Heater core

[Jeepmedic46]

Looks like I need to replace my heater core on my 2000 Sport with the 4.0. Blows a little heat not much. This is an expensive fix. Has anyone done it in their cherokees? Looks like the whole dash has to come apart.

 

[cruiser54]

If it ain't leaking, flush it!!!

 

[Anak]

If it ain't leaking, flush it!!!

This!

Among other things, winter is really not when you want to be trying to manipulate all that old plastic of which your dash is composed. You are far more likely to break pieces that would survive the experience if you did the job in the summer months.

 

[gba88]

As already stated, if it's not leaking, try flushing it. Have you checked the temp of the in/out hoses? The motor in the blend door/the blend door itself can get messed up on the 97+ too.

On a previous 99 I worked on, the blend door was jammed and I thought this was heater core related. Once I fixed the plastic diverter, all was well.

On the same 99, probably 6 or so years later the heater core started leaking (condensation on windshield in the mornings, eventually wet under dash to the left of passenger foot well). I did replace it, and it was a B!tch! 14 hours over the course of 2 days. If it goes in my current 99, I'm probably just going to bypass it and get one of those defrosters that run off the cigarette lighter. You have to empty your AC system if you have one and while you are in there, might as well replace the AC evaporator/coil.

 

[XpedientJ]

QUITE sure that THIS is the product I used when, after being without much heat for over a year....due to not wanting to pull the whole dash, which I had had to do once before....this kit
was purest gold, since it worked, and can be installed through the glove-box opening...

https://heatertreater.net/jeep-cherokee-97-06

 

[Jeepmedic46]

I’ll check out the Heater/Treater door. Not leaking on the passenger side. Seems to be leaking on the drivers side. It would get done in a warm garage. Cold and plastic definitely don’t mix.

 

[cruiser54]

so, it IS leaking?

 

[cruiser54]

does the inside of your windshield fog up if you use Defrost?

 

[RCP Phx]

Not leaking on the passenger side. Seems to be leaking on the drivers side.

That would suggest that it is not the heater core leaking!

 

[Jeepmedic46]

It’s not leaking on the passenger side. Doesn’t really blow hot air and get warm in the winter. I was told it needs a heater core. Thank you everyone

 

[cruiser54]

We're not trusting the person who told you that.

 

[gba88]

It’s not leaking on the passenger side. Doesn’t really blow hot air and get warm in the winter. I was told it needs a heater core. Thank you everyone

Yeah, if you see NO EVIDENCE (leaks on the PASSENGER side, or mist/condensation on windshield), I would not just assume that is the problem. Definitely check the blend door and motor as I mentioned in my original post. You really need to check the temp of the in/out hoses to the core also. Might even be a sticking thermostat, who knows. You said it was leaking on the driver side, are you sure it was coolant and not water? You should be able to tell with a uv flashlight or black light or really by smell/viscosity.

Just saying...be SURE you know the problem before tearing into a job like this just because someone told you that's what it was(assuming they did not show you hard evidence of their claim).

 

[RCP Phx]

You have 2 separate issues. (1)The leak is going to be harder to track down, (2) The heater core, which has three components regarding temp. The heater core circuit does not have a "t-stat" so either the core is restricted or the blend door isn't function properly which could either the door itself or the temp control knob.

 

[75SV1]

Third issue: is your engine getting up to temp? I have done the blend door. Also check the blend door actuator. Its electric on the 2000. That can also be related to a bent blend door shaft. I'd also flush the heater core. Blow through the hoses. Then maybe put in some type of cleaner. Flush again.

 

[maxbraketorque]

Its important that the heater core circuit flow water. The heater flow circuit is the primary means to allow water to circulate to the tstat while the tstat is shut. If the heater core is clogged, then your engine won't warm up properly. It could overheat without you knowing it. If its actually clogged, it should be bypassed or replaced ASAP.

 

[cruiser54]

I'm confused^^^.

How does a clogged heater core cause overheating engines?

 

[75SV1]

My experiences with two 4.0L when the engine didn't heat up, was that the thermostat failed. One a Mr. Gasket Hi-flow came apart. Another stuck open.
On the blend door motor, I detached it with the wires on it. Checked rotation with the key on, and used the heater dial. Also, with it detached, the blend door rotation can be checked using a flat blade screw driver to turn the blend door from the bottom.

 

[maxbraketorque]

I'm confused^^^.

How does a clogged heater core cause overheating engines?

Gotta ask how hot water reaches the tstat while its closed. If no water is flowing to the tstat, then the water around the tstat will warm up much more slowly than if engine coolant is circulating to it. If there is no flow, the water in the head around the combustion chamber and exhaust ports can become much hotter than the water at the tstat. The overheating effect is temporary because eventually the tstat will become hot enough to open.

The common belief is that tstats have a bleed hole to allow a small amount of circulation, but most tstats do not have one, and even if a tstat has one, the bleed hole is tiny and won't let a high volume of water pass. With that in mind, have a look at the heater core water flow circuit. It siphons water off the primary circuit right at the tstat housing and then returns it directly to the water pump which then sends the water through the engine coolant passages. This creates a substantial flow of warmed water to the tstat while it remains shut. If the heater core is clogged, then no warm water flow to the closed tstat, and instead, the tstat opens when the stagnant water at the tstat warms up.

An interesting question is what temperature differential occurs between the tstat and the head in this scenario. In the summer when outside temperatures are higher, the tstat temperature may not severely lag the head temperature, but in the winter, the lag may be more substantial.

A clogged heater core in combination with a closed tstat is also bad because there will be substantial cavitation at the water pump during this period, causing more rapid degradation of the pump vanes.

 

[RCP Phx]

. With that in mind, have a look at the heater core water flow circuit. It siphons water off the primary circuit right at the tstat housing and then returns it directly to the water pump which then sends the water through the engine coolant passages. This creates a substantial flow of warmed water to the tstat while it remains shut.

That only applies to the +97 models, how do you explain the earlier ones that have a control valve in the circuit?

 

[maxbraketorque]

That only applies to the +97 models, how do you explain the earlier ones that have a control valve in the circuit?

Presumably its a bypass rather than an on-off valve.