"Pre-oiling" a vehicle's engine?

The issue concerns a spark-ignition engine that has not run for a while (say, a week or more) and thus presumably has little to no residual oil lying around on wear surfaces.

I heard the following technique suggested: Momentarily disable the ignition and use the starter to crank the engine for 8 - 10 seconds, then re-enable ignition and start normally. The idea is that oil will flow while metal-to-metal motion is slow, which results in much less wear than allowing the engine to run at high RPM before oil has arrived.

My question: does this have any actual merit?

What type of engine is it? I have never heard of that for a (modern) car. My RAV4 manual doesn’t even suggest a warm-up period during the winter no matter how long it has been sitting.

I have heard various folklore about rather primitive airplane engines but I have no idea if they actually help anything. The only one that has some evidence is to actually use it every couple of weeks so that rust doesn’t introduce internal corrosion. The same is true with power equipment like lawn tractors but that is just to burn off any condensation and older fuel.

I can’t see how a slow cycle is going to be much better than just starting an engine normally and letting it do its thing. Sometimes they sputter and blow off smoke as they burn off residual fluids but that burns off quickly and I have never seen any evidence of wear from it.

No. In older engines with an oil pump driven off the distributor you could pull the distributor and run the oil pump with a drill.

In a modern fuel injected engine it will start and idle quickly which is what it needs. whether or not it’s firing during the first rotations means nothing. You just want to keep the rpms down.

An oil film wil remain on all relevant parts more or less indefinitely. This will be adequate to protect those parts till oil flows through them.

Back in the 1930’s in cold places like the Arctic when you were out of range of calling for help and the less than reliable aircraft engines in those conditions, battery removal engine covers, oil dilution or removal for keeping it warm, pre-oiling and other things were done to ensure engine starting.

It was a matter of life & death. Battery & oil got the tent, the heat from a fire , etc., before humans and the pilot was the next in line. In the 1960’s, many planes, both civilian & military had oil dilution systems installed. Our 1954 C-180 had it and so did many other planes that I flew had it.

I can attest to this. I helped restore an old fire truck a few years ago. The person we got the truck from said it had set in their barn for 40+ years without starting, and they had no idea when it was run before that. When we tore into the engine, the pistons still had an oil film on them…it wasn’t much, but it was there.

yeah, oil- being an incompressible fluid- will start flowing the instant the pump is spinning. the residual film on the moving parts is enough to prevent excessive wear.

Pre-lubing is occasionally used in the world of high performance street engines. The car’s oil pump fills a pressurized vessel as the engine is running, and you can discharge that vessel into the oil gallery before starting. When guys spend $50K on a turbo’d pro-street engine, they see this as cheap insurance against wear and fried turbo bearings.

Here’s an option: http://www.engineprelube.com/

I’ve helped to spin the props on a C47 before starting up, but other than that I’ve never heard it described as desirable on a car.

We always rotated our spare equipment every 30 days to prevent false brinelling. Chronic light vibratory loads can and do drive the lubricant film out from between parts in close contact. It often happens when an idle piece of equipment is subject to vibratory loads from nearby operating equipment or by passing traffic.

For a shaft in a horizontal alignment it should be turned 270 degrees every month. That avoids the whole ordeal where you’ve got an installed spare pump sitting idle for two years, and when you need it it fails within 30 days. People hate that.

It has merit but not for a modern car that has just sat for a week or two.
Maybe if it was prepped for long term storage.

The better way though would be to pressurize the main oil galley from an external pump made for doing this, or on older vehicles, pull the distributor and run the oil pump drive with a drill motor, if you’ve nothing else.

If it was a large issue, as a car sitting for a week is not unheard of, there would have been a electric oil pump that would recirculate the oil before startup.

That is usually looking for an hydro-static lock, oil in the head of one of the upside down cylinders. An everyday concern for round engines or inverted engines.

Also that helps the starter to turn the engine or lets the battery/starter combo not be used for turning the engine.

Also does a pre-oil sorta. Every start on a round engine they do not hit ignition or mags until the engine has gone through a complete cycle on all cylinders.