Thread: What should2.4 tdci compression pressure be?

My understanding on other engines (petrol experience talking here- lower Compression ratios) is that you are looking for consistency, but also need to cross check to see if any potential compression leak is occurring thru the valves, rings or another path (ie something cracked )

Were figures dry or wet compression results?
I'm assuming your bloke has done the test both ways and maybe has quoted the highest possible result he could achieve for each pot?


As for the compression pressure, I haven't dug thru the manuals or anything, but is it not possible to get a rough 'ideal' compression pressure off the compression ratio of the engine, given that we could assume 1atmosphere (14.7psi) or 1 Bar pressure at the cylinder's bottom dead centre?

Compressions were tested dry and cold; engine was cold (or cool) by the time the inlet manifold and glow plugs were removed, I too have only petrol engine experience but I'm not 100% sure whether a wet compression test can be done on a diesel without hydraulic lockup or at least risk of damage? A straight mathematical conversion based on compression ratio would give some meaningless theoretical numbers based on 100% volumetric efficiency which is unrealistic even at cranking speed, although when I do the maths based on 19:1 compression ratio it comes out way less than the actual compression pressures from the test. Just wanting to compare them with what others have experienced or what is a known good number for this engine.
The diesel mechanic is a very experienced bloke- one of the few mechanics I'd trust my work to; he stated that in his experience, figures less than around 330psi can give poor cold running. The engine has done 255,000km.

I had given a passing thought to hydraulic damage as result of a wet compression test. But this is not my area of expertise and, err, someone had to reply

Irrespective of the numbers, I guess the take home message is that even if the engine is low on compression, it's consistently low. Which is much better than being inconsistently low I guess!