Ky66

99 grand 4.0. I’ve had issues getting smog for years. Changed out all sensors, thermostat, new cats, etc etc. I’ve also pulled the entire dash and replaced the heater core and blend doors, gaskets.

it still won’t pass smog, and the temp won’t get above 160. Which i think is what’s causing engine parameters to be off thus failing smog with a ridiculously high NOX reading. But I also notice that the right side defrost vent stays cold, and the left side is halfway warm. Kinda points to an issue with hvac box I think? Worked great when I replaced everything a few years ago. I only drive about 100 miles a year which is mostly on a wheeling trip. Any suggestions as what to replace again? Heater core? Tstat, o2 sensors? Blend doors again? Would hate to have to pull the whole dash and steering column again lol

bluejeep2001

Sadly, you have wasted your time on stuff that has no issue...meaning a heater core and blend door and anything in the dash will not help/ increase engine temp. Most people have issues keeping below 215. What year jeep and where are you located..always need that info when posting because each jeep series is different

Ky66

Mentioned it was a 99 in originally post. 160k miles. Sacramento area CA. Mostly hot temps throughout the year. If coolant isn’t flowing through the heater core properly wouldn’t that affect coolant temp? Maybe a hose is clogged? Like I said I replaced the thermostat with a stock one which I think is around 195? Or 210? Did a radiator flush at that time as well. It’s been a few years and I rarely drive it. Flushed the block and head with full pressure hose water until it was clear. So if it’s nothing to do with hvac or under the dash, what’s next? Btw it wasn’t a waste of time for the dash stuff, the core was leaking and it needed a bunch of new hvac parts anyway. Compressor, filter dryer, evap, lines etc. So that needed to be done either way. Unfortunately it seems like a blend door is now not functioning correctly.

bluejeep2001

Only meant it was a waste of time in respect to it running cool. When its up to operating temp, can you hold the radiator hose? Do you have an obd2 reader. First thing in the morning compare coolant temp with intake air temp. Should be very close to each other. Your coolant temp sender might be reading low

cruiser54

It's not the heater core or affiliated parts to that system causing the engine to run hot.

Is it running hot? Have you verified the actual temp with an infra-red pointer?

Perhaps your coolant temp sender for the dash gauge is defective.

Perhaps your radiator still has junk in it that won't flush out and it needs replacing.

Ky66

It’s not running hot, I think it’s running cold. Even when beating the **** out of it on trails and in the snow, it never gets hot. But my main issue is I can’t ever pass smog test, it rates ridiculously high on NOX. My thought was that if it’s not getting up to high enough temp, the parameters are off so ecm is trying to compensate. I’ve ran the gas tank sea foam and the throttle body sea foam twice each. Never really smoked so I’m pretty sure the combustion chambers are clean. High nox means high cylinder temp which can be cause by soot build up but I don’t think that’s it. I guess I’ll change some sensors again

cruiser54

What does the in dash temp gauge read?

bluejeep2001

Rumor has it that the engine runs cool, approx 160. I have a Robert shaw from flowkooler ...the 195 model and today in 40 deg at highway speeds i ran between 192 to 198 the 30 miles home from work. that was with heat full hot to dry out a wet carpet. with heat to full cold, i ran 1 degree hotter. If your running cool but have high cyl temps then maybe your running lean and need to clean out the injectors....its tough to diagnose a car that gets driven 100 miles a year..I do that in 2 days..that means ****ty gas and who knows what else builds up in the months of unuse