Just by chance I read this article this morning concerning two engine failures. One by coolant leaked into the engine oil and the other when fuel diluted the oil.
Just thinking but logicly it would seem that if one was using a thicker oil then one would have a wider margin of safty in the event of oil dilution.
Personally I don't feel there is any margin for error in these types of problems with the 5W20 weight oils:
Engine failures
by Jim Kerr
Automotive engines contain hundreds of parts that operate over wide temperature ranges and speeds. They are expected to run smoothly, be economical on fuel, produce low emissions and last for hundreds of thousands of kilometres. The technology in modern engines allows all of this to be possible, but sometimes things go wrong.
Twice in the last week, I have been asked to diagnose engine noises. The two vehicles had low-pitched intermittent knocking sounds that would change when the engine speed varied. It was also louder when the engine was warm. It didn't take long to diagnose - I have heard this sound before and it was an expensive noise. Both engines had failed connecting rod bearing and damaged crankshafts.
The first engine, a V8 in a 1995 Dodge Ram pickup has already been repaired. It needed new engine bearings, a rebuilt crankshaft and an overhaul gasket set. The replacement parts alone totalled several hundred dollars and ten hours labour added to the repair costs. This truck had always been pampered and has less than 90,000 kilometres on it. This is low mileage for a modern vehicle, so why did it fail?
The second engine, a V6 in a 2000 Montana van still needs to be repaired, but the knock in it was even louder than the Dodge, so I expect the repairs will be even more extensive and expensive. This van has only 75,000 kilometres on it. Again, the real puzzle is why did this engine fail and how could it have been prevented?
A little further diagnostic work helped find the root cause of the problem with both engines. Although the failures were similar, the causes were not similar at all. The Dodge engine failure could be traced back to an antifreeze leak while the Montana engine was done in by driving it with a misfire. We can learn from their mistakes.
Several weeks earlier, the Dodge V8 had started loosing engine coolant. Usually coolant leaks are external and you find a puddle on the ground but this engine had an internal coolant leak. A failed intake manifold gasket had allowed coolant to seep into the engine and down into the oil pan. The only indication there was any problem was the coolant level in the radiator overflow tank kept getting lower.
The manifold gasket was replaced, the manifold surface was machined and the engine oil was changed but the damage was already done. Enough coolant had seeped into the oil pan that some had been sucked up by the oil pump and pushed through the engine. Unfortunately, coolant and engine bearings don't mix well. The bearing surfaces smear and begin to fail. So the real cause of the bearing and crankshaft failure was a coolant leak.
How could this have been prevented? Changing engine coolant at the recommended time intervals (every two or five years) found in the owner's manual will help maintain anti-corrosion protection in the cooling system. Monitoring engine coolant level regularly could have also prevented this failure because the leak could have been corrected before major damage occurred.
The Montana Van's engine failure was caused by another relatively small problem. The owner was towing a large boat a couple hundred kilometres home from the lake and the van seemed short on power. He thought the problem was with the transmission. The actual fault was one misfiring sparkplug.
With one sparkplug misfiring, the V6 engine only runs on five cylinders so the power is down, but when a cylinder misfires, other problems develop. The fuel injection system's oxygen sensor detects the unused oxygen from the misfiring cylinder in the exhaust gas stream. This causes the sensor to falsely signal the engine computer that the air fuel mixture is too lean, so the computer injects more fuel.
Excessive fuel injected into the engine couldn't all be burned so some ran past the piston rings into the crankcase. The fuel diluted the engine oil so it couldn't provide adequate lubrication for the bearings and they failed. A sample of the engine oil showed a high percentage of gasoline, verifying our diagnosis of the cause.
The moral of this story? Ignoring obvious problems can cause expensive repairs. If the owner had stopped at a repair shop, it would have been easy to diagnose a misfiring sparkplug and the problem could have been corrected for only a few dollars. Even towing the vehicle two hundred kilometres would have been cheaper than the cost of repairing this engine.
Modern engines are extremely durable and reliable but they still need attention to make them last. A few minutes checking fluid levels or getting a tune-up would have prevented both these vehicle's problems. Don't let it happen to you.
http://www.canadiandriver.com/articles/jk/040616.htm