slow Reader
Nov. 27, 2014 9:27 a.m.

I am going to look at a 89 Mercedes 420 SEL with ~200k miles. The owner says everything works except the odometer (stuck @ 192k). AC and Heater work. No rust spots.

I have no experience with big Merc but have always been wanting one as a gangsta cruiser. What do I need to look for? Are transmission and engine reliable? This would be my errand runner and weekend cruiser.

Nov. 27, 2014 9:50 a.m.

I like 'em. No facts to offer, just my $.02 opinion.

Nov. 27, 2014 10:43 a.m.

I would say to look for a diesel powered Benz and run it off used vegetable oil. I have no experience with a Mercedes.

slow Reader
Nov. 27, 2014 11:40 a.m.

I like diesel as well but haven't found one that was clean. For whatever reason, I only see abused SDL around here.

Travis_K UberDork
Nov. 27, 2014 11:46 a.m.

Vegtable oil kills them pretty fast, I wouldn't do that. Other than a bit worse mileage, getting a gas one isn't that terrible of an idea. If the front suspension is worn out enough to be noisy plan on $1500+ to fix it, but then it will be good for another 200k. I would say if its cheap and you like it why not? Its a $60k car you can get for less than 6 months of payments on a new fiesta or something.

TRoglodyte SuperDork
Nov. 27, 2014 5:03 p.m.

Gas mileage is low,heat and air are problematic. Transmission is at end of service life if not replaced. Fast for a big ccar and fun to toss around

Nov. 27, 2014 5:17 p.m.

In reply to Travis_K: Companies make kits to run used vegetable oil on older diesel engines. It also only takes a little bit of work to turn used vegetable oil into biodiesel. Some buses in big cities run off of biodiesel fuel.

lrrs New Reader
Nov. 27, 2014 6:08 p.m.

In reply to Travis_K: I ran an 84 300d on veggie for 50k miles. Dual tank system based on a greasecar kit I got from a guy that had it in his truck that he traded in. Always started on diesel until warmed up then veggie for my 35 mile trip to work and purge cycle for the last half mile to get diesel back to the injectors for the next start. Sold it last spring to a guy that was going to continue using veggie. My free supplies dried up when companies started buying it from the mom and pop restraunts to make bio d.
It was running better when I sold it with 200k on the clock than when I got it.

yupididit Reader
Nov. 27, 2014 6:37 p.m.

Aren't the 4.2 v8 more problematic than the 5.6?

Travis_K UberDork
Nov. 27, 2014 6:45 p.m.

If you make biodiesel properly it can be fine, or they can last a decent amount of time running on vegetable oil, but I certainly wouldn't, nor would I pay much for one someone had used for that.

slow Reader
Nov. 27, 2014 7:32 p.m.

Some pictures of the car

slow Reader
Nov. 27, 2014 7:34 p.m.

Thanks for the advices so far. Sounds like I need to check the engine and transmission. What else? Are the engine and transmission likely to fail? Any signs?

Kenny_McCormic PowerDork
Nov. 28, 2014 2:17 a.m.

The V8s are pretty solid, but have typical German upkeep, I know they require somewhat periodic timing chain jobs and will absolutely grenade the top end if neglected long enough(the guides tend to come apart with age, it's not a terribly expensive job).

The W126 Benz is like a mechanical engineer's wet dream, grease zerks on the door hinges. I read the service manual for fun sometimes. And in black they are IMPOSING, like late 60s-early 70s Cadillac imposing, but more stately.

Lugnut Dork
Nov. 28, 2014 8:30 a.m.

I don't know much about the 420. I had a W126 560SEL and LOVED it. Still in my top ten. Solid, muscley, comfy and a bit stately. In black you'll come across either as a diplomat or a member of the Armenian mob.

If the AC goes that is some major work to get everything sorted again.

It's possible I liked that old S-class more than my current XJR. I keep thinking about buying another one.

conesare2seconds HalfDork
Nov. 28, 2014 11:24 a.m.

