Checked compression today...
 

Did a compression test on my 300D. Warmed up the engine to the operating temp. Let it sit for a little while until I was able to handle it. Removed the hard lines, glow plugs. Reamed them all out - was meaning to do that for awhile - they were REALLY carbon-packed...

Started doing the compression test through the GP holes, but quickly realized that the space is too tight in there so switched to Injector holes and continued. Replaced the heat shields as I re-installed each one. Anyway, here are the numbers (psi):

#1 350 350
#2 320 315
#3 300 300
#4 300 305
#5 305 305

Think these numbers are pretty good - wonder what others think... Was under the impression that anything above 220 psi is within spec.

It was a little concerning to find some oil around the injectors and heat shields when I pulled the injectors off... Also #2 and #4 GPs were oily and wet... not sure if that's normal - but I guess since the compression is not perfect maybe it's just the way it is.....

i was under the impression that anything above 320 was alright, not 220

220 isn't even enough for the engine to start. My 240's 616 had 200-250 across the board and it wouldn't even start with ether.

I would say that it is not real good
 

I think real good is another 100 plus pounds up, at around 425 with very little variation. I think 305 to 315 is way too low. How about the valves. Have they been adjusted recently. You might find a valve adjust will really change things.

I'd say their fine. Numbers are going to be lower at your altitude. My SD showed around 330psi dead cold and it runs fine. I think MB says 220 is a minimum to run.

what fitting did you use

I agree. My engine is 320-350 and can start at -20*f with only glowplugs.

Fitting...
 

Used a Compression check tool for diesels from Harbor Freight (around $35)... it has a number of fittings that you can choose from...

You can check it thru the glow plug holes using the 90 degree fitting in that kit.

My book says 220 cold minimum.

Oil on the gp's doesn't sound good, did you brush them on something when you removed them? A little oil leaking from the cam cover is quite common.

Hey all,

What is considered oil on the GPs? Actual oily buildup? I took out my old loop style plugs last week and they were black, but not oily per se.

Black is burnt carbon, normal.

If it starts and runs OK, and you've adjusted the valves recently, why worry? It's silly to re-ring, rebuild or replace the engine, (corrective action for low compression) isn't it?

if you reamed the glow plug holes before the compression test you may have got some carbon particles on the valve seats while cranking the engine.If it starts and runs OK i wouldnt worry too much about it,however if you feel that it is not running good then perhaps another compression test is in order. Don

Not planning to do rebuild...
 

Right, it would be silly now - I have no plans to re-ring the engine any time soon (if ever). It started leaking some oil recently from under the valve cover and in other places, so I thought I would do this check to see where we are...

Did valve adjustment about last April - I may do another one this summer just for grins to check things out again... but overall the car runs pretty well - especially on the highway.

Looking to start making bio-diesel so this is just another step in checking the engine and working my way through the vehicle and frankly learning about its strengths (and weaknesses). Thanks all for your insights.

Nice...its great to have a baseline so if problems do come up you have some data to fall back on.

You may consider doing an oil analysis from Blackstone if you are really keen on having a pre-bio history (I didnt do this).

dd

220 is minimum cold, all readings should also be within 15% of each other. I will post mine from a worn out 1985 300d with 460K miles tomorrow for reference/perspective. It does NOT start easily.

Here's what I found last fall, starts great.


" #1
09-11-2008, 03:34 PM

mobetta
Registered User

Join Date: Mar 2006
Location: minnesota,hey.
Posts: 1,690
compression test results
I finally got around to changing out the glowplugs in the wagon. I've been rolling w/ 4 plugs for a couple weeks. I also reamed out the holes, using a tool made by a fellow forum member.(Thanks for the expedited service, Diesel911)

I reamed and check compression numbers, put in 5 new duraterm's from NAPA. I hope the w/ clean holes they will last longer than the last set I put in(4/5 did not last a year)

anyhow- heres the numbers
312,xxx miles

1-420 psi
2-425 psi
3-405 psi
4-420 psi
5-395 psi "

my brand new chinese P.O.S. gauge must be wrong and I will borrow another to crosscheck.
My 460,000 mile 300d had these readings taken after removing all the injectors and car was completely cold:

1) 125psi
2) 200psi
3) 190psi
4) 150psi
5) 180psi

I've been on filtered ATF for the last 20K. The injector spray pattern is fine and I just adjusted the valves with no improvement in compression OR ease of starting. It is sometimes VERY hard to start even when warm but with those numbers I'm surprised it starts at ALL!!! It does run and idle well after starting!

john

I wouldn't doubt those numbers with that kind of abuse.

???
 

why do you say that? Do you think the ATF has coked the rings since its been on ATF?

It's possible..... though it hasn't hurt the injectors any judging by the nice conical spray patterns.

john