I have evaluated thousands of machines powered by diesel engines. Though I am not a professional diesel engine mechanic,
I would like to share some of my observations with you. I have completely overhauled many diesel engines and hundreds of gasoline engines. Machines are dangerous and you can be seriously injured trying to operate them. Remember, don’t start an engine unless you are sure you know how to stop it! I use the term red flag, in the following paragraphs to indicate that I think an engine may have a serious flaw and should be given more consideration
Murder? Suicide? We will never know the answer. It is reported that on September 29th 1913, Rudolph Diesel was on a ferry crossing the English Channel, perhaps to take his diesel engine invention to the British, having disagreements with German policies. He met his grizzly death in the cold waters of the English Channel, his body discovered in the water 10 days later. It is interesting that subsequently the German submarines were powered by the Diesel engine.
Diesel engines have followed the original basic design since their inception, compression firing of the fuel driving a piston down, through a connecting rod turning the crankshaft. The crankshaft is connected to what ever the engine is powering like a transmission, hydraulic pump or a hydrostatic drive unit. Key word here, Compression. As an engine wears, the compression will diminish and the engine becomes weaker, less efficient and burns more oil and fuel.
When I have to evaluate an engine, I want the engine cold, if possible I want to be the first one to start it that day. Some distinct clues may be present only when the engine is started cold. An engine that has been started, and run for only a few seconds may conceal indicators of injector bleed down, glow plug abnormalities, ether necessities, battery and starter issues. Cold starting the engine is important because a cold engine that is weak (low compression) might not start with out the aid of a starting agent like a jumper battery or ether (starting fluid). If the engine is cold then the cold starting device that the machine has incorporated into the starting procedure like glow plugs should be utilized. Many machines have automatic glow plug countdown timers. I watch for the timer and let it tell me when to start the engine. Some diesels don’t have any cold start aids and they should just crank and start. I am adamantly against the use of starter fluid (ether) however, I have used it and I have known of machines that have used starting fluid for years and are still running, but in my opinion they are not running as good as they could. If I need ether to start a warm engine that is a red flag, if the engine is very cold ether is an acceptable starting agent, however, only a split second of the spray should be enough for an engine to start. If more ether is required there may be a lot of internal wear on the engine or other problems. If a hot diesel requires ether to start that is a big red flag and I don’t buy it unless I have a major overhaul figured into my pricing.
In extreme cold temperatures, I don’t discount a hard starting, smoky, shaking or clattery sounding diesel too seriously because diesel fuels can gel. Gelled fuel does not spray correctly from the injectors, duplicating some weak engine characteristics. Once started and smoothed out the bad characteristics should quickly dissipate, unless there is a weak engine or a fuel related problem, possibly even ice in the fuel or fuel filter.
Oil laboratory analysis is a good way to find out what contamination is in the oil, if you can get one done on an engine you are interested in then no harm done. However, most of the time the engine inspection is a hurried affair and if the oil has been recently changed the results of the test could be misleading. I check the oil to make sure that there is oil in the engine, visually inspect the oil and lastly smell the oil. The oil should be translucent gold or goldish brown if it was recently changed. Black engine oil is very common and acceptable, as a byproduct of combustion diesel oil quickly turns black. Creamy milky grayish oil is a sign of water or antifreeze mixed in the oil, a big red flag. I look at the oil closely for flakes of metal to be floating on the dipstick, this might be more evident after running the engine, but if I see metal flakes something is wearing badly and a is red flag. I wipe the oil on a rag and if the oil spreads out quickly, that is a sign that there is diesel fuel mixed in the oil and a reason for concern. I smell the oil to determine if it smells like diesel fuel or if it smells burnt. Oil that smells burnt is a sign that the inside of the engine has been very hot. I have disassembled engines in my garage that were hot and my garage had that burnt stink for weeks. Overfull on the dipstick is a good reason to check the oil again, after running the engine. There might be fuel in the oil or this might be a sign that the oil pan has antifreeze in it, remember, oil is lighter than water. The oil pump pickup tube sits in the very bottom of the oil pan, not a good scenario if the oil pan has an inch deep layer of antifreeze below the oil.
