Bypassing the heater core?

[Brasscatz]

What are the pros and cons?

I installed the aux fan bypass switch and it has helped, though on my way home today I reached 227* at times. It cooled off faster with the fan running, but I need to get the temps better than that. My issue is mainly in stop and go traffic, not so much when I'm cruising at 70 mph.

Everything except my fans, fan clutch, radiator, and heater core is new on my cooling system... and I got to thinking... It's not cold enough here in Houston to need the heater, so why not bypass the heater core? I had an old pickup that didn't have the heater core hooked up and it ran just fine.

Are there any drawbacks to bypassing the heater core other than not having a working heater?

[4.3LXJ]

No, it will just recirculate the coolant. But I don't see how that will help your overheating problem

[Brasscatz]

No, it will just recirculate the coolant. But I don't see how that will help your overheating problem

I'm pretty sure that my heater core is leaking somewhat, plus I'm thinking it's possible that there is some slight blockage possibly preventing maximum cooling

[4.3LXJ]

I'm pretty sure that my heater core is leaking somewhat, plus I'm thinking it's possible that there is some slight blockage possibly preventing maximum cooling

If it was blocked, it would not affect cooling. The heater core takes coolant from the head that is hot and passes it through the core and then to the water pump. None of that coolant goes to the radiator. If it was blocked, in theory it would help since the amount of recirculation would be down.

[Brasscatz]

If it was blocked, it would not affect cooling. The heater core takes coolant from the head that is hot and passes it through the core and then to the water pump. None of that coolant goes to the radiator. If it was blocked, in theory it would help since the amount of recirculation would be down.

Very good point, thanks Steve. So also in theory, bypassing would reduce the amount of circulation as well and possibly help too?

[XJ Wheeler]

Bypassing it would be pointless for cooling. If you're not using the heater the heater control valve keeps coolant from going to the heater core anyways (at least its suppose to). So it would be about the same as if you bypassed it. Now if the leak gets bad enough then bypassing makes sense.

[Brasscatz]

Bypassing it would be pointless for cooling. If you're not using the heater the heater control valve keeps coolant from going to the heater core anyways (at least its suppose to). So it would be about the same as if you bypassed it. Now if the leak gets bad enough then bypassing makes sense.

I'll be honest, I have no clue how bad the leak is or if there even is one for sure! I know I smell antifreeze anytime I turn any kind of air on though and I'm also loosing coolant somewhere, but I can't find where. I haven't been checking my passenger side carpet for wetness... maybe I should do that. Also thinking of bypassing the core tonight since it'll be a quick thing... it's free and it won't hurt anything so might as well try it, right?

[Carves]

What are the pros and cons?

I installed the aux fan bypass switch and it has helped, though on my way home today I reached 227* at times. It cooled off faster with the fan running, but I need to get the temps better than that. My issue is mainly in stop and go traffic, not so much when I'm cruising at 70 mph.

Everything except my fans, fan clutch, radiator, and heater core is new on my cooling system... and I got to thinking... It's not cold enough here in Houston to need the heater, so why not bypass the heater core? I had an old pickup that didn't have the heater core hooked up and it ran just fine.

Are there any drawbacks to bypassing the heater core other than not having a working heater?


Cold toes ... are about the only drawback I can think of .. :D

Have a play/experiment, with the heater hoses by all means ... but just IMHO ... you probably ought to track down what part of your cooling system is not up to scratch ... rather than fussing with the heating system .. ;)

[XJ Wheeler]

I'll be honest, I have no clue how bad the leak is or if there even is one for sure! I know I smell antifreeze anytime I turn any kind of air on though and I'm also loosing coolant somewhere, but I can't find where. I haven't been checking my passenger side carpet for wetness... maybe I should do that. Also thinking of bypassing the core tonight since it'll be a quick thing... it's free and it won't hurt anything so might as well try it, right?

You can try, maybe its a fluke. But generally, unless there's a leak, the heater core only helps cool the vehicle down when the heater is on. Had to use the ol heater trick to get to my destination a few times. When you have the heater turned off the heater control valve essentially bypasses the heater core on its own. Turn the heater on and coolant then flows through the heater core, allowing the vent to wisk across it to warm ya. This also acts as a small radiator, that's why it helps cool in a pinch.

[Mudderoy]

Mine hit 230 today, 80 degree air temp. It cools off as I start moving. I'm going to swap in the high flow water pump and see if that drops the in traffic temps, otherwise I'll be turning the A/C off during the summer and turning the heater on full blast just to keep it below 230 to get home.

