I followed these when I was purchasing my own S Class. These are some very good tips and things to look for. The Cars are great but remember that you will spend some big bucks because these were the flagships of Mercedes in their days. BTW, what everyone says is that these were the best large cars produced by MB. And they are right.
Good Luck.
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Older S Class Buying Tips
As with purchase of any used vehicle it is buyer beware. For every legitimate, honest person or dealer selling an automobile there is an equal and opposite willing to bend the truth and fudge reality. We trust you will find us in the former category.
Many times there are cars that are lower priced. You usually get what you pay for. Unfortunately some also charge more and do not give the full value that the price reflects.
Below is some information that may be of assistance when looking to purchase a W 126 Mercedes-Benz, aka Mercedes Flagship Models like the 560SEL and 560SEC.
8-Cylinder
The 8-cylinder engines are by far the best suited for this heavy car. They offer great comfort, performance and versatility but at a price of higher fuel consumption. In the long run the longer lasting, more durable V8 will probably save you money and provide better enjoyment.
The new V8's introduced starting in the fall of 1985 have proven to be quite reliable with the versions starting in the fall of 1987(1988 Models) being highly recommended. It is common to go several hundreds of thousands of kilometers without problems.
The 420 starting in 1987 is recommended over the previous version. There is a disadvantage to the 420 in that it does not have the acceleration stabilizer mounted on the rear axle like the M117 (500 & 560) series so it has a tendency to 'squat' on take-off especially in the more powerful post 1987 version.
The 5-cylinder 350SD has a tendency to develop cracks in the cylinder head. The 6-cylinder version offered after 1985 is a much better choice.
The 380 version until 1985 has a tendency to wear out their camshafts quite early.
Engine
Most of the engines in the 126 series have a tendency to sweat a little which is quite normal and nothing to be afraid of. Valve cover seals can dry out over the years allowing small amounts of oil to escape.
Can a slightly slipping sound be heard ("chechecheche") with an opened hood and a running engine? The sound comes from the pulley and drive belt system and is quite harmless. Usually it is the alternator that shows some wear, but that does not mean it is worn out at all. A good test is this: If the engine is running, the red battery indicator light should be off. If the light keeps burning, the alternator may be broken or the contact between the alternator and the battery is disconnected. The light should not burn faintly either. If this is the case, one of the diodes in the generator might be defective. As a result the alternator will provide a current that is too weak and the battery will be drained during use. If you want to be completely sure, test the alternator while the engine is idling: Switch on some power absorbing features like the high beams, the heater, rear windshield heater, seat heaters, etc… Now measure the voltage between the plus and minus poles of the battery with a voltmeter. If the voltage remains below 12 volts, the alternator or the battery is defective. Check the state of the battery: is it older than 3 years? Does the capacity of the battery match the prescribed capacity in the owners manual of the car? Please bear in mind that a bad battery is no reason not to buy the car. It is a reason to adjust the price of the car.
If leaks in the neighborhood of the engine exhaust manifolds are audible, than the exhaust manifolds or the manifold seals may need replacement.
If a ticking sound can be heard when the engine is cold and if that sound goes away when the engine has run for a while, the hydraulic valve clearance compensators are usually the cause. If the ticking does not go away, then the camshafts are likely to be the cause. Because of the timing chain there are no timing belt problems. The very durable double timing chain does have a maximum life span, though. When in use for over 200,000 km(124,000 miles) the chains can stretch a little, causing synchronization problems between the camshaft and the crankshaft.
Cars that have been parked or stored for a long time often develop leaking water pumps. Usually the gaskets have dried out and do not seal properly anymore as a result. It is important to observe the water pump when a cold engine is started. Usually the gaskets reseal themselves when they are in use again, but replacement might be necessary. One look at the coolant expansion tank (or in the radiator when the car has no expansion tank) can reveal leaks in the cooling system. This does not mean that the water pump is at fault. Very often, the gasket of the expansion tank cap is at fault. Replacement is cheap. It is also important to feel around the water hoses: The hoses are threaded on the inside, surrounded by a black rubber layer. It can happen that the threading underneath this black rubber layer has burst open. In that case, the hose is no longer watertight. Other causes of coolant loss can be determined by looking at the exhaust:
Exhaust fumes white with cold engine: Everything okay. Just condensation.
Exhaust fumes white with warm engine: Pull over and carefully (!) open the cap of the coolant expansion tank. Do you smell exhaust fumes? That can indicate leaking cylinder head gaskets (rare) or a cracked cylinder head (very, very rare).
Exhaust fumes are blue: Only after a cold start? Not that bad. The valve stern seals tend to dry out over time. If oil consumption gets too high, you might want to renew the valve stem seals. A cracked cylinder head is very rare - in that case you might also notice cooling fluid mixed in with the engine oil (check with dipstick).