Starter and ring gear teeth
If I hear the starter motor make a loud sqeeeeeeeeerrrrrrrrrrrrrrrrriiiiiiiiiiiiiippppppp noise when I turn the key then there is probably a problem with the starter bendix and possibly the flywheel teeth. red flag! The starter bendix is the part of the starter that engages the flywheel ring gear teeth. Starter bendix’s go bad frequently, not a major expense. If the flywheel ringgear teeth are chewed up then the expenses will increase considerably, requiring removal of the engine or what ever is on the flywheel side of the engine to access the ringgear. Usually I try the starter 2 or 3 more times. The teeth may engage and start the engine. If the gears never engage, I try to turn the engine by hand to match up a different set of teeth. Engines have a tendency to stop spinning in the same place and those spots on the ring gear get all the wear. If the starter then engages the ring gear teeth I know that I have a ring gear problem. I frequently start an engine several times to make sure that there isn’t a starter bendix or flywheel tooth problem. I have replaced many starters and not many flywheel ring gears. I listen to the engine as I crank it, the engine should have even pulses dragging against the starter motor. If there is a sudden freewheel sound as if there isn’t a drag against the starter then there is a possible weak cylinder with low compression, red flag. Costly and, and possibly something that might not show up starting a hot engine. If the engine doesn’t start after cranking look for a fuel shut off. Many older diesels use mechanical fuel shut off cables, if it is engaged then there will be no fuel and no start. Excessive cranking with no start up or a smoky start is a good reason to suspect internal engine wear. Once the engine has started I look and listen. I look at the exhaust and listen to the fireing of the cylinders. If the engine has a miss (uneven fireing pulses) that quickly (a couple seconds) smoothes out possibly along with moderate exhaust smoke that also clears up then I don’t fret. However, if the exhaust smoke and uneven running takes much longer to clear up then I suspect a fuel or compression problem, red flag! I have seen relatively new diesels start with the uneven fireing and smoky cold start that are healthy engines. Again, I am not too concerned if it clears up quickly.
Blue White Tinted Exhaust Smoke
A perfectly healthy diesel will have no visible exhaust smoke except for start up and acceleration. A little blue smoke (oil burning) on start up is normal and some diesels will have a bluish smoke at idle that should disappear with increased throttle. I don’t like to see any blue smoke but not all diesels are perfect. I remember one of my automotive teachers comments about a light blue smoke from an old truck engine, he said, “That’s just good lubrication”. (Today that truck wouldn’t pass emissions testing, sorry teach). Blue smoke that stays in the exhaust throughout the RPM range is another reason to do more investigating. If I see a lot of blue smoke, red flag! I always keep in mind that blue smoke in the exhaust is a sign of lubricating oil burning in the combustion process, not a definite reason to say that the engine is worn out. Oil can be slipping past the engine rings because it is diluted with diesel fuel. There can be a bad turbo charger seal, a clogged air filter (a very bad sign about maintenance), or there can be oil in the fuel!
Black Exhaust Smoke
Heavy black smoke is a sign that the fuel is not efficiently burnt and is not necessarily bad if it is upon acceleration. However, if there is a constant heavy black smoke all the time the engine is running, red flag! There is a problem, fuel is not being properly burned and a further check is necessary. The engine may be worn out! The unburned fuel was more evident (Black smoke), than the oil burning (Blue smoke)!
White Exhaust Smoke
Sometimes with a sweet smell
This situation is caused by antifreeze getting into the cylinders because of a blown head gasket, cracked cylinder head or other remote methods, red flag! Not only are there repairs necessary but I look for reasons that the engine was probably overheated. It may have been the thermostat, radiator, water pump or loose fan belts. This is a good time to remove the oil fill cap and if the underside of the cap is grey gummy sludge, red flag! This is a good sign of poor maintenance or water in the oil. Don’t forget that water is a byproduct of combustion, a steamy exhaust especially in very cold weather is acceptable, however, it should clear up as the exhaust system and engine heat up. I also keep in mind many machines have exhaust pipes without rain caps, the exhaust pipe can fill with rain water and take a while to evaporate as the system heats up. I have been coated more than once with a black shower, a mix of carbon and rain water from the exhaust pipe.
Ok so now the engine is running, I listen to it, getting past the noise of the combustion knock and try to determining if there is excessive knocking noise. If there is heavy knocking, red flag! Shut it off! This could be the equivalent of a fuel burning grenade. A knock inside of the engine means that heavy metal parts are making contact in a violent unlubricated manner and they can come apart. Do not stress test a knocking diesel, especially if you don’t own it.
