M116 - Source of Gas in Oil? - PeachParts Mercedes-Benz Forum

Strife · #1 11-29-2008, 01:17 AM

It's a long story, but a smell of gasoline in the oil of my 85 380SL, 119K miles, persists after an oil change and driving perhaps 100 miles. I can't really continue driving this car until the source of the problem is found and fixed (and the oil changed, again). The engine runs well and a spark plug change concurrent with the oil change showed eight normal but worn, tan-colored plugs. The car does seem to "sputter" briefly when it's sat for a while hot, which it didn't do before. It starts wonderfully (other than the brief hot "sputter") in all weather, hot or cold.

This has nothing to do with the timing chain, tensioner, cam gears, etc because I changed them recently and timing is 2-3 degrees off at most. I very strongly suspect that these parts were prematurely worn due to the gas in the oil (the chain/tensioner lasted 25K).

From what I understand, there are three sources of gas in the oil. Is this a complete list?

1. Leaky cold start valve (theoretically, it could be a failed signal to it, causing it to be on all the time, but I'll check for this)
2. Leaky injector(s).
3. Leaky fuel regulator/damper(s) - this car has two.

Because of the age and mileage of the car, I'm willing to put in new fuel injectors and fuel regulators/dampers "shotgun" if I have to. I don't have the facilities to test the injectors and new ones for this car are on sale and not as expensive as the 560's. The dampers - well, they are 24 years old, and so are the injectors.

What would be my plan of attack on this? Here is what I'm thinking to do:

1. Check the signal and the function of the cold start valve (that it doesn't leak when not energized). I have a known working spare.
2. If (1) OK, replace the injectors (I have the holders, gaskets, and o-rings for these, but not the injectors)
3. If (2) fails, replace the dampers (I don't have these).

What would you "shotgun" first? The injectors or the dampers? Is the "sputtering" above a clue (that it's an injector or cold start injector?).

Obviously, I'm really worried about this - it seems like this car is getting away from me, in terms of keeping up with the number of things that go wrong (I know it's 24 years old, but I am trying). While inspecting the regulator/dampers, I also discovered that the ball for the accelerator rod had disintegrated into small pieces of plastic bits next to the LH damper, leaving the rod scraping on a metal fuel line

mpolli · #2 11-29-2008, 02:36 AM

Are you sure your nose is calibrated that well? If you are willing to throw that kind of money around then you might throw some first at Blackston Labs for a test to just how much gas is really in there. If your nose works that well then you might put them out of business. Up to 1% gas is OK AFAIK.

Strife · #3 11-29-2008, 03:14 AM

Well, I'm definitely not one to just throw money at a problem, OTOH I will spend money to prevent spending a lot more money.

here's why I thought the gas smell was excessive:

0. After 100 miles?
1. I have a 560 with about 3K miles on its oil and the oil smells like...well, oil.
2. This is a new phenomenon.
3. I recently had to replace a timing chain (definitely "stretched"), broke a guide, replaced worn cam gears, and replaced an apparently leaky tensioner after a suspiciously short 25K of service. If the oil was diluted with gas, certainly this would affect its lubrication and being thinner, one would suspect the tensioner would be more prone to leaking.
4. The "sputtering" when starting from warm is new. Other than this, the engine runs so well I have to look at the tachometer when stopped at a light to know that the engine is running.
5. The oil was amazingly dirty after only 3000 miles, much dirtier than before. I've read that gas in oil is a great "engine cleaner" - at least, until something like a bearing lets go.

t walgamuth · #4 11-29-2008, 06:48 AM

I concur to have the lab check the gas content in the oil. If the amount is small, and you get the car good and warm I would think it will burn/ evaporate out.

The spluttering might be it getting a little extra fuel on start up. My sec did that for years with no ill effect. The color of the plugs suggest its not a problem that continues after the start up.

If the cold start was staying on it wouldn't run right after it got warm, IMHO.

Strife · #5 11-29-2008, 12:50 PM

Well, maybe I'm panicking over nothing. But I really dodged a bullet over the premature timing chain wearout and I'm not comfortable because I don't know exactly WHY it happened. I ordered an oil test kit today, but I can't send it in to analyze for 400 more miles. I suppose that they can extrapolate wear, fuel, etc based on mileage.

mpolli · #6 11-29-2008, 02:56 PM

As far as leaky injectors and cold start valve can you test that with a pressure leak down test? If the pressure is maintained then it is not leaking. As far as waiting 400 more miles, they will test it at any time, you just won't get good wear results, but they can certainly tell you how much gas is in it. But it might make more sense to wait. One thing that causes gas in the oil is lots of short trips. I used to have a 2 mile commute (the good old days) and got my oil tested at about 10,000 miles (M1 0W40) and it was still good according to Blackstone but had about 1.25% gas as I recall, and he said that was OK and caused by short trips.

ctaylor738 · #7 11-29-2008, 04:08 PM

The modulators are easy to check. Just pull the vacuum lines off, smell for gas, and test with the Mityvac just to be sure.

