Home > Project Cars > 1983 Mercedes-Benz 500SE W126 > 1986 Mercedes-Benz 500SE Part 1: Not for the Fainthearted

1986 Mercedes-Benz 500SE Part 1: Not for the Fainthearted


From 1979 to 1991, Mercedes-Benz produced the W126 series as its top-of-the-line Sonderklasse (Special Class or S-Class) model. It achieved several awards including the Wheels MagazineCar of the Year” in 1981; the U.S. Highway Loss Data Institute “Safest Passenger Car of the Year” in 1988 and 1989; the third-ranked luxury vehicle in J.D. Power’s 1990 Initial Quality Survey (IQS); and the highest customer ratings in the J.D. Power Sales Satisfaction Index in 1987, 1988, 1989, and 1990.

The W126 series became the most popular Mercedes-Benz S-Class and its 12-year production run was longer than any S-Class before or since. In fact, when its W140 predecessor was introduced in 1991, the W126 was produced for an additional two years in South Africa, which was a testament to its popularity in the export market. W126s have been prominently featured in films long after production ended while many world leaders of the time were driven around in a W126. Even today, many countries still use the W126 to transport their heads of state.

Wishing on a (Tri-) Star

In January 2013, we chanced upon an ad on Sulit.com.ph (now OLX Cars): “1986 Mercedes Benz 500SE (W126); Excellent paint, intact body; Cold aircon; Good underchassis; Newly tinted (dark tints); One click start; Nice interior; Ideal for collectors or enthusiasts; All electrical working even the sunroof; Registered 2012”. That this S-Class was being sold for the price of a used Japanese compact sedan compelled us to take a closer look.

The W126 as posted on sulit.com.ph

Viewing the 500SE on January 20, 2013

The seller, Don Christian Pecaoco, was a European car enthusiast and was quite candid about his car’s history and its issues. We saw some cosmetic and mechanical issues with his “young timer” classic Benz, which is one-of-2,351 500SEs produced in 1986, and we guessed it will be quite expensive to get it right. But we took the plunge anyway and negotiated with Don on a price that we were all comfortable with.  On January 23, 2013, we became the proud owner of a 1986 Mercedes-Benz 500SE.

Don Pecaoco and our 500SE on delivery day

Sonderklasse Einspritzung

For those who are unfamiliar with Mercedes-Benz’s model designation, 500SE stands for 5.0-liter (500) S-Class with fuel-injection (Einspritzung). Underneath the hood lies an aluminum-alloy single overhead cam (SOHC) 4973cc M117 V8 engine that produces 245 horsepower and 400 Newton-meters of torque, which are transmitted by a 4-speed automatic to the rear end.

In the February 1980 issue of Road & Track magazine, Motor Sports Editor Joe Rusz wrote that the 5.0-liter W126 “performs comparably” to the 450SE 6.9-liter W116, which was regarded as a high-powered “sleeper”. After a fast 240 km/h test drive on the German Autobahn with a 500SE, he declared that “the era of the high-performance luxury sedan is far from over.”

Back to Original

With all these accolades bestowed upon the W126, we decided to keep our 500SE as original as possible. But, first things first. On 26th of January, we freed the left rear wheel by having a sheared-off broken wheel bolt removed at YRS Motorcycle Modifications in Mandaluyong, which is owned by our good friend, Gregorio “Yoyong” Buncio.

Broken wheel bolt held the left rear wheel hostage.

YRS technician welds a lug nut to the broken bolt…

… but it sheared off when he tried to unbolt it.

He then decided to drill the broken bolt away…    

… until the lock broke off a freed the wheel.

On February 1st, we drove our 500SE to Yock’s Auto Electrical Repair Shop and Auto Supply along Roosevelt Avenue in San Francisco Del Monte, Quezon City, where we replaced the defective Japanese alternator with a reconditioned 90-amp Bosch unit. We sourced a surplus alternator mount (MB part no. 1171550735) and an upper adjuster bracket to replace the original parts that were hacked to fit the non-original alternator.

Electrical service of our W126 at Yock’s

Japanese alternator is not original to our German car.

Surplus-sourced alternator mount

The mechanic undid the bolts holding the adjuster bracket…

… and removed the old alternator and modified mount…

… to clear the space around front of the M117 V8.

The original alternator mount and the new Bosch alternator were installed …

… and the adjuster bracket was replaced.

Accumulating MB Parts

After these initial repairs, searching and accumulating original and authentic MB parts suddenly became our passion. Don Pecaoco, our 500SE’s former owner, sent us a Hirschmann automatic antenna (126 820 03 75), a spare MB fuel distributor, a third brake light from a W124, an original jack, and some original clips that were missing from our car. He even threw in an authentic Deutsch license plate.

We searched online and found a set of beige W126 floor mats that came off a 300SD and matches the tan interior of our project car. Upon installing the floor mats, we realized that the whole interior of our 500SE needed to be cleaned, restored and detailed.

We found a set of genuine MB floor mats from a W126 300SD.

The driver’s mat has a large “Mercedes-Benz” heel pad and Tri-Star logo.

Perfect fit on the passenger’s side and at the rear.

Keeping It All Bosch

We then tackled the mechanical repairs and endeavored to fit German-made parts and accessories to our German car. We installed a fresh set of Bosch Platinum Plus sparkplugs that slightly smoothened the rough engine idle. When its fuel pump conked out, we accumulated some Bosch parts before we took our Benz to Rangeland, which is owned by our friend, Roberto “Bobby” Jose.