So now I have a running engine that is not knocking, it is very important to get the engine hot at this point, I have experienced cold engines that were devoid of noises that had a pretty bad rapping sound when hot. This is commonly caused by a loose connecting rod bearing or main bearing that develops play as the parts expand. I have also experienced the opposite situation in which a cold engine is louder mechanically than when it heated up, because the internal parts heated up and fit better. There are too many noises and reasons for those noises, I’ll say that if I hear a lot of mechanical clatter, red flag and figure expensive repairs. A diesel may have a vibration at low idle that subsides at a working RPM, that is usually normal, however, a shaking diesel across the RPM range is a concern, red flag! Shaking could be caused by a dead or weak cylinder, meaning expensive repairs are in order. I like to load a diesel down at full throttle by dead heading the hydraulics against the relief valve, (for instance, holding a loader bucket tilted back until it cannot go any further). If the engine drops excessive RPM’s or stalls out it could be weak. When I am done running a diesel engine I will always restart it after I shut it off. It should restart instantly and it is one more check of the starter bendix and ring gear!
Blow-by is the pressure created inside of the engine by the compression gasses passing the piston rings. I check blow-by by removing the oil fill cap, feeling and seeing the pressure or smoke that blows out the oil fill hole at a low idle. Some blow-by is normal, I try not to freak out unless the blow-by seems puffy, very steamy or excessive. Most engines have a crankcase vent tube mounted to the valve cover or the side of the block. If I can find the vent tube I’ll just inspect blow-by exiting from the tube. Really worn out engines with a lot of blow-by might have a lot of smoke in the engine area that can exit through the radiator grill. If the radiator utilizes a pusher fan, it will look like there is smoke blowing out of the radiator grill. Frequently this oil vapor will accumulate on the radiator fins and collect dirt, clogging the radiator. Red Flag! When the vent tube allows the blow-by to exit under the engine I have seen what almost looked like another exhaust pipe exiting the bottom of the engine because of the excessive blow-by smoke. Diesel run on is a dangerous condition, in which the diesel engine will actually run on the excessive blow by gasses that have been routed back to the air intake of the engine. Diesel run on means that the engine can run full speed until it blows up, it can’t be shut off unless the air intake is blocked. Scary red flag! I also carefully remove the radiator cap and look in the radiator with the engine running to see if any engine compression gasses are entering the radiator forming bubbles, if I see bubbles in the radiator, red flag. At the same time if there is any oil floating on the antifreeze, then this baby needs further checking and a big red flag.
The turbocharger is probably one of the most abused optional pieces on the diesel engine. The abuse takes place innocently because the operator never knows that the turbocharger (turbo) should receive special treatment. A turbocharger may achieve internal impeller speeds in excess of 100,000 RPM. Proper lubrication is vital. A minute or two of warm up before high RPM’s allows the bearings to get a good coating of oil. Letting the engine idle for a minute or two after a high speed run will allow the turbo to slow down and cool down. A turbo spinning after the oil supply has been shut down prematurely wears out the bearing surface and cooks the oil in the bearing chamber, a situation referred to as coaking. A bad turbo charger will allow oil to get past the seals and into the intake manifold or the exhaust manifold and show a lot of blue exhaust smoke and oil consumption. A turbo with a lot of bearing play will actually damage the impeller blades and produce no boost, thus the engine will not have normal power. A whistling exhaust sound is a common occurrence and can be a sign of trouble. However, I have experienced many whistling turbo’s that have no problems. I have heard that carbon and or dirt build up on the blades of the turbo can contribute to the whistling. Rattling noises from the turbocharger or oil leaking from the turbo are definite red flags.
Try to visually inspect the engine, if there are welds on the block where it had been patched then I red flag it. Leaks from gasket surfaces and seals are repairable but must be figured into the cost. Excessive oil or antifreeze leaking from gaskets and seals may be a sign of a lot of blow-by and or overheating.
There is really a lot to cover just trying to remember all the things that I look for when inspecting a diesel. Most of the time it is very easy, the engine is dry, clean, starts easily, has no exhaust smoke, and is quiet. Imagine designing and building the very first diesel engine, marketing and patents were a nightmare. It took years for Rudolph Diesel to get his engine to operate. It may have driven him mad, maybe it was suicide as has been written. I wish that Mr. Rudolph Diesel could have witnessed the vast use of his invention. We can all be grateful for his invention that was many years ahead of its time.