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Discussion Starter #1
is it possible that it *ISN't* the dreaded rod issue?

I bought the car from an estate last week. It gives every impression of being very well maintained. It has 339,000 kms and until this turn of events, i was sure i'd gotten the deal of the century.

It appears to have burnt through .5 liter of fresh Mobil 1 in about 350 kms.

Thoughts? Ideas? Experiences?
 

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MBZ '87 300SDL, MBZ '85 380SL, RR '77 Silver Shadow II, MBZ '98 E300TD
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is it possible that it *ISN't* the dreaded rod issue?

I bought the car from an estate last week. It gives every impression of being very well maintained. It has 339,000 kms and until this turn of events, i was sure i'd gotten the deal of the century.

It appears to have burnt through .5 liter of fresh Mobil 1 in about 350 kms.

Thoughts? Ideas? Experiences?
Yatzee,

339,000 kms is a fair mileage, but not excessive. However, a half liter of oil per 350 kms does sound like consumption far in excess of normal.

Do you have a sense for how long this car sat before sale? It could be rings sticking in their lands due to infrequent oil changes, which results in poor oil control and reduced compression. Check the inside of the valve cover for deposits; a well cared for engine will have no sludge or deposits on the inside of the valve cover. Change the oil and oil filter with a good quality diesel oil (synthetic, semi-synthetic or regular mineral based), change oil and filter again in another thousand miles or so and check your level every 250K or so to determine if there has been any improvement.

If you have defective rods, the issue tends to manifest in the first few tens of thousands of km. All told, this probably affected less than 25% of the cars, but with so few 350SDs and 350SDLs imported, the impression one might come to believe is that it is neigh impossible to obtain a 3.5L car without defective rods that if not already bent are on the verge of doing so. Some go so far as to insist on proof of engine replacement prior to purchase (when the compression test would reveal much).

If after a few K of diligent oil and filter changes no improvement is observed, have a compression and a leak down test performed. If there are problems discovered during these tests, the only practical solution is a motor replacement, or at the very least an engine tear down (which dealers don't generally do). The dealer may or may not be willing at this point to cover those expenses - have them do the compression and leakdown tests so that they cannot question the outcome of these tests in deciding next steps.

Regards,

-bh
 

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Discussion Starter #3
Do you have a sense for how long this car sat before sale? It could be rings sticking in their lands due to infrequent oil changes, which results in poor oil control and reduced compression. Check the inside of the valve cover for deposits; a well cared for engine will have no sludge or deposits on the inside of the valve cover. Change the oil and oil filter with a good quality diesel oil (synthetic, semi-synthetic or regular mineral based), change oil and filter again in another thousand miles or so and check your level every 250K or so to determine if there has been any improvement.
There was an oil change sticker on the inside of the windshield that shows that the car has been driven about 1000 kms since 07. I know the person passed away early 08, so I imagine it has sat since then. I put Mobil 1 ESP in the car with an original filter on Friday. I had the cross-over pipe off today and it had a couple mm of crud which i cleaned out. The intake is full of soot - it will be a project at some point (but my 87 was much worse when I 1st got her)

Another clue is that on mid throttle, I get a pretty good puff out the back. I initially thought it was due to old diesel, but I've burnt through quite a bit of the weekend and it still happens. Are turbo seals an issue on these cars?
 

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There was an oil change sticker on the inside of the windshield that shows that the car has been driven about 1000 kms since 07. I know the person passed away early 08, so I imagine it has sat since then. I put Mobil 1 ESP in the car with an original filter on Friday. I had the cross-over pipe off today and it had a couple mm of crud which i cleaned out. The intake is full of soot - it will be a project at some point (but my 87 was much worse when I 1st got her)

Another clue is that on mid throttle, I get a pretty good puff out the back. I initially thought it was due to old diesel, but I've burnt through quite a bit of the weekend and it still happens. Are turbo seals an issue on these cars?

Is the puff white, bluish gray or is it black? Turbos on these cars are really not an issue. They can get noisy from worn bearings, but it's impressive how well a turbo from an old car you get out of the junkyard actually works on these beasties.

Keep your eye on oil consumption - an undiagnosed issue with connecting rods remains a possibility, but only if the symptoms do not clear after a few oil changes.

-BH
 

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Did you checked for leaks? I had similar problem - oil loss. The oil cooler pipe was wet, but there wasn't any oil drops on the floor. The oil droped out during driving, when oil pressure increased. The pipe is fixed, and I didn't refill engine since 1000km.
 

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I would say blueish grey. I thought it might be a bit better last night, but it might be wishful thinking.
That would be oil being burned. Do you have any significant oil leaks as well? My 300SDL leaked like a sieve when I obtained it I knew I'd have to replace almost every external seal on the motor. Still, this doesn't generally result in the kind of oil quantity loss you describe.

Valve seals are another area to check. Valve guides can also contribute. If the car has received regular attention while it was driven, the guides may still be fine and therefore not allowing much oil passed the valve stem, but the valve stem seals are nearly guaranteed to be petrified. This will be contributing to your problem. The new seals are of a better material, but unless you have an air compressor and the right fittings to pump up the cylinders and hold the valves firmly closed, I wouldn't suggest replacing them just yet.

