Debugging a 1975 420 SL - Mercedes-Benz Forum

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post #1 of 12 (permalink) Old 10-29-2005, 11:18 PM Thread Starter
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Debugging a 1975 420 SL

I am considering the purchase of a signal red 1975 420 SL hard top. Car is immaculate with 205,000 miles.

Has a few issues, however, that I would appreciate your feedback on.

When the engine is started (it always turns over straight away, not bad for a 30 yr old car) it smokes for about five minutes. Blue smoke, obviously burning oil.

There is also a persistent oil leak on the passenger side of the motor. I can't tell exactly where it is leaking from, but it leaks directly onto the exhaust manifold. Would I be optimisic to assume that this is a valve cover gasket, or is it more likely to be leaking from the headgasket? From what I have seen with other cars, the headgasket usually leaks into the water jacket.

Also, what kind of a transmission do these cars have? Assume that it is a ZF. How many miles are expected before a rebuild is necessary?

Thanks in advance for your assistance.

Jackson
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post #2 of 12 (permalink) Old 10-30-2005, 01:19 AM
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RE: Debugging a 1975 420 SL

Hello and welcome

First off it will be a 450SL - a 420 engine was not introduced until 1986 in the 420SEL.

Never assume with these cars - I thought it was just valve seal on my one resto and it turned out to be guides. No real idea until you actually get in there!

Good luck.

Tory



1990 560SEL - W126
-929 nautical blue metallic & 262 navy blue leather
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-Euro spec Japanese import (KAT edition)
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-285 hp@5200 rpm, 324 lb/ft@3750 rpm
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post #3 of 12 (permalink) Old 10-30-2005, 04:31 AM
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RE: Debugging a 1975 420 SL

Smoking is easy to isolate in any engine ,but do it the best way.Before you aggree on price get a GOOD mecahnic to do a Leak down test on the engine.NOT a compression test!.A leak down test isa what every mercedes trained mechanic does ,in one simple proceedure the head gasket is tested for leaks in the water jacket,the valves a re tested for burnt or otherwise damaged seats, and the rings are tested for sealing.
A leak on the passenger side can be either the top rocker cover vent hose cracked or the cover seal damaged .Both can be symptoms of worn rings pressurising the sump,try removing the oil filler with the engine idling,any fumes at all indicates worn rings,a blue haze means either you get the car for a rock bottom price or you walk away.
re your trans,It would never ever be a friggen ZF!!![:(!][:(!][:(!]that is the other crowd over in Munich who put that rubbish in their cars!( From someone who has had to fork out for wrecked ZF components in the past)
Mercedes have......Mercedes transmissions.Keep it serviced by someone who knows how and it will last forever.[:)][:)]
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post #4 of 12 (permalink) Old 10-30-2005, 11:42 AM
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RE: Debugging a 1975 420 SL

Quote:
w108 - 10/30/2005 1:19 AM

First off it will be a 450SL
Correct, for his 1975
Quote:
a 420 engine was not introduced until 1986 in the 420SEL.
My research indicates the 420Sl was introduced in 1985, and ran 'til 1989, but only 2148 were produced. These were european models only, so One in the US must have been imported by an individual or private importer.

I agree with the diagnosis... Start with the seals. They are easy and cheap enough to replace.

Cheers,

RMS


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Where is it again that we are going... And why are we in a handbasket?
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post #5 of 12 (permalink) Old 04-24-2014, 10:38 AM
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oil change for a 1975 sl 450 benz....help
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post #6 of 12 (permalink) Old 04-24-2014, 10:46 AM
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post #7 of 12 (permalink) Old 04-24-2014, 10:55 AM
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post #8 of 12 (permalink) Old 04-24-2014, 10:59 AM
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Quote:
Originally Posted by ROCBENZ View Post
oil change for a 1975 sl 450 benz....help
What kind of help?

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post #9 of 12 (permalink) Old 04-24-2014, 11:03 AM
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what type of oil does a 1975 sl 450 take.....
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post #10 of 12 (permalink) Old 04-24-2014, 11:34 AM
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Quote:
Originally Posted by ROCBENZ View Post
what type of oil does a 1975 sl 450 take.....
Boy oh boy, there are a lot of opinions on this, but I don't think MB engines are all that special with respect to lubricants, so really any brand name oil would work. You can search this site and others on whether or not one should use synthetic oils with these older engines (I never did), whether or not it would be worth it to do that, but in warmer weather go with 15w-40, in colder temps go with 10W-30.

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