Looking at 1986 300SDL - PeachParts Mercedes-Benz Forum

cmbdiesel · #1 10-15-2013, 07:49 AM

Looking at picking up an 86 300SDL.
Car has been sitting for a couple years.
Are there any chassis issues which would be different from a 83SD? (have one of those, pretty familiar with what to look for)
This vehicle should have the 603.961 engine?
Are there particular things to be looking out for with this engine?
Any tips on discovering these issues when checking the car out?

Thanks,
cmb

vstech · #2 10-15-2013, 08:21 AM

aside from the engine/transmission differences, the car is VERY similar to the 83, the hood opens with a center tongue pull instead of the two latches behind the grille, the rear subframe is COMPLETELY different, nothing but the calipers/rotors will interchange with the 83.
the front brakes are different, bigger, better.
dash has some changes, and the climate control pbu is changed, as is the sunroof control, and the window buttons are different...
I'm sure there are other changes, but they'll be minor...
oh yeah... the back doors are about a foot longer!

daw_two · #3 10-15-2013, 10:45 AM

Once you drive, listen, enjoy a 300SDL, you won't take your 300SD on a road trip anymore. I don't recall your height/weight dimensions, but I really enjoy SDL time --- I'm 6'2", about 210lbs.

cmbdiesel · #4 10-15-2013, 12:31 PM

Quote:

Originally Posted by daw_two

Once you drive, listen, enjoy a 300SDL, you won't take your 300SD on a road trip anymore. I don't recall your height/weight dimensions, but I really enjoy SDL time --- I'm 6'2", about 210lbs.

6'4" and around 200lbs.
I think the kids in the back seat will be the big beneficiaries, especially the one behind Dad...

Do these have a propensity for shock tower issues? or other body issues?
Anything engine wise to be on the look out for?

daw_two · #5 02-06-2014, 11:42 AM

Quote:

Originally Posted by cmbdiesel

6'4" and around 200lbs.
I think the kids in the back seat will be the big beneficiaries, especially the one behind Dad...

I have plenty of room sitting behind the driver's seat when it is adjusted for me. If you really want to treat the kids to something special, look for a 560SEL in the junkyard with the reclining seat option and put that in your 300SDL.

OH. One more thing about an 300SDL. There's room enough in the back seat for a party.

vstech · #6 10-15-2013, 12:53 PM

body wise, they are pretty much tanks.
inspect the body for rust, but they are not known for that issue. the rear trailing arms can disintegrate from rust...

standard fare stuff on the engine, vacuum pump, fan clutch, belt tensioner, etc...

djustin973 · #7 10-15-2013, 01:11 PM

Once you go SDL, you'll never go back!

I'd say the only things to look out for are the rear control arms having a tendency to rust out, but they're not to bad to replace. There is also a chance that the guide rod mounts (does the 83 SD have those?) have rusted out. Many opponents of the 603 engine will say their heads are prone to failure if overheated but most SDL drivers agree that the issue is not as bad as some make it sound. My SDL has the head with a "bad" reputation and it is fine at almost 500K.

cmbdiesel · #8 10-15-2013, 01:31 PM

Thanks. I just did the trailing arm on the drivers side of my SD. PITA but not really that bad.
I'm going to watch the 603 engine starting video (Listen to this om603, tell me your thoughts.) when I get someplace I can hear it, just to get an idea what a 2 year sitting 603 might sound like.

vstech · #9 10-15-2013, 01:32 PM

yes, the front of the SDL is the same as the SD, except for the brake size.
the rear however, is quite different. more in common with the 124 than the 83SD... I'm not sure of the rear trailing arm scenario on it though. I do know that the SEC has a REALLY cool forged aluminum trailing arm setup that could fit in...

sixto · #10 10-15-2013, 02:23 PM

Quote:

Originally Posted by vstech

the rear however, is quite different. more in common with the 124 than the 83SD...

??? Parts might not be interchangeable but MB didn't change suspension philosophy on the 126 from '85 to '86. It's the same semi-trailing arm suspension with a pair of forward subframe bushings and rear attachment through the differential. Nothing at all like the 5-link and floating diff rear suspension of the 124. Maybe you meant the W140?

An original #14 cylinder head casting on a 603.96 is cause for concern, particularly in a car for sale or that's been sitting for a while. Is overheating the reason it's not a driver? Many live a long happy life but your purchase will cost you about $2500 more if the head turns on you.

