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  #1  
Old November 23rd, 2010, 15:55
blistovmhz blistovmhz is offline
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yet another heat issue

98 xj sport - 160,000km

Ok, its -30C (thats -22f for a majority of you) and I'm going to be sterile after another week of this.

Temperature readings (taken after 20 minutes running):
Ambient outdoor: -32C
dash - ~74C
OBDii - 74C
Hose to heater core: 56C
Hose from heater core: 40C
Hose from block to rad: 56C
Hose from Rad to Block: 56C
Air temp at vents: 10C
Air temp in cab: -20C

I flushed the heater core a few months ago and it seemed to flow pretty well, but I don't really have much to compare to other than my 90xj which blows ~45C at the vents and the water temp is ~88C.
The 98 warms up to 74C in about 6 or 7 minutes at -30C so I think its mostly safe to assume that my thermostat is working?

Possibly related, the air ducts XXXXin' howl when its set to defrost and/or heat, but are mostly quiet when set to vents. Not much air flow out of defrost or heat (front or rear). The hold/cold door sounds like its closing all the way (though it'd be great if someone knew how to verify this without taking the dash apart).

What direction should I go first? I've got limited access to a garage and its -40C by evening

Last edited by blistovmhz; November 23rd, 2010 at 16:02.
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  #2  
Old November 23rd, 2010, 16:07
birchlakeXJ's Avatar
birchlakeXJ birchlakeXJ is offline
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Re: yet another heat issue

My gut feel is that the heater core is partially clogged.

I agree that the thermostat is most likely working but when is the last time it was replaced?
I'd probably replace it with a Jeep or Stant SuperStat 195 degree stat just to be sure unless it has been replaced recently.

If you are not getting much air from the heater, that may be a separate issue.
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  #3  
Old November 23rd, 2010, 16:26
joe_peters joe_peters is offline
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Re: yet another heat issue

Agree with BirchlakeXJ.

The 97+ are subject to blend doors in the air box breaking. Some information on that: http://www.heatertreater.net/jeep%20...e%2097-04.html
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  #4  
Old November 23rd, 2010, 17:27
Robs92XJ Robs92XJ is offline
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Re: yet another heat issue

How are you measuring temperature at the hoses? According to the numbers you posted, you have a delta T across the heater core of 16 deg Celsius, about 30 degrees F, which seems pretty good to me. If your core was clogged, the return hose to the engine would be much colder than 40 deg C, I'd think.

You also have a zero delta T across the radiator, which only makes sense if the thermostat is closed and nothing is flowing. But if that were the case, the temp readings for the heater supply to the core would be greater than for the radiator hoses, and yet they are the same.

So I think that with the extreme heat from the engine and the extreme ambient cold, the readings may not be accurate.

Anyways, if your readings are even in the right ballpark, you are running way too cold. With the engine warm, your coolant coming out of the thermostat housing should be about 210 F (100 deg C). Your sensor, if accurate, says you are at 74 C (165 F).

Also, your heater supply hose should be essentially the same temp as your coolant temp sensor reading. But you are almost 20 deg C (36 deg F) colder there. Doesn't make sense, maybe your sensor is flaky.

How old is the thermostat, and what is it's temp rating? Even if it is relatively new, that sounds to me like the first thing to replace, based on your temp readings.

The other issue may be mixing doors, but I don't know much about 97+ hvac systems.

Good luck
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  #5  
Old November 24th, 2010, 08:36
blistovmhz blistovmhz is offline
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Re: yet another heat issue

See the problem here is that everyone sounds correct
Thermostat definitely seems like it needs to be replaced, (although last night the coolant managed to get up to 88C, still not hot enough), and it also seems like the blend door is broken.

Robs92xj, Measuring both with an IR gun as well as with the remote thermometer on my multimeter (mid range fluke) so the temps gotta be right. That being said however, the hoses may be insulating more on one side than the other.

My buddy also pointed out that the heater core may also be caked with dust and that could explain both the poor heat and flow at the ducts. Going to try the thermostat first.

While we're here I'm going to mention another issue I'm trying to figure out (i know its bad form to ask another unrelated question in the same thread but I'll just throw it down in passing and hope someone knows exactly what I'm talking about).
Jeep is clanky on accel/decel, on bumps and on hard braking. I thought it was motor mounts so I took apart the dclamps and shoved another piece of rubber in just to check if it would temporarily solve the problem. Nope. Transmission mount seems a bit flexy, but right now the clunk happens on even light accel. Sounds exactly like a broken motor mount, but can't see enough movement in the motor to make sense. Can't see anything else bouncing around. Ball joints and suspension are all tight.
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  #6  
Old November 24th, 2010, 10:58
Robs92XJ Robs92XJ is offline
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Re: yet another heat issue

You said you took the readings after running the engine 20 minutes. Was it just idling, or were you driving it? At -22 deg F it might take considerable longer than 20 minutes to warm up just by idling.

