Around 2012, we started to see fast, fun small cars with high-performance 4-cylinder engines that were turbocharged, such as the Focus ST, Mazda speed 3, and others, which got lots of horsepower out of small displacements and still got decent fuel economy. The engines made more power than normal aspirated engines could provide.
But like any turbo engine, they develop these common problems over time. They had an unintended consequence called low-speed pre-ignition that brought about fun problems for these quick cars.
What is LSPI? What sort of problems did it bring about for these interesting performance cars? What can you do about it?
What is Pre-Ignition?
Manufacturers have lived with and designed gasoline engines around the threat of pre-ignition for years. Most gasoline-fueled piston engines can suffer from this problem, and builders have found ways to keep it well in hand.
Pre-ignition occurs during the compression stroke of a piston just microseconds before the fuel-air mixture is ignited by the spark plug. The temperature rise in the fuel-air mixture during compression and hot spots inside the combustion chamber cause this event.
When pre-ignition occurs, power is lost, and if this occurs over many miles, burned piston tops may result. Generally, using a higher-grade fuel (higher octane rating) will mitigate this problem.
Low Speed Pre-Ignition
Compared to bog-standard pre-ignition, low-speed pre-ignition (LSPI) is a monster. Sometimes it’s called stochastic pre-ignition (SPI). Discovered in the early days since the T-GDI engines described above were released upon the world, LSPI began to rear its ugly head.
There are cars out there that came back to dealers with broken/crossed-up piston tops, and even bent/broken connecting rods, too. What was going on? Engineers for the manufacturers got involved, and here is what they discovered:
A very high-energy pre-ignition event would occur during an individual piston’s compression stroke, well before intentional fuel-air ignition could occur.
When this happened, and the piston being pushed upward by his three buddies couldn’t skirt the issue and reverse direction, extreme pressure would often crack or break the top edges of the piston, and possibly even bend the connecting rod too.
Engines thus inappropriately affected could come forth from the rear end of the car, clattering to a stop, and in some cases require complete rebuilds.
The Cause of Low Speed Pre-Ignition
Familiar with typical pre-ignition events, the automotive engineering community was at a loss as to what caused the LSPI events. Engine tests and analytical work commenced in earnest.
Manufacturers met with fuel and oil producers to develop an attack plan, and here’s what they found:
During the compression stroke, small balls of residual fuel and oil squeeze out around the top of the piston. This plume, heated through compression, ignites. The almost simultaneous pull of injected fuel also ignites and attempts to shove the piston backwards, thereby causing engine damage.
In short, LSPI is simply ugly pre-ignition. Oddly, it plugs into turbo boosted small displacement engines with direct injection for higher compression ratios.
The precise reason why has yet to be fully reconciled; however, tests found that improvements to engine lubricants mixing techniques reduce the likelihood. LSPI oils soon became available to fill the shelves at your favorite auto parts and big-box stores.
Lubricant Blends That Help Minimize LSPI
Whether you change your oil at home or take the car to a shop, dealer or oil change franchise, you should know the technical specification for the kind of oil put into your car’s engine.
This isn’t hard to learn. And because of the severe threat of LSPI to small T-GDI engines, if you drive one of these cars, this info will be very important to you.
Several brands of motor oil have made upgrades in response to trying to decrease LSPI risk. These upgrades are reflected in the specification data printed on the containers of oil you see lining the shelves at your local parts store. WHAT should you look for?
On the back label of your favorite oil, you’ll usually see a circular code, referred to as the “donut”. In the center of this donut, you’ll see the viscosity rating for the oil, like 10W-30, for example. The API (American Petroleum Institute) specification will also be found, like API Service SN.
You may see the oil rating mentioned in various texts, in bold characters, sometimes in a column far to the right of the donut. For example, “Meets or exceeds the requirements of: API SP, SN PLUS, SN, SM “.
Or you might find the specific car manufacturer’s specifications, as in “Chrysler MS12633”, and perhaps even the names of specific car models, such as “Nissan GT-R”. You may see other specification designations also, like “ILSAC GF-5” or “GF-6”.
So, for the small displacement turbocharged gasoline engine, what oil specification would be preferred? Here’s the short list. The oil you use must meet one or more of these specifications:
- API Service SN Plus or API Service SP
- ILSAC-GF6 or -GF6A
- GM Dexos 1 Gen 2
Check Your Owner’s Manual
Any one or all of the above specification notations could be found on the container for an oil suitable for your T-GDI (Turbocharged Gasoline Direct Injection) engine. If you have a car model year 2019 or older, your owner’s manual may not reflect these newer specifications.
Regardless of this, these new oils should be used. They are blended to be backwards compatible with oil requirements for older T-GDI engine-powered vehicles.
European and Japanese cars may have other specifications for approved lubricants. If you own one of these T-GDI cars, you would be well-advised to contact your dealer service department. Request their recommendation for current motor oils (or oil specifications) that have been specifically updated to help minimize the threat of LSPI.
Last, if you take your car to a local shop or dealer for oil changes you should be graciously proactive. Arm yourself with the oil specification requirement for your car, and ask the service manager if they are using such an oil in compliance with your car’s needs.
If they are not, you’d be wise to find a new shop for your oil changes.