3.1L - Unusually High Fuel Economy Possible?

**michaelb721** · 09-01-2009

Hi,
I'm curious to know if any of you are getting very high gas mileage from your 3.1L equipped cars. I have a friend at work who drives a Pontiac Montana van (of all things) with a 3400 engine in it. (A 3400 is very closely related to the GP's 3.1L engine, if I understand my research correctly.) He swears he doesn't have to fill it up but once a month!

He's a good honest guy, so I know he's not just saying that to put something over on me. He goes on long distance trips and then tells me it took him less than half a tank of gas to go where his Nissan Maxima would practically be running on fumes to do the same. He lives a few miles closer to work, but he still has to drive the same roads I do, and I have to get gas every 4 days or so.

My Grand Prix has a 3800 V6, which runs smooth and has more power than I know what to do with; but in town the gas mileage is just killing me. (Remember $4/gal. gas? I'm sure we'll see it again!) You can go around a corner in my GP, and watch the gas gauge dip down - and the problem is that it doesn't come back up! I've tried lots of gas-saving techniques, but I'm still pretty disappointed with my results overall. I'm considering trading in my 3800 GT to get another GP that has the 3100 engine, but I would like to hear from you to see what I could realistically expect for gains in fuel economy. My other choice would probably be to move to a smaller car, but I would like to explore the possibilities of a 3.1L first. I kind of like my GP otherwise.

Thanks. I appreciate any input you may have.

**nicksilvergt99** · 09-01-2009

Wow no cause whatever you save on gas you will be putting into the engine. First off I don't mean to offend se owners. But one, most are ugly, two a 3.1 isn't nearly as efficent or as durable as a 3800. The 3800 gets better gas milage according to Pontiac. Stick with the 3800

**josemolina2008** · 09-01-2009

I've got the 3.1 and to me it gets pretty good gas milage. I drive 17 miles to and from work five days a week and I fill up only once a week, and I'm not that light on the gas pedal. But performance wise it is sssllllooowwwww... I was just messin' around with a friend of mine who has the 3.8 Camaro and he pulls on me quite considerably. If I was you I would just stick with yours.

**nicksilvergt99** · 09-01-2009

And I get 17 mpg drivin like an ass. Upwards of 26 mpg on the highway and 18-19 on average

**michaelb721** · 09-04-2009

OK, thanks for your opinions. After some more research, I've decided against trading for a 3.1L GP... but it sure WOULD be nice to only fill up once a month!!!

**nicksilvergt99** · 09-04-2009

Tell me about it lol

**MizzBecca** · 09-13-2009

I have a 3100 SFI in my car, and I get 30 mpg city. I usually fill up once a every 2 weeks and I drive a good 50 miles a day to n from work.

Theres a pic in my albums when my car got 412 miles to a tank driving to tennesee. Of course, it's all highway miles, but my dad said that's almost as much as his truck gets, and I have a 15 gallon tank, while he has a 26 gallon tank.

**PowerStroker** · 09-16-2009

GM stopped producing the 3100 because they were money pits. They ended up putting more money/research into the 3400. Now, its one of the best motors they make. The 3800 is great and everything, but not everyone needs the power. If I could go back and buy a GP with what I know now, I would've never even THOUGHT of buying a 3100...

**peegh** · 09-30-2009

I have a 2003 prix with the 3.1 and I get always get 425-450 miles per tank. I live 45 minutes from work so its everyday on the highway usually at 70 mph. So I have no complaints about the car. But yes I would still love to have gotten the 3.8 sc version instead lol

**RareGMFan** · 10-03-2009

Wow. SO much misinformation here...

Originally Posted by nicksilvergt99

First off I don't mean to offend se owners. But one, most are ugly, two a 3.1 isn't nearly as efficent or as durable as a 3800. The 3800 gets better gas milage according to Pontiac. Stick with the 3800

Pound for pound, the 60° 3.1 is MORE efficient, and just as durable as the 3800, not to mention sounds a ton better with aftermarket exhaust work. The only real downfall to the 3100/3400 motor was GM's retarded idea of using nylon/silicone for the intake gaskets, which were inevitably prone to failure. When the LIM gasket goes, depending on how bad the sepage is into the block, it can either lock up the motor, or the coolant destroys the bearings, leading to a spun bearing. Me and several of the ClubGP guys JUST witnessed a Grand Am GT pull into the shop we were hanging out at with this exact problem last night; 3400 BTW.

