yea the new age motors are designed to run hot not cold. that will down your mileage some but not that much. if you put that t stat in and started noticing it try this... take it out and put the stocker back in and see if you keep getting bad mileage

 

Since the cold snap, it takes for ever to get GOOD heat out of it. I might just throw the stocker in till the spring or so. I really don't like running my car when it's soo damn hot here in the summer. That's why I run Synthetic oil too.

I don't like my car running hot anyway. I've had a lot of over heating problems w/ past cars. Don't trust it.

But the mileage DOVE this past week.

 

Alright, let's get down to brass tacks...

How are you gauging your MPG? Are you filling it up, resetting your trip odometer, running it x miles, refilling it, then calculating it? That simple task alone would rule out any other problem than your fuel gauge being off.

 

Colder engine plus colder plugs may make for quicker plug
fouling, and it doesn't need to foul completely before starting
to degrade spark. If you misfire a cylinder then excess oxygen
passes to the exhaust, tricks the O2 sensor and jacks the
fuel.

On a stock setup car your engine temp is determined by the
fans (when it's hot or you're getting no radiator airflow) and
the 'stat. 'stat always sets the minimum temp, fans set the
top. Stock tune is for hot. Winter with airflow is going to
bring you down to 'stat temp (177F or so for a 160) rather
than the 220+ you might see in the summer (fan limited).
That's a large ECT differenct and could affect the tune.
But so can winter temps on the sidewall of long tube headers
just making the O2s slow, sleepy and telling the PCM all
about yesterday's news when it's trying to trim mixture.
Babying it all around town doesn't help that any, they need
heat to work.

 

How did you spend that much money on that?? A new set of plugs is $10 and you can get front and rear pads for like ~$125 even if you buy it brand new from the stealership.

 

I have the NGKs too and I think most change them around 25K miles. I've not noticed any issues and I've had mine for some time. If a plug(s) wasn't igniting the mixture, you would likely feel it and throw a SES. I had a plug wire fall off and the code appeared in about 2 minutes, and it idled like crap of course.

 

your car is basically operating full time with the choke on.i took the stat out of my car and it usees more gas sittin in the driveway warmin up then it does when i drive to work 30 miles away.but when it warms up the mpg comes with it .it also idles higher until the temp gets up it takes about 30 min to heat up goo enough to idle correctly.so do this put the stocker back in and just remove it completly when the spring and summer gets here.the car is just tryin to warm up to operating temp and runs on closed loop which is the choke.

 

Open loop is determined by the oxygen sensors. THey 'warm up' @ 700 degrees and start sending signals. Before that the computer uses a base mixture based on air intake. Correct me if I'm wrong. I do under stand the 'choke' theroy. It makes sense.

The $200 I was referring to is; $18 for Plugs, $87 for Hawk front pads and $180 for the WS6 Store Rotorworks package. (My brakes SUCK! The pads are worn too.) I had D+S rotors on my last car and they were worth EVERY penny, so I don't want to hear any "driveway Jems" comments, please.

The $80 I was refering to is the labor charge for Diagnostic work. I guessed at their hourly rates. I worked at a Chevy dealer as a tech in the past, so I know how it works. They charge and hour for DIAG (even if it doesn't take the tech an hour to diagnose.)..

W/ the air temperature being so low latley, along w/ the 160 Stat, I wonder if the O2's might have gone back into closed loop if they cooled down too much? -Kinda like what was said in the above replies.

 

You just put the fuel filter in, check for leaks. that kind of gas mileage is unheard of. Is your car running rich? I have been running my car for a couple of months with enough mods and no tune, and runs rich with about 5mpg dif., but nothing that wild. Even if your O2's were gone or not functioning right your car wouldn't idle correctly and stall. Run it and change RPM's in the same parking spot and look for a leak. The Choke coul have something to do with it but then again you would smeel the rawl fumes and slight stalling after start up.

 

No, Open/close loop is determined by coolant temperature.

 

I am pretty sure the ecm uses coolant readings and the O2s information to determine if the car is up to operating temps to lock into closed loop.

There has got to be something giving the CM bad info causing it to stay in open loop and dump extra fuel to aide with the warm up. I am running a 160 stat and still get almost 20 in the city and 27 on the highway.

Take the car to a local dyno person who has some exp with LS1 or F-body's. See what the A/F looks like under part throttle, try to have the tuner mimick a normal drive cycle and dont worry about a WOT run.

What tranny does the car have, if it is an auto it is not unlikely the torque converter lockup clutch went out causing the converter to not lock up. That would cause some gas milage loss as well.

Like was said, go at this smartly and quit throwing parts at the car. You can throw $500 in parts to find out that a $50-$80 diagnostic fee with a $10 part could of have fixed the problem.

 

I am with the go get proffessional help crowd. Guessing is just going to cost you more money in the long run.

I have lots of idea's on what it might be. But if I tell you, you will just chase your tail longer.

Knowledge is power, get some info. Stop wasting time. Your in a car club? No one has A/tap? No LS1er's close that can help?

 

Yeah, hit up the PCM Diagnostics & Tuning section.

 

1st Pull all your plugs and check em...
2nd swap your fuel filter with the old one
3rd change T-Stat back to the original (180 right?)

there is an hour and a half of free labor and all that can be done in your driveway and for free is you kept all your old parts (I keep all my old parts just in case)

if that doesn't straighten it out go spend the 50-80 bucks for a dyno and have them log the run and A/F under normal driving conditions

 

Go into the forsale section and look for some....

Also......CLEAN UR MAF!!!! (Mass Air FLow Sensor)
What happens is allot of people clean their K&N Air Filter....but too much oil and it gets on the maf and dust builds up on it.......Which makes gas mpg turn to crap...

DO u have any kind of miss?
Listen closely to ur exhaust at an idle....(Put ur ear near the pipe) and listen for a spudder here and there.......if u have one......Check all ur connections on ur spark plug wires .....if all good......change em along with spark plugs......

I had a couple probs between the two

 

What was the outcome?

 

^^^ Damn 13 months later, lol.