That leaves the more onerous potential issue of ring gap causing loss of oil control. Take the car in to get a compression and leak down test to determine whether oil control is shoddy at the valves or at the rings - cross fingers that it is just the valve seals (though that would be a very unusual level of valve seal oil leakage).

Good luck.

-BH
 

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definitely something rubber is leaking in your cylinder heads. usually valve stems go bad when an old car has sat for over a year. there are some decent products to temporarily fix the problem
 

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Discussion Starter #9
She's ain't oil tight underneath, that's for sure! :) I know that the vacuum pump seal is leaking, the oil level sensor seal is leaking, and something on the turbo side (not sure what yet) These leaks make for a slick underpan, but no drips on the ground. The rear main is starting to show signs of leaking, but again, no drips.

I thinking more and more that the leak is internal. I've been reading on various forums that there is an issue with the front oil passage of the head gasket leaking oil into cyl #1. Or it could be ovalized cylinders... either way, the head has to come off, right?

Is there any advantage to taking a look inside with a boroscope?
 

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She's ain't oil tight underneath, that's for sure! :) I know that the vacuum pump seal is leaking, the oil level sensor seal is leaking, and something on the turbo side (not sure what yet) These leaks make for a slick underpan, but no drips on the ground. The rear main is starting to show signs of leaking, but again, no drips.

I thinking more and more that the leak is internal. I've been reading on various forums that there is an issue with the front oil passage of the head gasket leaking oil into cyl #1. Or it could be ovalized cylinders... either way, the head has to come off, right?

Is there any advantage to taking a look inside with a boroscope?
Don't bother - at least not yet. Do the compression and leakdown tests - these will reveal much to determine the next course of action.

BTW the exterior leaks you describe are common as spit on these cars. $150.00 will pretty much freshen up the whole lot of exterior seals for sensors/senders, turbo drain, oil pan sub-pan, vacuum pump, valve cover and the whole lot on the injection pump (crankcase to IP, bottom cover of IP, side cover), etc.

-BH
 

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She's ain't oil tight underneath, that's for sure!

The rear main is starting to show signs of leaking, but again, no drips.

I thinking more and more that the leak is internal. I've been reading on various forums that there is an issue with the front oil passage of the head gasket leaking oil into cyl #1. Or it could be ovalized cylinders... either way, the head has to come off, right?

Is there any advantage to taking a look inside with a boroscope?
that sentence made no sense.

you mind as well find a set of rebuilt heads because after 10years i'm sure their f*cked. the rear main will be a PITA to do and once they go pretty quickly.

no, just remove the heads.
 

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that sentence made no sense.

you mind as well find a set of rebuilt heads because after 10years i'm sure their f*cked. the rear main will be a PITA to do and once they go pretty quickly.

no, just remove the heads.
Benznoob,

While he may yet have to take measures to this end, pulling the heads would only really allow access to a potentially leaky head gasket. If it's the bottom end, the whole engine needs to be stripped and built back up again. The 3.5L heads and gaskets don't generally go bad on this motor (very few reported head cracking or gasket blowing events). I continue to advocate for having a dealer perform the cylinder compression and leakdown tests to ascertain root cause - the dealer may yet be compelled to cover all or most of the cost if it proves to be connecting rods after all with their own tests confirming it.

-BH
 

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Benznoob,

While he may yet have to take measures to this end, pulling the heads would only really allow access to a potentially leaky head gasket. If it's the bottom end, the whole engine needs to be stripped and built back up again. The 3.5L heads and gaskets don't generally go bad on this motor (very few reported head cracking or gasket blowing events). I continue to advocate for having a dealer perform the cylinder compression and leakdown tests to ascertain root cause - the dealer may yet be compelled to cover all or most of the cost if it proves to be connecting rods after all with their own tests confirming it.

-BH
The heads haven't seen oil in 10 years, which is more than enough time for the rubber to deteriorate. they're meant to be lubricated by the oil. half the systems in the car will be messed up from sitting so long. that's why it's smarter to buy a car with more mileage than one that's been sitting forever.
 

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The heads haven't seen oil in 10 years, which is more than enough time for the rubber to deteriorate. they're meant to be lubricated by the oil. half the systems in the car will be messed up from sitting so long. that's why it's smarter to buy a car with more mileage than one that's been sitting forever.
I missed that bit about 10 years sitting up. To be sure, a rather extensive repair list is to be expected.

To the OP, sorry mate, you may have run out of luck on this one.

-BH
 

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Discussion Starter #15
well, looks like I might have worried for nothing. During the last 500 kms, she hasn't burnt anything from what I can tell. I guess I'll be check the oil level every fill up until she goes into storage.

I've got other things to resolve, but i'm pretty happy about this!

one thing - car hasn't been sitting for 10 years - maybe 3 at the most.
 

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well, looks like I might have worried for nothing. During the last 500 kms, she hasn't burnt anything from what I can tell. I guess I'll be check the oil level every fill up until she goes into storage.

I've got other things to resolve, but i'm pretty happy about this!

one thing - car hasn't been sitting for 10 years - maybe 3 at the most.
Yatzee,

Glad things worked out for you - 3 years is long but not ridiculous, if a seal leaks it was probably due for R&R, just keep an eye on the usual spots for oil leaks and anticipate the valve seals will be due at the next opportunity.

Good luck.

-BH
 
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