That is awful gas mileage. Like very very awful. You're saying you can't get more than 125 miles out of a 15.9 gallon tank?

My engine has never been as close to stock as yours since I bought my car. But when I used it as a daily back in 2018 I was getting damn near 300 miles from a tank of gas.

Even now with a built engine (high comp & cammed & larger fuel pump) I can still get 200 miles from a full tank of gas.

Something doesn't seem to add up there. If that really and truly is your case then you need to be pulling the plugs and see how rich it's running. That's dangerously rich.

Or perhaps your fuel gauge is off. Like way off. So you're filling it up early. How much gas does it hold per fill up? If you're close to empty it should hols at least 12 or 13 gallons.

I can't speak to the 420a platform, but I'm at 270k on the factory bottom-end of my 6bolt 4g63. It burns oil too and has decent amount of blow-by. A crankcase breather catch-can did wonders to help keep the intake cleaner. I'd think a comparable maintained NA motor would be in better shape than a turbo setup like mine. Watch out for oil-soaked coolant hoses - those have a tendency to blow at the most inopportune time. Keep up with the maintenance, fix your coolant and oil leaks, pressure wash your engine bay and it'll (hopefully) be happy for another 50k+.

Do you ever smell gas after you've gone for a drive? I get 200+ miles/tank with spirited city driving, which isn't great, but much better than what you are seeing. It's definitely worth your time to investigate your fuel consumption further.

If you are going through a quart of oil in 500 miles and have horrible gas mileage, pull the plugs and do a compression test. Unless you have a pretty bad oil leak, I'd bet you are burning oil in the pan - weak rings letting combustion gasses blow by, reducing power and burning the oil in the crank case.

And, yes, I'd say based on the info you gave and my assumptions that you are staring at a rebuild in the very near future. A compression test and leak down test will provide a lot of info that will help guide the decision.

BLACK'98DSM said:

That is awful gas mileage. Like very very awful. You're saying you can't get more than 125 miles out of a 15.9 gallon tank?

My engine has never been as close to stock as yours since I bought my car. But when I used it as a daily back in 2018 I was getting damn near 300 miles from a tank of gas.

Even now with a built engine (high comp & cammed & larger fuel pump) I can still get 200 miles from a full tank of gas.

Something doesn't seem to add up there. If that really and truly is your case then you need to be pulling the plugs and see how rich it's running. That's dangerously rich.

Or perhaps your fuel gauge is off. Like way off. So you're filling it up early. How much gas does it hold per fill up? If you're close to empty it should hols at least 12 or 13 gallons.

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Yeah when I first got the car , it sat from 2017-2021. I did the oil change, changed the timing belt, water pump and clutch. Most gas mileage I got ever was 210 miles off a full tank. When I’m close to E I full up with about $45-50 and it comes out to like 14 gallons or so around there. I go to work which is like 2 miles out and my gym with is another 2 miles out from my job. The full tank can last me almost a full 2 weeks with just work gym and pleasure. Gonna look at the plugs when I have a chance.

dwb said:

I can't speak to the 420a platform, but I'm at 270k on the factory bottom-end of my 6bolt 4g63. It burns oil too and has decent amount of blow-by. A crankcase breather catch-can did wonders to help keep the intake cleaner. I'd think a comparable maintained NA motor would be in better shape than a turbo setup like mine. Watch out for oil-soaked coolant hoses - those have a tendency to blow at the most inopportune time. Keep up with the maintenance, fix your coolant and oil leaks, pressure wash your engine bay and it'll (hopefully) be happy for another 50k+.

Do you ever smell gas after you've gone for a drive? I get 200+ miles/tank with spirited city driving, which isn't great, but much better than what you are seeing. It's definitely worth your time to investigate your fuel consumption further.

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I see, yeah I haven’t seen oil soaked coolant hoses every. Yes I do smell gas sometimes when I drive, it usually when I’m gonna park the car or when I start to drive I can kinda smell it. Maybe new fuel injectors or a fuel pump or spark plugs might be the problem?

CKOPOCT said:

If you are going through a quart of oil in 500 miles and have horrible gas mileage, pull the plugs and do a compression test. Unless you have a pretty bad oil leak, I'd bet you are burning oil in the pan - weak rings letting combustion gasses blow by, reducing power and burning the oil in the crank case.

And, yes, I'd say based on the info you gave and my assumptions that you are staring at a rebuild in the very near future. A compression test and leak down test will provide a lot of info that will help guide the decision.

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Okay I will check the plugs and do a compression test when I have the chance to. Hopefully it’s nothing major because I do baby the heck outta the car but even still if it’s running dangerously rich like the other guy said, it can go south even baby the car maybe.

210K miles is high for these engines especially in the eclipses because people think they are fast. Normally the N/A engines have the piss beat out of them. Turbo cars can be beat on too but seems to be much more common with N/A cars. The cold air intake with no other mods is a good sign that may be the case.

Compression test will tell you if your engine is mechanically sound or not. Everything else is just bench racing. If compression is good then you need to look at other things for the reason your fuel mileage is so bad

Another consideration: fuel injectors. When was the last time they were cleaned? If the answer is, "Cleaned? What does that mean? Like run a bottle of STP through the system?" then you might be experiencing a sore lack of atomization due to dirty injector nozzles. The injector dwell might be off as well due to the age of the injectors themselves (assuming they are still the factory injectors).

As to your comment about smelling gas, that'd only be from a fuel leak (which would also explain bad gas mileage). If you smell gas, follow the fuel lines from the fuel rail back and see if you notice any obvious fuel leaks. If not, consider checking fuel pressure.

At 215K there's a whole lot that can be causing low fuel mileage, weak power, and oil consumption. Start with the basic diagnostics to gain data on what is weak and worn. You can find info in the forums here on how to check and test just about everything on the car. Oil consumption is going to be either burning or leaking. If the driveway is dry and your coolant is a clear neon green, then you're burning it. As to the fuel mileage, start by considering the age of the components and determine what might need attention: air filter, fuel filter, injectors, O2 sensors, etc. Check the basic maintenance items and make sure things are all primo. If after doing all that you are still experiencing problems, it's time to go deeper in your diagnostics, to include possibly an engine rebuild. Bear in mind it is possible to simply rebuild the engine and still end up with problems (because the problems are with the injectors, various sensors, etc.).

CKOPOCT said:

Another consideration: fuel injectors. When was the last time they were cleaned? If the answer is, "Cleaned? What does that mean? Like run a bottle of STP through the system?" then you might be experiencing a sore lack of atomization due to dirty injector nozzles. The injector dwell might be off as well due to the age of the injectors themselves (assuming they are still the factory injectors).

As to your comment about smelling gas, that'd only be from a fuel leak (which would also explain bad gas mileage). If you smell gas, follow the fuel lines from the fuel rail back and see if you notice any obvious fuel leaks. If not, consider checking fuel pressure.

At 215K there's a whole lot that can be causing low fuel mileage, weak power, and oil consumption. Start with the basic diagnostics to gain data on what is weak and worn. You can find info in the forums here on how to check and test just about everything on the car. Oil consumption is going to be either burning or leaking. If the driveway is dry and your coolant is a clear neon green, then you're burning it. As to the fuel mileage, start by considering the age of the components and determine what might need attention: air filter, fuel filter, injectors, O2 sensors, etc. Check the basic maintenance items and make sure things are all primo. If after doing all that you are still experiencing problems, it's time to go deeper in your diagnostics, to include possibly an engine rebuild. Bear in mind it is possible to simply rebuild the engine and still end up with problems (because the problems are with the injectors, various sensors, etc.).

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Thank you man. The info definitely helps. Again thank you