Engine oil (for european cars)

[spork2367]

Originally Posted by grahambehan

Thanks for your input

Since contact pressure is the main driving force in terms of film shear and therefore wear, it is very iimportant.

It's important, but even if the film shear strength isn't exceeded, the engine still experiences wear. This isn't a question of immediate engine failure, it's about long term wear.

The LT5 has some advantages with respect to retention of lubrication at star up since it has an iron to iron contact at the cam to tappet interface.

You would be surprised at the amount of oil retention at this area even after years of standing idle.

I've torn apart dozens of old junkyard engines, including several LT5's that sat on pallets for years. So I'm pretty aware of how much oil is retained and where. The fact is, while that provides protection against oxidation, it provides very little protection against scuffing that occurs prior to full oil pressure/flow. That is one of the primary reasons zddp, zdtp, and molybdenum were added to engine oil.

If the oil film is broken down at a bearing interface it is due to poor design or operating outside design parameters, so I understand placing as many band aid as possible.

There are dozens of real world conditions that lead to a breakdown of the hydrodynamic load capacity of an engine oiling system. Cold starts, excessively cold engine oil, imperfections (within spec) of cam grinds, imperfections in engine bearings, contaminates in engine oil, short term oil starvation due to g-forces, to name a few. Obviously we would like to make the oiling system as robust as possible. Especially for a vehicle that has limited replacement parts. High zddp oil is much cheaper than a set of cams.

The original question was pertaining to the use of a certain oil in a stock LT5 with 25 k miles, in the context of the question the answer is yes.

In that sense, he could use Italian walmart oil and his engine isn't going to fail due to oil

Now if we wish to discuss modified engines, extreme use or other extenuating circumstances, then the answer may be different.

At the end of day there are many opinions, all I have is facts having evaluated and reported on most of the lt5 engines following many very arduous durability tests that led us to release for production in 1990 and 1993 MY.

Graham

I'm in no way questioning your knowledge of the LT5. You've likely forgotten more about the LT5 than I've ever known/will know.

That being said, I work for a aircraft piston engine manufacturer that has produced flat tappet engines for 90 years. I manage quality, including our reliability engineer. There is a reason we recommend zddp additive for every engine we produce. There is a reason we use molybdenum assembly lube when building engines. There is a reason we spent millions of dollars perfecting DLC coating on our lifter faces. Engines wear regardless of whether design parameters are exceeded. They wear regardless of the performance level of the engine. We have a lab that exceeds that of most tier one automotive manufacturing facilities. We have done our due diligence on cam/tappet wear.

The fact is, the engine oil specified for the LT5 that was produced after 1996 has less zddp than the engine oil produced prior to that. Will an LT5 run with lower zddp content oil fail immediately...no. Will it fail after 200,000 miles...no. (at least not due to oil). But all else being equal, an engine that has been run with high zddp oil, over time, will show measurably less wear than one run with low zddp oil. That is based on 90 years of reliability data, not my opinion as a shade tree mechanic.