Could I suggest one relatively cheap and easy way of determining the condition of the engine.... and that is to have an oil sample analysis.
The construction equipment industry uses oil sampling extensively on engines and drive trains (gearboxes, transmissions, transaxles etc) on machines that are on longer term contract hire or covered by repair and maintenance agreements. Regular oil sampling is used to help determine when an engine or transmission is due for an overhaul and therefore allows machine downtime to be scheduled in advance. This also obviously avoids major failures which are more expensive to repair and result in both unscheduled and more prolonged downtime.
The oil samples provide a detailed analysis which tells it's own story as to the condition of just about every aspect of an engine or transmission.
For example
- wear metals (such as bronze indicating wear from main bearing and big end shells)
- particle quantifier (for ferrous particles which gives an indication of general wear)
- the levels of Soot, Oxidation, Sulphation and Nitration to determine the condition of the oil
- tests for water, antifreeze (for such as head gasket problems) and dillution with fuel (fuel pump shaft seals problems)
- magnetic test to provide visual indication of ferrous contamination (and if there are larger particles it can often be determined which part of the engine they are from)
- oil viscosity test
The results are usually translated in plain and simple terms so you don't have to go get an engineering degree to find out what it means.
Companies getting regular sampling carried out usually pay between £10 and £15 per test so even as a one-off I wouldn't imagine that it would cost more than about £25 and the results are usually available on-line within a few days.... obviously it would cost more if you had someone drain off a sample for you rather than doing it yourself.
One good source of information is from the Finnings web site......
http://www.finning-sos.co.uk/Finnings are the Caterpillar distributors in the UK and so are obviously used to testing oil from diesel engines.... but there are plenty of others who can also provide this service and most supply a sampling kit for you to use and post off to the lab.
Of course it is always better to have a sample of oil that has been in the vehicle for a reasonable period of time so if the oil in your engine has been changed fairly recently then I'd do a few more miles in order to get a sample that will yield meaningful results.
Martin