Car -- 1981 300D NA . Talked about it a lot here and gotten a lot of help.. It wont start below 35F, weak starter possibly that does not engage well in cold, lots of blow by -- soaked air filter every month, and it leaks and/or blows out a quart of oil every 200-300 miles. I finally did a compression test today. I did not get to the leak down test. I have a few questions. Here are the results:

Warm Engine (at least when i started )
Cylinder -- Dry(PSI) -- Wet(PSI)
1 -- 250 -- 325
2 -- 325 -- 375
3 -- 375 -- 420
4 -- 282 -- 330
5 -- 340 -- 380

Acceptable values for engine at operating temp
Normal -- 323 to 353 PSI
Minimim -- 220 PSI
Permissable Diff -- 44 PSI


So , None are below minimum but 2 are out of normal and beyond the pemissable difference and 3 are in normal range and decent. The worst one shot up 75 psi on the wet test. is that enough of a jump to indicate rings? Or is a leakdown test necessary still to determin that? What is a "significant jump " for a wet test? Are those numbers low enough to make it hard to start in cold? I have a donor engine (in the 1980 300CD ) that i am going to test compression but it starts right up in cold and does not leak oil or have much blowby. 160K on working odometer and its probably original. Should i swap the engines or perhaps look into a valve job for the suffering engine?

sorry for all questions. thanks for any help.

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What Would Rudolph Do?
1975 300D, 1975 240D, 1985 300SD, 1997 300D, 2005 E320 , 2006 Toyota Prius

Big change between dry and wet compression=bad rings. If you have a shop or garage to work in and feel comfortable doing the work, you could probably just do a ring job and keep it going for many more miles. I'd probably throw in some fresh bearings while I was at it.

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.

can seal valves too. my buddy who ran a funny car tells me.

are your tests cold or hot?

have you adjusted your valves? this much variation seems like possibly valves to me.

on the other hand tight valves shouldnt cause excessive consumption. what kind and weight of oil are you using?

just reread your post. you can prob change the motors for less than a valve job by a good deal. that is prob your best bet, unless you are running 10w40 gasser oil or some 0w40 synthetic, and then i would suggest striaght 30w rotella for a while to check to see if it would help.

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

thanks all.

Engine was hot when i started taking off fuel rail and taking out injectors. I guess that counts as hot. Edited previous post. thanks. Does compression rise of fall as engine cools down? I'll do it agian in glow plugs later and get right down to business and see if it changes.

I adjusted the valves this winter 2 or 3 months ago. I thought i did a good job and car ran better but it was my first time.

I'm running 15W-40 Rotella or Castrol. I will use 30W next change. Didnt want to in winter. Ill use 30W next time.

I'm guessing engine swap is probably best bet in any case considering all issues -- starter going and, oil leaks and blow by greasing up filter all the time. I would like to know its weak points before i pull it unless you can tell them with the engine out of car? Or with engine out of car , it is probably better to do bottom and top end at same time? I should probabyl do a leak down test before i pull it.

thanks.
.

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What Would Rudolph Do?
1975 300D, 1975 240D, 1985 300SD, 1997 300D, 2005 E320 , 2006 Toyota Prius

You could also swap engines, then have all the time in the world to tear down the weak one & decide if you feel like fixing it ...

is higher on a hot engine.

the leak down test will tell if valves are leaking or if it is all rings. you pressurize the cylinder and listen for the escaping air in the intake exhoust and crankcase, i believe. personally i have never done one.

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Actually, 250psi is roughly the physical minimum compression to ignite diesel. (Depending on ambient air temps.)

If the starter really is bad, I reccomend you replace it. Also, glow the plugs for as long as possible. Something like 30-40 seconds.

Also, Rotella "synthetic" may help too. Members of the board claim it helps the engine spin faster when starting.

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1976 BMW 2002- 100k
1995 BMW 325i 175k
1984 Mercedes Benz 300D Turbo Diesel- 270,000 mi

1981 Mercedes Benz 240D- Estimated 300,000+ mi Returned to the earth

Try www.auto-rx.com It is a sludge and carbon remover that slowly dissolves sludge and carbon in your engine and loosens stuck rings. It has worked well for many people.

Steve

Adjust the valves and do the test again, just in case. Many a Mercedes engine has gone on to live a long life with numbers even lower than yours. On my '79 I always plugged the block heater in even in spring and fall to help it start faster. Just makes it a lot easier on the engine. Good glow plugs, clean ground connections, a nice tight starter and very strong battery, will let that engine last for many more years.

I would run that engine untill it wont start anymore, then use the donor engine.

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1981 300D 147k
1998 VW Jetta Tdi 320k
2001 Dodge Ram 2500 141k
1979 300D 234k (sold)
1984 300D "Astor" 262k(sold)
Mercedes How-To and Repair Pictorials
I love the smell of diesel smoke in my hair

This seems like a good time to ask if anyone has ever tried that engine Restore stuff. It's supposed to seal up the rings better and bring compression up but I'm very skeptical of miracle fluids. Has anyone ever tried Restore and measured compression before and after?

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1987 300SDL 167k
1992 Volvo 740 140k
1990 Volvo 740 250k
1989 Volvo 240 269k

Anyone want to trade an old Volvo for an '87 300sdl?

Yes I have tried it. No it does not work. A liquid cannot replace metal that is gone from wear. They do a nice marketing job, too bad that it does not work.

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1981 300D 147k
1998 VW Jetta Tdi 320k
2001 Dodge Ram 2500 141k
1979 300D 234k (sold)
1984 300D "Astor" 262k(sold)
Mercedes How-To and Repair Pictorials
I love the smell of diesel smoke in my hair

I would recommend running a good synthetic for a few thousand miles, changing the starter and making sure the glow plugs are operating. All of them.

My old, now retired, 1982 240D was nearly hopeless when my daughter was using it in Troy, NY. I changed the starter, and the engine mounts, as well as switched to Delvac 1 and the car started like new for another 5 years. Occasionally needed a glow plug. It finally died with my son driving and letting the machine run down on oil. It had developed a rear crankshaft seal leak and that Delvac at 70 mph going uphill would run out. That is another story. Yours sounds very revivable. Delvac 1 and other good synthetics intended for Diesels will clean the carbon out, and let the rings seal as intended.

Good luck. Jim

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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)

Hi,

Those numbers look a little low. I had a smoking 300TD (search threads for sad story) and it had marginal compression by the MBZ books. It smoked like crazy. My guess is you want to be on the high side of those numbers.

As for a leakdown, a friend showed me how I could just unhook the 1/4" npt connector on my harbor freight diesel compression tester and flow gas through the fitting on my glow plug. A real tester does exactly this with a flow meter inline that tells you high flow (bad) or low flow (good). The cool thing about the poor man's test is you can now listen at your oil filler, check your radiator for bubbles, listen to the intake, or listen to the exhaust pipe for hissing to see where your leak is. (make sure you're at TDC on compression stroke) Cool huh?

On my bad cylinder, I think I was getting compression of 275 which is bad but it isn't zero...but when I hooked up the compressor the air just came whooshing through the oil filler cap like there was a hole the size of a pencil in my piston. Lesson? Compression is a dynamic test, leakdown is static. You see different things. I later took apart the engine and found that my piston rings were cracked in 2.

My pal gave me a leakdown tester as a gift when the whole thing was over.

Yoko

They look a little low but not that bad. Unless you really want to do a swap, I'd.
Use 5w40 Delvac 1 in the crank for much faster cranking.
Fresh glow plugs and a rebuilt starter.
Then just plug it in.

She will start.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200