Over-filled engine oil

  • Thread starter new6ton
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  • #1
new6ton
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Main Question or Discussion Point

It is said that if you overfill the engine oil. It can damage the engine. Why is that and is there a way to test if there is already damage?
 

Answers and Replies

  • #3
Baluncore
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A high oil level is not always the result of overfilling. It can result from coolant entering the sump following damage to the block such as a cracked sleeve. The lubrication pump then picks up coolant and pumps it to the bearings.

Excess engine oil can cause oil splashing by the crank, resulting in foaming of the oil with;
1. Excess oil leakage from seals and gaskets.
2. Bearing lubrication failure due to aeration of oil causing low oil pump pressure.
3. Less likely is hydraulic locking due to oil induction past the rings into a cylinder. That can cause crushed big-end bearings, bent connecting rods, and a broken crankshaft.
4. Very rarely, when fuel is turned off, some old and worn diesels will run slowly (backwards?), on engine oil thrown onto the cylinder wall by the crank of an overfilled engine.

To identify damage first check the oil level and spills, listen for noise. If there is low oil pressure you will need to examine the bearings. Look for water in the sump when you drain the oil.
 
  • #4
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The infamous gray smoke is a good indication of a blown gasket where you are now burning and leaking oil and soon to be stranded somewhere soon.
 
  • #5
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If the oil is filled to high in many engines, you can get foaming.
 
  • #6
Ranger Mike
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  • #7
tech99
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With a modern car Diesel, it is normal in Europe to have a particulate filter. This filter requires purging every few hundred miles by passing extra hot exhaust through it. The hot exhaust is obtained by injecting additional fuel into the engine, and to avoid the driver noticing an increase in power, it is injected at bottom dead centre. Any small extra power is absorbed by the ECU secretly switching things on and charging the battery at maximum rate. The surplus fuel has a tendency to get past the rings, and as a consequence, it is common to see the engine oil level progressively rise. The oil is diluted with Diesel and so it also becomes of progressively poorer quality. If the engine is serviced at correct intervals this will correct the rising oil level, but if left, it is possible for the Diesel-rich oil to get past the rings, where it provides fuel for the engine, which will then run away uncontrollably. In this situation it cannot be stopped and will ultimately be destroyed.
 
  • #8
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In this situation it cannot be stopped and will ultimately be destroyed.
Wow. Thanks for sharing. I hadn't heard of that before.
 
  • #9
Baluncore
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If the engine is serviced at correct intervals this will correct the rising oil level, but if left, it is possible for the Diesel-rich oil to get past the rings, where it provides fuel for the engine, which will then run away uncontrollably. In this situation it cannot be stopped and will ultimately be destroyed.
You are conflating two distinctly different situations, so the catastrophe is not as bad as you make it out to be. The difference in the situations is in the path by which the non-standard fuel reaches the combustion chamber.

An engine will run on thrown sump oil only if it has worn rings. In that case it will also have poor compression and will run slowly, usually backwards, after the injected fuel is turned off.

The situation where an engine can run away and possibly destroy itself requires an engine with a stoichiometric fuel contaminated airflow, which is an extremely rare situation, usually turbo bearing failure.
https://en.wikipedia.org/wiki/Diesel_engine_runaway
 
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