4.0 very little heat - JeepForum.com
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post #1 of 16 Old 10-18-2021, 03:59 PM Thread Starter
mustang67ford
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4.0 very little heat

I have a 99 laredo with a 4.0 and have been experiencing very little heat even with heat on high and temp turned up. My t-stat is fairly new. Radiator and water pump was recently replaced as well. Warmed it up and checked my heater hoses, both felt to be the same temp so assuming no heater core blockage. No wet floor so assuming no heater core leak. I don't believe I have blend doors as I have simple heat controls; speed, temp, and position. What do I check next? Is there still a door someplace the temp dial opens/closes? I don't recall ever having much heat, but seems worse now. Maybe air trapped someplace from getting rad and pump replaced? I noticed I do need to top off my reservoir some.

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post #2 of 16 Old 10-18-2021, 04:02 PM
Soem0
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Heater core could be plugged. This doesn't mean a leak. Also your blend door or the actuators could be stuck closed not allowing the air to get out of the climate box
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post #3 of 16 Old 10-18-2021, 04:10 PM Thread Starter
mustang67ford
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Heater core could be plugged. This doesn't mean a leak. Also your blend door or the actuators could be stuck closed not allowing the air to get out of the climate box
I think since both my heater lines feel to be the same temp, the core isn't plugged. I also don't believe my jeep has the blend doors.
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post #4 of 16 Old 10-18-2021, 04:17 PM
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Just to verify, are you getting good operating temp on the water gauge in the instrument cluster - between 190-210? Was gonna say you mentioned having a thermostat replaced, in which case they might have put in a lower limit one which is causing everything to run cooler.

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post #5 of 16 Old 10-18-2021, 04:23 PM Thread Starter
mustang67ford
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Originally Posted by carlsondrew3 View Post
Just to verify, are you getting good operating temp on the water gauge in the instrument cluster - between 190-210? Was gonna say you mentioned having a thermostat replaced, in which case they might have put in a lower limit one which is causing everything to run cooler.
. Reads a little under 210 mark on dash so I would assume getting up to temp. What do I check to make sure the outside cold air is getting cut off when turned to heat?
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post #6 of 16 Old 10-18-2021, 07:12 PM
Mattyjm
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Quote:
Originally Posted by mustang67ford View Post
I think since both my heater lines feel to be the same temp, the core isn't plugged. I also don't believe my jeep has the blend doors.
Your heater core may not be plugged all the way, but it could probably use a good flushing. My 2000 WJ 4.0L had this same problem, so I gave the core a good flush and it helped immensely for a couple years until my heater core started leaking.

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post #7 of 16 Old 10-19-2021, 02:22 AM
Delta0
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If you connect your heater to a garden hose does water flow through it rapidly?
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post #8 of 16 Old 10-19-2021, 06:11 AM Thread Starter
mustang67ford
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I would like to keep it simple at first and make sure the outside air is shut off. Does anybody know how to do this and what does the heat dial control? I have not tried a heater core flush though I have read that if the heater lines arw both hot, it is bot clogged. I don't really want to have to undo coolant lines just yet and would like to rule other things out first.

I did find a small coolant leak where the little overflow tube hooks to the radiator by the rad cap. Not sure if there should be a clamp there as it is a very small line so put a zip tie on it.
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post #9 of 16 Old 10-19-2021, 10:37 AM
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Originally Posted by mustang67ford View Post
I would like to keep it simple at first and make sure the outside air is shut off. Does anybody know how to do this and what does the heat dial control? I have not tried a heater core flush though I have read that if the heater lines arw both hot, it is bot clogged. Yeah, you'd think so Mustang wouldn't you?
However, the outflow hose will still feel hot when most of the tubes are blocked.
That why I asked if you have a good flow when you attach a garden hose.
I don't really want to have to undo coolant lines just yet and would like to rule other things out first.

I did find a small coolant leak where the little overflow tube hooks to the radiator by the rad cap. Not sure if there should be a clamp there as it is a very small line so put a zip tie on it.
I think my WJ's overflow tube comes off the coolant container, which has a yellow cap, and sits further back in the engine room.

Undoing coolant lines isn't a big deal as long as you clamp the lines close to the bulkhead / firewall before you detach them.
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post #10 of 16 Old 10-19-2021, 11:32 AM Thread Starter
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Quote:
Originally Posted by mustang67ford View Post
I would like to keep it simple at first and make sure the outside air is shut off. Does anybody know how to do this and what does the heat dial control? I have not tried a heater core flush though I have read that if the heater lines arw both hot, it is bot clogged. Yeah, you'd think so Mustang wouldn't you?
However, the outflow hose will still feel hot when most of the tubes are blocked.
That why I asked if you have a good flow when you attach a garden hose.
I don't really want to have to undo coolant lines just yet and would like to rule other things out first.

I did find a small coolant leak where the little overflow tube hooks to the radiator by the rad cap. Not sure if there should be a clamp there as it is a very small line so put a zip tie on it.
I think my WJ's overflow tube comes off the coolant container, which has a yellow cap, and sits further back in the engine room.