Exhaust fumes are gray to black: The air/fuel mixture is too rich. Wrongly adjusted engine or a very dirty air filter that needs (very urgent) replacement. Also test the fuel injectors.
Cars that have been stored for a long time or that have driven many short stretches are prone of having defective or leaking exhaust systems or flanges. This is caused by the residue of sulphur, one of the ingredients of fuel: In every engine and exhaust system that is left to cool down, condensation will form. This condensation disappears when the engine is in use again. If the engine does not get hot enough to remove the condensation, the sulphur residue will chemically react with the condensation water to form an acid. This acid will corrode the exhaust system.
A good indication of the state of an engine is an engine compression leak test, but does it say anything about the future of the engine? Regrettably it is not possible to look inside the engine. The exact life expectancy of an engine cannot be determined, but do not fear: The life expectancy, especially of the V8, is very long. Distances of half a million kilometers and more are not uncommon at all, almost as much as that of an average truck! There is a simple test to check whether the engine has compression leaks: With the engine idling, carefully remove the oil filler cap and push it on with a finger. If the cap is pushed upwards slightly, then there is a pressure build up that is usually caused by a compression leak in the engine. A compression leak test is recommended in that case!
Automatic transmission
The automatic transmission should shift gently (no thuds when it changes gear, everything should go smoothly). If all gear changes are hard, then the problem usually has to do with the pressure modulator settings. We are entering a dangerous area here, though: When the gearbox is set too softly, the hydraulic clutch will wear out quickly, because the slipping will cause an excessive amount of heat build up. This can be noticed during an up shift, when the engine revs up a little while shifting. If the gearbox is set to firmly, the load on the drive shaft and the rear differential will be too high. In this case, the road to the MB dealer should not be avoided: They will adjust it within minutes for a minimal fee. If the gearbox only thuds at some shifts, for example from 3 to 4, then the internals of the gearbox may be worn out. Automatic Transmission repair is usually very expensive and a replacement transmission can cost you as much as used compact car.
Rear Differential
Some of them develop a whining noise, indicating wear of the differential gears. This wear generally doesn't mean that the differential has become unusable. It is more important to visually inspect the differential housing. Most have the tendency to sweat quite a lot, not really a problem. If they leak, then the sealing rings need replacement quickly to prevent the oil level from getting too low. If the rear differential runs dry it can lock up during driving, causing complete destruction of the differential. This in turn can cause hazardous situations and even a serious car crash!! The oil in the rear differential housing generally is not being replaced anymore (against maintenance schedules) these days. When the sealing rings need replacement it is the ideal time to change the differential oil as well.
When a trailer hitch is present, inquire whether the car has pulled heavy loads. If it has, you should not buy it. The drive system (especially the automatic transmission and the rear differential) has been taxed heavily.
Wheels
Do the tires show regular wear? If not, the balance or alignment of the wheels may be faulty. In this case, get the car rebalanced and realigned as soon as possible. Also check the bearings and ball joints for play. These parts are heavily taxed by a heavy car like the 126 (especially the V8).
Steering
If steering play is encountered during the test drive (something many of the V8 have because of their high weight then do not worry: The power steering system is of the circulating ball type, like many trucks have. The play can be simply corrected by adjusting a set screw by any MB shop. Whether the play can be corrected by adjustment can only be determined by measuring the friction in the center range of the steering wheel. If the friction is too high, an expensive power steering system change is unavoidable. Stay clear of cars with extremely wide tires. Power steering systems of these cars are usually history.
The power steering pump is also prone to leakage. Usually this is recognizable by large amounts of oil residue present around the pump. Be sure to check the oil level in the pump reservoir.
The height of the rear end of cars with self leveling suspension is usually a bit lower, but this can usually be adjusted quite easily. A level controller is connected to a torsion bar on the rear axle by means of a linkage. In most cases the level controller is at fault, but not always: The level controller is equipped with a damper that works as a delay system. This delay system prevents that the suspension reacts on every little pothole that is encountered, only the ride level needs to be kept. Also: cars with self leveling suspension usually have weaker rear springs in order to improve that function. The level of the hydraulic oil in the expansion tank should always be checked.
Be careful with hydropneumatic suspension: It is very comfortable and it gives a smooth ride, but this maintenance free system tends to develop leaks when ageing. Traces of wear on the suspension bellows unavoidably point towards expensive repairs. The conventional suspension of the 126 is well balanced and therefore generally operates without problems, that is why we advice against hydropneumatic suspension.
Brakes
Check the braking system thoroughly: The brake disks and pads are usually well worn. All cars with ABS, the rear brakes tend to wear out more quickly, especially on the more powerful V8 versions.
