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post #21 of 25 Old 08-03-2012
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Re: How to do compression check?

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Originally Posted by IronSpinnaker View Post
They actually only tell you anything if done on a schedule with the data trended on a graph. All engines have wear metal present in the oil. The presents of wear metal means the engine works. The oil analysis only shows you the rate of deterioration if you have multiple points of reference over time.(like at scheduled oil changes) 10, 20, or 30 % increase in wear metal in a three months scheduled oil change is normal.... 100% increase in the same amount of time is bad.
They can tell you if something is out of wrack. Blackstone has a pre-purchase test kit (includes a pump to get oil out) and will give results same day they receive the sample. I agree it is not as good as a trend, but it could find coolant from a small leak in the head gasket, the most common issue. It will show very high levels of metals if there is a bad bearing. It can also indicate if the oil has not been changed in a long time. There is a lot of info in there. I have no interest in Blackstone, but have used there services in the past and found it to be useful information.
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post #22 of 25 Old 08-03-2012
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Re: How to do compression check?

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Thanks Barry.

What I am asking Iron is the following. When he offers the opinion that a responsive start on a cold engine is a sign of good compression does that include using glow plugs on engines, like the M25xp, that have them. Response from anyone that has experience with diesels would be appreciated.

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Yes. If an engine has glow plugs, they should be used for a cold start test.

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post #23 of 25 Old 08-03-2012
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Re: How to do compression check?

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Originally Posted by dsmauney View Post
Thanks Barry.

What I am asking Iron is the following. When he offers the opinion that a responsive start on a cold engine is a sign of good compression does that include using glow plugs on engines, like the M25xp, that have them. Response from anyone that has experience with diesels would be appreciated.

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DaveM
Yes - if you have glow plugs, use them. An engine with poor compression will usually be harder to start and often idle unevenly, although both conditions can be caused by other things.
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post #24 of 25 Old 08-04-2012
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Re: How to do compression check?

Yes; use them. A Pre-chamber Diesel is designed with lower compression than a Direct Ignition Diesel, which is why they have glow plugs.

Ignition takes three things, fuel air and heat. In a Direct ignition diesel the compression of the fuel and air causes the heat for ignition. In a Pre-Chamber diesel glow plugs are used to gain the heat at a lower Compression. If you have glow plugs your engine was designed to be started with their use. It will start without them usually, but it will be much harder and that is normal.

You can see blowby if you remove the oil cap, you would have exhaust coming out the fill spout. That would be a very good indication that engine has significant wear.

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Last edited by IronSpinnaker; 08-04-2012 at 08:30 AM.
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post #25 of 25 Old 08-04-2012
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How to do compression check?

Thanks Iron. Neat idea on oil fill cap. Appreciate other input.

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