Please advise on which octane gasoline to use in our new/used 1973 280C.

Regular unleaded gas works fine. You can use the next grade, 89 octane, but I have never really noticed any performance difference.

'73 280, '74 280C and a fuel injected (Megaquirt) '72 250C with a M115 engine all running regular unleaded with no problems.

The "Euro" engines are a different matter as they have a higher compression. Minimum 89 octane in them. Unless yours is a 280CE then regular will do.

Thank you.

I use mid grade in my 450
just make sure you use name brands, there IS a difference

__________________
Ron
2015 Porsche Cayman - Elizabeth
2011 Porsche Cayman - Bond,James Bond
Sadly MERCEDESLESS - ALways LOOKING !
99 E320 THE Queen Mary - SOLD
62 220b - Dolly - Finally my Finny! Sadly SOLD
72 450SL, Pearl-SOLD
16 F350 6.7 Diesel -THOR
19 BMW X5 - Heaven on Wheels
14 38HP John Deere 3038E Tractor -Mean Green
84 300SD, Benjamin -SOLD
71 220 - W115-Libby ( my first love) -SOLD
73 280 - W114 "Organspende" Rest in Peace
81 380 SL - Rest in Peace

Use regular unleaded. High octane gas can actually be worse for your engine. Unless you get knocking when using lesser octane, keep using the cheap stuff.

As for where to buy it, it all comes out of the same pipeline, it's all the same gas. The individual brands might put some additive in by the truckload, but the trucks all fill at the same regional distribution centers.

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On some nights I still believe that a car with the fuel gauge on empty can run about fifty more miles if you have the right music very loud on the radio. - HST

1983 300SD - 305000
1984 Toyota Landcruiser - 190000
1994 GMC Jimmy - 203000

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I have spoken to some pretty versed folks in the petral industry, additives do make a difference and are worth the extra few cents.
I know I will get grief on this , but I would not make such a blanket statement that all gas is the same, Ask the stranded diesel folks because of the water they pumped into the tank along with the fuel

__________________
Ron
2015 Porsche Cayman - Elizabeth
2011 Porsche Cayman - Bond,James Bond
Sadly MERCEDESLESS - ALways LOOKING !
99 E320 THE Queen Mary - SOLD
62 220b - Dolly - Finally my Finny! Sadly SOLD
72 450SL, Pearl-SOLD
16 F350 6.7 Diesel -THOR
19 BMW X5 - Heaven on Wheels
14 38HP John Deere 3038E Tractor -Mean Green
84 300SD, Benjamin -SOLD
71 220 - W115-Libby ( my first love) -SOLD
73 280 - W114 "Organspende" Rest in Peace
81 380 SL - Rest in Peace

I think that there are only a handful of distributors that supply everyone so it's likely that most gas is the same. Water in Diesel is a different story as it probably came from the tank at the gas station and not the tanker that supplied the diesel.

There is certainly no reason to run premium unless you have an engine that requires it.

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With best regards

Al

Ever since I switched to 93 octane the motor has much more power and it runs much better. With 87 the engine felt really slow off the the line.

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1985 300TD Turbo Euro-wagon
1979 280CE 225,200 miles
1985 300D Turbo 264,000 miles
1976 240D 190,000 miles
1979 300TD 220,000

GONE but not forgotten
1976 300D 195,300 miles
1983 300D Turbo 175,000 miles

http://i42.photobucket.com/albums/e3...e485-1-2-1.jpg

Most likely wishful thinking.

Alabbasi is right. Regular has a lower flash point than premium. So if your engine is designed for regular and you use premium, the explosion is actually delayed, causing an out-of-time situation (post-ignition).

__________________

Don't Chrome them; polish them

I would agree, MOST ( MOST)is the same, and using high octane is not necessary. Here is the great state of KY , I can tell you I have had some bad tankfulls of poor quality gas

__________________
Ron
2015 Porsche Cayman - Elizabeth
2011 Porsche Cayman - Bond,James Bond
Sadly MERCEDESLESS - ALways LOOKING !
99 E320 THE Queen Mary - SOLD
62 220b - Dolly - Finally my Finny! Sadly SOLD
72 450SL, Pearl-SOLD
16 F350 6.7 Diesel -THOR
19 BMW X5 - Heaven on Wheels
14 38HP John Deere 3038E Tractor -Mean Green
84 300SD, Benjamin -SOLD
71 220 - W115-Libby ( my first love) -SOLD
73 280 - W114 "Organspende" Rest in Peace
81 380 SL - Rest in Peace

In the Philippines, Our gas stations have minimum octane rating of 93 but we have 86 but only for tricycles only, If someone use that in his/her newer car, the engine will have serious detonation. My M115-powered 1966 200 runs on 93 octane gas with no problems at all and it gave the my car some grunt off the line.

There are some gas stations here that sells poor quality fuels (like gasoline mixed with kerosene ,diesel with water,frequently occurred b/c of condensation inside the station's huge tanks when almost empty). I fill my car bet. 5-7 am or when the outside temp. is cold. Cool fuel is the best!

In the Phillipines you probably use the MON rating - in the USA we use RON+MON/2 - the numbers tend to be a bit lower. Your 93 is probably like our 89.

When they started adding Ethanol to our gas around here my mileages dropped a ton. Also, my 300M has NOTICEABLY got water in the tank SEVERAL times - to the point where it barely started up on hills.

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Current:
2021 Charger Scat Pack Widebody "Sinabee"
2018 Durango R/T

Previous:
1972 280SE 4.5
2014 Jeep Grand Cherokee Limited "Hefe", 1992 Jeep Cherokee Laredo "Jeepy", 2006 Charger R/T "Hemi"
1999 Chrysler 300M - RIP @ 221k

This MB publication says that 1972-74 model year gas MBs should use gasoline with an octane rating of at least 87.
https://www.mbwholesaleparts.com/StarTuned/pdfs/LiquidJune06Star.pdf

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'81 MB 300SD, '82 MB 300D Turbo (sold/RIP), '04 Lincoln Town Car Ultimate

Sooner or later every car falls apart, ours does it later!
-German Narrator in a MB Promotion Film about the then brand new W123.