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many factors can affect MPGs LONG
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Posted by Dean (more from Dean) on Fri, 3 Dec 2004 06:13:11 Share Post by Email
In Reply to: lowish gas milage, Finch, Thu, 2 Dec 2004 23:32:21
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LOW MPGs

There can be several things contributing to this:

Low tire pressure as the season gets coldered - increased rolling resistance, more of an issue with shorter trips as the tires have a high rolling resistance when cold, especially if soft, and the tires warm up and become easier to roll after a while. Check your tire pressure. Snow tires should be inflated to higher pressures than summer tires. And a 15" snow tire will have lower rolling resistance than a low profile summer tire. Check tire pressure and run higher pressures.

Manual gear boxes need to warm up and that takes a long time. Autoboxen get to temp by the shared cooling system. 95 gear boxes have dyno oil in them that will have greater losses until warmed up than the synthetic gear oil.

Roof racks create high air resistance, and cold air is more dense and the penalty is greater.

Fouled plugs and injectors: And starting or idle issues? If so try Techron Concentrate to clean things up. If idle speeds not controlled after that, clean TB and IAC. The Techron will remove some of the combustion chamber deposits that create hot spots which increase the engines octane requirements (aquired octane demand). This may allow for better ECU controlled ignition timing for better MPGs and power. The 10.5CR of the 2.3NA engine will be much more sensitive to the effects of combustion chamber deposits than the lower compression turbo engine.

Ignition cables: For the 2.3NA engine, clean the cables, boots, cap and coil face when doing spark plugs.

Bad engine thermostat prolongs engine warmup or does not allow the engine to get to temp. This is a real problem if it occurs. It engine temps droop at highway speeds, it is fairly certain that the stat is bad and not closing as it should.

Dyno engine oil creates higher losses in a cold engine compared to a synthetic oil.

Dragging brakes or P-brake. P-brakes like to hang up in cold weather, just to make DIY work really miserable.

To eval MPGs, clear the SID at steady highway speeds with the engine fully warmed up. This removes the engine warmup penalty from the equation and lets you better eval the state of things better day to day, season to season. These vehicles are very sensitive to head and cross winds, so 3 out of 4 wind quadrants will hurt.

Fuel-1: Some fuel is 10% ethanol, and labled as such. The alchohol has a lower energy content. This may cost you 2MPGs on the highway. Note that these fuels are then costing you more than the prices posted on the pump!

Fuel-2: These engines will get better MPGs with premium fuel, so the cost savings of cheap fuel may not be what they seem. And the better fuel will keep the engine cleaner.

The T5 does loose MPGs in the cold, and in very hot weather. In contrast, the 9-5 Wagon, much bigger and heavier, gets better MPGs consistantly and does not loose much MPGs, or any, in the cold or heat. The T7 9-3's are probably the same.

I routinely got over 30 MPGs in my 95SET with SID resets on my then 38 mile commute runs.

Incorrect wheel alignment will not help. I used a very low toe-in setting with my suspension mods. Toe-in that is too much can have the tires fighting each other and on ice or rain, only one front wheel will have control at a time. Lots of ice on the highways at 75mph here...

Old tires are age hardended and will increase losses. Snow tires are less prone to this as they are not run in hot weather, even though they last for years. Some tire brands are much worse for this. Sidewall stiffening really hurts.

I got much better MPGs with M1 5W40 (Delvac 1) than with M1 10w30. And that had nothing to do with 10W warmup losses, as my SID was always reset at speed fully warmed up. The older engine with bigger running clearances simply run better on a W40 oil (quieter, smoother, better MPGs, felt better). Use M1 0W40 or 5W40(Truck and SUV). With your cold temps, the 0W40 might be the best way to go.

Exhaust: Some old stock exhaust systems get fouled or somehow restrictive.

Engine air filter: Autozone and others want to tell you that a 'dirty' air filter will decrease your MPGs. I do not believe that at all, only effect should be less power at full throttle.

I do not know how the 2.3NA engines motronic system reacts to heat and cold. No first hand esperience.

Lubrication system: Sludged oil and stuck piston rings would not help. What is the oil history of this vehicle? Some engine oil flushes and solvent type oil addatives may be of benefit if a history of dyno oil. Check that low oil warning system lamp works before cranking the engine. All of the pressure switches fail at some point, contributing to the loss of engines from sludging or oil pressure regulators that stick open.

95SET (rip) Mobil 1 0 or 5W40*, Saab synthetic gear oil, Saab Sports exhaust, low front toe-in + various budget performance mods.



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