The Quirks of the Mercedes-Benz 420SEL
During the 1970s, Mercedes-Benz was scrambling to ensure that it remained the leader in luxury sedans by designing its next S-Class generation. The company wanted to create a model with an improved ride, better handling, and improved fuel efficiency. In 1979, it formally introduced the W126 and its model-variants at the International Motor Show in Frankfurt, Germany. One of these variants was the long-wheelbase 420 version known as the 420SEL.
Common W126 quirks
The 420SEL was just one of the model-variants of the W126 released by Mercedes-Benz in 1979. Its German engineering has made the W126 a classic S-Class model with a twelve-year production run. But, it has also acquired a few quirks that its owners have learned to deal with.
For instance, W126 owners know to close the rear vent during the winter because it will always blow cold air, even with the heater turned on. They also know that the bounce test isn't a good indicator of how worn out their car's shocks are since the W126 model-variants aren't as springy as sedans from other brands. Instead, they will examine the shocks for any leaks to know if they need to be replaced. Finally, they know that they need to regularly clean the contacts between the seats and window switches so that they work all the time. Otherwise, this switch will work at odd intervals.
Difficulty with cold starts
The Mercedes-Benz 420SEL itself has had an issue with its fuel distributor. It may sometimes refuse to start cold even if it will fire up with a little gas and some backfiring. Despite cleaning the cold start valve with a cleaning solution, the fuel distributor may still have a hard time cranking up.
To solve this, 420SEL drivers need to ensure that their overall fuel mixtures aren't too lean as this can give them some trouble starting. Then they need to make sure that the cold start valve is getting power and ground when the motor is being cranked. The valve only works for up to 10 seconds when the motor is cranked while its cold, so make sure that it isn't spraying fuel out instead.
FAQs—Mercedes Benz 420SEL
My Mercedes Benz 420SEL overheated twice yesterday, and I'm determined to prevent that from happening ever again. How can I make sure of that?
It is not unusual for cars with high mileage to suffer from overheating. This is due to the fact that the factory engine parts as well as that of the cooling system have all gone old already. When temperatures climb beyond the normal range set for a particular engine, for whatever reason, overheating can happen anytime. The main reason of overheating is the failure of the cooling system to absorb and dissipate the excess heat produced through combustion. It can be due to coolant leaks, poor air flow, slipping fan clutch, loose water pump impeller, defective radiator cap, inoperative thermostat, or deposit in the water jackets. Even if the defect is only one from among these, engine heat can choke up.
Regular maintenance should save you from the hassle brought by overheating. When you do the check on a religious basis, you will be able to anticipate problems. Subsequently, you will easily single out the cause and have a replacement come handy already. Also, never settle for substandard replacement parts for your engine to reach higher mileage.
How bad will overheating affect the engine? Are the effects still reversible?
Seasoned drivers can easily single out a problem when any signs arise, enabling them to immediately provide the solution. But because of lack of experience, newbies fall into the trap of having to handle problems caused by earlier problems, which eventually lead to more serious problems like overheating. The consequence starts from detonation, followed by rattling, pinging, and then losing power. When it continues to detonate, the vital engine parts such as the rings and bearings will begin to suffer damage. Pistons may also swell as temperature spikes up, subsequently scraping against the cylinders.
Ill effects of overheating can reach the exhaust valve, creating scuffs in their guides and finally to loss of compression. Furthermore, thermal stress can swell the parts that are made up of cast iron and aluminum, like the head. This results in blown head gasket and then coolant leak. The overhead cam can also seize and break. And, of course, since the cooling system is directly connected to the engine, the steam going through it can damage the hose and old radiators with plastic end tanks. When major engine damage is severe, costly engine repair is your sole hope.
How do I know when my Mercedes Benz 420SEL head gasket is leaking?
A leaky cylinder head gasket shows no visible external leaks, but you will be able to notice white steam in the exhaust upon restarting or when idling. To confirm any suspicion, you can diagnose the problem by pressure testing the cooling system or through the use of a block checker. The latter uses a cylinder that has a special blue colored leak detection liquid that will turn to green when it detects combustion gas in the coolant. Also know that the head gasket leaks when engine oil is mixed in the coolant and vice versa. When the problem is confirmed, do not settle with fixing the leak with a sealant. Have a replacement always handy, so you can immediately replace the damaged head gasket.