1998 Jeep Cherokee heating in trouble

RYE12

MEMBER
1998 JEEP CHEROKEE
6 CYL
4WD
AUTOMATIC
128,000 MILES

Just bought this jeep used. Turned on the heat, was blowing cool air (actually outside temp). Flushed the radiator and coolant system, replaced the thermostat. (The top radiator hose had been running real hot. And didn't feel any real push of water through when I pinched the hose).

The heat worked briefly today, then when I went to go back out on the road, it was blowing luke warm & not hot.

Coolant level is fine. Heater inlet hose feels out, upper radiator hose still feeling real hot and not really getting a big surge of water through when I pinch.

I'm thinking maybe a bad water pump? Car isn't over heating. Had been running closer to 210 before new tstat, now running 190 to 200 (hard to tell exactly on the gauge.

Any ideas, suggestions? Should I replace the water pump. Not too expensive of a part.

5 Replies

CJ MEDEVAC

MECHANIC
11,004 POSTS

See my profile, Imma CJ Guy,

I would think that if your rig was running normal temperature, the water pump would be serviceable and be GOOD!

1) Are there any shut-off valves on your heater hoses?

2) Is it possible that maybe a heater hose is sucking flat or is crimped. Restricting flow?

3) How hot are the hoses going IN & OUT of your heater core?

4) Are the vacuum operated doors in your heater working? (In other words, does A/C, defrost, etc, blow thru the right vents)

5) On a CJ, water returning to the pump (via heater hose)Is the so called "Water you just stole the heat out of" (return)

6) The Really Hot Water, gets pumped out of the thermostat housing, and makes its way to the heater core. After "Used" it returns once again to the pump.

Since I know little about your system, Tell me step by step, where the heater hoses go. For instance:

Leaves thermostat housing goes to intake via Galvanized hose fitting, leaves intake via Galvanized hose fitting. Then goes into a vacuum operated switch via Brass hose fittings. To core. To pump ETC ETC.

Give me anything you can think of, detail is good!

I may be able to give you a few tests, to iscolate maybe where you problem lies. Dependent on your answers.

Your Turn (reply to question)

The Medic

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Wednesday, October 6th, 2010 AT 9:24 PM

RYE12

MEMBER
3 POSTS

Thanks for the reply.

I'm not sure if there are any shut off values but I iwll give you the lay out as best I can.

Water leaves the block via the thermostat housing. The upper hose to radiator connects to where the thermostat sits, the heart inlet hose connects to the same housing, but it goes through a seperate port, not subject to the thermostate. It is this port that the temp sensor sits.

Temp is running between 190 and 200 per the gauge, the thermostat is rated 195 so that seems right.

The heater inlet hose runs back to the firewall and the outlet hose runs back to the water pump where the lower radiator how connects as well different ports.

I will double check on the vents and the feel of heater outlet hose, the inlet hose seems very hot to me. Just as hot as the upper radiator hose (dont' want to hold them for long with a bare hand).

Thanks for any tips. I really appreciate them, I'm new to fixing my own cars, but I really want to learn how to.

Ryan

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Friday, October 8th, 2010 AT 10:59 AM

CJ MEDEVAC

MECHANIC
11,004 POSTS

It really sounds like the Hot Water is going into the heater coreif its going in and getting hot---then its coming out as well!

Really sounds like a Heater Box problem---doors not opening inside (broke or the vacuum line to the actuator has no vacuum FOR SOME REASON! (Maybe loose or the control is messed up)

Reply with any results ( I like replies)

The Medic

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Friday, October 8th, 2010 AT 4:36 PM

RYE12

MEMBER
3 POSTS

Thanks so far for everything.

I think I have figured this out.

I bought a digital therm. To test out the heat coming out. In the afternoon w/ outside air in the mid 60's, it was working awesome. Blowing out 110 to 120 degrees. Nice and hot.

At night, the outside temps dropped to the mid 30's and it was blowing at about 90. Thats when it dawned on me. There is no recirculating option for the heat, it is always blowing in fresh air from the outside. I found the outside air inlet and blocked it with a piece of card board to test. Temp got back up to 115 to 120 w/ air leaving heater.

I've never had a car/truck that had no reciruclator option for the heat (has it for the a/c, but not the heat. All the vents work when selected, ruling out a vacuum leak I think.

Question. If I build a molding for blocking the outside air intake (either with a plastic or rubber that is heat resistant) and install it to block the fresh air intake, will this cause problems for me?

Thanks,

Ryan

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Monday, October 11th, 2010 AT 10:46 AM

CJ MEDEVAC

MECHANIC
11,004 POSTS

On CJs, you do use outside air to assist the fan in blowing over the heater core----Just the way somebody designed it!

I would think that in a '98, it would recirculate the cockpit air without outside assistance (are you certain there is no door to close off the outside air?) Like is it "Vent Only", and nothing to do with heater operation?

Can you find a diagram of the heater, in an exploded view? In a Manual?

Did you click around You Tube for additional info?

Were you static or driving while air was coming thru from outside?

I see no reason that blocking the outside air would hurt anything, as long as you have great airflow over the heater core............and it is removed for other operations needed for summer use.........?

On several older rigs, I have cleaned the heater core and all of the vanes on the squirrel cage fanmade a heck of a difference in air flow!Think maybe thats all you need to do?

I took pics to show Dad his T-Bird airflow problem,----I washed out the core, in place (after removing the fan box), with Purple Power................plastic in the floorboard, and Mr. Gardenhose!

Core is left of the fan in the box (along with the evaporator)