Oh also I need to get the cowl induction hood back on.

[Brasscatz]

Cold toes ... are about the only drawback I can think of .. :D

Have a play/experiment, with the heater hoses by all means ... but just IMHO ... you probably ought to track down what part of your cooling system is not up to scratch ... rather than fussing with the heating system .. ;)

Oh sure... leave it up to Carves to ruin a Texan's fun :poke: I know what part is not up to scratch... it's in a Cherokee ;) Nah, it would've been just a temp thing and "try it and see".


Mine hit 230 today, 80 degree air temp. It cools off as I start moving. I'm going to swap in the high flow water pump and see if that drops the in traffic temps, otherwise I'll be turning the A/C off during the summer and turning the heater on full blast just to keep it below 230 to get home.

Oh also I need to get the cowl induction hood back on.

I think I just need to replace my radiator and pray.... for my wallet's sake - really for my wife's sanity lol. What happened to your hood? Do you have a spare that you use in the off-season?

[Brasscatz]

You can try, maybe its a fluke. But generally, unless there's a leak, the heater core only helps cool the vehicle down when the heater is on. Had to use the ol heater trick to get to my destination a few times. When you have the heater turned off the heater control valve essentially bypasses the heater core on its own. Turn the heater on and coolant then flows through the heater core, allowing the vent to wisk across it to warm ya. This also acts as a small radiator, that's why it helps cool in a pinch.

I've turned the heater on a few times myself. I thought the water flowed through the core continuously

[Carves]

Oh sure... leave it up to Carves to ruin a Texan's fun :poke:


:rotfl2: .... I wouldn't do that ... its your buggy to do what you want with. ;)


Have a play/experiment, with the heater hoses by all means ...









and yep ... continuous flow through the heater core on your model.

[Mudderoy]

Oh sure... leave it up to Carves to ruin a Texan's fun :poke: I know what part is not up to scratch... it's in a Cherokee ;) Nah, it would've been just a temp thing and "try it and see".



I think I just need to replace my radiator and pray.... for my wallet's sake - really for my wife's sanity lol. What happened to your hood? Do you have a spare that you use in the off-season?

Nothing. Matt bought a red one for his Jeep, didn't want to paint it black because it was nearly perfect. Let me borrow it so I could work on my hood. I've been goofing around, but Summer is coming up so I need to get the scoop bonded to the hood and get it on the Jeep. If I do it soon enough I can have it painted red to match the rest of the Jeep.

[cantab27]

done mine when heater core was leaking... done one winter down here not flash .....fixed leak with rad antie leak , was still sweet as 12 months later then sold it...only ever got hot twice why wheeling it but gave it a birth birthday re new rad, water pump blah blah ....never known so many heating problems but you tx guys...gets hot here plus the little aussie knows all a bout heat...

[Mudderoy]

done mine when heater core was leaking... done one winter down here not flash .....fixed leak with rad antie leak , was still sweet as 12 months later then sold it...only ever got hot twice why wheeling it but gave it a birth birthday re new rad, water pump blah blah ....never known so many heating problems but you tx guys...gets hot here plus the little aussie knows all a bout heat...

If you overheated the motor with the river as a heat sink, you'd really be doing something! :rotfl2:

[cantab27]

did boil twice why playing ...kinda stay away from the wet stuff to it cools down a bit ...seals dont like it...

[Mudderoy]

did boil twice why playing ...kinda stay away from the wet stuff to it cools down a bit ...seals dont like it...

Seals?!?!?! I didn't know you took it that far off shore! :rotfl2:

[bigjim350]

Not all the tx guys have the overheating problem, just the red ones. Mine stays 210 or under when wheeling or in traffic.

[Brasscatz]

Nothing. Matt bought a red one for his Jeep, didn't want to paint it black because it was nearly perfect. Let me borrow it so I could work on my hood. I've been goofing around, but Summer is coming up so I need to get the scoop bonded to the hood and get it on the Jeep. If I do it soon enough I can have it painted red to match the rest of the Jeep.

I think I'd leave it black. The contrast looks really good and you might be wishing you still had it black.


Not all the tx guys have the overheating problem, just the red ones. Mine stays 210 or under when wheeling or in traffic.

What can I say.... red jeeps are HOT!!! :D

[TimmyTXJ]

What are the pros and cons?

