03 3.7 strange over-heating issue(OBDII figures in post)

[jeepbeep]

Torque app readings:

Fuel Trim Bank One Short-Term 0.2-14.5

1x1 "normal fast fluctuation"
1x2 O2 0.7-0.9
2x1 "normal fast fluctuation"
2x2 O2 1.0-1.0

Only OBDII DTC0158(REAR O2 TOO HIGH)


Stuff new on it:
New Engine from NAPA
New before-cat O2s OEM
New coolant temperature sensor OEM
New radiator OEM
New Fan&Relay OEM
New reservoir OEM
New thermostat
Flushed&Burped coolant(HOAT 50/50 from Zerex 4.gal)

Sometimes fan doesn't come on without heat running, but even with heat running it makes it about 4-miles before overheating from cold-start.

 

[JeepinJarhead03]

my first guess is a bad t-stat , especially if its one of those fail safe pieces of . stuff.

and check the harness on 2x2. its probably unplugged, melted wire or not plugged up tightly or there's a clot of mud over the vent on the outside of the o2 sensor, it should be fluxuating similar to 1x2, sticking at 1.0v will usually be a bad connection


fan should come on at 217F-221F
fan should also come on when you turn on the AC on high

theres a newer heavier duty relay from mopar better protected from underhood temps

if your face is melting off from the heat in the vehicle its bit less likely to be a bad thermostat - and more likely that the fan relay and or fan is kickin the bucket

on the two speed fan models green is low, yellow is high , or jumper the low relay in the box, 30/87 i believe it is, double check that though

 

[tjkj2002]

x2 on t-stat.

Unless you got the t-stat from the dealer that would be my 1st guess since all aftermarket t-stats for the 3.7 suck badly and rarely work out of the box.

 

[jeepbeep]

Thanks for the responses.

Can running too lean or too rich or having the fan not work cause over-heat going 50MPH in 68F weather? I've had this blamed on my PCM by a mechanic or two due to a O2 short once. No other issues with my liberty besides over-heating though..

The numbers from Torque are supposedly showing "dumping fuel".

I'll probably avoid mechanics and do a flush except this time with an OEM thermostat(68174083AA). I'll probably replace the two hoses too even though the pressure test didn't show anything bad.

...Just got to wait till I get another day off of work which is so rare.

 

[JeepinJarhead03]

the clutch fans on ours are just an assist , theyre not designed to be primary cooling methods, so i dont know to what extent a mech fan will keep it cool all by itself

running at constantly above 45 with a properly working cooling system the electric fan is typically off. i dont think they break mid dummy gauge until 220+ ?

i know at 85 degrees like it is right now i can go crank it up and itll sit there 15 mins or more before the fan comes on and everythings workin properly, also if i drive it down to walmart and back (about 4 miles round trip @ 45mph) when i pull into the parking spot the fan will come on for about 30 seconds and turn right back off

 

[tjkj2002]

Normal operating temp for the 3.7 KJ is between 195 degrees and 219 degrees.The electric fan does not even turn on(unless A/C selection is selected on HVAC) till 219 degrees.

The gauge in the IC should be at the halfway mark when the coolant temp is between 178 degrees and 229 degrees.At 230 degrees to 259 degrees the gauge should read 3/4 and at 260+ is when it goes to full hot(for 3.7 only).

A shorted downsteam O2 sensor will never cause a overheat of the engine,they only monitor the cat's efficiency,the upstream O2's control the fuel mixture and if one of those fails the PCM will go into a rich state like it does when 1st started waiting for the o2 sensors to heat up and start working.

If it's taking 3 miles from cold to overheat,which 205 degrees is not overheating in the KJ, then you got a coolant flow issue which is either a bad t-stat,incorrectly installed t-stat,or the cooling system still has air in it.

The 3.7 has the t-stat on the lower hose so you must fill the engine 1st or it will be very hard to "bleed" the cooling system.There is a fill port(bleed port) on the front engine cover at the upper radiator hose.Fill the engine through there 1st before putting any coolant in the coolant tank.

Oh and putting a lower then recommended t-stat in a OBDII engine will cause more issues then fix unless you have the PCM programmed for the lower t-stat.The MIL will come on with a coolant temp under regulating temp codes.

And a side note if it has really overheated many times I'd check the head gaskets also,the 3.7 does not like to be overheated at all.

