Any side effects of a heater core bypass with A/C?

Bird Dog

Bird Dog

TJ Enthusiast
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Jan 8, 2017
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147
Location
Lexington, SC, United States
It is time to replace the heater core on my TJ. I don’t have the time right now to get to it since it is my DD so I am going to bypass the core to keep the coolant out of the floorboards for now until the weather cools off In the Fall. My general question is, are there any side effects of bypassing the core with the AC? I rarely use the AC but it is nice to have when I need it. I know I have to evacuate the system to change the core but are there any problems running the AC without a functional heater core? Thanks.
 
It should actually improve the performance of your A/C a small amount. A lot of modern cars have an automatic core bypass for when you max out the A/C.

Old Air Products makes a decent electronic bypass kit to improve AC performance, though it wouldn’t work to stop a leaking heater core.

The cheapest and easiest way is to use a double ended barbed fitting (you might need a size adapter) and merely plug the two heater hoses into each other end to end. Secure temporarily with a couple of worm drive clamps.


Be sure to set it up as an actual bypass that allows coolant to flow through the hoses to and from the water pump.

Do not deadhead the flow by plugging the hoses or installing shut-off valves. The TJ uses the heater core as the recirculation line, and by cutting it off you stop all forced coolant flow in the block until the thermostat opens.

If you do have to deadhead the flow in the tubes for whatever reason, drill a good size hole in the thermostat (I would do at least 5/16”) to use the radiator as the bypass to make sure there is some bypass flow. This is not preferred as it will take the engine longer to warm up, and performance, fuel economy, and emissions will suffer.

But deadhead the flow with no bypass and you risk boiling coolant in the block and creating huge expansion stresses as localized heating is not smoothed out by coolant flow before the thermostat opens.
 
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My heater core is bypassed and it has only come up once but with the core bypassed you cannot regulate cool air with the A/C running. It is always full cold even if you set the temp dial to full hot. Makes perfect sense, I just never considered it.
 
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Yea doing the heater core is about a 4-6 hour task + or - how much drinking you do. i did mine did all my light bulbs and stuff at the same time radio stuff. just make it worth ur time.
 
Thanks for all the great responses. The heat coming from the floorboard actually does better than the heater itself. I thought about making the bypass permanent but the big problem comes from defrosting the windshield with no heat source. We don’t have it like Floridians but there are a few spells of cold here in SC. I can still probably put off the replacement until December!
 
2017 Malibu 1.5 turbo, overheated on me , so the oil change facility put this head gasket block radiator stop leaking in overflow just in case to be preventative maintenance..well it was fine first day, then the next heated up, car went into safe mode low idle, engine cooling fans kicked on and temp began to drop rapidly, then car went back into operational drive mode. I didn't let it do it again, stoped at fuel station immediately, shit off engine, opened hood. Cooling fans ran good 5 more min. There was no boiling in the overflow, but at bottom of resivor could see what looked like sand, the coolant had become like pink Pepto vismol that had not been shaken up, it was grainy. I used the shop vac I had in trunk to suck it out resivor, put hose rite in cap opening created good seal, and it came out like a milk shake through coffee stirring straw. Needless to say, car made it back after filling overflow back up with 50 /50 mix coolant. Drove exactly 6 miles, it didn't heat up until last 3 miles, as I seen the temp gauge rise I accelerated steadily, placed car in neutral and coast doing apex. 50 mph. Through side access road that had some slight slopes, took away speed, then gained speed. Temp ran apex 210, and coolant fans kicked on. It never got into the red zone thank goodness. Normal operation is like 180 + 190. Being in Alabama, that may seem tad warm, but I have had the car since 2017, original owner and have 168 thou miles. Body is in excellent condition, interior is in good shape. So back at the home front I pulled from the fire wall the output hose for heater core, using the shop vac I placed hose in the overflow tank cap opening, and semi induced pressure so that it would flow through engine path and push any of that floating " cement' out, the appearance after all the gurgling and build up noise was that Pepto pink upon expelling from firewall heater core outlet connection from where I had removed hose already. I poured another 1.5 ltr. Of water into resivor and induced with the Vacume again until it was clear. After assembling hoses back and filling resivor overflow, I started car, it got up to operating temp, but blew the outlet hose off, not once, but twice, frustrated at loosing the coolant I stoped piddling with it for the evening. Could the thermostat be stuck ? Water pump ? There no leak or squeal noice coming from the pump, pulley is turning with serpentine belt ? Where is the thermostat ? I can not find any YouTube on 2017 Malibu 1.5 turbo, everything is 2016 2018 2019 2020 or it's Chevy Cruze, nothing on Malibu.....sad I know. Would it be feasible to bypass the heater core first and give that a shot ? I need AC and did read that the heater core is not needed for AC to work, it has separate cooling / radiator, but does utilize same coolant in system ? Will the system burp itself of any traped air ? Getting to radiator cap is 4.5 hour work, it's directly under the front upper portion of the body, the radiator mounting / housing frame, if looking at the engine str8 on, the cap for radiator sits directly below where the drop rod for hood would be locked at when hood is not propped open. Any special hose / clamps to util
ize on the bypass? I plan on flushing heater core be sure not leaking, don't need the heat at moment, least good 5 months. Alabama like Mexico at times. Thank you for allowing me to vent and inquire, least it's not the Malibu blowing off steam....please help, I'm lost on where to begin.
 
