AlexSoto

1996 Cherokee, 4.0

I've been fighting a cold running problem for a while. I've replaced the thermostat many times. At first I put some fail safe types from Kragen, but it seems those just kept failing and the temperature gauge would barely break the 160 degree mark. I've always been using 195 degree t-stats.

Finally I researched in the forums what's a 'good' brand and I bought a Stant Super Stant thermostat, thinking I'll get the top of the line model. It seemed to have helped as just my around town driving the Jeep would seem to warm up, but it never really would reach 210. I thought it was just because I live along the coast and it never really gets much above 65 degrees.

So last weekend I went on a trip. I drove about 3.5 hours straight. It was early evening to late afternoon. The Jeep seemed to run fine but I noticed it never really reached the 210 mark on the gauge. I thought that was strange since I was driving for so long. Then I finally pulled over to take a break and when I started it back up about 30 minutes later the Jeep started running really rough and the check engine light came in. It reported codes 171, 300, 301, 305. Those are lean/rich and intermittent misfires in cylinders 1,2 and 5. I cleared the codes, but from that point on I noticed that the Jeep would run very cold, barely break the 180 degree mark on the gauge during the relatively warm days.

On my way back home at the end of the weekend, I was getting terrible gas mileage, (8 mpg) and it was running really cold.

I'm hoping since I didn't buy a fail-safe thermostat, and that it's supposed to be a high quality one, that it's not the thermostat. I'm at a loss as to what else is causing the Jeep to run so cold. Anyone else got any ideas on how to troubleshoot it?

Thanks

Bbasso

https://www.cherokeeforum.com/f2/eng...too-cold-7169/

Radi

Are you sure your gauge is telling the truth? Might check the temp with an infrared thermometer just to rule out metering error.

AlexSoto

Thanks for the link. I couldn't find that when I searched.

So from reading that thread, it seems like folks where overly concerned on the heater output and not really troubleshooting the cold engine temps.

Regardless, some things I should do are:

- burp air out of system (I thought air in the system would cause over heat, not cold running?). I did flush my coolant a few months back, so I thought I covered this, but I'll try again.

- I should check my heater output, cold air means heater core should be flushed? How does that make me run cold? The poster in that thread mentions his dash heater controls work fine. I do have a problem with my dash control that only the highest fan speed causes air to flow. I thought it was just a worn-out dash control. What affect does the Dash fan controls have on the system that could cause cold running? Or is that a symptom of something else?

Thanks for the replies.

AlexSoto

Well haven't tried that, but since it is running rich (smell, plus poor MPG) and the gauge says it's cold, I'm guessing it's right. Where would you use the thermometer, upper hose?

Would need to pick up an IR thermometer too. Harbor Freight good enough?

Radi

Cheapie's fine. Check at the thermostat housing.
A rich mix will result in a cooler running engine too, I wonder which is the cause and which is the effect?

belvedere

I've had good luck with Superstats, but recently read on a forum of a guy having a couple of them fail. Might want to try an OEM stat.

AlexSoto

You think the stants would fail open? Or does failure mean that they open at the wrong temp?

AlexSoto

Haven't gotten around to getting to measuring the temp but I replaced the TStat with an OEM Jeep one. The temp is a bit better, but still never really hits 210 (per the gauge), but the heater blows warm to hot.

I spoke with another buddy and he said coolant temperature sensor (CTS) or the possibly the sensor at the back of the engine which is for the gauge.

I can understand if it's the CTS since that signals the computer, but if it's the gauge sensor, that doesn't explain why the car would run so rich and have poor gas mileage.

I looked in the service manual it says

To perform a complete test of the engine coolant temperature sensor and its circuitry, refer to DRB scan tool and appropriate Powertrain Diagnostics Procedures manual.

I'm not sure if the manual means a simple ODBII scan tool or something more sophisticated, anyone got any ideas and or access to the Powertrain Diagnostics Procedures manual?

It also does mention how to test the CTS alone by measuring resistance along the leads and checking if it's in the range shown. Since it's disconnected do I use the current air temperature as the reference for the resistance the CTS needs?

freegdr

burping is only for closed systems will have no affect on open system as long as radiator is full and level in bottles good your good

195 thermostat is what your temp should be running with a 195 thermostat, ive had two stick open on me think its because of the way its sitting in block most thermos lay flat

freegdr

cts onn yours does three things fuel,cooling fan and gauge,dont think you have the second sensor

AlexSoto

I've got a buddy that says his gauge is pretty much at 210 when he drives around. His XJ is a bit older and maybe doesn't have as good a radiator as mine does, but still would like to get my MPG back up to 'normal', still going to keep trying things...

freegdr

mines 89 just turned 200,000 195 temps all day long ac on hes actually running warm no check engine light ever on yours....

AlexSoto

Thanks,

No Check Engine Light.

I read all over that 210 is 'proper' operating temp for the I6. Is your MPG what you expect?

I need to figure out a way to check coolant temp while it's running. I guess I might try idling with the radiator cap off, not sure how 'good' of a test that is, but worth a shot I suppose.

djb383

U need to verify temp at the t-stat housing with a temp gun (Harbor Freight is decent). If ambient temp is +/- mid 60s, and running a 195 t-stat, that makes perfect sense for the gauge to display less than 210.

T-stat controls minimum coolant temp and the rest of the cooling system components, their condition along with ambient temp and driving conditions determine max coolant temp. So, if ambient temp is mid 60s, t-stat is 195, why would it run 210?????

On a '96, the dash gauge sending unit is at the rear of the head, drivers side. The coolant temp sensor for the ECU and efan is in the t-stat cover. Running rich could be a bad O2 sensor or other problems. '96 is OBD-II, preset fuel maps (O2 not working) control air/fuel mix until the O2 starts functioning, then mainly the O2 (and other sensors) control air/fuel mix when the O2 is hot enough to function.

Check/verify coolant temp.....modern EFI motors should run flawless when cold or hot.