Post Thermostat Replacement MPG Improvement

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The Critic

The Critic

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The original thermostat in the Saturn had failed after 122k so I replaced it with a Stant 14279 195F unit. The Stant runs a tad on the hot side (a bit over 200F I'm guessing), but the heater works much better.

I filled up the tank immediately after the thermostat repair, and after today's fill-up, the tank yielded about 26.3 mpg (maybe a tad more, my mom is known to top off a bit). Previous tanks have been in the 24.5 range. So, there's definitely an improvement in fuel economy.

I was hoping for the 3 to 4 MPG improvement that some people claimed to be getting, but I'll take a 2 MPG (or 10%) improvement any day.
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(imagine peezpoor Oz over Taiwanese Kungfu lip sync)

So, Critic, your tightwadeness has been your downfall again (lips continue to move - ending in toothy smile with eyebrows raised). You've spent m-a-n-y dollars (with head nod and
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had gestures) in wasted fuel for leaving this go so long.


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Originally Posted By: Spartuss
Did you replace the ECTS already?

Took care of that 30,000 miles ago.
 
Originally Posted By: The Critic
The original thermostat in the Saturn had failed after 122k so I replaced it with a Stant 14279 195F unit. The Stant runs a tad on the hot side (a bit over 200F I'm guessing), but the heater works much better.

I filled up the tank immediately after the thermostat repair, and after today's fill-up, the tank yielded about 26.3 mpg (maybe a tad more, my mom is known to top off a bit). Previous tanks have been in the 24.5 range. So, there's definitely an improvement in fuel economy.

I was hoping for the 3 to 4 MPG improvement that some people claimed to be getting, but I'll take a 2 MPG (or 10%) improvement any day.
grin2.gif



Nice! In these high tech, computer controlled, sensor for everything you can imagine, lean burn engines,,,,, (did I miss anything?) An engine that is not running at the temperature it was designed to run at will run rich burning more gas and causing problems, especially if it's running cooler than it should be. Too hot has its own set of problems. I'd say you did well!
 
Good for you . . . but changing my T-stat last October hasn't improved my fuel mileage any; in fact it's slipped by about 5%. Every tank since the T-stat replacement has been down, and I drive the same routes at the same speed almost every day of the week. The weather's gotten chillier (on occasion), but never cold, and I don't know if we get winter blend gas here. Certainly my numbers at this time last winter were better than I'm getting now.
 
Originally Posted By: Benzadmiral
Good for you . . . but changing my T-stat last October hasn't improved my fuel mileage any; in fact it's slipped by about 5%. Every tank since the T-stat replacement has been down, and I drive the same routes at the same speed almost every day of the week. The weather's gotten chillier (on occasion), but never cold, and I don't know if we get winter blend gas here. Certainly my numbers at this time last winter were better than I'm getting now.


Hotter is usually better until you run into detonation. If you're not already, try a higher octane and see if the mpg goes up. Once the computer starts pulling timing, it's all over.
 
We get 87 ($1.63 today), 89 (~$1.90), and 93 octane (over $2.00) down here in The Swamp. The car's rated for 87; I can try some 89. If the mpg does go up, what might that mean?
 
Shouldn't lower octane fuel increase mileage? Its like advancing the timing, everything improves until you get pinging then the computer pulls timing and your mileage drops.
Now I guess if you car is made for 91 octane and pulls timing all the time with 87 octane then switching up will improve mileage but most cars that are made for 87 don't use 91 octane fuel any differently and should get slightly worse mileage.
Ian
 
Second tank, 29.3 mpg. No change in driving style, but over this last week, the weather has been a good 15F warmer.

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Update in my case: I think the culprit's ethanol gas.

Near my place, we have a load of independent stations, a Chevron, a Shell, and Wal-Mart. Naturally the Shell and Chevron are the highest-priced; the indies are always 5-7 cents cheaper, about the same as the Sino-Mart. Now Sino-Mart has 10% ethanol gas, with a sticker on each pump saying so. Since mid-October, I've been gassing up at the other cheap ones, since they have no sticker.

Result: 20.6 mpg average. This is with 87 octane (the car's rating), 75% careful-foot city driving, almost no A/C use, Pennzoil Platinum 5w30 in the engine, tires at 2 lbs. over the placard recommendation. The disappointing weather here was what I'd call warm until mid-December.

Two weeks ago I gassed up at an indie station I've been bypassing, since they tend to be 7-8 cents a gallon more than the others, only 4 cents less than Chevron. Result today . . . 22.25 mpg!

I know, I know, it's early days yet. I need to use their gas a few more times. But if the trend continues, it suggests that (a) the other indies may be selling ethanol, and (b) without labeling it as such -- which is supposed to be against the law, right? (Ha. In this state, laws are merely suggestions, to be ignored when they prove inconvenient.)

Anyway, this is the kind of mpg I expected to see after my T-stat change!
 
Here's another update:

On last tank, the mileage was 27.8 mpg. That's still a few mpg higher than it was before the thermostat replacement.

On a 150 mile highway trip, the mileage was 38 mpg! My dad said he hasn't seen 38 mpg out of this car in more than 5 years. Could it be possible that the thermostat has been bad for that long?
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Dang I've always been under the assumption that a cooler stat would be better for the engine?? (you know since heat is the enemy)
 
Originally Posted By: oilyriser
mpg goes up even higher if you cover the rad a bit, and run the coolant near the fan relay set point.

I'm not brave enough to try that.

The thermostat already runs a bit too hot (I think I got a dud), so I don't want to push my luck.
 
Our CRV mpg is great since the t-stat. It's nearly equaling my Accord, grr. 24 is quite respectable this time of year.
 
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