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malibuZZZZZZZZZ said:
2017 Malibu 1.5 turbo, overheated on me , so the oil change facility put this head gasket block radiator stop leaking in overflow just in case to be preventative maintenance..well it was fine first day, then the next heated up, car went into safe mode low idle, engine cooling fans kicked on and temp began to drop rapidly, then car went back into operational drive mode. I didn't let it do it again, stoped at fuel station immediately, shit off engine, opened hood. Cooling fans ran good 5 more min. There was no boiling in the overflow, but at bottom of resivor could see what looked like sand, the coolant had become like pink Pepto vismol that had not been shaken up, it was grainy. I used the shop vac I had in trunk to suck it out resivor, put hose rite in cap opening created good seal, and it came out like a milk shake through coffee stirring straw. Needless to say, car made it back after filling overflow back up with 50 /50 mix coolant. Drove exactly 6 miles, it didn't heat up until last 3 miles, as I seen the temp gauge rise I accelerated steadily, placed car in neutral and coast doing apex. 50 mph. Through side access road that had some slight slopes, took away speed, then gained speed. Temp ran apex 210, and coolant fans kicked on. It never got into the red zone thank goodness. Normal operation is like 180 + 190. Being in Alabama, that may seem tad warm, but I have had the car since 2017, original owner and have 168 thou miles. Body is in excellent condition, interior is in good shape. So back at the home front I pulled from the fire wall the output hose for heater core, using the shop vac I placed hose in the overflow tank cap opening, and semi induced pressure so that it would flow through engine path and push any of that floating " cement' out, the appearance after all the gurgling and build up noise was that Pepto pink upon expelling from firewall heater core outlet connection from where I had removed hose already. I poured another 1.5 ltr. Of water into resivor and induced with the Vacume again until it was clear. After assembling hoses back and filling resivor overflow, I started car, it got up to operating temp, but blew the outlet hose off, not once, but twice, frustrated at loosing the coolant I stoped piddling with it for the evening. Could the thermostat be stuck ? Water pump ? There no leak or squeal noice coming from the pump, pulley is turning with serpentine belt ? Where is the thermostat ? I can not find any YouTube on 2017 Malibu 1.5 turbo, everything is 2016 2018 2019 2020 or it's Chevy Cruze, nothing on Malibu.....sad I know. Would it be feasible to bypass the heater core first and give that a shot ? I need AC and did read that the heater core is not needed for AC to work, it has separate cooling / radiator, but does utilize same coolant in system ? Will the system burp itself of any traped air ? Getting to radiator cap is 4.5 hour work, it's directly under the front upper portion of the body, the radiator mounting / housing frame, if looking at the engine str8 on, the cap for radiator sits directly below where the drop rod for hood would be locked at when hood is not propped open. Any special hose / clamps to util
ize on the bypass? I plan on flushing heater core be sure not leaking, don't need the heat at moment, least good 5 months. Alabama like Mexico at times. Thank you for allowing me to vent and inquire, least it's not the Malibu blowing off steam....please help, I'm lost on where to begin.
Click to expand...

You do realize that this forum is for Jeep Wranglers, don't you?

Also, paragraphs help...a lot.
 
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Chris said:
You do realize that this forum is for Jeep Wranglers, don't you?

