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Old 04-19-2011, 01:45 AM   #1
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Question Heater core won't get hot

Driving a '99 TJ with 186k miles, which we just acquired. We found that the heater will not get hot, and have done some troubleshooting.

The hoses to and from the core don't get hot, but when I disconnect them and flush with a garden hose, there is water flow both directions. The first time I did it, the water that came out wasn't pretty. Water in radiator was nice and green, and the guy I bought it from said he had replaced the radiator recently. I figure he didn't flush the system so the heater core was clogged. Flushed both directions until water pretty much cleared up. Put it back together, but it didn't solve the problem.

Why would a heater core that allows water to flow through in both directions not get hot? I thought the connections to the block might be plugged, but they aren't. I can get water from the inlet hose (disconnected from thermostat housing) through the heater core, back to and through the water pump, radiator or block and back out the pipe that the hose attaches to.

I connected the supply hose back to the thermostat housing and disconnected the return to the pump to see if I could get water out the return hose. Connected a piece of scrap garden hose to the pump return line and elevated it above the radiator fill neck so the system would stay full except what comes through the heater core. Filled radiator, then start the engine. The water circulates from the block to the radiator (top radiator hose gets hot) but there is no flow coming out the heater core return hose.

How is this possible? Bad water pump? Water pump installed wrong? Bad thermostat? HELP!!!!

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Old 04-19-2011, 08:42 AM   #2
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you can test your thermostat by using a cooking thermometer and a pot of water. see if it opens at the right temp, or for the cost just replace it. however testing it completely eliminates it from the equation.
my first guess would be the water pump, if water flows freely when pushed by the pressure from the hose, but not any other time, that could be it. the anti-freeze probably was fresh and green because it hadnt circulated much at all.
he probably replaced the radiator because it wouldnt heat up and he assumed that was the faulty item.
usually if the water pump has water coming from the small hole in it, the "weep hole", then that is the sign of a bad one but it doesnt always do that. you should be able to leave the rad cap off, have it full and run the engine, once the thermostat opens, you should be able to see the coolant circulating. if not, its the pump.

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Old 04-19-2011, 09:36 AM   #3
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Water circulates

When we were doing all of the above, with the cap off I could tell there was circulation between the block and the radiator. The water bubbled and burped because we had dumped some water in the process and let air into the system. Sounds like I need to take the t-stat off and look at it.

The engine runs at the proper temp, so I don't think it's bad. Wondered if there was a way you could install wrong it such that it would block flow to the heater core. I can get water flow out the pipe that the heater hose connects to, so I don't think that's happening.

I saw something in the FSM (I think) about a water pump which is designed to rotate one direction on certain model years, but the other direction on different model years. I'm an engineer, and I've heard of centrifugal pumps running backwards being able to put up flow, but not as much head pressure. It's a long-shot, but I wondered if anyone had experience with the wrong pump being installed. Seems like there would be other differences (bolt hole pattern, shape, etc.).

All speculation is appreciated....
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Old 04-19-2011, 09:52 AM   #4
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Try running it without the thermostat in place, that will remove that from the equation. If that fixes it, just go get a new 195 degree thermostat. I don't have experience with running the wrong water pump that has a reverse circulation but they're out there for TJs so maybe. But do try running it without the thermostat first and see if that corrects it. And you're absolutely certain there is no flow through the heater core? Even when there is flow, the heater won't produce heat for the passenger compartment if the blend door inside the passenger compartment isn't opening properly.
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Old 04-19-2011, 09:57 AM   #5
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check the operation of the temp blend door as well
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Old 04-19-2011, 12:08 PM   #6
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I had a similar problem; no heat. Turned out to be the "Actuator",which I presume is some sort of switch behind the dash.
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Old 04-19-2011, 12:50 PM   #7
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Water pump.

I had the exact same issue. No heat, hoses not getting hot. Replaced t-stat. Same thing.

