Gas mileage & plugs

550Doug · Mar 23, 2018

Can gas mileage improve significantly just by changing spark plugs? Buick 2003 Park Ave.

DR. EVIL · Mar 23, 2018

In a word, NO. Todays's plugs don't wear like plugs did 30 years ago. I had new plugs installed on
wife's 2003 Mercury Mountaineer with 4.6L V-8, made absolutely NO difference in mpg. Car had 150,000
miles on it.

Biggest influence to MPG on any car is your right foot. Use cruise control whenever possible. Can
easily improve MPG 1 to 2 mpg.

showcrop · Mar 23, 2018

(quoted from post at 04:55:11 03/23/18) Can gas mileage improve significantly just by changing spark plugs? Buick 2003 Park Ave.

I would say yes. Because today's cars run so well people don't even think of looking at spark plugs. An original owner who keeps a car for 2-4 years would not dream of checking them, and a second owner if He doesn't think of it when He buys it may never get to changing them. After 150,000 miles the electrode will be eroded away to where the gap is four times what it was originally, and eventually the spark will quit making the jump for short periods of time which will over time gradually get longer and longer.

Billy Shafer · Mar 23, 2018

Well if you replace the bad plugs with new ones it can. Otherwise no. My brother bought a set of those wonder plugs. Gas mileage didn't
change.

WayneLee · Mar 23, 2018

I think it can if the old plugs have over 100k miles.

BarnyardEngineering · Mar 23, 2018

In all these "yes" scenarios, the engine is misfiring. You will notice a misfire, and/or the engine will throw a code. The plugs have to be extremely bad to be firing intermittently.

When the engine is running well with the old plugs, as in not misfiring, new plugs will make absolutely no difference in MPG.

Bret4207 · Mar 23, 2018

I would say yes, and doing a general tune up, as in air cleaner/filter, fuel filters, etc, helps too. Getting the tires aired up to the max recommended makes a huge difference on some vehicles, like 3-4 mpg on my truck that the shop put 32 psi in tires that want 60psi!

David G · Mar 23, 2018

Unless they are worn, I would say no.

oldproudvet · Mar 23, 2018

Plug gaps erode with with usage. Today's high energy ignition systems will fire plugs with gaps approaching .080-.100 gap. This puts tremendous strain on the ignition system and is usually the reason for failed coil packs etc. A plug that should fire around 40,000 volts that's now requiring 80,000 volts to jump an eroded gap is nothing but potential trouble. + Most cylinder heads are aluminum now days, and you stand a very real chance of the plug corroding to the head which, when it breaks trying to remove it is a real mess. Change often, and anti sieze the threads. I very seldom let anything exceed 20,000 miles. 35 years teaching post secondary automotive in MN Voc schools lets you see EVERYTHING, believe me.

Steve A W · Mar 23, 2018

I had a 1989 Ford F150 with the 300 inline 6.
When I got it a buddy of mine said something
about spark plugs won't last 150k miles.
The gauntlet of challenge was thrown.
I tuned it up at 35k and the next tuneup was
185k miles. The truck never ran bad so I stuck
to the challenge.
When I finally tuned it, it started a little
better and gained a whopping 3mpg.
So there was an improvement in mpg but not a lot.

Steve A W

2002sliverado · Mar 23, 2018

I have had 2 3800 V6 engines in cars and still have 2 of those engines. My parents have had 2. Your question has me wondering if your mileage is suffering, and you are wondering if changing plugs will make an improvement. If everything else is functioning properly, an improvement is probably going to be rather minimal. As one suggested, maybe a couple miles per gallon is about all you are likely to find. On a 2000 Park Avenue of ours, and on a 2000 LeSabre of my parents' car, we noticed a distinct drop in fuel economy. In both cases we found it be a bad fuel pressure regulator. Once replaced, all was fine. As I recall, there was no noticeable issue in how the engine started or ran. It was just a matter of poor fuel economy, and it was something on the order of around 8 miles per gallon. One comment I have heard about these engines, is the coil packs can start to fail if your are running on old, worn out plugs. I have never had that experience, but it is something I have had a few people share with me. The only vehicle I ever suspected I had an improvement in fuel economy with a plug replacement was a 1998 Dodge Ram truck with a 5.9 liter V8 engine.

showcrop · Mar 23, 2018

(quoted from post at 05:19:51 03/23/18) In all these "yes" scenarios, the engine is misfiring. You will notice a misfire, and/or the engine will throw a code. The plugs have to be extremely bad to be firing intermittently.

