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  #1  
Old 04-30-2011, 12:29 PM
funola's Avatar
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My compression test results = good

I said I would take compression tests every so often on my 83 300D that's been running on a custom 2 tank WVO system for the last 45K miles. Odometer currently at 290,xxx but it's higher since Odo was non functional when I bought it.

#1 400 psi
#2 420 psi
#3 420 psi
#4 420 psi
#5 420 psi

Mercedes spec for a new engine is 320 to 350 psi. I do not know why my numbers are higher but some of the reasons could be:

1. Gauge inaccuracy
2. Differences in adapter (volume), glow plug vs injector hole
3. Carbon buildup in combustion chamber thus raising compression

Anyway I am happy with the evenness of the readings between cylinders. The engine is running great. Quick starts, no smoke, good power and fuel economy. Until next time.....in about 15 to 20K.

ps,

1. test was done with a hot engine via glow plug holes
2. Modified HF compression tester to eliminate leaks and make it easy to use. Basically just the gauge and glow plug adapter (modified) was used

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Old 04-30-2011, 01:03 PM
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Spec for a new *gas* engine might be that.
400 for a diesel is a reasonable target.

Make sure you inform the alternative fuel forum on this board too!

If you don't mind the asking here, what's your latitude / zone in the world, and how have you heated the WVO / SVO near and up to the IP, and beyond - using ILH?
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Old 04-30-2011, 01:21 PM
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Quote:
Originally Posted by scottmcphee View Post
Spec for a new *gas* engine might be that.
400 for a diesel is a reasonable target.

Make sure you inform the alternative fuel forum on this board too!

If you don't mind the asking here, what's your latitude / zone in the world, and how have you heated the WVO / SVO near and up to the IP, and beyond - using ILH?
It depends of the particular diesel engine.

Below is the compression specs from Mercedes tech data manual. I haven't used a gasoline compression gauge in a long time but as I recall, the gauge tops out at 300 psi, which puts the middle at 150 where the gauge is most accurate, which is on the high side for gasoline engines.

I'm in CT. No ILH. Clean oil is key. I'm more interested in my vaccum gauge indicating VO filter condition than VO temp, I know my VO temp is good. I currently have 20k on the VO filter and the vacuum gauge hasn't moved (5" HG). I switch when engine coolant is 80C.

.
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Last edited by funola; 04-30-2011 at 07:46 PM.
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Old 04-30-2011, 03:18 PM
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yeah, those numbers are good. I like to shoot for 450 on diesel motors, when warm.
it's all about speed of cranking, heat retained in the compressed air, ring/cylinder condition, and valve timing allowing air to build pressure in the gauge...
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Old 04-30-2011, 06:31 PM
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Quote:
Originally Posted by vstech View Post
yeah, those numbers are good. I like to shoot for 450 on diesel motors, when warm.
it's all about speed of cranking, heat retained in the compressed air, ring/cylinder condition, and valve timing allowing air to build pressure in the gauge...
Each diesel motor has different compressions according to manufacturer spec. The compression will be what ever the motor will put out. How do you shoot for 450?
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Old 04-30-2011, 07:23 PM
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Funola,
I am getting ready to check the compression on my WVO engine, as well.
I will test cold & hot.
How did you modify your HF compression tester? I have the same one. Photos, perhaps?

Jeff
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Old 04-30-2011, 07:42 PM
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The HF has too many fittings and valves that eventually leak and the hose is too fat. I eliminated the pressure release valve, modified the glow plug adapter to accept a 1/8 push to connect tube fitting. Used 1/8 nylon for the line and a JIC fitting at the gauge for pressure release.

Here's a video. Note how slow the starter sounds? That's been fixed.

http://www.youtube.com/watch?v=a5AB-Es6MZk

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