P1281 After Heater Core and Thermostat Replacement

[LibertyFlip]

Hi all,

I have a 2003 Liberty Sport 4x4 with the 3.7 V6.

About a month ago I replaced the heater core (very lukewarm heat), water pump (there was bits of plastic in the impellor when I replaced the timing chain last year? seemed like it would be good preventative maintenance), and the thermostat (used Mopar 68174083AA - had a Gates replacement recently, but after reading through the forum switched to a Mopar one to avoid issues down the road). Soon after, I started getting the P1281 code (engine temperature too low).

Using a scanner, it seemed to heat up to 175° ish and hold steady. Thinking I may have gotten a defective thermostat, I pulled it and tested in a pot of water next to the Gates one of the same temperature. Both of them started to move at 195° and fully opened well in 200s.

I re-installed it, with the bleed port on top (matched up with a dot on the thermostat housing, just to the right of the upper bolt). It seemed to start working fine over the next few days, but it was 80° outside and I wasn't using the heater. Heat would rise to 210-215 and hang out around there. This last week it's been 40s-50s so I've had the heater on, and the temperature won't go past 175° while driving again.

It really seems like it's correlated with the heater core, if I turn it off while moving the coolant temp will rise into 185-187 range, and if I'm stopped with the heater off, it will still reach 210-215 temperature just fine.

Am I missing anything? My heat works great now and I've been loving it, but it doesn't seem like the Jeep would have been designed to not reach operating temperature while the heat is on. I did not use a Mopar heater core - is it possible that it's drawing too much heat away? (Is that even a thing?)

I think my blend door stops (or actuator) are broken, as when I turn to full heat, it seems to "push through" and hit cold again, but if I stop the dial a few notches below full heat it works alright. Is it possible that this is letting too much air flow through the heater core somehow?

I feel like I'm grasping at strings, but I can't figure this out and I'm getting horrible gas mileage. It'd also be cool to take it easy on my 180k mile cats..

Thanks in advance for any help!

 

[LibertyFlip]

A few additional details from messing around with it for a few minutes today:

I'm pretty confident that the temperature sender is correct - a laser thermometer matched the temp readings on the OBDII scanner.

Today when the scanner read 180°, both upper and lower radiator hoses were hot. Because of this I'm suspecting a difference in the coolant temp at the thermostat vs. the sender on top of the engine.

I've had to top it off with coolant a few times since doing the heater core replacement/thermostat change, and don't see any leaks as far as I can tell. When hitting the gas there's a noise in the dash. It's directly related to rising RPMs, and sounds a lot like flowing coolant. Is it possible that there's air bubbles stuck in the system somewhere - causing this noise and the difference in temperature?

 

[LibertyTC]

Hoat or Zerex G-05 coolant & Mopar thermostat only. It has the brass bleed air hole built into the 195 degree thermostat.
Cold in the AM check coolant level to be in the middle at cold line.
Check each morning add coolant as necessary, it can take a few days for the air to work it's way out. Give it a couple of days.
There is a hex air bleeder also behind the top rad hose.

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When hot Crack the bleeder slightly, coolant will come out a bit.
Observe leak until no bubbles are seen. Have paper towels or rags handy around /below.

 

[LibertyFlip]

Thanks LibertyTC. I ran across your info in several other threads as well as I was researching this. I've filled with Zerex G-05 and used Mopar thermostat. I filled through the bleed hole until that was full, then through the tank while having the bleeder cracked.

I'll keep an eye on it and keep topping it off/bleeding as I drive and see if it works itself out. As I've done that over the past few days, it hasn't seemed to effect the temperature readings - but I'll keep working at it.

I did notice tonight when I got home that the cooling fan was running, while my temp still read 178° ish. That seems super low for the fan to be switched on, but I also saw that it watches battery temp and A/C. I didn't have the A/C on, but maybe the battery temp was high enough to trigger it?

I appreciate the help and will keep this thread updated as I figure anything else out

 

[LibertyTC]

I think your panel is the same as an 04. The electric fan will run and also cycle compressor in any of the selected* positions= normal.

You must be registered for see images attach

 

[JeepJeepster]

It should be the same. They changed it in 2005 so that the compressor will run in the floor position also. I put a 2005 controller in my 04 but taped off the contacts for the compressor in all positions except the pure defrost.