There's the famous residual pressure test - press on the upper hose about 24 hours after the engine was shut off after getting to operating temperature. Resistance in the upper hose indicates residual cooling system pressure which usually indicates cylinder head cracks. Oil in the coolant reservoir might be a good sign because it will indicate a failed head gasket. Cylinder head cracks alone don't cause oil to mix with coolant. You have to trust that the seller didn't remove the reservoir cap before you pinch the upper hose. Small random coolant puddles under the engine also suggest excessive cooling system pressure as the system finds ways to depressurize when the engine is shut off.

Are you buying it as a runner or hauling it away? I don't think a non-runner is worth more than $1000 because of all the things you can't check like the transmission, AC, suspension, etc. And for $1000 it should have a great body and interior.

Are there service records?

Sixto
87 300D

chilcutt · #11 10-16-2013, 11:11 AM

Hopefully..it's color is dark Blue.

sloride · #12 02-06-2014, 11:07 AM

Quote:

Originally Posted by sixto

??? Parts might not be interchangeable but MB didn't change suspension philosophy on the 126 from '85 to '86. It's the same semi-trailing arm suspension with a pair of forward subframe bushings and rear attachment through the differential. Nothing at all like the 5-link and floating diff rear suspension of the 124. Maybe you meant the W140?

An original #14 cylinder head casting on a 603.96 is cause for concern, particularly in a car for sale or that's been sitting for a while. Is overheating the reason it's not a driver? Many live a long happy life but your purchase will cost you about $2500 more if the head turns on you.

There's the famous residual pressure test - press on the upper hose about 24 hours after the engine was shut off after getting to operating temperature. Resistance in the upper hose indicates residual cooling system pressure which usually indicates cylinder head cracks. Oil in the coolant reservoir might be a good sign because it will indicate a failed head gasket. Cylinder head cracks alone don't cause oil to mix with coolant. You have to trust that the seller didn't remove the reservoir cap before you pinch the upper hose. Small random coolant puddles under the engine also suggest excessive cooling system pressure as the system finds ways to depressurize when the engine is shut off.

Are you buying it as a runner or hauling it away? I don't think a non-runner is worth more than $1000 because of all the things you can't check like the transmission, AC, suspension, etc. And for $1000 it should have a great body and interior.

Are there service records?

Sixto
87 300D

Can anyone explain the residual pressure test? I would think that a crack in the cylinder head would relieve pressure, and not hold it for the 24hrs. Wouldn't the contraction of the coolant while cooling also reduce pressure. This is in reference to a 603.961.

sixto · #13 02-06-2014, 04:11 PM

Quote:

Originally Posted by sloride

Can anyone explain the residual pressure test? I would think that a crack in the cylinder head would relieve pressure, and not hold it for the 24hrs. Wouldn't the contraction of the coolant while cooling also reduce pressure. This is in reference to a 603.961.

I'm no metallurgist so this is a wild guess - cylinder compression expands the crack so compression gasses get into the cooling system. System pressure decreases as the engine cools but doesn't get to ambient.

Sixto
87 300D

barry12345 · #14 02-06-2014, 09:41 PM

Quote:

Originally Posted by sixto

I'm no metallurgist so this is a wild guess - cylinder compression expands the crack so compression gasses get into the cooling system. System pressure decreases as the engine cools but doesn't get to ambient.

Sixto
87 300D

Nein, Nein, Nein. Well maybe.

Actually you are mostly right.

Personally I think the coolant expands and contracts with temperature change in a linear fashion .. Any cylinder byproducts create a pocket of pressurized air. The air has to lose a lot of it's volume for it to drop pressure. It takes a far greater temperature change than our coolant systems operate in. Plus that only lowers the gas pressure a little.

It does not drop off signifigantly with just cooling back to ambient as the coolant has.

This is in the early stage of a crack where it takes considerable force to drive the by products through the crack. There is no pressure mechanisim to allow their return through the crack other than what the rad cap limit is.

Althrough there is Lots of pressure in the cylinder to force the cylinder by products out of the crack when running.

If the crack where advanced it would blow the coolant out of the system. Or/and allow back flow of the coolant into the cylinder.

So in my humble opinion the hard rad hose test is only for modest crack detection. Larger or more developed crack or cracks will look more like a head gasket failure.

As I said up front you are basically right. I just tried to clarify it a little being the crack acts as a one way valve until is gets bigger. Plus a volume of gas under pressure does not loose pressure as the coolant does for all practical purposes.

compu_85 · #15 10-16-2013, 11:18 AM

The iron head 5 cylinder cars had aluminum hoods and trunks. The 6 cylinder cars have "standard" steel body panels.

-J