Re: How does a person evaluate a used diesel?


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Posted by Gil on October 14, 2000 at 01:16:41:

In Reply to: How does a person evaluate a used diesel? posted by Gordon Maney, Editor, Power Wagon Advertiser on October 09, 2000 at 21:21:26:

There can be many avenues to explore when trying to evaluate a used diesel engine. If the engine can be run one of the best is to evaluate how it starts and initially runs when it is cold. If it starts right up and hits on all the cylinders to start with thats great. If it misses on some cylinders and then they kick in as it warms up thats a good indicator of low compression or poorly atomizing injectors or nozzles. Most of the time it is a compression problem. Another possibility is that if the engine is equippped with starting aids (glow plugs or intake air heaters) they may not be operating properly.
As previously mentioned the color of the exhaust is another piece of the puzzle - white smoke is caused by unburned fuel, blue smoke is caused by oil and black smoke is caused from overfueling/ lack of air. Many of the things that you would check for on a gasoline engine you would also check on a diesel - is the oil pressure within the manufactures specs at idle when the engine is hot? Is the oil pressure steady at a given engine rpm or does it fluctuate?
As previously mentioned, oil analysis is another good indicator of engine condition. The oil sample should be taken after the engine has been run and is still warm. Take care not to contaminate the sample with dirt in the process of getting it. Ask what kind and wt of oil the oil is. A good oil analysis lab will be able to confirm what you've been told. Also check with the engine manufacturer to see what oil is correct for the engine. Running the wrong wt or series of oil in an engine can cause all sorts of internal cylinder and ring problems. Offer to buy a new oil filter if you can take the present one off to have a look inside. Remove the oil filter, cut it open and remove the paper and have a look at it for metal hi lites, dirt and sludge.
Get the engine serial # and model #. Most heavy duty diesel engine manufactures can provide you with a history of the engine as far as who it was originaly sold to, what kind of repairs it has had (if performed under warranty or in factory approved shops) what the rated hp and RPM are along with various other info. Also you may be able to get copies of the maintenance records from whomever owned the engine.
If the engine is turbo charged remove the hose or crossover pipe between the turbo and the intake manifold and have a look inside of it - dirt should not be present. A light oil film is acceptable in some engines but a obviously wet surface indicates wear in the turbo shaft seal rings. If possible have a look at the turbine fins in the exhaust side - they all should be there. If any are missing it's a good sign that something from the inside of the engine has gone through it - not good!. Look at the block for signs of oil and water streaks from leaks. When the engine is running, crack the throttle hard and watch for oil or water to come out from between the head and the block. Look around the cylinder head exhaust ports at the exhaust manifold. Is there signs of wetness? Again this is caused by unburned fuel or passing oil out the exhaust and the causes for this are numerous. If possible pull a valve cover and have a look inside. Mayonaise - water and oil combined is not good. The interior surfaces should be resonably clean in a well maintained engine given todays oils and filters.
Take a look at how the engine is dressed- what electrics, accessories, flywheel housing, fan hub, accessory drive pulleys and etc are on the engine - will you need to change things? Does it have a vacuum pump for brake assist? A reasonably priced engine can get expensive fast if you have to start changing a lot of items - especially if what you are taking off is not in demand for trade in and you have to buy the new items outright. If you haven't run the engine confirm that it is the correct rotation (remember LH rotation marine or special application engines).
I could probalbly go on and on. Through the years I have found the cold start up analysis to be one of the most reliable quick indicators of diesel engine cylinder condition. Beware of an engine that has already been run/is warm when you get there.
Happy engine hunting - hope that I helped some.


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