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Hey gang! I picked up a 1989 420SEL limousine with a 300SD turbo diesel. The guy I purchased it from washed the engine several years ago and said it never started after that. He insisted the engine was fine, but he must have damaged something electrical.

What would be the top things you guys would inspect or replace to get it running? I appreciate your input.
 

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1986/1990 W126
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It might even run again by now, apart from algae problems maybe.

Hopefully a diesel expert might know, I'm not familiar with them. Welcome to the forum by the way.
 

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Thanks! Hopefully it kicks over.

I just bought a battery.. I'm gonna start with the basics... battery cables, starter, starter solenoid, drain the old gas etc...
 

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1986/1990 W126
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Yep any old fuel needs to be out of the car at this pointbefore trying anything.
 

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350SDL, '17 GLS450, "Grandpa's Roadster" Project Car
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I wouldn’t believe his story at all
I think he meant the story the guy who sold it gave you.

A 420 with a Diesel? That's pretty odd to start with.

When you say it won't start, can you be more specific? Does the starter crank the engine over? Does it crank fine but not fire? Any chance he got water into the engine and hydrolocked it?

Diesel fuel doesn't go bad like gas does, but, if there's water in the fuel it can grow algae in the water which then clogs up the fuel system. There should be a small "prefilter" in the fuel line before the engine driven pump. Check it for contamination. You can take the fuel line off the filter and blow in the filler neck to force fuel out of the fuel line to see if it is contaminated.
 

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I once bought a Morris Minor 1000 traveler that was in a garage for 15 years, I replaced the engine oil and flushed the coolant replaced some hoses, never did anything to the gas tank or the old gas that was sitting there I fill it up got a new battery and got it running
drove the car for about a year no problems but that was a 4 cylinder engine stick shift
Right hand drive car
 

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'90 560SEL Blauschwarz/Black
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Just for grinnies... Check and see if there are spark plug wires on top of the engine... 420's are 8 cylinder gasoline engines. If there are no spark plugs then they must have put a diesel in. The 300 and 350 diesels are all straight 6's too.

I NEVER washed my 300SDL engine with a pressure washer. Too many ways to screw it up.

Check fuses and relays too.
 

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I once bought a Morris Minor 1000 traveler that was in a garage for 15 years, I replaced the engine oil and flushed the coolant replaced some hoses, never did anything to the gas tank or the old gas that was sitting there I fill it up got a new battery and got it running
drove the car for about a year no problems but that was a 4 cylinder engine stick shift
Right hand drive car
Ethanol in fuel has killed all that off, sadly.
 

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I had a neighbor that washed his engine on a Mercedes I can't remember the model but it was in the 2000's model, car never started again he had it in his garage for sale and no one will buy it, but this guy claimed he had the hose on the engine washing off the degreaser he had put on it to clean it, I heard Mercedes engines are not to be washed.
Maybe you bought a Lemon?
 

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Discussion Starter #13
Thanks everyone! I'm putting a list together of what all of you shared... then going step by step.

John350 asked if the engine is cranking. So far nothing happens when I turn the key. I just get dash lights etc...

It's kind of an odd car... meaning a 420SEL limo with a diesel engine. ProgMuscle asked if there's any plug wires. There's none that I can see... definitely looks like a diesel. I forgot to mention there's a second gas tank in the trunk area for long distance traveling. Do you think water could have got into the valve/hoses (that selects the fuel tank) in the engine compartment?

If something happens to cross your mind why the car won't crank please pipe in. I'll keep checking in and seeing what you guys recommends. As always, thanks again for your advice. Lots of gratitude on this end.
 

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So far nothing happens when I turn the key. I just get dash lights etc...
Well, you have to address that first. Trace the signal from the ignition switch to the starter solenoid, for starters (no pun intended). If you're careful, and brave, you can jump from the battery (+) to the solenoid (might be a yellow wire) to see if it cranks then.

What exactly did the seller tell you? Did he say "it never ran" or "I couldn't get the starter to work"?
 

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this happened to me on my first car (VW Jetta) decades ago. Turns out I had gotten water into the fusebox and destroyed it. I was 18 and sprayed the hose LIBERALLY into the engine back then (didnt know any better). Since then, I never use a hose. Lots of those red shop rags, spray on degreaser, then wipe off with damp rags. Might not be as effective but much less risk for me
 

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Hey gang! I picked up a 1989 420SEL limousine with a 300SD turbo diesel. The guy I purchased it from washed the engine several years ago and said it never started after that. He insisted the engine was fine, but he must have damaged something electrical.

What would be the top things you guys would inspect or replace to get it running? I appreciate your input.
When I first started driving diesel sedans some 40 years and many cars ago, an old diesel mechanic I knew told me to never pressure wash a hot Diesel engine because the injection Pump with super tight tolerances might lock up from the temperature differential. Don’t know if it’s true.

if your V/8 420 somehow has a diesel in it...
 

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on a diesel there is a connection on the passenger fender where you can jumper wire it to turn over. i went thru this with a 300 turbo diesel. im my case it was a broken neutral safety switch located on the side of the transmission that was the problem. there is a connector under the dash on the drivers side with purple wires. i ended up jumpering that switch inside the car to get the starter to crank with the key while the safety switch was still busted. try this, turn the key on then put the gear selector in reverse. now see if your backup lights are lighting up. if not id look into the switch.
 

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Discussion Starter #19
Hey guys! That's some great feedback. I finally got the car to crank, but it won't start. I better drain the gas tanks (yes, it has 2). Any pointers about draining the fuel tank?
 

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If this car is in fact a diesel then you could try to prime the fuel and see if it will start, that is if you want to. On the side of the fuel pump you'll see a knob looking thing. Unscrew it a half turn to release it and start pumping it. When you hear it make a squak kind of sound push it back in and tighten it. Try to start if you want to. Are you sure the secondary tank is for diesel? It may well be but a lot of times those second tanks are waste oil fuel tanks.
 
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