I installed the aux fan bypass switch and it has helped, though on my way home today I reached 227* at times. It cooled off faster with the fan running, but I need to get the temps better than that. My issue is mainly in stop and go traffic, not so much when I'm cruising at 70 mph.

Everything except my fans, fan clutch, radiator, and heater core is new on my cooling system... and I got to thinking... It's not cold enough here in Houston to need the heater, so why not bypass the heater core? I had an old pickup that didn't have the heater core hooked up and it ran just fine.

Are there any drawbacks to bypassing the heater core other than not having a working heater?

Some alternate thoughts...
Have you inspected the fan blades? If they're chipped, cracked, or flexing funny your capacity to draw air through the radiator core would be reduced. Same thing goes for the shroud, if it's broken at all you loose air flow. Are you sure your fan clutch is working properly? If the clutch is bad your fan might not be pulling any air in at all.

I would look at ways to get the hot ambient air out from under the hood too, may not be a huge difference but every little bit helps! I wonder if removing the front skid would help the air circulate better?

[msmoorenburg]

ok time for some stupid questions

How old is your water pump? (Tony's original pump had a plastic impeller)
Have you tried some stop leak to postpone the heater core replacement?
Can you hear your mech fan just off idle?
How old is the thermostat?


I hit 220 yesterday in traffic (normal since I was rolling with the windows down)

[Brasscatz]

Some alternate thoughts...
Have you inspected the fan blades? If they're chipped, cracked, or flexing funny your capacity to draw air through the radiator core would be reduced. Same thing goes for the shroud, if it's broken at all you loose air flow. Are you sure your fan clutch is working properly? If the clutch is bad your fan might not be pulling any air in at all.

I would look at ways to get the hot ambient air out from under the hood too, may not be a huge difference but every little bit helps! I wonder if removing the front skid would help the air circulate better?

Fan blades are good and so is the shroud. I'm not positive the clutch is perfect, but I'm 95% sure it's good. I've been contemplating cutting holes in my hood towards the front. Not sure if the skid would help or not, but anything is worth a try.


ok time for some stupid questions

How old is your water pump? (Tony's original pump had a plastic impeller)
Have you tried some stop leak to postpone the heater core replacement?
Can you hear your mech fan just off idle?
How old is the thermostat?


Water pump, hoses (except heater hoses), thermostat, thermostat housing, are all under a year old. Both the water pump I installed and the one I took out had metal impellers.
I have not used any stop leak, but that's a thought. I don't know about hearing the mech fan off idle... from inside? I'm not sure... I haven't listened for it lol. I've only listened for the aux fan.

The previous owner neglected the hell out of the cooling system. There is more rust and gunk in there that I find every time I take off a part to flush it. I removed the heater hoses and there is plenty of flow through them, but I squeezed them and it crunched so I ran water through it and a bunch of rust flakes came out.

I have run flush chemicals through this thing, and I've also flushed with water numerous times and there is still crap in it??? Am I going to have to replace EVERYTHING to get rid of all this rust crap? This is one of the reasons I want to replace the radiator. Maybe there is impedance in the rad and I don't want to ruin a new rad until I can get all the stuff out. This will include replacing my reservoir cuz even with a pressure washer I can't get that thing clean.

[Floridajeepcherokee]

How difficult is replacing heater core in 98 Jeep Grand Cherokee 2wd equipped with 4.0 motor???

[Brasscatz]

Not difficult at all. Just route the hoses where it eliminates going through the firewall. I'm at the airport on my phone, or I'd post a pic for you

[Mudderoy]

Not difficult at all. Just route the hoses where it eliminates going through the firewall. I'm at the airport on my phone, or I'd post a pic for you

He was asking about replacing the heater core.

[4.3LXJ]

How difficult is replacing heater core in 98 Jeep Grand Cherokee 2wd equipped with 4.0 motor???

Unfortunately, you have to pull the dash board to do it. Very time consumine

[Brasscatz]

He was asking about replacing the heater core.

Oops!! Thanks!!

[Floridajeepcherokee]

Thanks, I bypassed it this morning.

[Floridajeepcherokee]

After bypassing it, I vacuumed the inside carpet. Any tips as far as preventing mildew/mold and further drying or getting all moisture removed? baking soda?

[Brasscatz]

Baking soda, sure, but believe it or not kitty litter does a good job.

Sent from my Samsung Galaxy S4 because my microwave couldn't do it