Body/Corrosion
These cars are notorious for having problems with the clear coat. If you do not know what to look for or how to check the clear coat take the car to a body shop for inspection prior to purchase. It can look a lot better than it really is. Problem areas are along the roof line right by the drip rail and anywhere along edge of rear window seal. Look for discoloration in paint, usually a clear or milky color rather than the color the car should be.
Be careful with corrosion: cars of the first series did not have as effective rust proofing as the second series (after fall 1985). Because of this fact is it difficult to determine specific weak spots for this series. Generally speaking these cars should be checked thoroughly, especially at the jack supports and the wheel arches. It speaks for itself that the few weak spots of the second series can also be found on the first series. The second series received additional zinc coating and are well protected. In fact, the 126 series still outperforms many younger cars when it comes to rust-proofing. Often, rust spots on the second series are proof of bad workmanship on bodywork repairs.
Known weak spots:
1. C-pillar, inside, where the chrome trim ends. There are usually small rust spots visual.
2. Rear windshield. Both above and underneath the windshield rust spots may be visible. Especially underneath, where it is difficult to detect. Immediate rust proofing is usually needed in this area. Also watch out for chrome trim on the wheel arches. When you remove the trim, you are likely to find rust spots, paint damage or parking dents. As with all cars, the underside of the doors should be checked. It is common that moisture can make it's way into the door. The water should be able to escape from the bottom of the door through special holes. These holes tend to get rusty, especially when they get blocked up by dirt and debris.
What is the condition of the trunk area?- Is it damp inside? When the trunk is damp the rear windshield seals may be worn, enabling water to enter the trunk via the rear windshield. Also very important: Be sure to remove the spare wheel and check whether the spare wheel storage area is undamaged. Many workshops tend not to repair damage to the storage area because it's hidden out of view anyway. Also check the air vents in the trunk.
The door holders, especially those at the rear, are also one of the shortcomings. If they make a clacking sound when opening or closing the door, they need replacement. When replacement is postponed too long, the door can get stuck when it's open! If the door holder is unpainted (brass colored), then it has been replaced before. Usually the door holders are repainted to match the bodywork again, but this is a purely cosmetic action.
Is the width of the seams between body panels, engine hood, trunk lid and doors equal? When they're not, leave the car alone. Usually this points to badly repaired body damage. When comparing the width of the seams, you can compare one side of the car to the other side. The doors can be misaligned a bit, but that is quite rare. Be sure to check the door hinges for crash damage (in case of doubt, consult with a MB workshop).
One should also place the paint under some scrutiny. Does the quality of the paint job match the mileage of the car? Are there discrepancies in gloss, tint or (with metallic paint) the number of metal particles in the paint? Usually a sign of repainting. Was it repainted because of accident damage? If the selling party appears to be ignorant to that fact or if he denies such events, then gently tap the various metal parts on the part in question and compare the sound with parts on the opposite side of the car. When the other side sounds more massive, there could be some priming work present, indicating an accident repair job. It is much more difficult to detect repairs if new body parts were installed (for example the trunk lid). Be warned that paneling from non-MB sources is usually not of the best quality: They're cheap, but also made of a thinner, lesser quality steel and therefore more prone to rust.
Interior
In some cases the thin flexible B-pillar covers may come loose at the edges. This is not very problematic. Just remove the pillar and glue the material back into place. More problematic is the quality of the dashboard panels in blue interiors. The solvents used to keep the plastic flexible show their age: The plastic will shrink, causing tears in the dashboard plastic. This effect is barely seen with other interior colors and therefore not a significant threat there.
Cars that have been exposed to high outside temperatures usually show this fact on the wood decoration: Both the versions with zebrano (a tropical wood) and burl wood are made up of several layers. The base is an aluminum strip on which a thicker wooden base is attached. On top of this wooden base the zebrano or burl wood is attached. This strip of veneer is covered with several layers of transparent varnish. The background of this construction is passive security: The aluminum strip will prevent the wood from fracturing during collision impact. (MB actually crash tested the wood lining of glove box doors). The drawback of this construction is that the materials work separately from each other during changes in temperature, causing fractures in the wood (generally only the door panel inlays and glove box door inlay). This effect gets worse as wood tends to dry out and shrink with age. Price of the wood parts should not be underestimated. The 126 does not have any nonfunctional switches in it's center console, therefore there is a large number of center console wood layouts, dramatically increasing the price of this part.
Options
Check whether the air conditioning works. If it doesn't function, most workshops in most countries may only refill the air condition system with FCKW-free coolant (R134a). When the outside temperature is low, the air-compressor will only work the windshield defroster (switch to upper setting on non-climate control cars). If the compressor cannot be switched on via the windshield defroster switch, the air-conditioning system may have developed leaks. When the system pressure gets too low, an emergency switch will shut it off automatically. Because of it's typical construction, the automatic climate control version is not without problems. Replacement of a control unit can get expensive, other than with normal air conditioning systems. We therefore prefer the normal air-conditioning rather than the automatic climate control. The 126 system will shut down the compressor when the selected inside temperature can be reached and maintained without using it. The automatic climate control in the 126 controls the blower settings as well. This means that in cars with automatic climate control the driver and passenger can only select a certain temperature zone for both, allowing only a small margin between left en right temperature settings.
