) 21.1° C (70° F) 26.6° C (80° F) 32.2° C (90° F)
Minimum Air Temperature at Floor Outlet 52.2° C (126° F) 56.1° C (133° F) 59.4° C (139° F) 62.2° C (144° F)
If the floor outlet air temperature is too low, Both of the heater hoses should be hot to the touch. The coolant return heater hose should be slightly cooler than the coolant supply heater hose. If the return hose is much cooler than the supply hose, locate and repair the engine coolant flow obstruction in the cooling system.
OBSTRUCTED COOLANT FLOW
Possible locations or causes of obstructed coolant flow: Pinched or kinked heater hoses. Improper heater hose routing. Plugged heater hoses or supply and return ports at the cooling system connections. A plugged heater core. If proper coolant flow through the cooling system is verified, and heater outlet air temperature is still low, a mechanical problem may exist.
MECHANICAL PROBLEMS
Possible locations or causes of insufficient heat: An obstructed cowl air intake. Obstructed heater system outlets. A blend door not functioning properly.
TEMPERATURE CONTROL
If the heater outlet air temperature cannot be adjusted with the temperature control knob on the A/C Heater control panel, the following could require service: The A/C Heater control. The blend door actuator.
The blend door. Improper engine coolant temperature

If the thermostat is ok and you've got a full coolant level, next try touching the water lines going through the firewall to the heater core. Both lines should be hot to the touch. If only 1 is hot, you have a blockage in the system. If both lines are hot then you may need to replace your heater core. Also have a pressure test done on your cooling system before you go spend a lot of money because you may have a problem there which would prevent enough pressure from building up to push the hot coolant through to your heater core.

Follow these steps:

Check coolant level, then start engine until it is warm and the thermostat opens. You will tell when it does when the needle on your temp gauge goes cold when it reaches around 180-200* and then goes back up. Now turn on your heater full blast and go to the engine compartment. You will see a heater valve located on the passenger side, next to the washer reservoir. It is a black thing with 4 heater hoses connected to it. Feel the hoses. When everything is working correctly it should be like this:

Hose going to waterpump will be hot
Hose going to (I think the thermostat housing) will be hot
2 Hoses going to heater core (mounted behind firewall) will be hot

1. If only 1 heater core hose is hot, heater core is clogged--
UNCLOG: remove 2 hoses going to heater core when engine is cool, hook water hose end to one of the sides and flush out gunk from heater core. Reconnect hose and you should be good.

2. If neither hose core hose is hot, heater control valve is bad or vacuum is bad--
Test Vacuum: remove vacuum line from heater control valve, you should feel the vacuum **** on it when pressed to your cheek and the heater control valve actuator should move when you unhook the vacuum line. If you have a good vacuum, it's probable the valve available at autozone part # 5941 for around $21.

To get heat while you wait to replace part, unhook silver arm on heater control valve that is hooked to the plunger. This will give you heat all of the time, but it is controlled by the bottom hot/cold switch on your heater control unit so you won't get hot in the cab. It will just circulate heat through the core.

1st thing to check is the coolant level. I've seen cars w/ no heat, or very little quite a few times caused by low level in cooling system--not low enough to overheat the engine, but enough that circulation of coolant to heater core is affected (no or little hot coolant circulation to heater core=no or little heat),
Is the engine temp gauge in the normal range? If it's in the low range, engine not reaching operating temp. it could be caused by a thermostat stuck in the open position (or no thermostat, sometimes people remove them when their car overheats, and this should not be done).
Here's how the system works: the heater 'box' contains a heater core (a mini radiator) w/ a fan and hoses connecting the heater core to the engine cooling system. Hot engine coolant is circulated thru the heater core. When u activate the heat switch on the dash, a flap door opens to expose the heater box to the passenger compartment. The fan switch on the dash activates the fan, which blows air thru the core, which heats the air.
So, if it's not the coolant level at the radiator, the fan is obviously working, the engine is reaching operating temperature, I would say it must be the flap door that opens, isn't opening fully, or isn't staying open. It could be the dash switch is defective (not supplying current to open flap door) or less likely the flap door is binding somehow. Hope it's as simple as correcting coolant level, if not, the dash switch control should be checked