What kind of gas mileage are you getting? (city/hwy) My 4.5 makes an SUV seem like an economy car.
Tom

That sounds about right...it's more like a dually with a 5th wheel horse trailer.... 91+ octane BTW.....

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Over 21 years I owned several:
w108
w110
w111
w115
w116
w123
w124
w126
w212

I average about 13.5 mpg on the 4.5, usually see 12-13 city driving and 15.5 pure highway. These beasties aren't known for being easy on the gas. Keep a close eye on your odometer and trip meter too, for a while I was showing 8 mpg and less but I found my odometer would stop registering miles when the temps got just right.

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Mike Tangas
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72

'02 CLK320 Cabriolet - wifey's mid-life crisis

2012 VW Jetta Sportwagon TDI...at least its a diesel

Non illegitemae carborundum.

Use th' cheapest fuel available. Mileage is pretty consistent @ 16mpg.

15 mixed, 17 on the highway, probably 12 in town.

Use only premium unless you want to do a very expensive valve job soon -- it if doesn't knock on regular, the mechanical advance in the dizzy is stuck.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

This is a little off subject but I once had a 1970 280SE 3.5 coupe with 4 speed stick, swapped the rear axle from a 3.92 to a 3.23, and consistently got 25 mpg on the highway, 18 to 20 in the city, on premium of course.

The question of octain in the 4.5 engine has come up before. I have run nothing but 87 in both my 280SEL's and am starting to run 87 in my 450 SLC. I have NEVER had problems doing this [an from owning a boosted 300ZX turbo I know what pinging sounds like]. It may be that certain 4.5's have different compressoin ratios but the ones I've owned like regular 87 just fine!

Anyone have a comment on this?

The real problem isn't pinging on acceleration (although that can be bad if severe), but detonation at highway speeds which you may or may not hears. This can drill neat holes in the pistons (not on a benz, though), and will roast the exhaust valves while decreasing performance.

Modern gasolines are considerably better than what the cars were designed for, so I would expect using 89 octane would be safe, but engine damage will quicly eleminate any economy.

On the older cars with mechanical advance (up to 1980, I think, may be wrong), a sticky advance will both reduce milage and prevent spark knock since you don't have full advance. So will incorrect timing procedures, most notably disconnecting the vacuum at the distributor on most V8s -- they have a vac retard system, it must be connected and working to set the timing right, otherwise on the older 4.5Ls, you will be 12 degrees late. Makes the car a log wagon an burns tremendous amounts of fuel. If the retard doesn't work, set timing to 7 degrees BTDC, not 5 ATDC.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

According to page 16 of the "Owner's Emission System Manual" for the m117 engine covering the 280SE SEL 4.5, 300SEL 4.5 and the 350SL:
For ping-free operation, gasoline with a min. RON of 91 must be used. Also unleaded or low-lead was reccomended to avoid deposits on the plugs.

__________________
Over 21 years I owned several:
w108
w110
w111
w115
w116
w123
w124
w126
w212

my 3.5 gets about 12.5-14mpg (havent taken it on a long drive), and it likes 89 or better, 87 it pings a little

i think i have 9.5:1 compression, vs the 4.5's 8:1 though

a RON of 91 is equivelent to what on the rating scale actually used at the pump?

I have always heard that 3.5 required premium and that 4.5s would run fine on basically anything.

All about octane.....
http://teaching.ust.hk/~chem342/leture_notes/energy_2b.ppt

__________________
Over 21 years I owned several:
w108
w110
w111
w115
w116
w123
w124
w126
w212

So can we conclude that the 4.5's compression ratio allows for low [87] grade gas? Once again, never had problems /w any of my three 4.5's here in steamy hot california.

Mine taps a bit while accelerating on the highway on 89, I usually use 93 octane. I do have the timing set up a few degrees extra in an attempt to get better milage.

Remember, this is D-Jet, and it leans out considerably at highway speeds and light throttle, so it's entirely possible for it not to knock under accelerlation but to do so at cruise, when you won't hear it.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

The US delivered 4.5 motors were 8.0:1. This means you can use the cheapest gas available. That's the bottom line. On the other hand, European market 4.5 motors were 8.8:1, and will benefit from mid grade fuel.

I have a '73 450SL w/198K miles. It's never had the head off, or any engine work. It runs fine, and with regular valve adjustments over the past 14 years of ownership, does not suffer any top end ticking.

Mileage? Ick. Try 11 city and 14ish mpg highway.

Many things cause pinging. Check the injector seals for leaks. Verify the injectors spray pattern. Check distributor advance. Check all vacuum. Check ECU.

Todd