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Stock XJ Cherokee Tech. All XJ Non-modified/stock questions go hereXJ (84-01)
All OEM related XJ specific tech. Examples, no start, general maintenance or anything that's stock.
If this were the case, it would seem that '97-up heater cores should last longer than '96-earlier ones.
It doesn't seem that this is the case. The majority of the threads on heater core replacement are '97-up.(I did a quick search, and the first page that popped up, only 1 was '96-earlier)
Either folks aren't replacing as many '96-earlier ones, or they are just not posting about it. (or most folks have already replaced the '96-earlier ones, and there are a bunch of older posts that i did'nt look at)
My '96 heater core is still original .
There may be some other factors in play here, such as the '97-up heater cores are subject to many more heating/cooling cycles throughout it's life, which may contribute to fatigue in the soldered/epoxied joints or core tubes................As opposed to the '96-earlier ones which may sit idle for quite some time with no heater use?
If this is the case, I would rather replace a HCV than a heater core.
Good point on remembering to turn the heater on while flushing.
I would guess a bunch of folks forget this step.
One minor detail.
97 and up were inferior cores compared to the previous design of 96 and earlier.
Changed?
Heater hose routing?
I show the heater core being the same...
I don't imagine it would make any difference to heater output, if you ran the hoses one way or the other?
The heater core nipples r 2 different sizes (at least they r on a '98), 5/8" and 3/4", as already stated. At the firewall the 3/4" nipple is on top and the the 5/8" nipple is on the bottom. The heater core "inlet" is the larger 3/4" upper hose/nipple and the core outlet is the smaller 5/8" lower hose/nipple......which is just the opposite of the diagram. I would think there could easily be a difference in heater output if the hoses (which r 2 different sizes) were installed incorrectly. For the most part, the diagrams in the FSM's r correct however, not all r.
Only real consideration with bypassing the valve is that its harder for the AC in summer. 97-up they fully isolate the heater core in the dash, but earlier years the air blows next to the core in summer and through the core in winter, so you do get some shedding (heat from the core moving onto the AC stream). If you have good AC you can overcome.
If you want to run the valve, get the one for Renix years, it is metal instead of plastic
Good point......and the smaller hose is on suction side of the water pump.
Originally Posted by freegdr
Smaller hose goes out as to slow down water flow so more heat can be absord thru and into the cab via heater core.
These may be good points in theory, and I would add my theory to this......
Normally I would assume the larger hose would be the heater inlet. The hose would be the hot side, and as coolant passes through the heater core, heat is absorbed and radiated away. The coolant would condense slightly, and pass back to the engine in the smaller hose.
However, this is not the case.
Here is the replacement heater core. It fits all years of XJ and MJ whether it has A/C or not.
It is oriented this way in all years of XJ/MJ.
The tube on top is the larger tube.
Looking from inside the vehicle.
Looking from engine bay.
This is the cooling system routing for '91-'96 HO with HCV, and is true to my factory original setup.
This is the cooling system routing for '97-'01.
The factory hose has a step-down in size at the end where it emerges from the heater core.
Mine also steps down as it comes out of the top of the heater core, and heads back to the water pump.
Only real consideration with bypassing the valve is that its harder for the AC in summer. 97-up they fully isolate the heater core in the dash, but earlier years the air blows next to the core in summer and through the core in winter, so you do get some shedding (heat from the core moving onto the AC stream). If you have good AC you can overcome.
If you want to run the valve, get the one for Renix years, it is metal instead of plastic
I don't think you could use a Renix valve on an HO Cherokee.
They are completely different designs (besides the plastic/metal difference)
The main reason that comes to mind for the design that flows coolant into the bottom of the heater core, and out the top when I study the pictures, would be to burp any air in the heater core up and out.
If it were to flow into the top of the core, and down and out the bottom, the design of the heater core itself could trap some air inside it (which would never be allowed to escape) and would diminish the output of the heater.
Anyway, that's my expert opinion on it..............
Only real consideration with bypassing the valve is that its harder for the AC in summer. 97-up they fully isolate the heater core in the dash, but earlier years the air blows next to the core in summer and through the core in winter, so you do get some shedding (heat from the core moving onto the AC stream). If you have good AC you can overcome.
If you want to run the valve, get the one for Renix years, it is metal instead of plastic
Nah. I live in Arizona and there is no down side to eliminating the HCV.
These may be good points in theory, and I would add my theory to this......
Normally I would assume the larger hose would be the heater inlet. The hose would be the hot side, and as coolant passes through the heater core, heat is absorbed and radiated away. The coolant would condense slightly, and pass back to the engine in the smaller hose.
However, this is not the case.
Not sure what u r saying.....the larger top hose/nipple IS the heater core inlet/hot side from the motor and that coolant flow diagram for '97-'01 XJ's is as wrong as wrong can be. The hot water (from the motor) enters the heater core at the larger top core inlet nipple, not the bottom (smaller) nipple as that flow diagram shows.
One of those goofy diagrams shows a vertical flow and the next shows a horizontal flow rad.......really?????? Again, how goofy (wrong) is that.
Here is the replacement heater core. It fits all years of XJ and MJ whether it has A/C or not.
It is oriented this way in all years of XJ/MJ.
The tube on top is the larger tube.
Looking from inside the vehicle.
Looking from engine bay.
This is the cooling system routing for '91-'96 HO with HCV, and is true to my factory original setup.
This is the cooling system routing for '97-'01.
The factory hose has a step-down in size at the end where it emerges from the heater core.
Mine also steps down as it comes out of the top of the heater core, and heads back to the water pump.
See my post at the top in bold. Not sure what u r saying.....the larger top hose/nipple IS the heater core inlet/hot side from the motor and that coolant flow diagram for '97-'01 XJ's is as wrong as wrong can be. The hot water (from the motor) enters the heater core at the larger top core inlet nipple, not the bottom (smaller) nipple as that flow diagram shows.
One of those goofy diagrams shows a vertical flow and the next shows a horizontal flow rad.......really?????? Again, how goofy (wrong) is that.
See my post at the top in bold. Not sure what u r saying.....the larger top hose/nipple IS the heater core inlet/hot side from the motor and that coolant flow diagram for '97-'01 XJ's is as wrong as wrong can be. The hot water (from the motor) enters the heater core at the larger top core inlet nipple, not the bottom (smaller) nipple as that flow diagram shows.
One of those goofy diagrams shows a vertical flow and the next shows a horizontal flow rad.......really?????? Again, how goofy (wrong) is that.
What I am saying is the smaller tube on the bottom is the heater inlet!
You have it backwards.
The larger tube on top is the heater outlet.
The diagrams I posted are factory Jeep service diagrams, and they both show horizontal flow radiators?
I am not sure where you got your info from?
Maybe someone should start a poll.............Have people post how their factory hoses are routed.
What I am saying is the smaller tube on the bottom is the heater inlet!
You have it backwards.
The larger tube on top is the heater outlet.
The diagrams I posted are factory Jeep service diagrams, and they both show horizontal flow radiators?
I am not sure where you got your info from?
Maybe someone should start a poll.............Have people post how their factory hoses are routed.
01-08-2015, 05:09 PM
