Troubleshooting Blue Smoke from a Diesel Engine

First off, blue smoke from the exhaust always means that the engine is burning oil. Of course then, what we need to do is to find out what's causing this engine to burn oil.

Reasons for blue smoke from diesel engine

(1) Bad rings.
(2) Bad valve stem seals.
(3) Leaking turbocharger seals.

Well, one common cause is "bad rings". An engine with bad rings will not only burn oil, but it'll also show signs of power loss, especially when going uphills. With that said, let's start the car troubleshooting.

If the engine has less power, particularly when going uphills, then the rings are bad. The combination of 1) blue smoke coming from the exhaust and, 2) a loss of engine power (especially up hills) is a sure sign of the rings being bad.

Let's get a little background information on this. The purpose of the rings is to keep engine oil from entering the engine's combustion chambers and, also, to maintain compression. Why does an engine need compression? So it can generate power.

Now then, when rings are bad (for example... worn), the seal between the piston and cylinder wall is sloppy. This condition allows the oil to leak into the combustion chamber and thus burn... hence, blue smoke. Also, bad rings cause weak compression which means weak engine power. The worse the rings are, the more blue smoke and the weaker the engine.

What to do?

You'll need either a ring job or a new engine. As one would expect, this is going to be serious money. Therefore, is this vehicle still under warranty? If yes, you are covered. If no, first take this vehicle to a machine shop that specializes in this vehicle's make and have the mechanic positively verify that the rings are indeed bad. 

This can be done with a "wet compression test". This involves removing a spark plug, screwing a compression gauge into the spark plug hole, and taking a compression reading while the engine is cranking. Next, the compression gauge is unscrewed and some oil is squirted into the cylinder. 

Engine Compression Test

The compression gauge is then screwed back in and another compression reading is taken (again, while the engine is cranking). If the second reading is significantly higher than the first, the rings are indeed bad. After considering the cost of a ring job (or a new engine), you may want to consider replacing this vehicle. Good luck.

If the engine does not lose power, particularly when going uphills? Well, another thing that'll cause an engine to burn oil is "bad valve stem seals". With this condition, blue smoke will come from the exhaust mainly while accelerating. With that said,  if you notice blue smoke mainly when accelerating then valve stem seals are bad.

As indicated that the blue smoke coming from the exhaust mainly when accelerating. This is generally an indication of bad (e.g. worn) valve stem seals. What's going on here is that the oil is leaking past the valve stems and into the combustion chamber. This oil then burns (in the combustion chamber) and comes out of the exhaust pipe as blue smoke.

What to do?

You will need to have the valve stem seals replaced. If this vehicle is still under warranty, this will be covered. If not, you are facing a big expense. Only have the valve stem seals replaced and nothing more. Once this is done, see if it corrects the problem - in most cases it should. If not, you'll probably need a complete valve job.

However, the blue smoke does not appear when accelerating, then there is one other possibility. This involves the seals of the turbocharger. Of course, though, this only applies if this vehicle has a turbocharger.

If your car has a turbocharger, turbocharger seals may be leaking. Occasionally, the seals of a turbocharger leak, thus causing the oil to reach the exhaust system of a vehicle. The oil smokes when it comes in contact with hot exhaust components. This smoke is then funneled through the exhaust pipes and out the tailpipe.

What to do?

Take this vehicle to a garage and have the mechanic check to see if the turbocharger seals are indeed leaking. If this is the case, have the problem fixed. If this vehicle is still under warranty, this service will be covered. Try to find a garage that is approved by the AAA. Such garages tend to be fairly reputable and, best of all, if you have a dispute after the work is done, the AAA has the policy to investigate the situation and resolve it.

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