Libertyflip, where did you see that the battery temp will turn on the cooling fan? Ive noticed my electric fan will come on when its really hot out but the engine isnt calling for it. I've always wondered if the transmission can call for it also but Ive never been able to find that in the FSM.

 

[LibertyFlip]

LibertyTC: Right on, thanks! It was in Def/Floor mode, so that must have been what was triggering it. My A/C is still currently discharged from the heater core replacement, I've been waiting for warmer weather to do a proper charge, but will probably hold off until I check out the blend door/actuator so I don't have to discharge it again (just in case). Planning on replacing the seals, orifice tube line, and receiver drier when I do that as well, as it's been discharged for about a month and didn't hold full vacuum last time I tried that out.

Today update, coolant wasn't low at all. I'll see what the temp does next time I drive, but I'm not super optimistic, as it was still low last night.

JeepJeepster: I ran across that last night when searching through cooling fan threads, it's been posted a couple of times but here's one of the links! It's in the 2nd post from uss2defiant

https://www.jeepkj.com/threads/help-fan-relay.57994/

 

[LibertyFlip]

Out of curiosity, does anyone have a chart of what the ohms for the temperature sender should look like for the KJs? I tried looking, but found a few generic charts and nothing specific to these Jeeps.

I've been planning to make a trip to the local U-Pull-It yard, I might grab a few out of the 3.7s there and compare them all. If nothing exists and I end up grabbing those, I'll post some results.

 

[JeepJeepster]

Strange, it says when engine temp is above 204F. Mine doesnt kick on till engine temp is 217F.

 

[LibertyFlip]

I believe that 204F is with the A/C running. In my adventures through cooling fan threads last night, it seemed like 217F is the on temperature without A/C - here's another reference link! This one is post #18 from LibertyTC

https://www.jeepkj.com/threads/adding-a-true-water-temperature-gauge.63811/

 

[JeepJeepster]

Naw, the fan will run even when the engine is cold if the A/C is on.

 

[jeeptorino68]

Is the thermostat in the right direction?

 

[LibertyFlip]

Thanks for the reply, and yeah I'm confident that the thermostat is in the right direction. I definitely have coolant flow, both hoses are hot and there's a definite difference in temperature between highway and in-town driving.

Since I tested the thermostat and confirmed opening at 195F, I feel like it has to be either air in the system causing a wonky reading (which there seemed to be, I added coolant after the next 3-4 drives after filling), or a malfunctioning temp sensor? The only thing with the temp sensor is that it has shown 215-220F after this thermostat was installed (sitting in a drive-thru on a 70F day with no air on in the cabin). So it doesn't completely stop functioning at a temp, but maybe the Ohm readings are off by several (30ish) degrees at the high end of the spectrum?

 

[LibertyFlip]

Afternoon update! I went outside and tinkered some more, and I think I'm on to something.

When I originally measured the temperature at the temp sensor with a thermometer, I held the thermometer in front of the engine and aimed it. I don't exactly know how these work, but I got wildly different readings doing that compared to holding the thermometer directly above the sensor and aiming down - I'm thinking it may have to do with the laser reflecting slightly?

Anyway, these readings were taken at the same time today (sorry for the upside-down thermometer):

PXL_20210318_213729854

• LibertyFlip
• Mar 18, 2021

Thermometer Temperature

Screenshot_20210318-163826

• LibertyFlip
• Mar 18, 2021

Torque Screenshot

When the thermometer measured 195F, scanner read mid-high 170s.

For the sake of cost, I'm probably going to spend a few bucks and grab some used ones from the junkyard to see if they make a difference. If they do indeed, I'll most likely spring for a new Mopar sensor.

Will keep updating as I find out more

 

[LibertyFlip]

The thrilling conclusion to my troubles:

My Liberty had a Stant 74172 coolant temperature sensor that was 'off' in the high temperature ranges.

I grabbed a few OEM sensors from the junkyard over the weekend, and the first one installed seemed to fix the problem - but I was using it in 60F weather without the heat on. I just drove this morning to get some breakfast, and it's 37F or so meaning I was using the heater as well. This is when I was having problems and could not get the engine to surpass 177F or so previously. It hit 198F on my drive this morning and stayed there without dipping back below 195F.

I have not ohm tested any sensors, but I kept the Stant one and an extra OEM one, if I have some time or if someone requests, I would be happy to rig up a way to set them in water and test the ranges.

Thanks everyone who replied to this!

Moral of the story: use OEM sensors. (just in case you haven't seen that in literally every other thread on this forum)