Given the current gas prices, I thought this might cheer people up. Maybe not though.

But for me it's good news in making a trip from Eastham on Cape Cod back to my home in SE Connecticut, I averaged 27.96 mpg out of my '87 Brougham, going between 55-70 MPH and including a 5 mi traffic jam and about 12 mi with the A/C on.

I think it was thanks to synthetic oil and regular tuneups, because I run the car on 87 octane all the time and hardly used cruise control on the trip.


What's the best you've ever done for MPG with your RWD Caddy?

In my 94 Fleetwood Brougham V4P (7000# tow package) with 15W40 Rotella T, LT1. 23 highway, average 18.5 to 19 city/highway mix. 3.42 gears.

I got 19.9 yesterday, with AC off half of the trip, holding to 1-3 mph over posted, cruise as much as possible.

oh... *RWD* and *Caddy* are 2 important words :)

otherwise, my best RWD Caddy mileage is 12 town and 17 highway

425 cubic inches, heavy foot, no over drive... yup, not the car I drive to save on gas to say the least :)

1989 Brougham - 10.5 - 11 in town, 10.5 - 11 highway.

Summer of 1985. Road trip to Roachtester, NY.

2 cars side by side:

1977 Coupe Deville 19.4 MPG at steady 60 MPH mostly highway no traffic roll. Same car same week same weather, day trip to Toronto up the QEW at 70 MPH only got 14 MPG!

1981 Coupe Deville 8/6/4 (working) 60 MPH highway roll (right in back of the '77) 21 MPG using cruise control.

Figured from actual gasoline fill not hokey dash readout. I personally filled both cars with gas before during and after to eliminate errors. BTW both of these cars were dead nuts even in a standing start race until about 70 MPH when the 425 would start crawling ahead.

Summer 1993 Fleetwood 75 FWD (sorry I know you said RWD only) HT4100 factory limo. Steady roll to Baltimore Marina from Central NJ. 27 MPG with 8 passengers.

January this year 1980 Cadillac Fleetwood Coupe 368 carbonated factory settings never touched. Still has idle mixture caps!
Hurried midnight roll to Ocala, Fla. Mostly 70 MPH highway on route 95. 18-19 MPG. Unbelievable to me for a 3 speed trans and carbonator.

1982 Trans Am fitted with 1975 Cadillac 500 12.5:1 compression early Cadillac EFI, 2004R trans with functioning lockup. Steady roll to Gaithersburg MD 24.5 MPG. Same car got about 12 MPG combination highway city with a TH400 installed while waiting to figure out if my trans guru could patch up the broken TH200!

Strange enough my 1976 Delta 88 Royale Olds 350, THM375, 4860#'s, 2.73's got a best of 23 mpg a few times. Mostly was around 18-19, but these freak ones it would do once in a while. The time I first got 23 was on a 100 mile round trip, peaking around 100 mph, and coasting up all the hills and gently accelerating down the hills to get back up to 100. So I might lose 30-40 mph on a hill, but gain it back on the other side. I drive up the river road (highway 79 from St Charles, MO) to Hannibal, then over to 61 and back to St. Louis. It was pretty fun.....

My 301 Turbo Trans AM (301 turbo V8) got an average of 23 mpg highway at 55 mph. If I was up to 65 it dropped down to around 19-20. This is a 4030 lb car, 3.08's and 28 inch tall tires. I feel I could have got an easy 23-25 mpg with OD. I drove a 1977 Grand Prix, 301 2BBL (135 hp) with THM400 and 2.73's and it got a solid 25 mpg all the time. It was pretty impressive how well it did for such a heavy car. Performance was lackluster, but tolerable.

I have always wanted to build a small port (read high velocity) headed 455 for my T/A and do some fuel economy experiements. Sure, it will hurt power, but gear it to work the powerband that monster will have (brutal low end), say 2.56's and THM200 4R OD or better yet, a 6 speed stick and 3.08's. This will keep rpms way down, and keep it in a range that is very efficient for the 455 with high velocity ports would run. I think that if you have high velocity ports, it doesn't matter if it is EFI or Q-Jet, it will do admirably.

Take a look at this: http://www.cars101.com/fuel_economy.html

So far, honestly, I am not impressed with any of these car's mileage. I think I will take the minor hit and drive my big Cadillac! You would think with the light weight, OD's, smallish engines cars would do better on mileage!

My 95 FWB with 5.7ltr LT1 gives me 22-24 regularly on high way cruising at 70-75 mph. I drive a lot between Madison, WI and O'Hare, IL on Highway 90 where this almost never any traffic jams or Cops. And yeah I use cruise control all the time.

I always use 10W-40 Mobil1 synthetic and have twin spark platinum Bosche spark pugs installed.

10W40? I didn't think Mobil still made it. At least, I haven't seen it. I was running 0W40 for a while in my 91 SDV.

Dang, I will have to watch for you on the highway! I drive it now and then, look for a tan 94 FWB with a 6 foot black (hard to see) whip on the back! That antenna still freaks speeders out.....

But then again, you knew that....