Trying My Patience, the little blue 280SE 4.5 that could(n't) - PeachParts Mercedes-Benz Forum

BradleyP · #1 11-13-2005, 01:51 PM

Well, as some of you know, I have recently had the heads done on my newly acquired '72 280SE 4.5....Post work, I have noticed a few oddities, the car has become quite cold-blooded, and in fact the night I picked it up from the shop, it wouldn't run until the mechanic set the idle up on it....

Replaced the alternator belt last monday, then my girlfriend was complaining about the crappy gas mileage (No odometer, so she couldn't exactly figure out) and I noticed an odd black stain leaving for work BEHIND her car a few days ago. Well, yesterday, I filled the car up and paced off the mileage from last night and today and refilled the car a few minutes ago...85 miles on 8.6 gallons of 89octane. Now, when we bought this car, pre head job (and sometimes only runnning on 7 cyls :-\ ) we were getting upwards of 15-18mpg.

And back to the black stain, she was warming up the car before we left for church this morning, and I see the cloud of white coming from the exhaust, and to no avail, what was causing the black stain on the gravel in my driveway. Mostly water it appears (We had a 40deg night last night) but after returning from church, the mass of the stain is still there.

This is my first 4.5, and frankly I'm lacking any kind of direction on what to start looking for....Any ideas?

Thanks in advance,
Brad

tosbt · #2 11-13-2005, 02:36 PM

The 4.5 is very hard to get tuned properly with out a CO2 meter. I would check and see if your tech used one. As to gas miliage If I ever got 18 miles per gallon I would flip backwards while shouting " thank You Jesus". I get about 10 around town and I may get 14 on the highway I am not sure, this engine likes gas and the car runs to much better when you give it to it.

Tomguy · #3 11-13-2005, 02:42 PM

Everyone here gets better mileage than I do, but then again, nobody here drives their 4.5 as hard as I do.

I have my 4.5 running rich because I like the power. It causes more carbon to build in the exhaust. When it's cold, if you stand behind the exhaust, you'll quickly be pelted with black spots all over as the water condensing in the exhaust takes out carbon with it. Is it possible that water dripping from your tailpipe left a carbon spot? My 4.5 has never dripped water like some cars do, it's always coming out in a black mist. But it's possible I suppose.

nhdoc · #4 11-13-2005, 08:01 PM

My 4.5 also spits out a sooty stream when cold, for the first couple of minutes if you leave it idle it will leave a black streak behind the tailpipe, but it is just water washing out some of the crud in the exhaust system.

Mine runs really well but does not get more than 11-14 MPG regardless of how I drive it. I think if you ever see 18 on one of these I would call the guiness book people

WANT '71 280SEL · #5 11-13-2005, 10:14 PM

Any gas car should have water come out of the tailpipe. If you have water coming out that means it's well tuned as that is one of the bi-products of the combustion process. So if there's water, your car is pretty well tuned.

Thanks
David

billrei · #6 11-14-2005, 04:34 PM

I just did a mileage check on my 3.5 and I only got 13.4 mpg on mostly highway driving. I was pushing it (70 - 75 mph) up Highway 101 then Rt 1 to San Simeon however and had the AC on low for some of the trip (love this S. Cal Fall weather!!)

tosbt · #7 11-14-2005, 04:55 PM

Quote:

Originally Posted by billrei

I just did a mileage check on my 3.5 and I only got 13.4 mpg on mostly highway driving. I was pushing it (70 - 75 mph) up Highway 101 then Rt 1 to San Simeon however and had the AC on low for some of the trip (love this S. Cal Fall weather!!)

At 75 or so I think that is about right. Mine is a 300SEL 4.5, love that air ride! Gets about 14, I still don't think its tuned right., whats your temp gauge look like?

Tomguy · #8 11-14-2005, 05:22 PM

On a trip back from AC in my 4.5 (in February), I averaged 89.9MPH and still managed to get 12.3MPG, which is the best milage I've gotten on my 4.5 to date. I don't do much highway driving and when I do, it's usually floor it, pass a bunch of slowpokes, get stuck behind a truck at 50, floor it, pass him, and repeat. My temp gauge on the highway barely breaks above 175 ever, highest I've seen on the highway is probably 185 (far below the line between 175 and 250).

I'm betting some vac lines were left unconnected after the head job, most likely the one from the throttle body to the firewall (switch), then to the distributor. If this line is connected improperly (or not at all) and timing is set to 5°ATDC per specs, you'll be late and sluggish and get poor mileage. Check that line as well as the others. If that line is missing, have the timing set to 7°BTDC until you replace it and verify it works correctly.

tosbt · #9 11-14-2005, 05:38 PM

I have ordered some CITRIC ACID for my impending flush job. I do not think this engine has been flushed in 25 years, my running temp always runs near 200 and sometimes beyond, I have done everything. New thermostat, water pump, had the radiator corred ect ect. Next if this does not work I intend to have a custom radiator made for this car.

billrei · #10 11-14-2005, 08:31 PM

Temperature has not been a problem so far. My temp is about 90 degs C at the maximum. The aux fan as never has to kick in. If the citric flush does not work you may find that corrosion has attacked the water pump housing causing the clearance between the impeller and housing to increase. I have seen some nasty examples where galvanic corrosion has turned the heads and waterpump to dust leaving craters that look like the surface of the moon.

billrei · #11 11-14-2005, 09:00 PM

Quote:

Originally Posted by Tomguy

On a trip back from AC in my 4.5 (in February), I averaged 89.9MPH and still managed to get 12.3MPG, which is the best milage I've gotten on my 4.5 to date.

My 3.5 has a 3.69:1 rear axle ratio which is great for punch off the line but the motor is turning fairly high revs at speed. At some point I might switch to a 3.27:1 rear axle like the 4.5's have.

I had another 300SEL 3.5 a couple of years ago and I could get about 15.5 mpg on the highway with that. I have the engine from that car in storage so at some point I might switch engines.

Bradley has to be mistaken about the 18 miles per gallon for a 4.5. With a 250SE W108 with a manual transmission and 3.27:1 rear axle (from a 4.5) I could get 18 to 20 mpg. But that's with almost half the displacement of a 4.5!!

alabbasi · #12 11-17-2005, 07:29 PM

I have had some serious issues getting my W108 to run right. This car is a nightmare to get running right. I have taken it to "experts" who charged me hundreds of dollars to tell me to sell it.

You need to find a guy that really knows these cars (not someone who says they do). You need to make sure this guy is honest and you need it set up on a CO meter to get it 100%.

If you live close to Atlanta, I can recomend a guy.

Tomguy · #13 11-17-2005, 07:49 PM

I've never put my 4.5 on a CO meter. Maybe I'm just that good at tuning it by tone and smell. The plugs always look just a bit black but not much, which I take as a sign of a "Healthy rich".

billrei · #14 11-17-2005, 08:35 PM

This would be cool if it was not so darn expensive: http://www.dynojet.co.uk/wideband/index.html

If you could couple this to a Megasquirt system you would probably have the ultimate setup...maybe when gas hits $5/gal...