We used a set Bosch Platinum spark plugs to tune up the M117 V8.

Trying a roadside fix for our 500SE’s broken fuel pump.

Our 500SE gets unloaded at Rangeland

In good company

In June 13, 2013, a brand-new Bosch fuel pump (0 580 254 911 – 390) was installed in our 500SE at Rangeland, where it was also given an oil change using a Bosch oil filter. The Bosch Europa horns and Bosch wipers were also installed but the Bosch engine ignition parts were not used because they were the incorrect parts.

Our small hoard of Bosch parts

Bosch Twin wipers

Bosch Europa horns

At the Bosch Service and Training Center, Round 1

A week after the installation of its new fuel pump and its oil change, the engine idling of our project car became quite erratic, hunting between 900 and 500 rpm. In June 28, 2013, we drove to the Bosch Service and Training Center along Chino Roces Avenue in Makati to have the Bosch K-Jetronic fuel injection system of our 500SE diagnosed and adjusted to fix the erratic idling.

To establish a baseline reading, Woodrow “Woody” Sinogbojan, automotive aftermarket technician and trainer of Robert Bosch Philippines, hooked our 500SE to their diagnostic equipment, including an exhaust gas analyzer with a sniffer hooked to the tail pipes. He found that the M117 V8 was running very rich, which fouled the spark plugs, caused poor performance, and produced high CO2 emissions.

Woody programs the Bosch FSA 750 engine analyzer

Exhaust sniffer attached to the tail pipes

1st tests showed Lambda (1.658), Hydrocarbons (3977 ppm/vol), CO2 (5.61%)

Once the engine cooled, Woody removed the spark plugs and inspected them. He installed a new set of Bosch spark plugs and high-tension wires, started the car, and then fiddled with the ignition distributor and the Bosch K-Jetronic fuel distributor using the analyzer to adjust the settings. The car idled smoothly, the Lambda and hydrocarbon particulates readings were lower but the CO2 emissions were higher.

Spark plug from cylinder #3 was wet while #4 was fouled.

Spark plugs on the other bank of the V8 were good.

New Bosch high-tension wires

Adjusting the fuel distributor

2nd tests showed Lambda (1.107), Hydrocarbons (2355 ppm/vol), CO2 (10.51%)

At the Bosch Service and Training Center, Round 2

Unsatisfied with the repairs, Woody asked us to return on July 1 to perform a compression test on our V8. Once we arrived, he first installed the new Bosch battery that we ordered, then cleaned all the electronic contacts and relays, checked the air filter and all the belts, and did some diagnostics on the anti-lock braking system (ABS) servo and control unit.

Brand-new Bosch S5 car battery installed

Woody then subjected our 500SE to another round of diagnostic checks before he conducted the compression test on each cylinder. After the test, we found that cylinder #3 showed a lower compression reading than the rest. Uh-oh. Is this the part where we’re looking at an insanely expensive repair bill?

Woody performs another set of diagnostics on our M117 V8

Printout of the Compression Test

Chemical Engine Cleaning

We sought advice from an expert on V8 engines, Lito Galvez of MSG Garage, who said the loose compression could be caused by something simple as sticky valves or gumming of gasoline deposits on the intake valves since our 500SE hasn’t been driven much by its previous owner. He suggested to try chemical cleaning first before worrying about engine repair expenses. We contacted Ricky Zulueta of BG Power Stroke, and after a few days, he arrived with BG General Manager Jay Tulao and technician Art Catahan to perform a “home service” on our 500SE.

BG performed a compression test to establish a base line reading.

They poured BG 109 Compression Performance Restoration into the engine…

… BG 44K Fuel System Cleaner in the fuel tank…

… and used BG Air Intake System Cleaner while the engine was running.

Our recently-installed Bosch oil filter looked dirty after all the BG chemical cleaning.

BG added MOA Engine Oil Supplement to help protect the engine.

They poured the Universal Cooling System Cleaner into the radiator hose…

… and flushed the radiator of sludge and rust.

Before and After

BG added a can of Universal Super Cool coolant for good measure

After the BG chemical engine cleaning services and after topping the vital fluids, the compression in all cylinders increased including #3 and the idling remained smooth. I was very excited to drive our 500SE, which was now running a lot better.

From One Workshop to Another

Sometime in October 2013, our 500SE overheated while stuck in light traffic. We found that the thermostat had stuck shut so we had it removed. It performed poorly again after it overheated and a friend, Kurt Hahn, offered to diagnose and fix the problem. Despite being a former authorized BMW Service Center, Kurt’s mechanics at Hahn Manila along Panay Avenue in Quezon City, got the Benz to run a bit better, albeit resorting to unorthodox fixes. Well, at least, it runs.

We weren’t confident with all the affordable, er… cheap fixes we did to our 500SE. So, upon the recommendation of Mercedes-Benz Club of the Philippines (MBCP) president Rene Nuñez, we had it towed to German Motors along Calle Industriya in Bagumbayan, Libis, Quezon City on January 22, 2014. At German Motors, Service Advisor Boy Cundangan carefully inspected our W126 and accomplished a Repair Order Sheet as we pointed out some areas of repair.

Flatbed towing to German Motors

German Motors service adviser receives our car…

… and inspects it thoroughly.

Finally, our project car was being fixed in a proper and professional MB service shop. What problems will they find? Will our repair bill be simply expensive or extremely beyond our reach? Will our idea of finding an affordable fix for an expensive car be dashed to pieces by reality? To find out, log in next week for the continuation of the restoration story of our 1986 Mercedes-Benz 500SE.