Trying to figure this one out....

I have 2 jeeps, one is a 96 cherokee sport, the other is an 88 cherokee pioneer.. both 4.0/aw4 combos (except the 96 is the HO variety and the 88 is the non-HO renix variety).

I'm trying to figure out what is going on with the low heat and cool engine temps (plus lousy mpg on the 88).

coolant levels are fine on both
readings taken with engines hot, but idling

88 info
-interior heat is 114 deg (center top duct on vent)
-temp of coolant to the heater core is 140-145
-temp of coolant from the heater core is 55-60
-outside air is ~ 25 deg
-coolant to radiator shows 184 deg, then drops suddenly to 174 when the tstat opens, and climbs back up to 184 or so
-tstat isn't open but a few seconds it seems by the temp changes
-fan clutch is stiff, engine temp seems to make no difference
-engine temp gage shows ~ 180-185 deg

96 info
-interior heat is 124 deg (center top duct on vent)
-temp of coolant to the heater core is 130
-temp of coolant from the heater core is 80
-outside air is ~ 25 deg
-coolant to radiator shows 188-190 and fairly constant (no significant drop when tstat opens)
-fan clutch is easy to turn, even when engine is warm
-engine temp shows ~180-185 deg



Now, on the 88, the temp diff across the heater core is 85-90 deg. When you add in the outside air temp, you get 110-115, which is exactly what it reads inside. But on the 96, the temp diff across the heater core is only ~ 50 deg, which when added to the outside air temp should give you 75 deg inside, but I am getting 124. So, something is different and I'm not sure what.

The heat in the 96 is adequate but could be better, while the 88 is less than adequate. I am sure the tstat in the 88 is bad (not working right and cycling excessively), and the fan clutch is also suspect (which when combined may answer the lousy mpg), but I am not sure if the heater core in the 88 needs to be flushed or not. Not sure if it will help, as it seems at first glance to be working well because the temp drop in coolant equals the temp increase in air flow. But when I compare it to the 96, the temp drop across the heater core does not equal the increase in air temp inside the cab.

Looking for some advice on what may be causing the differences and how to remedy them. I know the renix era engines are notorious for lousy mpg when the engine runs cold, which may answer part of my problem, but as for the heat, a new tstat may help, as if it adds 10 deg to the engine temp, it should also add 10 deg to the air temp in the cab, which would get me back to the same as the 96.

Thoughts/ideas/jokes ???????

Shouldn't you have 195 degree stats in them, I always figured our engines need to be around 195-210 to operate normally.

Also flush the cores, It really seems to be the magical heat remedy. I just flushed mine a Few days ago and it went from warm to roasty n toasty.

You didn't mention anything about what t-stats your running and they are the most critical to a good system.
Also are you using IR to get these temps?

Vent diverter flap not sealing and allowing colder outside air across the core?

Yes, I did use an IR to get temps.

I do not know the tstat rating in the 96, but the 88 has a 195 in it, I put it in myself 4 yrs ago (~ 25k miles).

I assume the 96 has a 195 tstat in it due to the readings it gives when running

On both, I can hear the flap move when the airflow is changed from vent to heat, but it may not be fully sealing.

Also, both seem to have the same blower fan speed when on all settings


The 88 use to run ~ 210 per the dash temp gage, but now reads a lot lower. The 96 I haven't had long enough to say, but the PO said it has always run cooler then the 88 or any of his cherokees he has owned and he has owned at least 4 of them. I got both of mine from him.

As RCP suggested, the thermostat in your 88 is opening too soon. Time for a new one. Also, the high temperature drop across the heater core in the 88 is most likely due to poor flow through it as kt alluded to.

I would put in a brand new 195* stat AND flush the core. If you do a search on here, it has been written up. Put a hose with garden hose connector on each free end and alternate feeding pressure to each end of the core. Catch a somple of the flush in a bucket and continue alternating the pressure until it flows clear each way.

MoFo nailed it, but you already provided the information for your own answer--the thermostat in the 88 is opening too soon.

Stant SuperStat Premium 195 degree. Buy it. Install it.

Same thing has been happening to my '91 as long as I've owned it (same as your '88). The temp on mine fluctuates while im driving too. Thermo stat opens, temp decreases significantly. Heat on knocks the temp down drastically.

