Compression reading
 

I did a comprssion test on my 1998 E300 TD. The 606 engine. I have a reading of about 250 PSI. Is this good?

Hot? Cold, how many revolutions (testing each cylinder, hot, 8 is typical). If it's hot, it sounds low. If it's cold and you have a reason to, (hard starting, oil use, other causes investigated) test it hot.

it was tested cold. I can't test it hot because it's having trouble running, which is why i'm testing in the first place. Just tested the first cylinder.

Well that is a very incomplete compression test. You must test them all to get any idea of the condition of the engine. You say it runs rough. Well, then it must run a little bit. So fire it up and try to get and keep it running for five minutes. Then pull all the glow plugs asap and go down the line and test each cylinder. It still takes a good battery to get a good accurate reading. If you have a home garage charger, put it on the battery and leave it on for the test. Install the gauge and crank for 8 or 10 cylinder pops. Then go to the next one. Then you might want to give each cylinder a small shot of motor oil. Give them each a teaspoon full. Hit the starter and crank it over for a couple a seconds. Then repeat the compression test. When testing write down the test number(compression reading) next to the cylinder number for future reference. Report results back and I think we can tell you a lot about that engine. If it is really difficult to get it too run, let the hood open and sitting in the sun for a couple of hours will warm things up also. After all, it is summertime except for a few places like Leadville or the North Slope.

specs for the 606

low limit 18 bar

brand new: 29-35 bar

difference between clyinders- 3 psi

They told us in mechanic school that wet compression tests on a diesel are a bad idea-too much chance of a hydrolock.

yeah you can if your shooting too much oil in the chamber, ie drowning the chamber in oil. But that chance is slim if you disable the fuel system ignition should never happen. just curious what tech school you go to?

US Navy Construction Mechanic "A" School. I graduated in April of '01.

That doesn't sound right. How could the compression be higher than the compression ratio? I don't think that the CR is above 25.

Delta E = Q-W, and W is large, and negative (sign convention is confusing too + work is work the volume does, - means work done on the volume). If it happens fast, you call heat flow zero. Conservation of energy matters as well as the gas law. Absolutely classic thermo, unless brain rot has set in, 39 is after all, only days away for me.

Since energy is conserved, the gas gets hot as you compress it. Considering boyle's law, or the gas law only (PV=K) You're neglecting energy added as work done on the control volume.

As a check, consider spiffy new 61x compression of say, 410 psi. This is north of 27 bar, yet the volume ratio is what, 21-22 for that family?

Happy to bust out my thermo book and scan it if you want the greek letters, lemme know. I might even have a relevant part of my propulsion book scanned what says the same thing.

Sounds about right now. I am about a decade and a half older than you. Brain rot has already set in.:rolleyes:

Huh?

thats right from mercedes....

just checked agian and those the correct numbers so I dont what numbers you got but whatever they are they are wrong.

my diesel compression tester goes to a 1000psi for the big rigs. Looks like you need to learn more about diesel engines

420-507 psi is normal for a diesel engine

looks your engine needs to be rebuilt