Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help



Go Back   PeachParts Mercedes-Benz Forum > Mercedes-Benz Tech Information and Support > Diesel Discussion

Reply
 
LinkBack Thread Tools Display Modes
  #1  
Old 03-04-2007, 04:04 PM
Registered User
 
Join Date: Jan 2006
Posts: 172
Smile Compression Tested - Yayy!

Finally got around do performing my compression test. I have no idea what the car's history is before 240K miles, the valves were no where near adjusted correctly, uses a bit of oil (although not much at all if I keep the oil level closer to the lower mark on the dipstick it seems) and it won't start below 20 degrees so I was a little concerned. My results:
360
340
350
330
380
I'm not sure what range they should be in, but that has got to be pretty good for 260K miles. If nothing else, they are all almost within 10% of each other. I used the $30 Harbor Freight tester (worked great) on a warm engine (driven to operating temp in cold weather and sat for about an hour or so) and used the glow plug holes. It reached max. psi after 10 cranks (shot right up pretty quick too: about 100 psi per crank until it reached about 300 then slowly built up to max.)
Does anybody know the compression range when new?


Last edited by Jkid; 03-04-2007 at 06:16 PM.
Reply With Quote
  #2  
Old 03-04-2007, 04:10 PM
t walgamuth's Avatar
dieselarchitect
 
Join Date: Apr 2005
Location: Lafayette Indiana
Posts: 38,613
first suspect is always glow plugs.

i hear a bit over 400 psi warm.

tom w
__________________
[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.
Reply With Quote
  #3  
Old 03-04-2007, 05:51 PM
toomany MBZ's Avatar
Registered User
 
Join Date: Nov 2006
Location: central Va
Posts: 7,820
Are your results after setting valves? Compression range is around 350 and up, warm. Not bad with those miles. The 10% rule is pretty good.
__________________
83 SD

84 CD
Reply With Quote
  #4  
Old 03-04-2007, 06:30 PM
Registered User
 
Join Date: Jan 2006
Posts: 172
Quote:
Originally Posted by toomany MBZ View Post
Are your results after setting valves? Compression range is around 350 and up, warm. Not bad with those miles. The 10% rule is pretty good.
After. Adjusted them last year - drove almost 10K miles and adjusted them again not too long ago. My brother made the comment "too bad the 330 is right bext to the 380". I wonder what the lowest has to do with being adjacent to the highest?

The glow plugs seemed to test out okay. But I think I'll just replace them all now knowing that the compression is not an issue.
Reply With Quote
  #5  
Old 03-04-2007, 06:35 PM
t walgamuth's Avatar
dieselarchitect
 
Join Date: Apr 2005
Location: Lafayette Indiana
Posts: 38,613
i can't see where they are matters.

tom w
__________________
[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.
Reply With Quote
  #6  
Old 03-04-2007, 07:11 PM
toomany MBZ's Avatar
Registered User
 
Join Date: Nov 2006
Location: central Va
Posts: 7,820
Quote:
Originally Posted by Jkid View Post
After. Adjusted them last year - drove almost 10K miles and adjusted them again not too long ago. My brother made the comment "too bad the 330 is right bext to the 380". I wonder what the lowest has to do with being adjacent to the highest?

The glow plugs seemed to test out okay. But I think I'll just replace them all now knowing that the compression is not an issue.
Good for you checking after. An article in Star magazine suggestes a leak down test is a more acurate measure of engine condition. When taking compression test, note if gauge drops after cranking. Did on the '82. Yet, has no trouble starting, but VERY sluggish till warm. Will check banjo connections soon. Your test on GP's, with ohm meter? Have you checked voltage with plugs on? I checked the SD plugs, [ohm only] one was bad, replaced, no change, replaced all, still no change for single digit temp starts. Scratchin' my head on that one. One cylinder being low beside another, may mean rings vs gasket. Gasket eaiser, read cheaper to correct.
__________________
83 SD

84 CD
Reply With Quote
  #7  
Old 03-04-2007, 07:23 PM
240Joe's Avatar
Registered User
 
Join Date: Nov 2000
Posts: 525
Don't worry about compression or leak down tests. And don't change all the glow plugs just because. Make sure each glow plug meets the spec and make sure the voltage is getting to all of them.

Next in the list of cold starting tips is to make sure the battery is good and make sure the starter is good. Just because it turns doesn't mean a starter is good. When starters get old in these cars, they lose RPM and that can make all the difference in the world.

Another couple tips are to use synthetic oil and make sure the ground strap under the car is clean and tight (worth checking now if you haven't yet).

240Joe
Reply With Quote
  #8  
Old 03-04-2007, 08:29 PM
Registered User
 
Join Date: Jan 2006
Posts: 172
Quote:
Originally Posted by 240Joe View Post
Don't worry about compression or leak down tests. And don't change all the glow plugs just because. Make sure each glow plug meets the spec and make sure the voltage is getting to all of them.

Next in the list of cold starting tips is to make sure the battery is good and make sure the starter is good. Just because it turns doesn't mean a starter is good. When starters get old in these cars, they lose RPM and that can make all the difference in the world.

Another couple tips are to use synthetic oil and make sure the ground strap under the car is clean and tight (worth checking now if you haven't yet).

240Joe
The glow plugs are all receiving good voltage and I tested all but number 5 (didn't have the right wrench yet to get it out) outside the block. They glow a nice bright orange. I never really wanted to change them 'just because', but I've heard a lot of people say that new one's will help.

I swiched to syn. oil and replaced the - battery cable and the end on the + cable at the battery (very easy to do and most corrosion in the cables seem to be at the battery). I think this may have helped a bit (maybe good for another 10 degrees). Now that I see my compression is good, maybe it is time to rebuild the starter (I always suspected it).
I'm pretty sure my battery is good. I know it's only a year old, but I suppose I could have killed it somewhere along the line (like when I drove it with no alternator for a while).

Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On




All times are GMT -4. The time now is 10:02 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2024 Pelican Parts, LLC - Posts may be archived for display on the Peach Parts or Pelican Parts Website -    DMCA Registered Agent Contact Page