Compression at 278 to 286 across all cylinders!
 

I'm curious to see what others have taken for readings and what their mileage is. 1983 Mercedes Benz 300D. 285,198 miles :D Oops! I had read the wrong line, now this is correct!

Something is wrong. 250psi is whats needed to even start a Diesel.

Agreed.

Procedural error or faulty gauging.

I edited my opening for my post. Was reading the needle position incorrectly!:o

278 to 286 is still very low. Even my old engine is in the 325-350psi range. New ones are 400+psi after break-in.

That's what I thought and wanted to test for compression to estimate when I should remove the head and do a valve job/cylinder head over haul on it. The Valves were kind of tight when i bought it from the original owner.

Squirt some oil into the cylinders and let it sit for a few minutes then test again. If psi goes up its the rings, if not its the valves.

It probably wouldn't be a bad idea to look for another engine to rebuild and then make the swap with this one. I'll start looking in my area for a wrecked car with a good running motor.

What can you tell me about my engine based on these compression readings?

83 240D 4 spd manual

3/28/2008 compression cold engine: 220,000 miles
1. 320
2. 320
3. 320
4. 380

7/21/2007 compression hot engine: 219,000 miles
1. 360
2. 440
3. 400
4. 460

Those are good.

Tom W

Those are fine if on a cold engine according to my book.

It says down to 220 for reliable starting.

Tom W

A good friend who did a lot of drag racing says that oil will seal valves too.

Tom W

That's what I thought and my readings were taken on a cold engine. If I find another motor that is a bargain and a deal I just can't go wrong with, there will be another Mercedes Bens purchase made!:D

There's a typo/ Cyl 3 cold should be 320. I edited my post. Why do the cold not correspond with the hot readings? Why is cyl #4 higher than the rest?

Actually in looking at them there is more than desired difference between the lowest and highest.

The difference could be from valves, wear in cylinders or from carbon build up increasing compression.

The hot readings are higher because the rings and pistons have expanded with heat I imagine.

Tom W