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Old 06-09-2001, 01:43 PM
Posts: n/a
I purchased a 1986 420SEL, with 260K+ miles. It appears to be idled very high. So far, I have replaced the air compressor, a side mirror and a few fuses. It starts and runs O.K. but yesterday, I discovered the turns signals no longer work. Can somebody tell me where, under the hood the turn signal flasher are located? The previous owner told me that a friend jammed the wrong key in the drivers door. I have to unlock the passenger side of the car before I can open the drivers door. By the way, the locks are electrical. I can turn the key to the right, but not to the left. The nearest dealership is 100 miles away and they are usually booked when I am off and they are closed on Saturdays. What other options can I take? The factory alarm is another story. Sometimes it goes off when I don't know it on. I'm still trying understand this system. I also need info on the front auxilary fan. Does it cool the radiator or something? To make it short, I'd appreciate any information regarding what to expect with this particular model with all these miles. I would like to prepare this car for a 800 mile trip. This is my very first MB and my first time joining your forum. Please advise. Thanks!

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Old 06-09-2001, 03:47 PM
Robert Boyer
Posts: n/a
in reply to Maustin: 1986 420 SEL MB


I have the same car, but an '88.

I would check the fuses carefully again. I have encountered that the fuses on a car of this age, particularly if the car has been sitting for a while, will be weak and brittle. Replace ALL the fuses this time. I'll bet this will rectify your signal flasher problem.

The driver's door lock problem will require a new lock cylinder assembly-which should be done in the shop.

The front auxiliary fan should kick-in above the 80 C mark.
If not, the sending unit needs replacement. Monitor what's happening and at what temp.

The fan cools the car under hot temps-particularly, with the AC on.

Other things I'd check before an 800 mile trip:

1. Tires: check, visually, for wear and any bulge points. If so, get at least 2 new tires, and rotate so that the new tires are on the front. Then,, have the pressures properly adjusted while the tires are cold. For a trip of this nature, I would suggest about 30 front and 32-34 rear - depending on load. Also, have alignment (which is 4-wheel) and tire balancing checked. The balancing - to be good, which is essential on a 126 car - should be on the car, which requires balancing by a Hunter machine. However, proper on-car wheel balancing will affect the pleasure and comfort of your long trip.

2. Oil: Have an oil change done. Change it while the oil is hot. I suggest that you pick up the oil filter yourself to assure it is the right one. Use 20W-50 weight oil. I suggest Castrol GTX 20W-50 on an engine with this mileage, while subjected to the rigors of a long trip during the hot summer climate.

3. Check for oil and trans leaks. If you have the time and inclination and a few bucks, resolve them before the trip.

4. Check visually and manually all the rubber exhaust hangers. There are 4 points on this car. Look underneath the car at the exhaust system: 2 are at the rear bumper, and the other two halfway in. If they are missing or brittle, replace them yourself. They are cheap enough-and can prevent a failure resulting in tearing off your exhaust system entirely.

5. Check the shocks. If the car bounces more than once, and you want a smooth well-controlled ride, get the spec Bilsteins for the car. I would suggest HD's on the rear-since this is an SEL.

6. Check all belts and hoses. If loose (more than 1/2 inch play) on belts or appear cracked, replace them. In short, I'd replace all belts and hoses with OEM quality items. A cheap insurance policy. While you're at it, get a duplicate set - and keep them in your trunk.

7. Battery. This car calls for a group 49 battery. Get one that is NOT permanently sealed, and check the water level in it. Make sure the cable terminals and connectors are not frayed. If so, replace them as well.

8. Have the radiator and cooling system flushed and refilled properly. Hot weather is your enemy.

If you do some or all of the above, you should have a good trip - hopefully, uneventful as to the car's performance. This is a great car - if you are prudent and care for it. Good luck!
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Old 06-09-2001, 04:26 PM
Posts: n/a
Well, Maustin...are you prepared to make a bit of an investment in your Tuna Boat! I jokingly refer to my '86 420SEL "business Blue, 90K" as the "Tuna Boat"

1st - Under the hood, directly in front of the Driver's seat in the fuse box....all should be labeled, that's where you will find your wiper/fuse/relay.

2nd - remember that you have bought a very large heavy sedan and with that comes all the trials and tribulations that are inheritant with the SEL class. i.e.,

ENGINE: Fairly bullet-proof but has a few bugs, such as the timing chain guides. They are notorious for being brittle, turning brown and breaking, resulting in a very expensive fix repairing the mutiple valves in usually takes out in the process! Consider these upgrades to help it's overall well-being: MB air filters changed religiously (K&N's don't impress me on this particular car), try Mobile1 synthetic oil for your next change, flush the radiator, get a decent battery (try for the latest ratings), consider TimeValve SS cat-back exhaust system as a replacement for your current system, but be aware that their welds are debatable at best ( just sloppy production work) be prepared to have to reweld questionable joints in the system! Remember, you have a combo cast steel/aluminum engine and things do "move" so watch for gasket leaks on various components!

SUSPENSION: Remember what I said about the TUNA BOAT joke?
Front-end work is a mainstain in revamping your ride! Upper ball joints, tie-rod ends, swaybar bushings,steering linkage & steering box leaks, shocks; all need to be attended to! Lower ball joints are a costly endeavour. The SEL ride can be improved in terms of cornering (the tuna boat wallow!) by using lowering kits and yellow Bilsteins but you will sacrifice that "sedan-type ride" !

