What do I need for a 200D compression test? - PeachParts Mercedes-Benz Forum

WANT '71 280SEL · #1 07-31-2003, 12:52 AM

Well the intitial question explains it all, exactly what would I need to do a compression test on a '67 200D? I am looking at purchasing one and I wanted to know exactly what I would need so I could just do it there. Can I just use a gas compression tester? What size fittings are the GPs? Should I do it warm or cold? Heard both ways. I did a search and saw someone's "poor man's compression test." It involved using no guages on a vintage 190D which is pretty much the same as this. Said that once the engine started to warm up you shut if off then just start cranking for a few minutes until it built up compression and fired.
Is it really good to crank an engine for a couple minutes? And while the engine is cranking, aren't the GP's lit anyways?
Thanks
David

joshhol · #2 07-31-2003, 02:08 PM

If the valve clearances are set correctly, the glow plugs are good and it starts easily in cold weather, then most likely the compression is fine.

300SDog · #3 07-31-2003, 04:27 PM

Starter motor should never be cranked for more than 30 seconds to avoid burning it out. But 30 sec cranking intervals is time enough for the poor-man's compression test....... without glowing the plugs, where healthy diesel can start from cold on warm day with its compression alone. If it entirely flunks the poorman's test, it doesnt mean the engine is worn out.

Diesel compression guage measures up to 500 lbs pressure. They are expensive, maybe you can rent one, or just spring for professionally done compression test.... consider readings at mid to high 300's to be excellent..... high 200's can be considered good, as burning a little oil (1000 miles per qt.)..... anything at/below 200 should be considered crummy, as in worn out engine with cold start problems and high oil consumption.

Compression test is worthless if valves are out of adjustment..... Otherwise, the guage is attached at injector holes and requires two man operation with one guy cranking the engine, while another reads the guage - noticing how fast it achieves compression, and if discrepancy at/above 10% exists between cylinders. If you pull the injectors, entirely remove injector lines first - so they dont get bent out of shape. Hazard is allowing dirt particles to enter the fuel injection system, so cap all openings with masking tape.

Other pre-purchase diesel diagnostics include studying smoke (black, blue --> carbon build up, oil, unburnt diesel fuel.... Some blue smoke that clears at start up is normal, but it shouldnt be smokin like a burning tire all the time.... also listen for metalic noises (injector nailing) at cold start. Nailing indicates dirty or worn injectors. Oil is always black as pitch, and normal healthy diesel rattle is easy to identify.

Another thing is to remove the oil cap while engine is running, checking for 'blow-by' of engine oil from crankcase. Maybe ballance the cap on its opening and see if it flies off into the air, or just rattles around barely screwed into the opening at the valve cover. If the Heckflosse diesel has modern day air filter, instead of retro upgrade 'oil bath' style, then dirty air filter covered with oil will tell the same story of crancase blow-by as the oil cap test.

#4 07-31-2003, 07:23 PM

Hey David did you go look at the 200D yet?
Tim

#5 07-31-2003, 07:24 PM

Will the compression gauge that your uncle has work on that car, or is it different on diesels?

#6 07-31-2003, 07:25 PM

By the way go with the '79 300SD. I think that all around it is a better deal. Unless you can get the 200D for $600 or $700 dollars like we were talking about.

#7 07-31-2003, 07:25 PM

How much did that guy want for the 300SD?

#8 08-01-2003, 02:25 PM

WANT and I went and looked at the car yesterday. There was about 3/4"-1" of oil in the bottom of the air cleaner. Should it be there? How much would door seals cost? Those seals had pretty much disintegrated. It also had an aftermarket Mark IV air conditioner that did not work. We did not have the time to start the car because the owner had to leave. We will try to test drive it this weekend. We will get back to you then.
Thanks
Tim

PS: It is a four speed on the floor. When I went to put it in reverse, it seemed kind of difficult to do so. The clutch pedal was only about half as high as the brake pedal; is this normal?

#9 08-01-2003, 07:58 PM

I'm pretty sure that's an oil bath air filter, so don't worry about the oil in the filter.

300SDog · #10 08-02-2003, 05:14 AM

The primitive oil-bath air filter includes metal cannister with handle, filled with stainless steel 'scrub pad' material immersed in at least 1-2" of oil...... The idea was that oil would collect dust.

You'd soak the filter in kerosene to clean it. Itsa permanent filter that never needs replacing. The damned thing actually does better job of accumulating dust than regular filters do, hence it was reserved for diesels that also have massive fuel and oil filters.

Unfortunately, this relic has become scarce - with lots of imbecile mechanics throwing "new" paper filters into the oil bath and throwing away the original cannister.

Other amazing relics on this car can include hornet's nest glow plug indicator, separate starter button, barber pole speedometer, white ivory steering wheel, and taxi cab signal lights.

Be glad its got after-market AC system, this should be easier to fix than behind the dash MB AC.

Dont know floor shift pattern on '60s Benz, but suggest you try pulling up on the shifter when engaging reverse.... same as 123 240D and stick shift 116. On '60s column shift it means pulling the lever towards you and up.

"Low" clutch pedal sounds weird... Can you pull the pedal up with your foot?

Rubber door seals can run you $35-$50 each..... just for the door side. Dunno about body side seals.

Bottom line on this car - it was designed as international taxi cab that gets started in the morning and shut down at night, running all day long..... Forget about taking chances at intersections.
It wont win any races and reaches top speed of 65-70mph.

For your test drive, ask the owner for the keys and tell him you'll be back in 2 hours..... then take your time and visit your family mechanic to see what he thinks.

#11 08-02-2003, 09:49 AM

the oil bath filter is better in some ways, but the oil reduces the air flow a bit more. So it has it's darw backs. It was also used more in areas thay were prone to be dusty.

joshhol · #12 08-02-2003, 02:28 PM

Check the Clutch fluid resovoir. It may just be low on fluid. It's next to the brake master cylinder and uses brake fluid as well.

My Fintail had a slow leak and after much driving, the pedal wouldn't come all the way back up, but after refilling the res and pumping the pedal a bunch o times, it came back.