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1974 Mercedes 450 SL
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Discussion Starter #1
Hey everyone.

I just got a 1974 450 SLC from my parents. They have had it for a long time, but there was a problem with something, they didn't know. It was either the waterpump or the thermostat, it started running hot, so they decided not to drive it. It hasn't been driven in about 5 years.

I figured I will have to change the oil and filter before I attempt to fire it up.

Can you guys give me any advice on what type of oil I should put in and any other useful information that will help me not blow up the motor?

I appreciate the help.
 

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I wish my folks had given me a SLC ,but then it would have been a new car !![:D]
Before you try to start this car,Buy 1,a new fuel filter,
Oil filter,
aircleaner element
spark plugs
and 5 liters of 50# oil.
Next clean the fuel tank out ,undo the bung under the tank if you can get it out,If you can't,drain the old fuel out via the larger hose that runs to pump.That old fuel will stink like you wont' believe[xx(]So don't get it on your skin,and don't smoke around it either.
with the fuel tank cleaned out and your new filter in place,put about 5 gals of juice in the tank,with about 250mls of trans fluid.The trans fluid is amazing stuff and will help get rid of gunk in the injection system.
remove the spark plugs.
Clean out the radiator water,there is a bung in the bottom of the radiator.undo that and let it all go.again ,it's noxious stuff .run a hose through the radiator to loosen any crud you may be able to see.
To do it better,I would remove the radiator and get a Radiator shop to clean it.
check all the hoses for hard ,or swollen or just plain tired hoses.
Refill it with plain water for the moment.
I'll bet the batterie is shot after 5 years so plan on buying a quality one ,with exact specs for the car.
Anthing less won't have the guts to run the injection pump and you will be down on performance.
It is always best to change the oil hot,but with your car,i would just drain what you can,but do not forget the oil coooler,it also has a drain bung,next to the radiator it has a hose in the top and one in the bottom.undo the bung and let all the oil go.Change the oil filter and the air filter.
do it back up and drain the sump.leave the bung out for a bout 15 minutes to ensure all the old oil is gone.Replace the bung,fill with oil and crank the starter until the oil pressure comes up.
Replace the plugs and plug wires and see if it will start.This where a new battery is important.Start the engine with radiator cap off.
Run it ,WITH NO REVVING, until it is hot.Check the water level while the engine is idling.water level should reach the ridge under the cap,check for big bubbles rising through the water,and once the idle has stabilised the water temp should be normal and NO bubles should be visible in the water.
This is where you can find the symptoms of overheating.
if it checks out OK,dump the plain water,run the hose threough the radiator again and refill with Mercedes anti corrosion and anti freeze.Check your oil level.Ask your parents if they ever had the timing chain changed,If the answer is No,get it changed as soon as possible.A broken chain will really stuff your day.[8D]
 

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1974 Mercedes 450 SL
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Discussion Starter #3
Thanks!

I have a 89 BMW as well and I know Spark Plugs are critical in older cars, what brand/type do you recommend?

Good thing I asked about what to change out, would have never figured all of it out...

Do I need to change Trans/diff fluid as well? I could while I'm at it.

So remove the fuel tank completely, and clean it out? With what? Thanks!
 

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1974 Mercedes 450 SL
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Discussion Starter #4
I just remembered:

can I use reg fuel injector cleaner? I am kinda nervous about putting ATF fluid into the gas.

What's the gap for spark plugs for my vehicle?

Should I change ATF/Diff fluid as well, I might as well while i'm at it. Thanks
 

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The ATF in the fuel is used in Scandanavia to prevent sludging in the tank and i user it on my 6.3 .Every third tank full it gets 500mls.The 6.3 fuel pump is a $15,000 item ..so i have no worries what so ever using this stuff.Put it in your tank to clean the injectors and the valve heads.It won't hurt anything,if you put too much in it will smell a bit until it all gets burnt up.Removing the tank is no big deal,but just drain it in place.As i said there is a bung in the tank,but it can real stubborn to get loose.I welded a bolt to a peice of steel ,1 foot long and put the bolt head into the bung,you can see the size you need if get under and look.It looks like a large allen bolt.I swing on the "wrench" and if it needs it i put a pipe on it to act as a lever.When the bung comes out,you will see it has a filter built into it.Get a new bung or get it cleaned in a ultrasonic cleaner.i use a dentists one i bought off Ebay.
I use NGK bp6 plugs.Other brands are hard to get here.
These are bit hotter than the recommended size .but i do a lot of traffic driving and i find i will foul plugs if the correct size are used.
You can change the tranny fluid now,because when you pull the radiator to get it cleaned ,you will lose fluid from the two cooler lines.A filter is available from most sources.When you change the fluid,you must also drain the torque convertor.
It's easy enough to do,remove the little plate on the bottom of the convertor housing,you should be able to see the convertor,turn the engine over until a round lump appears on the outside circumference of the convertor,this has a 5mm allen plug in it.This the drain for the convertor.Let all the fluid out.
One thing i should add here is,if you have access to a pressure washer,thoroughly clean the entire underside of the car before you start pulling the tranny pan off.You do not need dirt in the trans,it will fail very Quickly if dirt gets in there.[xx(]
 

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1974 Mercedes 450 SL
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Discussion Starter #6
awesome, sounds like I got myself a project here...

What do I put back in the torque converter and how? Do I need some sort of pump or does it have a fill-plug on the top. When you say "when you turn the engine over" I have to take the engine out? I hope not, that will turn into a major project real quick... but the car is worth it... [:D]
 

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OOPS,sorry about the delay and the mixed meaning there,i'm in Austrlia,so we have the same language,different meanings,
By turning the engine over i meant,"cranking it "so that that you can see the little plug.To do this,i put a 17mm spanner on the power steering pump pulley bolt and turn the engine clockwise to "turn it over".If the belt is a little loose and it wont turn the engine,either tighten the belt or get someone to push down on the belt so it grips while you turn the engine over.
To refill the torque convertor you fill the trans with correct amount of trans fluid,through the dip stick,using a clean funnel.The convertor has about 2 liters so you will need at least 4 liters for the whole job.
 

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Old oil and old fuel,especially if it has been sitting for five years will DESTROY your Mercedes ,[}:)]
Anything that will go wrong will,plus you said your folks had an overheating problem.
What i outlined is what Mercedes dealerships USED to do before they joined the darkside,(DAIMLER chrysler....).
When you took your Merc in for a routine service they would do a huge list of jobs as it related to the cars mileage,thats why I only buy older Mercs with a service history.There is never any little surprises.
If you still have the little service booklet for the SLC .read it and you will see the list of jobs that were carried out at each service interval.
Thats why they "were" the best cars in there world[8D]
 
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