: Question about gas on 1978 Sedan Deville i bought today.



pompste
01-19-10, 05:52 PM
Hi,
I bought a 1978 Sedan Deville today off e-bay and i`m picking it up tonight----just 12 miles away from me! It`s in real good shape considering it`s 32 years old---been stored away for the past 4 years.Only cosmetic problem is the right rear BUMPER FILLER----pretty much cracked all the way off leaving a gaping opening.

Engine is so smooth running,almost too good.

Does the 425 V-8 take regular or premium no lead gas?

Thanks

sven914
01-19-10, 06:01 PM
The engine was designed to run on 91... I've never seen it.

I would use 89 most of the time and then use 93 every once in awhile to keep the engine happy.

Bro-Ham
01-19-10, 06:25 PM
The owner's manual for my 79 Sedan deVille says ANY unleaded gasoline is acceptable - Cadillac mentions no special octane requirements for the 425 V8.

Angry Matt
01-19-10, 06:36 PM
The 425 is an 8.0:1 compression, which means it was made to run on regular. I went for years putting high test in my '80's cars and not knowing any better.

sven914
01-19-10, 06:39 PM
The owner's manual for my 79 Sedan deVille says ANY unleaded gasoline is acceptable - Cadillac mentions no special octane requirements for the 425 V8.

Your right... That'll teach me for listening to a damn Allante tech.

It's a low compression engine so, 87 is fine.

drmenard
01-19-10, 06:40 PM
The 425 motor is low compression... Should be able to be tuned to run fine on 87 octane..

HAZZARDJOHN
01-19-10, 10:50 PM
For reference the owners manual in my 75 says 91 Octane Minimum (page 63 of the owners manual) and I have a lowly 8.5:1 comp. When I was in south dakota I had no choice but to run 87 as all other grades had ethanol and it ran fine, no knocks or pings. Now that I am back in MN I know of every gas station in the state that sells non oxygenated ethanol free 91 octane gas.

*Not to get into an ethanol debate, but lets just say I have seen what it does to my Cadillac, I run it in my truck (e10) but it will never touch my caddy again.

~HJ

pompste
01-20-10, 02:37 AM
Thanks for all your info everyone.The person i bought it from says he got better performance running premium gas.
Honestly,this '78 rides so much smoother than my '95 Deville because of the longer wheelbase.Now if i can find a solution to the "gaping opening" left by the totally cracked rear "bumper filler"----it leaves all the wiring exposed to the rear tallight--not good.

77CDV
01-20-10, 02:56 AM
Reproduction fillers are readily available from multiple sources. OEM is way expensive, but fiberglass reproductions are very reasonable. As for the octane, my 1977 owner's manual states gas with 87 average octane rating is recommended (regular unleaded). Been using regular in all my 77s over the years and have not have any problems.