Buying review Mercedes-Benz SL (R129) 1989-2001 Common Issues Inspection Engines

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Hi everyone, today we get to talk about one of the most beautiful convertibles of the 90’s, at least in my eyes. This Mercedes-Benz SL with the internal code R129.

Back in the day this car was the choice of business people, people with gold in the mouth and your local night farmacist.

We will see what to look out for when buying such a car second hand, it is worth it to own one nearly 2 decades after they went out of production.

First some history.
The car was built between 1989 and 2001 which was quite a long time.

Mercedes had some nice engines available for this SL.

Overall built quality is quite good, this car comes from a time that Mercedes was still quite over engineered, one of the last old school Mercs.

Engine wise there where the following choices;
When being introduced in the late 80s there were three choices.

There was a 300 SL with the M103 engine, this was a 3 liter inline 6 with 12 valves that produced 188 HP. The layout of the engine was a single overhead camshaft engine.

There was a 300 SL with the M104 engine, this was the 3 liter inline 6 with 24 valves that produced 228 HP. The layout of the engine was a dual overhead camshaft engine.

Top of the line was a 500 SL with a 5 liter 32 valve v8 that produced 322 HP. This was the M119 engine. July of 92 saw the introduction of the 600 SL with a 6 liter 32 valve v12 that produced 389 HP.

There was a choice of 5-speed manual or 4–5 speed automatic for the six-cylinder cars; the V8 and V12 could only be ordered with a 4-speed automatic gearbox. Late 1993 Mercedes-Benz rearranged names and models, the 300 SL was replaced by the SL 280 and SL 320.

The 280 had an inline 6, 2.8 liters big with 24 valves and dual overhead camshaft layout that produced 190 HP. The 320 had and inline 6, 3.2 liters big with 24 valves and dual overhead camshaft layout that produced 228 HP. The 280 had a manual transmission, the SL 500 and SL 600 continued in original form.

Most top of the line SL-models had the 4-speed torque converter auto 
There was a second facelift in late 1998, there was new external mirrors, new 17″ wheels and new bumpers also Mercedes added new engines to the line-up. Starting with the Sl 280, the inline 6 was replaced by a v6 with 18 valves in single overhead camshaft layout, the engine was2.8 liters big and produced 201 HP.

The SL 300 was a v6 with 18 valves that produced 221 HP and an SL 500, a 5 liter v8 with 24 valves that produced 302 HP.

Engines codes for the SL are the following;
SL 280 has the M112 with 2.8 liter displacement.

SL 320 has the M112 with 3.2 liter displacement.

SL 500 has the M113 with 5.0 liter displacement.
The V12 engine remained unchanged.

Enough about engine, engine codes and power output, lets focus on the weaker points of these cars;
The control-unit of the convertible roof.

The heaters of the seats

The electronic adjustments of the seats

Leakes of the valve cover gasket

Leakes of the power steering pump

Shock absorbers will wear and tear

Engine will sometimes hold back on the power, this could have multiple reasons all off which would be registered in the cars ECU

Sometimes the wire harness of the car could digest over time and so did the engine isolation.

The SL 300 with the 24 valve engine is prone to more valve head gasket problems, especially if the car was often driven for small distances or the previous owner saved money on maintenance. Always check if the convertible top functions properly, and check the breaks on the car.

This car has quite some performance and is quite heavy. Some engines use oil, so keep on eye on that as well. Using oil is always better then losing oil.

Most performance engines use some oil from time to time.

In some cases owners reported oil loss on the cardan shaft, but this issue does not only occur with the SL300 24 valve.

The Six-cylinder cars probably the most sensible. 

All these cars came with a standard, lift-off hardtop which is a two person job to remove. Instruments changed from mechanical to digital in 1996.

Best pick is probably the 224 bhp 320SL V6 from June 1998 with 5-speed automatic transmission. There were several limited editions, the first from June 2000 with 18″ six hole alloys.
Other weaker points of this SL;
Automatic gearbox prone to change gear on corners when you don’t want it to.

Hugely better replacement with electric folding hard top arrived early 2002 (and promptly sold out).

Watch out for the following;

Cars with doubtful pasts in the trade: Left Hand Drive to Right Hand Drive conversions. Clones. Cancelled Far East Export orders etc.

Check carefully for repaired body damage. Look for rust at the bottom rear sides of the hard top. Furthermore make sure the aircon blows cold.
Never buy a convertible with the hardtop fitted and no chance to check out the hood operation and the hood itself for mould or tears.

This car needs full oil changes every 3000 miles and the oil must be synthetic in nature. This figure is based on research i have done on this car. I am sure its a precautionary measure.

Most of these cars are used in the summer and are not daily drivers no more, so just change the oil after the summer season, regularly check the oil level.

The R129 SLs have very complex electrics, so the older the car is the more likely these are to be flakey due to moisture ingress, breaking down of insulation, etc. 

Best to buy as late year as possible.
Report of intermittent electrical problems with 1996 R129. 

Some report trouble with the SRS warning light on the dashboard, during this the wipers and the soft top motor dont work. Problem lays probably in the Signal Acquisition Module, or SAM in short. Every Mercedes specialist will have the tools to discover the origin of the electrical gremlins, these cars are potentially 30 years old so cables might be digest over time.
There are lot of enthusiasts for these types of cars, the faults and potential weaker points are well documented. For the sake of this video we reviewed the most frequently reported issues.

Many owners of these cars share their ups and downs on forums online, this is a great resource for tips & tricks during ownership of this SL.
Do your research before buying this Mercedes, for that you came to the right source but do a second opinion at an independent Mercedes specialist as well. These cars are potential money pits but overall built quality is from a time that Mercedes had a great reputation.

As said earlier on of the last old school Benzes that were built for life.

Hope this buying review was useful, if so, subscribe to my channel for future reviews.

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