Really, no GM '96 & up is immune to this threat due to Dexcool eating away gaskets as well. Euro had to replace his 5x,xxx mile motor on his '00 GP GT last year due to the gasket giving out, and leaking coolant into the oil. He spun a bearing a few weeks AFTER the gasket was replaced. Luckily, he had the GM extended warranty.

Originally Posted by MiZzBeCcA

I have a 3100 SFI in my car, and I get 30 mpg city. I usually fill up once a every 2 weeks and I drive a good 50 miles a day to n from work.

You have a gen I w-body, which is lighter. That could explain a slightly better fuel economy, but....even with that, 30 MPG city is crazy. Hell, even for highway, that's up there considering it's still well over 3,000 lbs. You've definitely got a freak of a car there.

Originally Posted by nicksilvergt99

And I get 17 mpg drivin like an ass. Upwards of 26 mpg on the highway and 18-19 on average

I usually average 32 - 36 highway, and 20 - 23 city in the GTP if I'm not getting on it. If I'm a bit antsy to get somewhere, it might dip down to 26 - 30ish, and 17 - 20. They can definitely achieve better than the EPA estimated (which is true in most cars' cases).

Originally Posted by PowerStroker

GM stopped producing the 3100 because they were money pits. They ended up putting more money/research into the 3400. Now, its one of the best motors they make. The 3800 is great and everything, but not everyone needs the power. If I could go back and buy a GP with what I know now, I would've never even THOUGHT of buying a 3100...

What the hell are you talking about? The 3100 and 3400 are basically the same motor. It's a slightly bored out 3100. Hell, the '00 and up 3100 even got the same bigger upper and lower intake manifold ports as the '96 & up 3400, and they never differed much in power (3100 peaked out at 175hp, 3400 eventually made its way up to 185hp). BTW, you do realize they stopped making the 3400 after '05, right? You said it's the best V6 they make, as if they're still making them. Oh, and you do realize they got rid of the 3100 "money pit" at the same time, not earlier, right?

They are no more of a money pit than any other GM motor, including the 3800. The only thing they're a bit more prone to than other GM motors is LIM gasket failures, due to the reasons I stated earlier. So long as you change those out with the updated gaskets before disaster strikes, you should be fine. Otherwise, the rest of the common issues with those motos are common amongst just about ANY GM motor, and no GM is safe from LIM gasket failures by any means, either.

The reason GM moved on is called progress. The 3.1 replaced the 2.8, the 3100 replaced the 3.1, and the 3400 was a bored out 3100. It's evolution. As the need for a more powerful motors arises to take on competition, and more technology is developed to take on this challenge, things change. It is the reason the severely outdated 3800 was FINALLY put to rest, and replaced. The 3100/3400 were based on an outdated motor (just like the 3800), and GM needed to scrap them in favor of something more cutting edge (3500/3600/3900, all of which are 60° motors, btw).

Michael, do you know what the actual MPG your friend is getting in his Montana is? Discussing gas mileage in the form of how long it takes each of you to fill up doesn't really give us much of a context to go off of.

**blown gt** · 10-08-2009

i went from conn down to fort jackson and got 500 miles out of a tank of fuel

**TowerLadder43** · 11-18-2009

Just ran my stock 95 Grand Prix SE with 3100 in it, 334 miles, 14.34 gals, roughly 22-23 combined MPG. I drive mostly highways back and forth to work, but there's a lot of traffic on the capitol beltway in the mornings, so that does have an effect.