BRAKES: Stopping such a heavy vehicle requires some serious braking, so be prepared for the following: rotors - warpage is their downfall, don't turn'em ever though MB says a certain minute amount can be, replace'em with ATE brand or whatever MB calls their OEM that paticular year! Pads -squealing is all to common! Once again, ATE pads or whatever OEM brand could benefit from having all right-angle edges chamfered, score the middle of the pad a hack saw and using only blue MB paste applied properly!

TIRES: To each his own on this topic, living in Montana, I use Pirelli P6000 Veloce 205/65 R15 92H M+S during the summer (love'um!) and studded whatevers during the serious winters! Others like the Michelins! Consider a four-wheel tire-on alignment from a dealer.

ELECTRICAL: God Bless German engineering! Talk about a wasp nest! Going to a dealer and having them plug in the Lambda tester for a seroius system goin' over is a good place to start! Self-diagnostics is another conversation in itself! Your original key should have a little red bump/nip on it that is indicative as the "main" key that sets the alarm, invest in a new dealer-ordered original key based on your VIN! Your locking system is a rather complex vaccuum system you will need to learn about.

Final words of advise!
KNOW YOUR SYSTEM, BE THE SYSTEM! INVEST IN THE SERVICE MANUALS! READ THEM! EDUCATE YOURSELF AND YOUR FRIENDLY LOCAL MECHANIC! Now that I got your attention via YELLING, the above is mandatory if you truly what to live and love your SEL! Shop wisely....nothing is "cheap" on this model,i.e., try FastLane (this site, )Ebay, Performance Products, etc. The MOST important thing I could possible advise you of is this website! Truly the most friendly, helpful, talented bunch of folks I've had the previlage of lurkin' around !
90% of all your questions you have or will have can be answered here by learning to navigate the past threads/replys/topics......I dare you to type in "420SEL" and spend the next two hours learning how to hate/love your tuna boat!
Trust me when I say I've only touched the surface of SEL info! Remember not to hold me responsible for the above info, opinions are like --------, everyones got one! ROTFLMAO!

Michael Best
Business Blue, 90K
TimeValve, Pirelli Veloce
Clear Turn Signals -Bosch

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Old 06-10-2001, 11:31 AM
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Join Date: May 1999
Location: New Location: VA Palo Alto HEALTH CARE SERVICES
Posts: 109

robert, ...harpman...

very productive post, ...thanks a lot.
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Old 06-11-2001, 10:53 AM
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Thank you! (1986 420SEL MB)

Thank you for the valued information! I have already began having all your suggestions looked into. There is another question I forgot to ask about. The dip stick to check the oil is bent slightly. Is this proper for this model? Remember, this is my first MB. Thanks!
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Old 06-11-2001, 11:06 AM
Robert Boyer
Posts: n/a
'86 420 SEL


Dip stick should not be bent; at least, mine is not, and none were on my other Benzes.

This might affect the level reading. If the others agree with me, then I think you should make certain you have the right dipstick. Check it out; then trust the reading. Good luck, again, bro!!! I'm planning my own 800-900 mile road trip for August-to go from Miami to the Outer Banks.
Getting the SEL set-up for the trip is more than half the fun!!!
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Old 06-11-2001, 05:26 PM
Registered User
Join Date: May 2001
Posts: 301
Unless you have verified proof that the Tchain guides were replaced within the last 100k miles (frequent oil changes) or 60k (infrequent oil changes)I would not start the car until the following has been done.

Go buy a valve cover gasket, take off one of the valve covers and check the color of the plastic guide. If it is some variation of white plastic, wonderful!!! If, on the other hand, it is a dark reddish brown, have the car towed to your favorite shop for a Tchain, tensioner and guides. Even if your guides are new you may still want have the chain checked for stretch.

Best money you will ever spend.

PS If you do need a Tchain job find a great inde shop, some places ask $1k+ for this job, mine was done for $500.
You should be able to get a top quality job for $500-$700.

Best of luck
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Old 06-11-2001, 07:00 PM
sixto's Avatar
smoke gets in your eyes
Join Date: Jun 2000
Location: Eastern TN
Posts: 20,834

Interesting. Someone else has a 126 that has a passenger side key mechanism that will unlock but not lock the doors. If you don't mind, can you tell me if you can press down the inside lock button on the passenger door when the door is open?

The factory alarm is set by locking the driver's door with the key. If your alarm bothers you and you don't need it, disable the alarm. On my car, and yours is probably similar, lift the front passenger carpet, remove the false firewall, locate the alarm box marked 'Becker Autosound,' remove the connector furthest from the floor. Leave the other one in place. On my car and one other member's, this disables the alarm without disturbing anything else.

Thanks and good luck,
91 300SE
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Old 06-11-2001, 09:04 PM
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Fred's Post

Right on the money, Fred!
Speaking from wife started the car in the parking lot with 65K on the odo....she calls me up and tells me "The car won't start!"......long story short & three valves + $1800 later, all is well! Guides broke on start up, chain jumped sprocket and one of the valves punched a hole through the right driver's side cover!

Good Luck on your trip!

MB aka Harpman

p.s. -Good advise on the alarm, Sixto! Thanks!

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