When I did a flush and reverse flush, I got gunk out of the core and thought I was good. When I tried to test it, I had Niagara Falls coming out of the pump. By the time I got the pump off (easy to do btw), I noticed the damned thing would barely spin. A few bucks later I'm installing a new one. If you go this route, note on the impeller if there is an "R" imprinted. This denotes reverse flow (which my 97 2.5L used). Things run a LOT smoother and my heater core warms up QUICKLY now (less than 5 minutes or so, depending on ambient temps).
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Old 04-19-2011, 03:50 PM   #8
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Jerry - thought about that, and also about just putting a hose from the t-stat housing straight to the water pump connection (bypass the heater core)

Herbie - I mentioned that in my first thread (which got no replies); blend door works fine

Paul - I think I may have read another post of yours that mentioned Niagara Falls...it isn't what I want to hear, but I may end up doing that, glad to hear it's easy; just to clarify, did you see water coming out the weephole in the bottom of the pump housing? I'm assuming there's one like other water pumps I've seen. I don't have a problem with coolant leaking (yet).

I bought a new thermostat and gasket while I was out at lunch. Noticed there's a punch-out on the gasket that looks like it lines up with where the heater hose supply is on the housing. I'd bet a nickel the guy didn't take that off all the way when he replaced the radiator. That wouldn't explain how I got water out of it when I disconnected the hose....
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Old 04-20-2011, 01:25 AM   #9
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No luck on the thermostat

Spent four hours on it this evening, to no avail:

- disconnected the supply hose to the heater core, cranked engine and watched to see if water came out the t-stat housing; it did NOT flow out, even though I had previously pushed water out that opening by flushing with a garden hose into the supply side, through the core back to the block and out the top; this maked me suspect either the water pump is wonky or there is some sort of anomaly inside the t-stat housing

- disconnected return heater hose at pump, back-flushed the heater core using garden hose, then blew compressed air into it to agitate things without pressurizing it, then flushed again; through all of this didn't get much gunk out, but did see some particles (hey - it's got 186k miles on it). Then blew air, drained as much as possible from the siphoning effect, elevated the hoses and put CLR in the supply hose until the water started to trickle out the return hose; put maybe 2-3 cups worth of CLR in and let it sit for a couple hours while we did the other stuff (see below); flushed out the CLR with garden hose and got some more gunk, but nothing dramatic

- went ahead and removed t-stat housing to examine gasket and t-stat; all seemed in good condition, the thermostat actually looked like it had been replaced when the radiator was done just before we bought it

- replaced t-stat, had a heckuva time getting the thing to stay put while we mounted the housing; first time it slipped, didn't get a good seal and leaked water before even putting pressure on it; redid that, got it to hold under pressure, and engine temp holds right where it's supposed to, but still no heat on the heater hoses

Next step is (unfortunately) the water pump. When I was running it after we had put everything back together, and it was heating up, the level in the radiator kept overflowing until the thermostat opened, at which point it sucked the water level down and I had to replace everything that had come out. Since I'm working on the theory that the pump is turning the wrong direction, would it be possible that it's trying to move water up through the radiator and over to the block through the top radiator hose? I cannot see it being able to do that, but I have to ask because it's been so long since I did a radiator flush that I've forgotten how much swell there is due to the water heating up in the block.

