I recently bought an 85 Vette, with its blown head gasket and random slew of issues, mods, and other personality traits.

I was super excited to have this piece of American history as my daily driver...until I realized it only got 9.5 average MPG! I wracked my brain, replaced the o2 sensor, front coolant sensor, scanned the ECM and cleared every code...fawned over the loose TPS like it was a newborn baby, carefully relearned how to drive, how to manipulate the automatic tranny while driving...cleaned the fuel system with an additive...and still...

At the end of a month's ordeal...I struggled to get 11.5 MPG. I was about to chalk it up to a poor engine rebuild job, when I decided to shell out the $13 or so it would cost to (finally) replace the air filter.

A quick 5 minute spin around the block instantly boosted my average MPG to 15, with a much smoother take-off and initial acceleration. I would've drove the car longer (and probably seen even better #'s), but my oil leak decided to grow and leave my car pouring smoke as it drove (as soon as you fix one thing...).

While all the other cures I threw at the car did greatly improve my ride, and would have had to been taken care of anyways, I just wanted to show an example of how a little common sense and pocket change can make a huge difference in a car. For the few of us that still remain who don't realize the importance such little things have, the moral of this story is clear: change/clean your air filter on a regular basis!!!

 

That looks like K & N washable filter. Look it over for a brand name. Your new paper filter
flows more air than it did dirty, so you are much better off now.

 

Hi

A clean airfilter is a must have.

The common oil leaks come from the valve cover gasket, and china walls under the intake manifold. I find the rubber type the best for the valve cover gasket, the china walls front and back between the block and intake manifold.

There are gaskets for the head to intake but the china walls need hight temp silicone.

You should see 20+mpg cruising on a highway, not so good in heavy start stop traffic.

Check your torque converter locks up, keep an eye on the tacho and check it doesnt change going over hills.
My 85 with 3.07 rear though 275 40 17 tires does around 1800 rpm at 62 mph, it doesnt change rpm going over hills.

Iff your TCC doesnt lock up you will see 1800-2300 rpm as she climbs up the hills, check the switches at the brake pedal for the cruise control. One is for the TCC if that is open with brake off your TCC will not lock, and suffer decreased mpg.

A C4 is not suited for a daily driver, buy a 4cyl Toyota for a daily driver if driving short distances in heavy traffic.

On the highway a well tuned/ maintained C4 has great fuel economy.

Press the reset switch on the dash to see how good these things are on the highway.... and how they can guzzle in stop start traffic.

 

I know that my econometer gives fictitious results seeing as how I am modified. However, does it work on a stock application? On my Ford Excursion/F series truck, we call it the "Lie-O-Meter" for good reasons. If it can be believed, I am getting over 25 mpg on the diesel. At stock levels it is accurate to within 3 miles higher. I never believe the damned thing.

Does it work well on STOCK Vettes?

Can something be modified to give me more realistic numbers?

 

The average MPG shown on my display is 2.5 MPG higher than real world (actual miles driven divided by actual gallons added). I track every fill-up on fuelly.com

Display = 24.5 MPG
Fuelly = 22.0 MPG

This is on a 100% stock 1995 base LT1/ZF6 with 60,000 miles on the odo. Air filter is a little dirty but not too bad.