Just got done doing my first valve adjustment on my 82 300SD, along with a diesel purge. This all got done while I was taking breaks for days at a time between attempts to get my tie rods off. After 32 years, they were incredibly reluctant to come out. Incredibly very very reluctant.

A quick backstory. I bought the car with 300k on it and 200k on the engine (factory shipped and replaced under warranty to the original purchaser). First year I had it, I put about 8k on it. Then took a job as a courier and put almost 30k on in about four months. No idea how long it had gone before I got it without a valve adjustment and it exhibited many of the common symptoms that I read about (difficult starts when cold; poor power, especially uphill).

So I finally get around to doing the valves, certain from my research that I'll find all ten to have zero clearance. Instead, they were almost all perfect. I didn't even bother adjusting 2 or 3 of them and some of the others only got adjusted because I wanted to feel like I did something after all the prep. All were extremely close to spec and not a single one was too tight to get a feeler gauge in.

Then, the diesel purge. After the amount of fuel and miles I put on, I made sure to buy two cans and new filters. I was certain that the returning diesel purge would be filthy and would make a mess of my filters. Didn't happen. Fuel was returned to the bottle looking exactly like it left and the inline filter shows no signs of any muck or dirty fuel. I don't even see any reason to switch the filters out now and I never got around to using the 2nd can of purge.

So, why is my car refusing to show its age? Shouldn't those valves be out of spec by now? Shouldn't the purge have cleaned out years of carbon? Does my car have a guardian angel/mechanic hovering over it? I'm confused.

Haven't been out on the road yet. About to go get the alignment, then to find a fan bolt that went missing during the adjustment. But after blaming my poor power on the valve clearance for almost a full year, I'm a bit disappointed and now worried that neither of these procedures seemed to be needed, leading to the obvious question: Now what?

For whatever it's worth, it has hardly any blow by, uses very very little oil, and still accelerates from 50-75mph with total ease.

While I wouldn't condone going more than 5k without checking valve lash and changing filters, it seems that these engines benefit greatly from being used long and often. The engine should not accrue large quantities of carbon and dirt in the fuel system as a by-product of use - this type of damage is more often caused by disuse and untreated fuel sitting for long periods of time. Carbon and gunk in the combustion chambers appear more with short trips and city use only where everything doesn't have time to warm up.

They are made to run, after all. Especially if your miles are highway, it's not surprising that fuel system is in good condition if you have been running fresh fuel.

If the engines properly tuned - valve lash, filters changed (even if they look clean), good oil of proper grade every 3k, chain wear checked, then run it!

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-1981 300SD 242k, stock - sold @ 250k
-1994 Toyota Pickup 4x4 R150F 5 Speed, 5VZ V6 swap.
-2004 Volvo V70-R 2.5T

Hard starting: glow plugs?

Poor performance: injectors?

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Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC

Glow plugs are young. I replaced all about 8 months / 5,000 miles ago.

The injectors presumably came with the replacement engine and would have about 230k and 27 years of service. From what I've read around here, they're likely going to require some attention soon if I expect to use this car for another 100k+.

I'm a bit surprised by how quickly and strongly it started after sitting in the driveway for about 18 days. From its history, I expected to have a weak start and probably a quick stall followed by another weak start that persists for about a mile or so until it warms up. So maybe I solved the issue after all, either through some minor valve adjustments, the diesel purge, or a new air filter replacing one that didn't look dirty but had at least 30k on it. Only time will tell.