Appreciate all the suggestions.... keep 'em coming!
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Old 04-20-2011, 09:07 AM   #10
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its easier to set the thermostat into the recess and then put the housing down around it rather than try to keep the thermostat in the housing defying gravity.
i dont know anything about reverse flow water pumps but when checking a system with the cap off the rad, i havent had one push water out of the top prior to it heating up. normally it does nothing until the thermostat opens, and then you can see it circulating.
i would just replace the pump, mainly since the amount of time spent redoing the same little things is probably more time than it would have taken to do the water pump
the upside is once its done, you know what you have and that its correct and clean.
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Old 04-20-2011, 09:16 AM   #11
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Hey! I have a 99 TJ!
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Old 04-20-2011, 10:20 AM   #12
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Quote:
Originally Posted by WBN3 View Post
Paul - I think I may have read another post of yours that mentioned Niagara Falls...it isn't what I want to hear, but I may end up doing that, glad to hear it's easy; just to clarify, did you see water coming out the weephole in the bottom of the pump housing? I'm assuming there's one like other water pumps I've seen. I don't have a problem with coolant leaking (yet).
Yeah, it was coming from the weephole at a good speed. If it was leaking from somewhere else, I couldn't tell. It did NOT leak at ALL until I did the reverse flush. Then the problem became apparent.
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Old 04-20-2011, 12:51 PM   #13
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Originally Posted by 99Wrangler4x4 View Post
Hey! I have a 99 TJ!
Well, that's nice... it's black just like mine. Too bad you've got the 4-cyl., guess that's better than not having a jeep... have you had this problem, or are you just trolling...
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Old 04-20-2011, 12:55 PM   #14
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Quote:
Originally Posted by randy and teri View Post
its easier to set the thermostat into the recess and then put the housing down around it rather than try to keep the thermostat in the housing defying gravity.
....
i would just replace the pump, mainly since the amount of time spent redoing the same little things is probably more time than it would have taken to do the water pump
the upside is once its done, you know what you have and that its correct and clean.
Yes, I set the t-stat into the recess, but the bottom bolt on the housing was difficult to get lined up with its hole on the block, so I think I bumped the thermostat when I was trying to get it aligned. Used a smidge of white lithium grease to hold it to the block long enough to position the housing the second time around. As for replacing the pump, that's apparent to me now, but I am cheap and didn't want to do it unless I had to...
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Old 04-20-2011, 02:34 PM   #15
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Quote:
Originally Posted by WBN3 View Post
Well, that's nice... it's black just like mine. Too bad you've got the 4-cyl., guess that's better than not having a jeep... have you had this problem, or are you just trolling...
I tried to help ya but I've never had this problem. Just thought I'd share
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Old 06-11-2011, 01:15 AM   #16
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Smoking gun?

Update (if anyone is interested):

Finally got around to changing the water pump, and this is what I found:



Really surprised it wasn't overheating, although with the t-stat sitting right on top of the pump housing, I suppose it could move enough water to keep it (the temperature sensor) cool. The real question is what kind of damage may have been done in the engine itself where small passages like the heater core weren't allowing much flow. Anyone out there seen this before?
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Old 06-11-2011, 09:57 AM   #17
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Mine liked like that when I replaced it. Amazing that the jeep was still running at all, but mine never even overheated. I flushed heater core, and around block, and radiator. Replaced all hoses,heater included.
You'll be fine.
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Old 12-07-2012, 10:16 PM   #18
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after seeing that i will be replacing mine just to know i have a new one.
Jeeps are amazing in their ability to run even thru a life of abuse.
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Old 12-08-2012, 08:09 AM   #19
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Update (if anyone is interested):

Finally got around to changing the water pump, and this is what I found:



Really surprised it wasn't overheating, although with the t-stat sitting right on top of the pump housing, I suppose it could move enough water to keep it (the temperature sensor) cool. The real question is what kind of damage may have been done in the engine itself where small passages like the heater core weren't allowing much flow. Anyone out there seen this before?

Did changing the water pump fix the no heat in the cab problem? My Jeep does the same thing and I am reasearching what options to look at for fixing it.

Jeff
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Old 12-08-2012, 11:20 AM   #20
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Did changing the water pump fix the no heat in the cab problem? My Jeep does the same thing and I am reasearching what options to look at for fixing it.

Jeff
Lack of heat from the heater is usually caused by a clogged heater core that can be fixed by flushing it back & forth with a garden hose.
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Old 12-13-2012, 10:06 AM   #21
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Quote:
Originally Posted by erickpl
Water pump.

I had the exact same issue. No heat, hoses not getting hot. Replaced t-stat. Same thing.