 

[JeepinJarhead03]

but to fully answer your question about a non working elec fan, yeah, it "can" but i'd expect it to over heat when i lowered my speed, not while @ speed

something about the whole thing is just tellin my inner grease there's something restricting coolant flow - well.. that and i know how many of those stupid fail safe thermostats ive tossed up in peoples gutters lol..

 

[tjkj2002]

that and i know how many of those stupid fail safe thermostats ive tossed up in peoples gutters lol..

I refuse to install those types of t-stats.

The auto parts stores around here push those hard and everyone wants them installed but I will never install one.

At work they know me well enough that something like engine sensors and t-stats better come from the dealer or I will throw it at them till I get a OEM part.

And I actually do throw the crap aftermarket parts at the service writers and walk away.The boss really didn't know what to say the 1st time I did it to him,chucked a gas cap right at his head.

 

[CactusJacked]

As I see it, with a cold engine overheating in 4 miles, blaming the thermostat is barking up the wrong tree. I can drive mine a good 10 minutes before the engine gets anywhere near running temperature. And up until that time, the thermostat is still closed, or mostly closed. For reference, say you have a 195 thermostat. This is the temperature at which it begins to open. The stat doesn't open fully till it reaches 15-20 degrees above it's rating. Perhaps you have air trapped in the system, a blown head gasket, etc.

 

[tjkj2002]

As I see it, with a cold engine overheating in 4 miles, blaming the thermostat is barking up the wrong tree. I can drive mine a good 10 minutes before the engine gets anywhere near running temperature. And up until that time, the thermostat is still closed, or mostly closed. For reference, say you have a 195 thermostat. This is the temperature at which it begins to open. The stat doesn't open fully till it reaches 15-20 degrees above it's rating. Perhaps you have air trapped in the system, a blown head gasket, etc.

You may have a issue,mine get's to 195 degrees rather fast.

Like now in the mornings it's about 50 degrees outside.I can start my Jeep(remote start),put on my boots,walk out to my Jeep(to this point about 90 seconds running),get in and drive 0.4 miles to my 1st stop light and by that time it just hits 195 degrees.Monitored via live data and not looking at the gauge.

 

[CactusJacked]

You may have a issue,mine get's to 195 degrees rather fast.

Like now in the mornings it's about 50 degrees outside.I can start my Jeep(remote start),put on my boots,walk out to my Jeep(to this point about 90 seconds running),get in and drive 0.4 miles to my 1st stop light and by that time it just hits 195 degrees.Monitored via live data and not looking at the gauge.

Apples and oranges. No issues here, mine heats up at a normal rate, similar to many other vehicles I've had in the past.
The differences are:
1) You're at a much higher altitude than I am. An engine can easily lose up to 3% of it's rated power for every 1,000 feet of elevation.
2) Your rig weighs a lot more than mine.
Both of these factors makes your engine work harder than mine = heat generation.
3) I have a manual trans, not a heat soak furnace of an automatic which contributes to heating up the engine and cooling system.

 

[tjkj2002]

Apples and oranges. No issues here, mine heats up at a normal rate, similar to many other vehicles I've had in the past.
The differences are:
1) You're at a much higher altitude than I am. An engine can easily lose up to 3% of it's rated power for every 1,000 feet of elevation.
2) Your rig weighs a lot more than mine.
Both of these factors makes your engine work harder than mine = heat generation.
3) I have a manual trans, not a heat soak furnace of an automatic which contributes to heating up the engine and cooling system.

1- Why I re-geared to overcome both altitude and weight

2- see above

3 - actually the complete opposite,a clutch produces much more heat then a auto trans can and a manual has no external cooling capability. My cooling system actually has to heat up my trans fluid before it can even shift into OD(safety feature) and I have yet to see the trans temps exceed 160 degrees even towing 4200lbs through mountain passes(I do have a 28,000GVWR AUX trans cooler in addition to the OE in-radiator cooler).

 

[jeepbeep]

OEM thermostat is on it's way. Mopar #68174083AA. Going to flush and fill with 50/50 premixed Zerex G-05 HOAT coolant 4+ gallons.

By the way mine is electric fan and the fan will not come on unless I turn the AC on(means relay, wiring, and fan motor are good it's firmware/PCM). On 2003 there is no high and low relay either it's a single relay with a single PCM signal wire going directly to a PCM pin. According to all diagrams I see.

I'm tempted to get the shroud and clutch fan and convert since that is what's on the towing packages it seems. I know on big hauling packages even on RVs the fan-clutch is a big factor in durability. The difference between a truck and RV engine build is usually just that and a cam.