250s leaking head gasket staining block - Mercedes-Benz Forum

 
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post #1 of 9 (permalink) Old 11-25-2013, 01:07 PM Thread Starter
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250s leaking head gasket staining block

Can anyone help diagnose the leaking/staining that appears to be coming from the head gasket down the side of the engine block in my '66 250s (photo attached). I would definitely assume it's a blown gasket, but I'm not seeing any of the normal telltale signs (steam in exhaust, oil in coolant, coolant in oil, loss of oil or coolant) and until quite recently the car was running just fine despite the apparent seepage. This has been happening a lot more slowly than the picture makes it seem... that's accumulated staining over months, maybe even a year.

Since I wasn't suffering any other symptoms I had just been just keeping an eye on this, but recently the car lost significant power after I crested a steep hill. Since then it idles fine, but then wants to stall out in gear unless I rev it and ride the clutch. I've checked out all of the more obvious causes (fuel and air delivery is fine, no detectable vacuum leaks or exhaust blockage). Kind of run out of ideas, and it has me circling back to this mess on the side of the engine block.

Basically I'm really hoping someone can tell me that the two issues might not be related, but I'm running out of ideas for what could be causing the new problem, and if I need to replace the head gasket, I might as well stop wasting time searching for the problem and get started.

Is it possible for a head gasket to fail like this without other symptoms? Could seepage like this be indicative of anything other than a failed gasket? Any help or guidance would be greatly appreciated.
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post #2 of 9 (permalink) Old 11-25-2013, 01:27 PM
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The coolant flows within channels separated both inside and outside by a wall, the gasket runs down the outside between the coolant channel and the engine bay, and it also runs along the inside between the coolant and the oil. My guess would be that the gasket has only failed on this outside section, so you probably are losing small amount of coolant via this outlet but it has not failed inside to allow oil and coolant to co-mix.

You may not see coolant on the ground and therefore think you're not losing any, but this is evidence to the contrary, and it probably burns off when the car is hot so little can accumulate on the ground, if any. When you open the radiator is the fluid level always at the exact spot, right up to the tongue? If not, fill it and keep an eye on it, I'd bet it drops very slowly. Finally, the head is aluminum and the block iron if it's like my car, so they expand/contract at different rates. You probably don't experience leaking until one part is hotter than the other causing a small gap to appear which let the gasket break, then once everything warms up together the gap is again closed, then when you stop the car and it cools off again the two metals again allow another gap which then closes once they are both fully cooled off to ambient temperatures.

You can choose to either fix it now or drive it while keeping an eye out and wait until it gets worse, but you risk blowing the gasket fully at any time which may not be convenient. This isn't your situation but sometimes the engine plugs (aka freeze plugs) leak and people think they have a blown head gasket.

-Marrs

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post #3 of 9 (permalink) Old 11-25-2013, 02:15 PM Thread Starter
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This is the best news I've heard all day, DirectLA. Thank you so much for the reply! I think you are probably correct in your diagnosis, especially about the expansion of dissimilar metals, because I've never seen any wetness there when my head is under the hood. No dripping on the ground either, and if you look at the photo closely you can see that most of the dripping doesn't make it all the way down the side of the block, so I assume it's happening when the engine is hot and boiling off before it drips off.

I have checked the coolant level and it's dropped maybe 3/4 of an inch in a year and a half since I last flushed the system. I transitioned from the green stuff to G05 at that time, so that may have helped spur the problem.

I also just remembered that I did a compression test when I first noticed the white leakage to try to rule out a failed gasket, and all cylinders were well within range. I only mention it now in case someone else comes across this thread in the future and thinks it might be OK to keep driving a car they think could have a blown gasket. I had already ruled it out to my own satisfaction, but recently started doubting myself because I can't figure out what's killing my acceleration.

I wonder if there is any point trying to re-torque the head bolts just to confirm they are to spec as a way of hopefully prolonging the life of the gasket. Just an idle thought for pursuing some day when I don't have a major performance problem to figure out and resolve.

In the mean-time I guess it's back to the drawing board for the stalling on acceleration issue. Like I said in my first post it came on all of a sudden after climbing a hill, so I've been looking for a sudden-onset type of problem. I guess I'll go back to the drawing board with a fresh tuneup and take it from there. Ahh, the pleasures of owning a classic car.
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post #4 of 9 (permalink) Old 11-25-2013, 03:28 PM
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Originally Posted by Elwood911 View Post
In the mean-time I guess it's back to the drawing board for the stalling on acceleration issue. Like I said in my first post it came on all of a sudden after climbing a hill, so I've been looking for a sudden-onset type of problem. I guess I'll go back to the drawing board with a fresh tuneup and take it from there. Ahh, the pleasures of owning a classic car.
Could it be as simple as your kickdown switch not working? I'm at a loss on that one other than to suggest searching various forums with terms like "stalls on hill" or "no acceleration on hills" and switch out "incline" for "hills" etc. for more results. Good luck and please keep us posted.

-Marrs

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post #5 of 9 (permalink) Old 11-25-2013, 04:30 PM Thread Starter
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The car has a manual (4 on the floor import from Germany), so no kickdown switch. I'll follow up whenever I do finally figure it out.
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post #6 of 9 (permalink) Old 11-25-2013, 04:59 PM
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I would definitely re-torque the head bolts, and adjust the valves because I had the cover off.

Suggest you check the basics on your stalling problem:

- vacuum advance
- point gap and timing
- no loose wires
- coil resistance
- accelerator pumps squirting
- plugs not fouled
- no vacuum leaks
- good fuel delivery
- float level good
- carb linkage adjustment

Chuck Taylor
Falls Church VA
1998 SL500
1959 220S
1970 280SL
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post #7 of 9 (permalink) Old 11-25-2013, 05:08 PM Thread Starter
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Thanks ctaylor738. I've gone through most of the basics in your list, but will check the following next:

- vacuum advance
- no loose wires
- coil resistance
- float level good

I adjusted the valves 2 years ago when I first got the car. Made a world of difference then, but I wouldn't think they should be out again already. Doesn't hurt to run a feeler gauge under there again just to be sure, though. I've also had a new valve cover gasket collecting dust while waiting for the next time I needed to pull the cover, so it will be a good chance to slap that on there.
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post #8 of 9 (permalink) Old 11-25-2013, 05:41 PM
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I think you should do a compression test again, since the last one was before the sudden loss of power.
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post #9 of 9 (permalink) Old 11-30-2013, 07:45 PM
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As an anecdotal aside, the M127 in my 220SE fintail does this too, and has for at least 10 years. It leaks to a much less severe extent than shown in those pics, but every now and then I notice a little residue on the block. I've always assumed it was a minor head gasket issue. I too notice nothing in the oil, no significant coolant loss, and the car runs fine, so I just keep going. Mind you, I don't exceed 1500 miles/year.
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