You can put a gauge on the system and see how fast fuel pressure drops after you shut it off to test for a leaky injector. That will also tell you if you have low control pressure, which would make it run rich.

It might be worth checking the o-ring in the fuel distributor.

Please keep us posted.

Strife · #8 11-30-2008, 02:24 PM

Well, I did a fuel pressure test, and here's what I got (in bars):

5.4 Basic pressure
1.9 cold engine, connector to heater of WUR off
4.1 Warm engine, heater on
3.5 with valve off ,engine running
Took 2 minutes to drop to 3.2
Took 5 minutes to drop to 2.8
2.8 seems to be holding for >1 hour

This car runs very well and always starts first crank. The concern here is leaks and gas in the oil. Maybe running a bit rich?

It is interesting to note, that when I connected up the gauges (car had not run in 20 hours), there were no leaks or spray, so I suppose that there was virtually no pressure. There were no leaks or spray when I disconnected the fuel lines over the LH valve cover when I replaced the timing chain stuff, either.

Should these pressures hold indefinitely? That's a lot to ask on an 24 year old car!

The WUR numbers seem a little high, and could be attributable to dirty screens, etc. The manual says that:
5.2-5.8 Basic
3.4-3.8 warm.

In a previous post, Chuck Taylor mentioned that 380's liked 1.0 cold and 3.4 may be better.

ctaylor738 · #9 11-30-2008, 04:30 PM

Those numbers look fine to me, consistent with a well-running car.

A very experienced tech recommended those control pressure settings to me. He feels it's better to have the CP a little lower for good warm-up and acceleration enrichment.

I would think that if you are getting significant fuel in the oil you would see sooty plugs, high CO, smoke out the tailpipe, lumpy idle, etc. But you don't seem to have any of those issues, so I'm at a loss.

Can you get a duty cycle reading?

Strife · #10 12-11-2008, 01:09 AM

Possible Explanation

My thermostat was not working properly, and the engine never really got up to true operating temperature, which, as they say, "is bad". I've replaced it and the gasoline smell has disappeared!

http://www.peachparts.com/shopforum/showthread.php?t=239713

ctaylor738 · #11 12-11-2008, 08:47 AM

This would have to be plain old inefficient combustion because the warm-up regulator controls the mixture, and its not affected by coolant temp.

mpolli · #12 12-11-2008, 05:16 PM

You really should switch to sniffing wine, there is more money in it.

Strife · #13 12-11-2008, 05:20 PM

Well, I do know that the tolerances of an engine (piston/cylinder, bearings, etc) are designed to be correct at the designated operating temperature. Aluminum has a much higher coefficient of expansion than does iron. So, I think a lot of this dirty oil was caused by blow-by.

I was going crazy trying to get the belt tension correct with a Krikit, and then the belt would tighten up a lot when the engine was warm. Sure enough, the distance between the water pump pulley and the P/S pulley is measurably greater when hot, at least on an aluminum block.

E150GT · #14 12-28-2008, 03:33 AM

Quote:

Originally Posted by Strife

Possible Explanation

My thermostat was not working properly, and the engine never really got up to true operating temperature, which, as they say, "is bad". I've replaced it and the gasoline smell has disappeared!

http://www.peachparts.com/shopforum/showthread.php?t=239713

Strife, did you notice increased fuel consumption during this time? Lately my 420sel has been getting about 12-13mpg down from 16-17 and I have been smelling fuel. I have also noticed dirty oil, but I cant say I can detect fuel in the oil with my nose. My heater gets warm, I'd say it blows out 100 degrees on high on a 40 F morning, but I cant seem to get the engine temp past 60C on my 13 mile drive to work. Tonight it was 51 F and the engine got to about 75C but I could not get it to go any higher. I suppose this sounds like a faulty thermostat?

Strife · #15 12-28-2008, 11:03 AM

Based on my experience, the engine definitely runs better now (the gas mileage is better), and the oil doesn't smell like gasoline as much (I would think that a lot of it that got in previously has been vaporized by heat). I'm going to do an early oil change because of this.

The temperature you describe is not normal. With a new thermostat on a 10 degree F morning, I now get up to 100C (not as quickly as I would like), then it popped back down to 80 very quickly, and then bounces between 80 and 90 after that, which is the normal operating range of this engine.

Another interesting thing I observed was oil pressure. Hotter oil = thinner oil, so the pressure will go down with temperature going up. I noticed that my oil pressure seemed higher than usual with colder temperatures and the bad thermostat. With the new one after an expressway jaunt, I'm at about 1.5 bars at idle, same as in summer. So, the oil wasn't really getting warm enough either.