While driving around, does the temp gauge ever get up to 210 F / 100 C ? If not then I would definitely say the Tstat is not working properly.

If it takes a seriously long time to get there, or doesn't stay above about 180 F after getting up to temp, then it would also be the thermostat.

When your temp gauge was reading 88 C, was the air out the vents any warmer?

As for the theory of the heater core being caked with an insulating layer of dust, if your temperature readings are accurate then I doubt that is the case, since you would not have such a large difference in inlet/outlet temps if dust was preventing heat from escaping the heater core. Seems far fetched to me that dust could cause that big of a problem (10 C air from the vents), anyways. I think your coolant just isn't hot enough.

Your low flow through the vents sounds like an issue my '92 has. I can crank the fan to high and hear it blowing hard, but not too much comes out of the vent ducts, not as much as in my old Cherokee, anyways. Since it still blows hot and keeps me warm, I haven't felt compelled to mess with it, but if I had to guess where the issue is, I would start with the door and actuator mechanism under the dash in the passenger footwell. Right after I got it I messed with that stuff replacing the blower motor resistor pack. Could have put it back together wrong- you might take a look in that area if the 97+ have a similar setup.

You might also check your manifold vacuum, since most of the mechanics in the HVAC system are vacuum operated (though I'm not sure about the blend door). If you are a little below spec, it might cause a sticky component not to open. If you are WAY below spec you will just get air out the defrost vents.

But I'd start with getting water up to the proper temperature.

For the clunk, have you ruled out driveline slop/play?
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  #7  
Old November 24th, 2010, 11:19
blistovmhz blistovmhz is offline
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Re: yet another heat issue

The blend door is mechanically controlled (cable) and seems to clunk from cold to hot pretty well. I'm going to start by swapping out the tstat. That extra 10C might be what I need. As for the weak air flow, I dunno. See what happens when I get some heat. I don't feel like tearing apart the dash.

I've checked the driveline all over. Motor mounts are sorta toast, but as I said they're super solid right now. The transmission mount is a bit flexy (and I've got a new one ready to go in), but the clunk shows up under very light torque now, only in forward gear. It REALLY sounds like the motor picking up on one side on accel, and dropping on decel, but when I go watch it, it doesn't move. The transmission definitely torques up towards the body a bit, but I don't see any rub marks anywhere. The DS's, CV's, and U-joints are all solid. Rear axle and suspension are all tight.
I'm almost positive its driveline because of the small amount of torque required to make it clunk. Sounds like something is hitting the bottom of the body (but i suppose everything sounds like that when the frame takes a knock).
What can it be aside from motor and transmission mounts?
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  #8  
Old November 24th, 2010, 12:41
Robs92XJ Robs92XJ is offline
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Re: yet another heat issue

I guess you checked all of the bolts on the motor and transmission mounts?

If it was the motor mounts, you might not notice too much movement when you rev it in neutral (assuming that's what you were doing). With the car in gear there's a lot more resistance from the driveline, making the motor want to flip over much harder. I wouldn't rule it out.

I'm not sure what you mean by dclamps, or by them being sorta toast but rock solid. Is the rubber that keeps the bushing for the mount bolt in place solid and firm? If not I'd replace them. If you've seen the transmission mount flex without any load (revving in neutral/park), imagine what it does under driving loads.

I'm not saying for certain that's causing your clunk, but if the rest of your drive line is solid, and you've observed that the engine and tranny mounts are worn, then I think that the mounts are the low hanging fruit, especially since they aren't too hard or expensive to change. Otherwise you are down to internal tranny/t-case slop, bad U-joints, or worn-out differential.

-Rob
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  #9  
Old November 24th, 2010, 12:46
blistovmhz blistovmhz is offline
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Re: yet another heat issue

Thats my thinking as well right now. Transmission mount is already in the back seat, and just ordered some M.O.R.E. Bombproof motor mounts.
Hopefully the motor doesn't fly out of the truck before I get the mounts
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  #10  
Old November 24th, 2010, 12:50
blistovmhz blistovmhz is offline
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Re: yet another heat issue

God I hope it doesn't turn out to be diff gears. Brand new 4.10's
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