Also, paragraphs help...a lot.
Click to expand...

d9GcSekamNL_rPfc7rg686w6NXX9f330JYj7dJ6OjJtpDbPQ&s.jpg
 
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malibuZZZZZZZZZ said:
2017 Malibu 1.5 turbo, overheated on me , so the oil change facility put this head gasket block radiator stop leaking in overflow just in case to be preventative maintenance..well it was fine first day, then the next heated up, car went into safe mode low idle, engine cooling fans kicked on and temp began to drop rapidly, then car went back into operational drive mode. I didn't let it do it again, stoped at fuel station immediately, shit off engine, opened hood. Cooling fans ran good 5 more min. There was no boiling in the overflow, but at bottom of resivor could see what looked like sand, the coolant had become like pink Pepto vismol that had not been shaken up, it was grainy. I used the shop vac I had in trunk to suck it out resivor, put hose rite in cap opening created good seal, and it came out like a milk shake through coffee stirring straw. Needless to say, car made it back after filling overflow back up with 50 /50 mix coolant. Drove exactly 6 miles, it didn't heat up until last 3 miles, as I seen the temp gauge rise I accelerated steadily, placed car in neutral and coast doing apex. 50 mph. Through side access road that had some slight slopes, took away speed, then gained speed. Temp ran apex 210, and coolant fans kicked on. It never got into the red zone thank goodness. Normal operation is like 180 + 190. Being in Alabama, that may seem tad warm, but I have had the car since 2017, original owner and have 168 thou miles. Body is in excellent condition, interior is in good shape. So back at the home front I pulled from the fire wall the output hose for heater core, using the shop vac I placed hose in the overflow tank cap opening, and semi induced pressure so that it would flow through engine path and push any of that floating " cement' out, the appearance after all the gurgling and build up noise was that Pepto pink upon expelling from firewall heater core outlet connection from where I had removed hose already. I poured another 1.5 ltr. Of water into resivor and induced with the Vacume again until it was clear. After assembling hoses back and filling resivor overflow, I started car, it got up to operating temp, but blew the outlet hose off, not once, but twice, frustrated at loosing the coolant I stoped piddling with it for the evening. Could the thermostat be stuck ? Water pump ? There no leak or squeal noice coming from the pump, pulley is turning with serpentine belt ? Where is the thermostat ? I can not find any YouTube on 2017 Malibu 1.5 turbo, everything is 2016 2018 2019 2020 or it's Chevy Cruze, nothing on Malibu.....sad I know. Would it be feasible to bypass the heater core first and give that a shot ? I need AC and did read that the heater core is not needed for AC to work, it has separate cooling / radiator, but does utilize same coolant in system ? Will the system burp itself of any traped air ? Getting to radiator cap is 4.5 hour work, it's directly under the front upper portion of the body, the radiator mounting / housing frame, if looking at the engine str8 on, the cap for radiator sits directly below where the drop rod for hood would be locked at when hood is not propped open. Any special hose / clamps to util
ize on the bypass? I plan on flushing heater core be sure not leaking, don't need the heat at moment, least good 5 months. Alabama like Mexico at times. Thank you for allowing me to vent and inquire, least it's not the Malibu blowing off steam....please help, I'm lost on where to begin.
Click to expand...

Sounds like you blew a head gasket. If the coolant is sludged up, that is a very clear sign that oil and coolant have mixed. Check your oil dipstick and see if there's sludge on that too.

Replacing a head gasket is a very involved repair that really can't be half-assed. A good DIYer with proper tools and an instruction manual could probably do it in a long weekend, but realistically, I'd consider having it towed to your local mechanic. Depending on how long it was driven after the gasket blew, there is a chance of having caused irreparable damage to the engine, meaning you might be looking at a whole new engine, or maybe a junkyard engine if you're tight on cash.
 
There will be no adverse effects from bypassing the heater core. I used one of these for months (5/8" one end, 3/4" the other, purchased at O'Reillys.)

1714230229991.png



Hotrodders have used bypass valves for years. I used to have a "summer/winter" valve in an old Ford pickup. The A/C ran much cooler when it didn't need to cool air heated by the hot coolant in the heater core.

I've wanted to add one of these, but have never gotten around to it.

1714229751933.png



1714229781951.png
 
Last edited:
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Andy-WhiteTJ said:
@AndyG , @John Cooper He's down your neck of the woods. Can you set him straight. He also needs to know how to spell Alabama (See his location). ;)

Edited for clarification
Click to expand...

Well if he hadn't typed a book, and could half way spell, beings as he is from "Alanama" and all I doubt it can happen.

And we are Holy Wranglers not to be confused with "Holly Wranglers"

Now what was the question again??????
 
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Steel City 06 said:
Sounds like you blew a head gasket. If the coolant is sludged up, that is a very clear sign that oil and coolant have mixed. Check your oil dipstick and see if there's sludge on that too.

Replacing a head gasket is a very involved repair that really can't be half-assed. A good DIYer with proper tools and an instruction manual could probably do it in a long weekend, but realistically, I'd consider having it towed to your local mechanic. Depending on how long it was driven after the gasket blew, there is a chance of having caused irreparable damage to the engine, meaning you might be looking at a whole new engine, or maybe a junkyard engine if you're tight on cash.
Click to expand...

And there it is, the explanation he was looking for........ and it run him off!!!!!
 
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