Undoing coolant lines isn't a big deal as long as you clamp the lines close to the bulkhead / firewall before you detach them.
I didn't say anything about the overflow hose being hot. I said both heater hoses were hot.
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post #11 of 16 Old 10-19-2021, 06:54 PM
kwarbington
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When I got my 2002 4.0L WJ with manual air and heat, the heat would not work, but both hoses to and from the heater core would still get hot. I back flushed it carefully with the water hose (do not attach the water hose, just hold the hose to the return hose by hand so you do not build pressure in the core and damage it), then reconnected it and had great heat, but I also had a pinhole leak in the heater core and faint smell of glycol in the cab. Got me through the coldest part of the winter, but eventually had to replace the core. I am guessing PO used stop leak because of leaking heater core, which stopped the leak, but as expected eventually plugged the heater core. When I flushed it out it started working again and also started leaking again. Also, the selector controls on the manual heating systems are vacuum operated, and if you have a vacuum leak, they will not work correctly. I am not sure if the hot/cold adjuster is pneumatic or electric, but maybe someone else will chime in. If you have to replace the core it is a very time consuming job, and very expensive to pay someone to do, but you can do it yourself without any special tools - with the exception of recharging the AC. There are some really good youtube videos and you can get a shop manual on ebay for maybe $20-30. I recommend you have a manual even though the videos seem pretty comprehensive. It took me 10-12 hours to do mine the first time (exclusive of charging the AC). I did another one 2 months later for a friend and did the entire job in under 3 hours. Charging the AC is not a big deal, but you need special tools and equipment for that, and it is more cost effective to take it to the shop for a single charge. Good luck!
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post #12 of 16 Old 10-20-2021, 05:07 AM
Delta0
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Originally Posted by mustang67ford View Post
I didn't say anything about the overflow hose being hot. I said both heater hoses were hot.
Very true Mustang.

You also said you have an overflow hose from your radiator.
I pointed out that I do not have an overflow hose from my rad on my GC.
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post #13 of 16 Old 10-20-2021, 04:26 PM Thread Starter
mustang67ford
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Originally Posted by kwarbington View Post
When I got my 2002 4.0L WJ with manual air and heat, the heat would not work, but both hoses to and from the heater core would still get hot. I back flushed it carefully with the water hose (do not attach the water hose, just hold the hose to the return hose by hand so you do not build pressure in the core and damage it), then reconnected it and had great heat, but I also had a pinhole leak in the heater core and faint smell of glycol in the cab. Got me through the coldest part of the winter, but eventually had to replace the core. I am guessing PO used stop leak because of leaking heater core, which stopped the leak, but as expected eventually plugged the heater core. When I flushed it out it started working again and also started leaking again. Also, the selector controls on the manual heating systems are vacuum operated, and if you have a vacuum leak, they will not work correctly. I am not sure if the hot/cold adjuster is pneumatic or electric, but maybe someone else will chime in. If you have to replace the core it is a very time consuming job, and very expensive to pay someone to do, but you can do it yourself without any special tools - with the exception of recharging the AC. There are some really good youtube videos and you can get a shop manual on ebay for maybe $20-30. I recommend you have a manual even though the videos seem pretty comprehensive. It took me 10-12 hours to do mine the first time (exclusive of charging the AC). I did another one 2 months later for a friend and did the entire job in under 3 hours. Charging the AC is not a big deal, but you need special tools and equipment for that, and it is more cost effective to take it to the shop for a single charge. Good luck!
Thanks for the info. I am trying to look figure out if Ioutside air is getting in. I don't want to mess with flushing the core yet. Some things are left best disturbed. I watched a couple videos on changing the core. Everything has to come out, even the steering wheel, from what I seen. That looked scary.
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post #14 of 16 Old 10-20-2021, 10:39 PM
kwarbington
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Does not matter if outside air is getting in. Outside air is supposed to come in 100% unless you are in bypass mode, and the heater should be able to heat the outside air and overcome the additional cooling from the AC when the defroster is on as long as the heater core and dampers are all working correctly. Flushing the core is really easy, you just pull the two hoses loose at the thermostat housing, and then hold the water hose to the return hose to flush it backwards with the other hose going to a container. A lot of junk should come out and your heater should start working after you reconnect the hoses, unless the hot/cold damper is broken and stuck on cold. If you have no heat or start smelling glycol in the cab after, you are going to have to bypass the core and live without heat or pull the HVAC unit and replace the core and/or fix dampers. If you can isolate the problem to a damper, there are some pretty innovative youtube options to cut into the HVAC box, but I have no experience to say that those options are a good or a bad idea. If you are hesitant to backflush the heater core, replacing the heater core may be a bit more than you should take on, but you need no skill or special tools to backflush the heater core. Should be plenty videos on youtube to show you how, and it is easy. Good luck!
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post #15 of 16 Old 10-21-2021, 02:40 AM
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Originally Posted by kwarbington View Post
Does not matter if outside air is getting in. Outside air is supposed to come in 100% unless you are in bypass mode, and the heater should be able to heat the outside air and overcome the additional cooling from the AC when the defroster is on as long as the heater core and dampers are all working correctly. Flushing the core is really easy, you just pull the two hoses loose at the thermostat housing, and then hold the water hose to the return hose to flush it backwards with the other hose going to a container. A lot of junk should come out and your heater should start working after you reconnect the hoses, unless the hot/cold damper is broken and stuck on cold. If you have no heat or start smelling glycol in the cab after, you are going to have to bypass the core and live without heat or pull the HVAC unit and replace the core and/or fix dampers. If you can isolate the problem to a damper, there are some pretty innovative youtube options to cut into the HVAC box, but I have no experience to say that those options are a good or a bad idea. If you are hesitant to backflush the heater core, replacing the heater core may be a bit more than you should take on, but you need no skill or special tools to backflush the heater core. Should be plenty videos on youtube to show you how, and it is easy. Good luck!
Exactly K.
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