Re: how to tell when a diesel is running good

Posted by jdemaris on January 22, 2005 at 14:40:02 from (209.23.31.73):

In Reply to: how to tell when a diesel is running good posted by maddog on January 22, 2005 at 10:33:01:

If it's running GOOD and EFFICIENT, it will run clean once it's warmed up and provide the power it's rated at without running overly hot. Also, once it's is warmed up, check hot oil pressure at idle. Cold starting can often be a good indicator for certains types of diesels, but not always. Many indirect injected engines, in perfect condition, will skip, smoke, and moan at cold startup - yet once they reach operating temperature they're fine. Even the case with some older direct-injection engines. If you have an engine that you KNOW ran clean and started well cold, and now does not - then that's a different story. We sold many new diesels that skipped, sputtered, and smoked when cold. Things are a bit different now with the EPA involved in most everything. If you have an engine that is suspect, then it will behoove you to pull the exahust manifold off, and look to see if there is excessive sludge, or smoke while running, in certain exhaust ports instead of being evenly distributed. If you find only certain ports that are plugging up, it's kind of analagous to finding fouled spark plugs in a gas engine. Those cylinders probably have damage - unless the engine has an in-line injection pump which can possibly overfuel individual cylinders.
If I were checking over a diesel engine in a non-technical way - I'd first acquaint myself with the nature of that particular engine so I'd now what to expect from it. Then, check the exhaust ports or pipe and look for excessive black sludge. Also look of excessive smoke when running it at a moderate load. And, needless to say, make sure it's hitting on all cylinders. If running the machine around is not convenient, put it in a high gear, hold the brakes on, and lug it down a few times. See it feels like it making good power, not smoking though the breather, and look for smoke out the exhaust at the same time.
Diesels can smoke real bad, black, blue, white, or a combination and still be mechanically sound. If the fuel delivery is turned up, or the fuel timing advance not working, or air is getting in the system, etc., a diesel can run terrible. I bought a truck for next to nothing because the owner was told by the dealer that it had a rod knock and was ready to blow up. Ended up it was a bad injector that was flooding a cylinder with raw fuel and causing a hydrostatic knock. Now, on the other extreme - I looked at a John Deere 350 crawler with a direct-injection engine. I know the machines, and they are usually good starters down to at least 45 degrees F with no assitance, sometime down to 20F. It was 80 degrees F and the guy was using ether to start it. Once it did start, it smoked and skipped for 10 minutes - but then ran fine except for a little blowby. Had good oil pressure and no exhaust smoke when hot. Pulled the engine apart and it had no top piston rings left at all, and the top ring lands on the pistons were just about gone.
So, I guess - in my opinion, it's not easy unless you've got a lot of experience - especially if it's more of a "once over" than a technical diagnosis - which might include a run on the dyno, a compression check, and an oil analysis.

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