Deceiving gas mileage?

[TremblantRanger]

Calculating... 13.5l/.946 = 14.27 quarts. 14.27/4 =3.567 gallons
100km * .62 = 62 miles.
62 miles / 3.567 gallons = 17.38 mpg.

Not good.

Have you checked the odometer is reporting actual true distance traveled, or is it being pessimistic?

If you were calculating using Imperial gallons, it would be worse fuel mileage.

I don't generally rev to 3k in normal driving unless I'm accelerating to merge with traffic.

Forgetting all the previous posts, cuz I'm lazy, and won't page back, have you checked fuel pressure? Air filter? Ignition timing(pre-set base if dist equipped)? Plugs & coil & wires? Does the upper radiator hose get so hot you cannot keep touching it for more than a second or so?(should.)
tom

Funny you should mention that, because I found aa part of the problem yesterday, and it's stupid... My friend was following me on the highway in his stock Prelude, and afterwards said "Man, you were haulin' butt back there!!!'... I thought I was going 60, according to my speedometer, but according to his car, I was doing more like 70... Turns out I the correction factor I applied for my 235/75-15 tire was wrong because I compared it with the tires that came with the truck which weren't the stock size to start with, giving me a 3% variation. So I checked the stock size in the door jamb, which was 235/60-15, went back on the calculator, and gave me a 10.7% variation which is right on the money. So applied to my last tank, it gives me 18.8MPG, apparently going between 60 and 70 (closer to 70 most of the time) which explains a lot. So next time I'll try going 55 (around 60-61 real speed) and see what kind of MPGs I get...

 

[TremblantRanger]

Oh and plugs and wires were changed since I got the truck, thermostat last december so touching the hoses are what you'd expect from a properly working cooling system, and I checked the air filter a year or two ago, which is the same since I have the truck, and looked lightly used, but gave almost no dust as I tapped it. I have distributorless ignition, so no adjustment there, and once changed one of the coils (the one for the exhaust side plugs I think) because the ohms readings where slightly out of whack so I took no chance. Also changed fuel filter 3 years ago. But fuel pressure is another thing I want to check soon.

 

[tomw]

If you remove a 'panel' style air filter, and hold it up towards sunlight, you should see lots of light penetrate the filtration element. You will not see the sun, but the panel should look bright as you peer through it.
The vendors use a 'mileage & date' to figure swap ranges. I use miles, and pretty much don't get into a lot of dusty conditions where I would clog a filter quickly. I ignore date suggestions as they want to sell me new filters I don't think I need.

If you have EFI, the only thing a clogged filter does is to lessen power developed as the O2 sensor will nudge the mix leaner as there's less air coming in. It will eventually reach its limit, and then yuck will be produced out the exhaust pipe, and mileage will drop.
A carb'd system has no smarts to know it is being choked of air(except less is flowing), and will pass fuel just as well, with the airflow through the venturi reduced, tending to reduce fuel flow, but if a vacuum develops, more fuel will get flowed.
One other thing that swapping tires for a non-OEM size does is put the engine into a different rpm range for 'normal' driving. Too low, and you could be lugging the engine, too high, and you spend more fuel spinning the crankshaft, producing useless power.
I just read something the other day about 'top speed'( a ticket ensued...) being higher in 4th gear than it was in 5th(overdrive). The engine had more torque at the higher rpm, enough to exceed the higher gear speed.
What rpm do you turn going 100kph? I think my 2.3 lima turns around 2100-2200 in 5th, but don't take that to the bank.
tom

 

[TremblantRanger]

Well tom, going 100kph as indicated on my speedo, it was even at 2500. but following my friend at a verified 100km/h (about 62 mph) I was around 2300 I think,,, I'll get back to you on that for the exact numbers. Weather over here is still a bit sketchy to work outside to check compression, fuel pressure and even the air filter, but my friend is moving to a house with a garage on april 1st which I'll be able to borrow to do all that. And yes, I did notice the engine lugging a bit more when I swapped from 215/75 to 235/75-15 tires; 5th is pretty much useless on any grade hill regardless of the momentum I have, and also on really windy days, which we had a lot this winter.

 

[TremblantRanger]

Yep, checked it in the last two days, and going a verified 62 mph the engine is now turning almost spot-on at 2300 rpm.