280 SE 4.5 gas milage

[psfred]

Hey guys!

I finally go the odometer working on the W108, seems I'm getting somewhere between 12 and 14 mpg.

Any thoughts on getting this a bit higher? I'd love 20, but will settle for 17. I'm going to get the mixture adjusted after I get new plug wires.

Also, have slow cold starts -- lights right up warm, but I have to crank a while cold. Cold start valve?

Peter

[MikeTangas]

The best I've been able to get is 16 MPG on the highway, 14.5 combined and 12.5-13 in town. I also run Red Line's Fuel System Cleaner at every fill up. I saw an honest 10% increase in mileage once I started using the stuff.

Could possibly need a cold start valve. I replaced mine only because it was leaking externally. Mine has always lit right off hot or cold.

[psfred]

Mike:

I was afraid of that.... I'm used to cars that get closer to 30 mpg than 10!

I'm still short new wires and re-gapping the plugs (currently Bosch Platinums). I'm going to make up a set of solid wire cables with only the resistor sockets on the end on the adivce of my locak Benz guru. He claims that will make the platinums work properly. I will also check the gap -- chances are they are out of the box, too wide for the low voltage coil in this beast.

I have black soot on the tailpipes -- this leads me to think it is running richer than it needs to (it surges cold, very rich then, I can smell it!)

Other than the cheap, worn out, out of balance tires and cheap aftermarket shocks (sad), this thing drives very nicely -- I could get REAL used to it except for the gas cost!

Peter

[MikeTangas]

Check the braided vacuum line that runs from the rear of the left head to the manifold pressure sensor on the firewall. Usually developes cracks and causes a rich condition. I replaced mine using 5/15" fuel injection line, but you need a small hose clamp for the nipple at the head.

[psfred]

Mike:

I trimmed that hose, was going to replace it and forgot. May do that tonight, it could cause starting trouble too.

I love this car, I'm sure glad I saved it from the junkyard!

Peter

[MikeTangas]

I'm betting you trimmed it because it had split at the sensor end. I did the same thing, but found when checking it closely it was full of cracks end to end. Better off replacing entirely. For the purists, the large braided hose is still available through the dealer, but they have to special order it from Germany at steep cost.

[psfred]

Right you are! That's why I was going to replace it, but got distracted with brakes, then the dash and heater levers and instrument cluster..... Never a lack of things to work on, eh?

Nice to have dash lights, still need to pull the heater valves and replace the o-rings -- work terribly hard cold, I'm afraid I will break the left heater lever.

I also have a broken glove box latch. I have it locked now to keep the light off, but will need to fix it soon. Any suggestions? Can I get a replacement latch? The hook on the end is broken off, don't known when it happened, as ti worked before I took the glove box off, found the bit as I was re-installing it.

Peter

[MikeTangas]

What I'd suggest on the latch would be look for one from an older 108. The late 108's had plastic pins, eyes and cup (for lack of better terms) the older ones were all metal. I had the same problem, found a replacement in the yard but it too had something broken, I just can't remember what. I ended up mixing parts from both years and getting a solid working latch.

[Rackne]

Try a different brand of spark plugs, in my 108 4.5 the bosch platinums ran horribly, possibly due to the lower compression ratio. The Champions were noticebly smoother, perhaps the larger spark area.

[psfred]

I may go back to Bosch Supers for that reason. The problem is that the Platinums are resistor plugs, and the wires are resistor wires with resistor ends -- too much resistance, hence no spark.

I do have a 'rolling' miss that is either missfire, dirty points, or dirty trigger points, all of which I intend to check this weekend if it doesn't rain.

I'm planning on getting some solid wire plug cables if I don't put Bosch supers in -- I like the platinums better, they last longer and have hotter spark, but only in combination with non-resistor wires!

Peter

[LuckyF8]

Hi Peter, sounds like your gaining on it! Get the tires and you will forget about all the fuel these cars suck up.

The best I got in my 4.5 was 17mpg, and that was on a 150 mile trip, with the cruse on at 70mph. Must have been down hill all the way! Normal around town 9 to 12mpg if I am lucky.

Mike seems to have a lot of good answers for these cars, nice to have him here.

[MikeTangas]

Peter,

Just stick a set of W7DC's in there. Can't beat those old copper core plugs.

[psfred]

Well, I got my wish -- I drove to Ohio today for the hood replacement ($9.99 for the hood, $150 for shipping, I drove an changed it!). Got about 17 mpg on the way home -- from 58 miles outside Cinncinnatti to Evansville, IN (about 280 miles) on less than 3/4 tank of gas. Marathon 89 octane.

Ran like a champ -- at 60 so very smooth and sweet. Serious shake above that, probably a bad tire (they are pretty sad) or a loose upper trunion on the right kingpin.

Wonder what it will do after I get it set properly!

Peter

[240 Ed]

Hi Peter,
Glad you had a nice romp in your 108!
FWIW, the cold start injector would likely be okay, as it doesn't do very much injecting its whole life.

But, a bad temp sensor would cause havac with everything, including running rich.

My left heater lever is very stiff when cold too, is this the cable or the valve...?

and thanks for the discussion on spark plugs! I never thought about platinums not working well with an older system...

[psfred]

Ed:

If it moves better warm than cold, it's the valve. Probably crudded up and the o-ring is shot. I'm going to try to get to mine this weekend, if I ever get to stay home for any length of time.

Peter