When the engine is running well with the old plugs, as in not misfiring, new plugs will make absolutely no difference in MPG.

Barnyard, perhaps you will always notice a misfire, but there are many among us who will not. There was a recent thread on a four cylinder Ford where the OP was told that he may not notice a misfire, and it is even more difficult to notice with a six cylinder.

showcrop · Mar 23, 2018

(quoted from post at 05:45:00 03/23/18) Unless they are worn, I would say no.

Bingo! They wear, or more accurately erode. Same effect. I changed plugs on a Ford Explorer a few years ago. The gap, as I posted earlier, was a good three times what it was originally. I did not notice a misfire but I sure did notice the drop in MPG!

jeffcat · Mar 23, 2018

Sparkplugs wear out so here is my suggestion. I have posted on here a
couple of times about the NGK IRIDIUM sparkplugs. My Expedition and
all of my lawn / garden tractors have them. They are a wonderful
thing. Go on Ebay to order them because they will be half price of in
the store. Cost more but are a super performance item.

Gary Mitchell · Mar 23, 2018

Do you use Iridium or Iridium Platinum plugs? Thanks, gm

DR. EVIL · Mar 23, 2018

The dissimilar metal corrosion is why the dealer changed the plugs and not me, was coil on plug ignition, and no coil problems with any of the eight coils for the life of the car, just over 205,000 miles. Dealer we traded it at made no excuses, he was wholesaling the car. Air conditioning failed. 5 years before that needed a new $800 valve body for the auto trans. Had a $600 A/C repair before the big failure. Oh, and I did the R&R of the alternator when it died on the way home from work one night. Think that was $200, car only made it about a mile after charge warning light came on. SO MUCH amp draw on cars today!

When the repair estimate exceeds the value of the car, it's only good for parts!

Wife loves her new SUV.

gab · Mar 23, 2018

I'd suspect a leaky fuel regulator before sparkplugs.

504 · Mar 23, 2018

My truck started misfiring, I pulled the plugs and the gap was .080,I set them at .060 and it ran better but not close to right. Locals wanted 14.00 each for plugs so Rock Auto got the nod. Cap,rotor,wires and a new set of Auto Light Platinums and the mileage came up 4 mpg.For less money than local)
I had a Ford mechanic tell me to change the spark plugs by the book or sooner,it seems the computer will burn out when a coil pack misfires,some kinda of back feed.

buickanddeere · Mar 23, 2018

Not unless the plugs can add BTU’s of energy to the fuels . A trick at county fairs to sell “ wonder plugs” . Was to have an engine with timing retarded a couple of degree from stock and very short reach plugs installed .
Then the shyster extraordinaire would install the mileage plugs he was selling and the run engine at the same throttle setting . The engine would idle dozens of RPMs faster than with the short reach plugs .
Trick is the “wonder plugs” had a very long reach . This physically advanced the effective ignition timing . Via lighting the air/fuel mixture near the middle of the combustion chamber instead of on the side of combustion chamber . Making the engine idle faster and fooling Billy Bob and Bubba into purchasing shyster’s over priced plugs .

dr sportster · Mar 24, 2018

And if the fancy BLASTO-FIRE magic super plugs worked new cars would come with them .But they don't.

Mike M · Mar 24, 2018

Had a lot of Buicks have bad front brake hoses not letting the front brakes release all the way. You may want to check that out too. I forget what year the plastic intake plenum was used up too. If you have one of those they are prone to suck dex cool into the engine. One day without warning it may act like it locked up when you try and crank it. It can let loose in an instant and fill up the cylinders.

Gas mileage & plugs

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