Compression Test Hot vs Cold - PeachParts Mercedes-Benz Forum

Phreetogo · #1 07-26-2003, 11:09 PM

I was just curious if the compression will be higher if you do a compression test after the car is warmed up? Or will it be the opposite effect. Just curious because I checked my compression cold because I am unable to start my car at the moment. Thanks John

dabenz · #2 07-27-2003, 11:50 AM

In a good engine the compression should go up when tested hot - the pistons, rings, and cylinder liners grow toward each other and the lubricating oil should still be on the cylinder walls. Whether or not you can tell the difference depends on your gauge. Generally you do a cold test and a leakdown test. Hot tests can be dangerous so they're generally reserved for those oddball scenarios.

By the way, how did the car run and what work did you do just before the no-start? Diesels are simple and lots of people here can help.

Phreetogo · #3 07-27-2003, 12:22 PM

I got the car on Ebay (which I'll never do again!) and flew out to arizona to pick it up. I drove it back here to colorado 8,000ft. The next day it wouldn't start. As of today it is now running again but seems to be lacking power, but it is a wagon and am not exactly sure how it should run. I had found algae in the tank. I drained the tank, cleaned the tank screen, threw in some biocide and changed both fuel filters. Adjusted the valves. Changed the air and oil filters, and put in new glow plugs. Now it starts up pretty good. Next i'm going to run some diesel purge through the injectors and see if that makes a difference. So that is where I am now. thanks John

dabenz · #4 07-27-2003, 04:10 PM

Sounds like you're off to a good start (no pun intended). Your next drill should be to figure out how to check the altitude sensor. Do a search for the ALDA or someone with experience can pipe up (daBenz doesn't have it).

#5 07-27-2003, 10:24 PM

Please don't just pour in fuel tank. Instead take two fuel lines and a jar and plumb it into injectors.
Do a search here lot of info.
If you just pour in tank or large fuel filter most will go back to fuel tank.
Shoul take about twenty min. to run through a can.
Charlie

Phreetogo · #6 07-27-2003, 10:38 PM

I know the scoop on dieselpurge it has instructions on the can : )
Thanks, John

gsxr · #7 07-28-2003, 06:14 PM

John,

All cars lose lots of power at high elevations, and 8000ft is way high. My diesels would be fast at sea level but quite sluggish at 5-6000ft in Reno. I can't imagine how they would be at 8000! Ugh. You could try messing with the ALDA (search archives), but after that, it may just be the way the car will operate up there in the clouds. If you ever get to lower elevations (say, under 2000ft) try a 0-60 timed run with a stopwatch (and a GPS to verify speedometer accuracy). Your car should be in the 13.5-15.0 second range. If it's much slower, something is wrong. This is the easiest way to determine "how it should run".

HTH,

ohcaptainron · #8 07-28-2003, 06:59 PM

Congrats on your new car. I live in Evergreen at 7500 ft, one of my cars is a 85 300TDT, the car performs very well at this altitude. Going up I-70 at 80 MPH on the steep parts.
The difference in performance at sea level is that the turbo lag is much less noticable. In order to improve it I blocked the EGR vacume line (better response off the line) and adjusted the ALDA and the turbo boost pressure to about .9 bar. My car has the KKK turbo so the adjustement is very easy, I believe that yours has the Garrett which requires the boost control valve to be disassembled in order to adjust the spring tension. Not hard just more time consumming. This will make a huge differance.
Good luck
Ron
1985 300TDT
1993 300D
1999 E300 sold
1999 E320 AWD WAGON
2003 E55 AMG
2004 E320 CDI on order

Phreetogo · #9 07-28-2003, 07:04 PM

I thought I had broken my alda. but turns out I didn't. As I was fiddling with it I turned it all the way in and tried running the car to see if there was any difference since I thought it was broken. Boy was there a difference!!! Now the car drives like crazy compared to what it did. Still no where near 0-60 in 15 more like 24 but it used to be a minute or so. I would love to see how it does at a lower altitude now.
So does this seem right that I would get more power turning the screw in? I thought it was supposed to be the other way around.
Any insight would be appreciated. thanks, John

gsxr · #10 07-28-2003, 07:17 PM

Ooops, I didn't make that clear. With a turbo you lose power at high elevations off-idle, before the turbo spools up. Once the turbo is working, power should be nearly equal to what you'd get a sea level at higher RPM's (say, over 3000rpm). At least it will work that way until you reach extreme elevations, like Pike's Peak, 14,000ft or whatever where the air is so thin there's not enough to feed the turbo intake.

Normally you get power by richening the mixture, turning the ALDA setscrew CCW. It could be possible that turning it in (CW) at high elevations could help. Interesting...