Is compression testing necessary?

Assuming a diesel engine is running smoothly, without any odd noises, and handles well, is there any need for a compression test?
The local dealer was offering to do a pre-purchase inspection +
compression test for "only" $600.
He said it was a good idea to do it, as the car is nearly at 200,000 miles.
I know the engine runs well, and suspect it's not worth doing the compression test, though the pre-purchase inspection would be something I'm definitely considering.
I think he's just trying to get some money out of me. :/
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Pete Stephenson
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The whole inspection thing for $ 600 smells like a major ripoff. Besides who in his right mind would use a selling dealer do a pre purchase inspection. If you absolutely need to do this, have an independent mechanic do it for you. Peter

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I agree, it does sound like a ripoff, hence my asking for confirmation on if the compression testing is good or not.
I was calling around to various mechanics and dealers looking for who would perform the most detailed inspection. If I could afford it, I'd get it checked at a few places, but can't afford that.

Indeed. That's precisely what I have planned.
I take it that a compression test probably isn't necessary if the car's running well?
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Pete Stephenson
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My pre-purchase inspection, including mechanical and compression checks (& perhaps leakdown, but I'm not certain) was a mere $20. And they're a VERY reputable shop in Westerville, OH, that's done VW for 30 years.
Collin
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Don't go to the stealership!
Find a local independant that know mercedes and go there. $150 Should get you a good inspections and a compression test.
Even if the engine runs well, a compression test is a good idea IMO to establish a baseline for any future issues, as the engine is new to you at this junction.
Marty
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$600???
Call some independent M-B shops, ask their price for a compression test and suspension inspection.
It won't be $600!
You now see why owners of out-of-warranty cars patronize independent M-B shops.
It's your money. Good to know its well spent on a good car or not spent on a car that will need more of your money.
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Here's a quick compression test IF the car still uses glow plugs to start: when the car is COLD try to start the car without waiting for the glowplugs. If it starts it has very good compression (it will work rough for a bit), if it don't start... well, it just means that it doesn't have very good compression. A 300SD I had started no problem with no glow plugs, it had a good battery of course.
cp

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wrote:

An excellent idea! A field-expedient compression test that costs nothing would definitely be something to try.
The engine starts and sounds good when started with glowplugs, and had good acceleration and handling on freeway onramps and at freeway speed. I doubt there's a compression problem, but your field-expedient test is something that would help me verify that everything's in good working order without having to spend a boatload of money on official testing. An inspection, yes, but compression testing sounds rather expensive...this might just be the ticket.
Cheers!
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Pete Stephenson
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Yeh, though I want to learn how to do a real compression test too :-)
cp
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IT'S NOT EXPENSIVE TO COMPRESSION TEST YOUR VEHICLE. Sorry for the shouting.
The above "test" might be handy but teaches you very little about the conditions of the engine internally. Temperature is also a big variable in the above equation.
Try to find a local independant garage that knows mercedes cars and ask about a a pre purchase inspection that includes a compression test.
It's worth doing, as in the future you can retest and KNOW if anything has changed.
Marty
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I've called three or four shops in the area and asked what they charge for a pre-purchase inspection and/or compression test. We'll see.

Good idea.
I'll probably end up doing the homebrew test, as well as the "real" one.
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Pete Stephenson
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