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 > Tech Help

LinkBack Thread Tools Display Modes
Old 11-28-2013, 11:53 AM
Registered User
Join Date: May 2012
Posts: 65
Wet Compression Test vs Leak Down Test

My 380sl has plenty of power, but it frequently emits a puff of greyish white smoke on exit ramps after hwy driving. So I decided to do dry and wet compression tests to see whether the smoke may be caused by leaky valve stem seals or rings

The results of both tests, listed below, showed that the dry readings on the right cylinder bank were all higher than they were on the left bank, probably because that head had to be shaved when I did the valves app. 70k miles ago.

Cyl_Dry Wet

1 _160 _180

2 _160 _180

3 _160 _175

4 _160 _190

5 _180 _200

6 _175 _180

7 _180 _200

8 _185 _200

Considering that the difference between the wet test and dry test on most of the cylinders was near or slightly greater than the acceptable 10%, I was wondering if anything could be gained by doing a leak down test, other than to determine how much the rings in each cylinder are leaking.

Thanks very much in advance for your usually well-informed opinions

Reply With Quote
Old 11-28-2013, 12:23 PM
Registered User
Join Date: Dec 2010
Location: upstate SC
Posts: 79
I would take a look at #6. You only gained 5psi difference from dry/wet. Somethings going on in that cylinder. Maybe Just do a leakdown on that one first..... fwiw
Reply With Quote
Old 11-28-2013, 10:54 PM
Registered User
Join Date: Jan 2012
Posts: 7,534
I don't use wet comp tests just dry and leak down. Compression is a quick way to find a weak cylinder, leak down tells you if the leak is rings, valves or compression to coolant.

Valve stem seals tend to smoke at idle / acceleration from an extended idle, slightly worn rings on deceleration ( closed throttle , high intake vacuum ), very worn rings at idle.

There isn't a direct way to test valve stem seals. Given your engine has time on it, changing valve stem will help. Parts cost is low, labor time consuming but not difficult.
Reply With Quote
Old 12-02-2013, 12:37 AM
Registered User
Join Date: Jan 2004
Location: Jacksonville, FL
Posts: 474
White smoke on coast down can also be caused by a bad transmission vacuum modulator. Remove the vacuum hose from the modulator to check for the presence of transmission fluid. Mark
Reply With Quote
Old 12-03-2013, 09:13 AM
Registered User
Join Date: May 2012
Posts: 65
The modulator was replaced 2 years ago when I had the transmission rebuilt. So I didn't check. But I guess that would still be a good idea. Thanks for reminding me

Reply With Quote


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 07:57 AM.

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2018 Pelican Parts, LLC - Posts may be archived for display on the Peach Parts or Pelican Parts Website -    DMCA Registered Agent Contact Page