Look for a record of timing chain & guide replacement, that seems to be the only concern with keeping the engine going. Seat bottoms get saggy but there's a kit for it that's cheap. Looks like a clean example. If the PO has kept the seats that nice for 200k and the HVAC is working, he has probably been good about maintenance. The W126 is built like a vault and as has been said, has presence. Radios are crummy by newer standards, but that's no hill for a climber.

slow Reader
Nov. 28, 2014 3:33 p.m.

Seller just informed me that there was a major power steering leak from the "gears" in the steering rack and there is a "small" leak in the cooling system which might be fixed by a new water pump.

How big deal is it to change the rack and probably the pump + hose? I didn't find a rack on RockAuto. Is it junk yard hunting time or should I just save the trouble and get a new one from dealer?

The "small" coolant leak concerns me. The seller says that the "coolant" light comes one periodically. He initially thought it was radiator cap and replaced it but now the mechanic said it might be a water pump. It doesn't really make sense to me. Does anyone understand the logic? Is that "coolant light" due to low coolant level or low pressure?

BoxheadTim UltimaDork
Nov. 28, 2014 3:48 p.m.

IIRC it's a coolant level light.

Travis_K UberDork
Nov. 28, 2014 3:52 p.m.

Its a box, not a rack. At least on the diesel one I had it was easy to change, I wouldn't be too worried about that.

yupididit Reader
Nov. 28, 2014 3:54 p.m.

Check on autohausaz for parts. I would wait for a 560sel to come up that's been decently taken cared of.

slow Reader
Nov. 28, 2014 5:15 p.m.

Thanks everyone for the advise. I see that that steering gear now. I looks to be $425 from autohausaz. Or I would just drive that tank manual style!

With the recent news, the car could be a Challenge build!

Kenny_McCormic PowerDork
Nov. 28, 2014 5:48 p.m.

Oh yeah, the front swaybar tends to rust out on the ends, it's a pain to replace, but new weld on ends that you replace with the bar installed are available. And I think all the LWB cars had air suspension in the rear(I believe there's a spring/shock combination available to delete it). Speaking of the ride, these things go down the road like they own it.

AaronBalto Reader
Nov. 28, 2014 6:51 p.m.

Just bought THIS '90 420SEL on Wednesday for $5k. A lot of cheese, but a one-owner perfect-looking car with 72k miles.

My (weak) understanding is that the drivelines are not the issue. It's the 100 things that can each cost you $1,000. Avoid cars with bad AC. Also, there are tons of these cars out there. Why even consider one that isn't really, really good? The difference between a beater and a show car is only a few thousand dollars.

I focused my shopping in wealthy areas--I wanted a car that had been pampered, garaged, and dealer maintained by one owner for a lot of years. And they are out there. Take a week to find one.

Lots of great DIY info at

And enjoy! What a sweet, cheap, awesome ride. I can't wait to hit the road in this beast.

slow Reader
Nov. 28, 2014 7:57 p.m.

AaronBalto, nice score!!! I might have to take your advice to wait for a nice example. Unless the seller is going to take scrap price then I am going to join the brotherhood of car hoarders.

AaronBalto Reader
Nov. 28, 2014 8:13 p.m.

Thanks, man. I am like a kid waiting for Christmas. The car is on Long Island. I am flying up there on Friday morning and driving back to Baltimore--in S-T-Y-L-E. I already ordered the oil change kit and am making my appointment for winter tires for Saturday. Christmas road trip to NYC coming up. So geeked.

LanEvo Reader
Nov. 28, 2014 8:48 p.m.

Expect 11-12 mpg in the city. Make sure the HVAC system works (PITA to sort). Be prepared for a big timing chain/guide job if it hasn't been done recently. Don't expect to pass smog (if that's in issue where you live). Try to find some Euro headlights, bumpers, and Penta alloys.

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