Never have been able to solve it, so don't know if this will help you out but:

New:
CSF 3 core Radiator, Stant Premium Superstat 195*, Heater core, Fan clutch, Stant 16# pressure cap.

Don't know how much more I can replace and its still doing the same exact thing.

Well, as an update: (to the 88)

1) flushed the heater core, nothing came out but clear water
2) checked function of heater control valve, no issues there
3) changed tstat, interior heat is now 125+
4) tstat housing leaks some
5) my intake air temp snsor is dead, and no one has them anywhere......
6) haven't been able to drive it enough to see if the temp gage reads higher now, but the main thing was to get more heat inside, and it did/does

Seems to be working better now, if I can just find a temp sensor, may even start to get better mileage.

edit: my table looked looked poop- I'll try to find a better table of values......

I haven't been able to locate an ACT sensor locally (or anywhere, for that matter) I would hit a few local parts houses that still use the paper catalogs and see if you can find another replacement sensor with the corresponding values and modify the threads and plug to make her work.

I started looking once, but found that I had a spare used one that tested good- problem solved for now.......

http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm

meh, it's in here and I'm too dumb to find a better table

TRCM said:

Well, as an update: (to the 88)

1) flushed the heater core, nothing came out but clear water
2) checked function of heater control valve, no issues there
3) changed tstat, interior heat is now 125+
4) tstat housing leaks some
5) my intake air temp snsor is dead, and no one has them anywhere......
6) haven't been able to drive it enough to see if the temp gage reads higher now, but the main thing was to get more heat inside, and it did/does

Seems to be working better now, if I can just find a temp sensor, may even start to get better mileage.

Click to expand...

Your mileage may improve just with the correct thermostat. Run a few tankfuls through and see what mileage you get. With the faulty t-stat, it was most likely not going into closed loop. I had the same problem on my 88 and after the thermostat replacement the MPGs came right back where they were supposed to be.

Now, now--just because a parts monkey tells you you can't have something, that doesn't mean that you can't have it:

MAT: Air Charge Temperature Sensor Part No. 1814
Marren Fuel Injection: www.injector.com/cart/pc/viewPrd.asp?idproduct=65&idcategory=12

So, other than the availability of IATs or MATs at the site in your link, Joe, are these hard to come by? Should we be bagging them at the U-Pick-Its when we get a chance?

the Renix is no longer offered-- that's the same one I was remembering when I went looking for one about 6 months ago, but I didn't recall it coming with the pigtail.
It wouldn't hurt to grab a handfull at the boneyard if you're planning to keep the ol' gal for as while.

Well, seems about nobody lists them as available (my old standby Delphi number is now obsolete).

5-90 turned me on to this source, and I have a spare set aside--they so seldom go bad, but I worry a lot--so I don't know, kind of cheap insurance.

Haven't checked into it, but I'm willing to be there is something off a GM that would match up.

I have a list of a dozen or so manufacturers and part numbers, and no one has them. Not availabe, discontinued, or obsolete is the answer I got. Even Chrysler/Jeep said no dealership in North America has it.


True Joe, someone may make something that can be made to work (and I will most likely go that route), but the actual part is not available, period.

TRCM said:

I have a list of a dozen or so manufacturers and part numbers, and no one has them. Not availabe, discontinued, or obsolete is the answer I got. Even Chrysler/Jeep said no dealership in North America has it.


True Joe, someone may make something that can be made to work (and I will most likely go that route), but the actual part is not available, period.

Click to expand...

True, but as long as the specs are the same I won't let having to change a connector or using an adapter or even drilling a new hole and threading it stop me from having a functional vehicle. Pretty sure the ECU doesn't care what it looks like, smells like, or how it is attached to the engine or harness.

got an Su343 in it......they make a pigtail for it, #235, but I had one. Wells part $'s

TCCM,
Could you please expand your post a little bit, like include the manufacturer name, sensor part number and the place(s) that sell the sensor and pigtail?
TIA.
MoFo

MoFo said:

TCCM,
Could you please expand your post a little bit, like include the manufacturer name, sensor part number and the place(s) that sell the sensor and pigtail?
TIA.
MoFo

Click to expand...

Those parts are Wells, do an e-catalog search here: http://www.wellsve.com/