**jbamonte** · 12-21-2009

My 3.1 2001 GP with 100,000 miles on the clock gets about 30 mpg on the highway and I usually drive 400 miles before I fill up. I changed the dexcool antifreeze to the green stuff about 3 years ago and have had no problems with the intake gaskets yet. I do keep a sharp on the intake gasket, though. I have heard that folks who have changed to the green stuff antifreeze seem to have a lot less issues with the intake gasket failures. I hope that this antifreeze change will alleviate that issue. i have heard many 3.8 and 3.1 motors will go 200K and over with these motors so you just do not know. On another note, I changed the single SE exhaust in July 2009 to a GMPP exhaust, which I found out after I received it that this exhaust is all Magnaflow (says it on both 2.5 inch polished stainless steel mufflers as well as the stainless steel resonator and yes, it does sound much better than a 3.8 motor with the same exhaust. The GMPP exhaust, aka magnaflow, is only $450 from gmpartsdirect, but is not advertised as a magnaflow exhaust, which usually cost $800 dollars. The switch from a single exhaust with a very restrictive muffler, to the 2.5 inch single pipe after the cat with a magnaflow resonator that splits to (2) 2.5inch y pipe to the mufflers which are straight through magnaflows was very straight forward. I also put in a 2.5 inch straight pipe after the cat for the O2 sensor and was shocked at the power increase over a stock 3.1 (my 2001 has 175 HP stock), very similar power to a stock 3.8 (175 +25-30=200-205 hp). This exhaust with the U bend delete will probably add 25-30 hp over the stock SE exhaust, with no loss in mileage (if you keep your foot out of it) and is better geared for this type of motor. A stock 3.8 turns around 2,000 RPM at 80 mph (they lug a lot) with the 3.1 turning around 2,300-2,400 RPM at the same speed. I have found this combo to be a real secret with the 3.1 motor.

**blueguy** · 12-22-2009

Originally Posted by jbamonte

my 2001 has 175 HP stock, very similar power to a stock 3.8

Wrong. 205 hp AT THE CRANK for the L36. Why are we STILL comparing apples to oranges like in every other thread you post in?

Originally Posted by jbamonte

This exhaust with the U bend delete will probably add 25-30 hp over the stock SE exhaust, with no loss in mileage (if you keep your foot out of it) and is better geared for this type of motor

Oh really? I'd like to see your dyno sheet to prove the 25-30 horsepower please. I'll believe you when you provide one. And until you do. I am beyond calling Bullsh!t. No exhaust system is going to add anywhere NEAR 25 horsepower. Maybe if your running a stock downpipe and catback on a TURBOCHARGED CAR...but not your puny 3.1. In fact...you say they are rated 175 horsepower AT THE CRANK. Figure a typical 20% Drivetrain loss (175 x .20 = 35) so minus the 35 from 175 (175 - 35 = 140). I'd say your exhaust system MIGHT have yielded you FIVE to SEVEN horsepower. No way in hell it added 25. But...I'll let a dyno do the talking...I mean...if you want to prove your math and horsepower addition chart. By all means...go ahead.

Originally Posted by jbamonte

A stock 3.8 turns around 2,000 RPM at 80 mph

Wrong. Beyond wrong. Go drive one. In fact...I have 3.29 gearing in my GTP...which is the same in the GT Grand Prix (If you didn't know...write that down in your notebook)...or SE for that matter (Wow...the 3.1 with a 3800 counterpart? No way)...and it is turning well around 2,500+ RPM's. So...nice try.

Originally Posted by jbamonte

I have found this combo to be a real secret with the 3.1 motor.

**jbamonte** · 12-25-2009

[QUOTE=RareGMFan;248121]Wow. SO much misinformation here...

Pound for pound, the 60° 3.1 is MORE efficient, and just as durable as the 3800, not to mention sounds a ton better with aftermarket exhaust work. The only real downfall to the 3100/3400 motor was GM's retarded idea of using nylon/silicone for the intake gaskets, which were inevitably prone to failure. When the LIM gasket goes, depending on how bad the sepage is into the block, it can either lock up the motor, or the coolant destroys the bearings, leading to a spun bearing. Me and several of the ClubGP guys JUST witnessed a Grand Am GT pull into the shop we were hanging out at with this exact problem last night; 3400 BTW.