When I did a flush and reverse flush, I got gunk out of the core and thought I was good. When I tried to test it, I had Niagara Falls coming out of the pump. By the time I got the pump off (easy to do btw), I noticed the damned thing would barely spin. A few bucks later I'm installing a new one. If you go this route, note on the impeller if there is an "R" imprinted. This denotes reverse flow (which my 97 2.5L used). Things run a LOT smoother and my heater core warms up QUICKLY now (less than 5 minutes or so, depending on ambient temps).
Was your jeep still running at the right temp. I have the heat problem too and think it could be the pump.
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Old 12-13-2012, 11:58 AM   #22
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I would supplement the heater core flushing process by adding a step of having a solvent sit in the core for a while and then flushing and backflushing. From what I've researched, the safe solvents for the core are a mixture or heated water and vinegar or a heated critic acid solution.

I've read that some people have used CLR with success but I think it is too strong and may cause damage. Others have used radiator flush or "minute" flush but I haven't seen any positive effective reviews of these types of solvents.
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Old 12-13-2012, 02:08 PM   #23
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Quote:
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Was your jeep still running at the right temp. I have the heat problem too and think it could be the pump.
It ran cool if anything (at least indicated on the temp indicator). Water just wouldn't circulate very well at all obviously. It never overheated though.
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Old 01-20-2013, 06:32 AM   #24
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When I was wrenching for a living the Jeep water pump with no impeller was seen on occasion. We attributed it to the new environmental friendly style coolant that turns acidic and and attacks the impeller metal.

Importance of the pH Value in Engine's Coolant / eutechinst.com

From the time the coolant is introduced into any type of engine it starts a gradual degradation process into corrosive acids. This degradation is a function of time, temperature and the types of metals used in the engine and components construction. Once the coolant turns acidic all engine metals start to dissolve. The results are leaking water pumps, heater cores and radiators.

With the increasing number of aluminum engines and components the corrosive process is accelerated since the coolant degrades much faster in contact with aluminum than in typical cast iron engines. During the preventive maintenance of any engine, in addition to the freezing point, the pH value of the cooling system should be checked.
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Old 01-20-2013, 11:34 AM   #25
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I've have the low heat problem as well. I have done the flush. Checked the blend door. Heat blows warm, but never hot. At around minus 15C I have just about lost all heat, and yet I see others driving with soft tops. I have flushed and checked enough that I have given up on the problem and wear gloves and a toque. After seeing this, I'm thinking it may be my pump. Does any one know if there is a test I can do before I pull it? A pressure test of some sort? Not sure if it matters, I have a '98 4L with no ac. I have heard jeep heaters are directly linked to the bowels of hell, all I have is a warm summer breeze.
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Old 01-20-2013, 03:15 PM   #26
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You can do what the op did. Drain and refill with water, then remove the heater hose from the water pump plug it (heater core side) Install another hose, Hold the hose up high - 18" above the radiator or so. Fire the jeep up. See what kind of flow you get. It should flow like a water hose. Only ru it quick as you should be pumping cooling water out of the open hose. The op got no flow out of the eleviated heater hose. The bad impeller would not overcome the head pressure (weight of the water in the evelated hose). I need to do the same test.
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Old 01-20-2013, 03:22 PM   #27
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Spent four hours on it this evening, to no avail:

- disconnected the supply hose to the heater core, cranked engine and watched to see if water came out the t-stat housing; it did NOT flow out, even though I had previously pushed water out that opening by flushing with a garden hose into the supply side, through the core back to the block and out the top; this maked me suspect either the water pump is wonky or there is some sort of anomaly inside the t-stat housing

- !

Looks like he just looked for flow out of the t-stat housing. I like the evevated hose because it requires a pump in good health to pass the test.
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Old 01-20-2013, 05:47 PM   #28
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I'll try this when I get a chance....I kinda hope these is no flow so the problem is solved.
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Old 01-20-2013, 08:42 PM   #29
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Changing the water pump is an easy job.If you have a lot of miles just go ahead and do it right if you have the money .Change water pump ,thermostat ,all hoses and serpentine belt and idler and tension-er and the fan clutch.If your radiator is questionable now is also the time to replace it.
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Old 01-23-2013, 09:47 PM   #30
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Waiting for a warmer day

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