- blow-by gasses from a hot engine. Put it in park after a drive and leave it idling. Open the hood and open the oil filler cap, setting it over the hole. If the gasses make the cap dance around or jump off the hole, don't buy that car.
2) cam shaft wear. With the engine off, open the oil filler cap and run a finger over the front cam lobe. It should be perfectly smooth. If you feel scars or tears, don't buy it.
3) While driving on a safe straightaway with no traffic, put the car in a lower gear and get the rpms going high with the engine locked into gear. Release the pedal and let the car slow down for ten seconds and then punch it while looking in the rearview mirror. See a lot of blue smoke? Don't buy the car. The smoke is likely the result of engine oil getting sucked past the valve guides as the manifold pressure increases.
4) Test the compression. 0-62mph times for a turbo wagon are 18 seconds, 22 for a non-turbo.
5) does the fuel level guage work? If not, there might be a lot of fuel fungus in your tank. It is easy to clean, but easier if you drain and pull it. If the fuel hose rubbers are old, they should be replaced (sent, return, tank screen and vent lines). The hard lines can be blown out with compressed air.
6) Does the odometer still work? They are very easy to break. Just pushing the trip odometer button while the car is in motion will break the odometer Frown If it doesn't work, ask for paperwork to confirm mileage. If they don't have it, you should offer them less.
The big thing with any diesel is compression. If the compression is low the engine will be hard to start. So any car that you look at make sure you start it when it is cold. Make sure the owner hasn't warmed it up before you've gotten there. A hot diesel with bad compression will usually start. A cold one with bad compression won't. Once the engine is up to operating temp unscrew the oil cap and let it sit there. If it sits there and jiggles around a bit the engine is still in pretty good shape. If it blows off and is spouting oil out don't bother with the rest of the car. The engine is pretty well worn. What this is telling you is how much blow by there is. It is indirectly telling you how worn down the piston rings are.
These cars like to rust in the hood hinge area and the rear wheel wells. This is due to people not cleaning the drains out which mean water collects. So look in both of those places for rust.