Really, no GM '96 & up is immune to this threat due to Dexcool eating away gaskets as well. Euro had to replace his 5x,xxx mile motor on his '00 GP GT last year due to the gasket giving out, and leaking coolant into the oil. He spun a bearing a few weeks AFTER the gasket was replaced. Luckily, he had the GM extended warranty.

What the hell are you talking about? The 3100 and 3400 are basically the same motor. It's a slightly bored out 3100. Hell, the '00 and up 3100 even got the same bigger upper and lower intake manifold ports as the '96 & up 3400, and they never differed much in power (3100 peaked out at 175hp, 3400 eventually made its way up to 185hp). BTW, you do realize they stopped making the 3400 after '05, right? You said it's the best V6 they make, as if they're still making them. Oh, and you do realize they got rid of the 3100 "money pit" at the same time, not earlier, right?

They are no more of a money pit than any other GM motor, including the 3800. The only thing they're a bit more prone to than other GM motors is LIM gasket failures, due to the reasons I stated earlier. So long as you change those out with the updated gaskets before disaster strikes, you should be fine. Otherwise, the rest of the common issues with those motos are common amongst just about ANY GM motor, and no GM is safe from LIM gasket failures by any means, either.

The reason GM moved on is called progress. The 3.1 replaced the 2.8, the 3100 replaced the 3.1, and the 3400 was a bored out 3100. It's evolution. As the need for a more powerful motors arises to take on competition, and more technology is developed to take on this challenge, things change. It is the reason the severely outdated 3800 was FINALLY put to rest, and replaced. The 3100/3400 were based on an outdated motor (just like the 3800), and GM needed to scrap them in favor of something more cutting edge (3500/3600/3900, all of which are 60° motors, btw).

Finally, someone who talks intelligently!!!

**matt5112** · 12-25-2009

The high value engine is based on the 3100/3400...

ANDDDDDDDDDD the 3800 was put to rest because the answer to fuel economy is direct injection and that happens to be easier with a smaller engine and DOHC because you have more space in the combustion chamber with more but smaller valves.

The LSx is there just to prove that OHV can still make stupid power... So don't knock OHV so quickly.

Ward's 10 Best Engines - Wikipedia, the free encyclopedia

enjoy.

**paulygp09** · 01-20-2010

I have had 3 cars.
'92 Buick Regal Limited, 2 door-3800 series 1, 4 speed w/overdrive=26mpg average.... 158,000 on car
'94 Pontiac GP SE, 4 door-3100, 4 speed no overdrive=24 mpg average 194,000... on car
'96 Pontiac GP SE, 2 door-3100, 4 speed w/overdrive=29mpg average... 117,000 on car
If your going for economy the 3800 just cant get what the 3100 can! but for the power go with the 3800. They are both credible engines!!!!

RareGMfan- AWESOME POST!

**PonchoGP** · 02-07-2010

Why are we talking about horsepower anyway? The post is about fuel economy as for that I have an '01 G.P. SE and get between 21-28 all around driving. Also have a 1986 Monte SS with a twin turbocharged ls1 out of 98 camaro and whe I kepp my foot out of it without the tubos spooled up I get about 19 mpg rarely! but that is also VP purple race fuel. 7 bucks a gallon! LOL

**jbamonte** · 02-08-2010

The reason one would be talking horsepower when discussing fuel economy is that the 2 issues are directly related. Generally speaking, the more horsepower, the worse the fuel economy will be for similar sized engines. If for example, a 3.1 and 3.8 engine make 175 and 205 HP respectively, one could generally assume the larger motor with more horsepower will have worse fuel economy than the smaller engine. Conversely, a smaller engine like a 3.1 making say 190 HP versus a 3.8 making 205 HP, the smaller 3.1 making almost the same horsepower as the 3.8 should have a noticeable advantage over the 3.8 since a smaller engine has less reciprocating mass due to smaller pistons. Ideally if you could make a 3.1 make about the equivalent power of a normally aspirated 3.8, the 3.1 should and does have a fuel economy advantage. My point above about my 3.1 making similar power with some minor modfications and compared to the previous 3 normally aspirated 3.8 engines I have owned is based on my real word experience with both engines. The SC 3,8 is a different story and I have never owned one to compare.