Do the power door locks including fuel cap lid lock) function correctly? In many cases the air pressure controlled system has air leaks. In these cases the air compressor will continue to run a bit longer after the locking or unlocking process has ended. Be sure to check all the door locks, and the trunk lid lock. The central locking system can be operated from the left door lock, the right door lock and the trunk lid lock. This means that once one of the locks is operated, all other locks should open or close. Note: the trunk lid lock can be excluded from this list by turning the key in the other direction (prevents theft from the trunk of the car, for example when waiting for a red traffic light).
You should be able to operate the slide roof (without tilt function on the first series) without any squeaking and cracking sounds. You can also check the functioning of the small spoiler in the slide roof: Does it spring up to the right angle when the roof is opened and does it retract correctly when the roof is closed again? Problems with the slide roof can be prevented by regularly greasing the components of the roof, something that is commonly overlooked during maintenance sessions. Also, the slide roof motor should switch off when the roof is closed. If it doesn't, the shut-off moment of the motor can be adjusted with a set screw. The motor is located behind the trunk lining on the left. Cars with dark paint colors often have small scratches on the slide roof. This scratching is caused by a sound insulating mat in the roof. In dark cars, this mat can deform when the car is exposed to high outside temperatures. Solution is to loosen the roof lining and cut the mat back to size - done. It is a job that takes some time, however.
When operation of the temperature selectors does not produce any results or the heater works indifferent from the chosen temperature, the cause may well be a defective or blown fuse. In any case, the source of the problem must be found. There is a possibility that heating problems are caused by torn membranes in the heating duo valves. Parts can be expensive, as the membranes can no longer be ordered separately from Mercedes-Benz. In many cases, one has to replace the complete valve.
The electric sun screen for the rear windshield usually doesn't work. Repairs are labor intensive because they can only be made after removing the complete package tray.
Testing the power windows: Do they operate without any knackering sounds? When they go a little slow in the upper part, do not worry. That is normal. Some 126s have been modified to reduce wind noise during driving: The window frame has been bent inside slightly, that's no problem. MB workshops did it themselves as well.
Airbags
At the B-pillar or in the glove compartment lid there is an airbag tenability sign. After passing of this date, the airbag(s) should be tested and, if necessary, replaced at a MB workshop. Mercedes-Benz has lengthened the tenability period though. They stated officially: '...with the present state of affairs, the period during which the correct operation of both driver and passenger side airbags will function reliably can be raised to 15 years. Mercedes-Benz has therefore increased the tenability date for all vehicles that were built before January 1992'.
Sometimes the mechanism of the ignition key lock can deter to a state where the key can no longer be turned easily. Heavy key chains that have hung from these locks for years are usually the cause of these problems.
Prices
The price list books used by car dealers, are generally speaking of no use, when determining a valid price. Reason: The price in these books is based on average dealer trading prices. Good W126 cars are barely sold through car dealers these days. Most change hands between owners directly. Cars that are sold by car dealers - especially the brand independent ones - are generally speaking of low quality. This causes the list prices to be low. It is therefore a tough question to answer: What should I pay for a W126? The selling price is usually a combination of what the seller wants to get and what the buyer wants to pay. The most important question you should ask yourself is:
"What is the car worth to me?"
Whether the car in question is the car for you, you should be able to answer using this document. And: When the car is really in a good state, one can be reassured that it was worth paying the extra money for it. So be sure to look at the quality of the car with a critical view!
It is not possible to produce a general value for these cars. Unlike the Volkswagen Golf, these cars are in too short a supply to speak about a 'general value' or a 'general state of maintenance'.
Rare Options
And: Most 126s that are supposed to have 'full options' usually have not. Here is a list of some of the options to look for:
Trip Computer-Is in the place where the tachometer usually goes. The tach moves into a small upper spot on the left dial.
Power Rear Sunshade
Headlight Washers and Wipers
Bucket Seats Front and Rear in the 4-door (Saloon)
ASR (Automatic Slip Control)
Automatic Locking Differential
Fire Extinguisher
Hydropneumatic Suspension (Pull Switch beside Headlight Switch with 3 settings)
Auxiliary heater (Located in center of console below ashtray
Amaretta Upholstery
Two Tone Horn (switch below ashtray)
Heated Seats (Front and Rear)
Lockable Tray under Armrest
Featured Mercedes-Benz 1988 560SEL
