The Difference Between Summer and Winter Gas

The Difference Between Summer and Winter Gas & the Need for Fuel Additives.

Summer has its benefits: Fishing season. Dirt-track racing. Wrenching in the garage with the door open and the tunes blaring.

Another benefit is a slight fuel-economy boost. That’s because refiners alter their gasoline and diesel formulations depending on the season, and summer gasoline contains about 1.7 percent more energy than winter-blend gas. Regardless of the time of year, it pays to know a little about what’s going in your tank to ensure you’re properly maintaining your fuel system.

Under Pressure

A primary difference between summer and winter fuels is their Reid Vapor Pressure (RVP). RVP is a measure of how easily the fuel evaporates at increased temperatures. The higher the fuel’s RVP, the more easily it evaporates.

Winter-blend fuel requires increased RVP. If the fuel doesn’t evaporate readily in cold temperatures, the engine will start hard and run rough at cold temperatures.

To achieve this, refiners often blend winter gasoline with butane, a relatively inexpensive additive with a high RVP. They adjust the RVP of the final formulation to as high as 15.0 psi to help the gasoline ignite readily in the cold. 

The Law Restricts Sales

Once the temperature warms up in summer, however, high-RVP gasoline can volatilize more easily, which contributes to increased emissions and air pollution. For that reason, federal law restricts sale of gasoline with an RVP greater than 9.0 from June 1 through Sept. 15. To comply, refiners reduce the amount of butane in the gasoline and instead use pricier additives, hence one reason gas prices generally increase in summer. The blending process also takes longer, adding to the cost. 

Some areas set even lower RVP standards in summer to further limit emissions. California, for example, has a 7.0-psi limit. Given the state’s climate, refiners may sell summer-blend gas as early as April 1 and as late as Oct. 31.

For the most part, the semi-annual switch from winter to summer gas and vice versa happens seamlessly and goes unnoticed by drivers. 

Lowest Additive Concentration 

Regardless of the season, gasoline contains detergent additives designed to keep fuel injectors and other fuel-system components clean.

Some automakers, however, think the additive content, called the lowest additive concentration (LAC), is insufficient for modern vehicles. It takes a low level of additive to pass the tests, and most gasoline on the market contains as little as 123 ppm of additive.

The low levels of detergent additives in modern gasoline allow deposits to build up on critical fuel-system components, and most motorists are unaware of how dirty the insides of their engines are. This provides a great opportunity to sell the benefits of AMSOIL fuel additives.

P.i.® and Upper Cylinder Lube

P.i. Performance Improver (API) is a potent, one-tank additive that deep-cleans your fuel system.

• Cleans fuel injectors, intake valves and combustion chamber deposits

• Reduces emissions and increases fuel economy up to 5.7 percent

• Use every 4,000 miles (6,437 km)

Upper Cylinder Lubricant (UCL) preserves and builds upon those gains. It also provides vital lubrication to the upper part of the cylinders. 

• Lubricates upper cylinders to fight wear

• Inhibits ethanol-related corrosion

• Keeps injectors clean

• Delivers 18 percent more lubricity than Lucas* and 20 percent more than Sea Foam* for better retention of horsepower and fuel economy.

For more information:
AMSOIL Fuel Additives.

What to do when a lawnmower won't start

Lawnmower Won’t Start? Do this.

A lawnmower that won’t start, especially when taken from storage, is almost always due to one problem: bad gas.

Storing a lawnmower in the fall without adding gasoline stabilizer to the fuel tank can cause the fuel to break down and plug the fuel passages. If fixing that problem doesn’t help, there are a few other common maintenance practices to try, as we explain below.

Here’s what to do when your lawnmower won’t start

Replace the gas

Over time (like the six months your lawnmower sat in your garage over the winter), the lighter hydrocarbons in gas can evaporate. This process creates gums and varnish that dirty the carburetor, plug fuel passages and prevent gas from flowing into the combustion chamber.

The carburetor bowl below formed corrosion and deposits during storage, which can easily plug fuel passages and prevent the engine from starting.

Ethanol-containing gas can absorb water from the atmosphere, which can lead to phase separation, which occurs when ethanol and gas separate, much like oil and water. Ethanol that has absorbed enough moisture and has sat long enough can foul the fuel system and prevent the engine from starting.

No matter how many times you yank the starter cord and pollute the air with your advanced vocabulary, the lawnmower won’t start if it isn’t getting gas.

In extreme cases, evaporation of lighter hydrocarbons can change the gasoline’s composition enough to prevent it from igniting. The gas may be fueling the engine, but it doesn’t matter if it won’t ignite.

If you neglected to add gasoline stabilizer to the fuel prior to storage, empty the tank and replace with fresh gas. If the tank is nearly empty, simply topping off with fresh gas is often enough to get it started.

On some mowers, you can easily remove and empty the fuel tank. Sometimes that’s more trouble than it’s worth. In these cases, use a fluid extraction pump or even a turkey baster.

Clean the carburetor

You’ve replaced the fuel, but your lawnmower still won’t start.

Next, try cleaning the carburetor. Remove the air filter and spray carburetor cleaner into the intake. Let it sit for several minutes to help loosen and dissolve varnish and gums.

On some carburetors, you can easily remove the float bowl. If equipped, first remove the small drain plug and drain the gas from the bowl. Remove the float bowl cover and spray the float and narrow fuel passages with carburetor cleaner.

This kind of “quick-and-dirty” carburetor cleaning is usually all it takes to get the gas flowing again and your lawnmower back to cutting grass.

If not, consider removing the carburetor from the engine, disassembling it and giving it a good cleaning. Be forewarned, however: taking apart a carburetor can lead to nothing but frustration for the uninitiated. Take pictures with your phone to aid in reassembly. Note the positions of any linkages or the settings of any mixture screws, if equipped.

If you’re at all reluctant, visit the servicing dealer instead. Also consider replacing the carburetor altogether. It’s a fairly simple process on most smaller mowers and it’s often less expensive than taking it to the dealer.

Clean/replace the air filter

With the air filter removed, now’s the perfect time to clean it. Tap rigid filters on a workbench or the palm of your hand to dislodge grass clippings, leaves and other debris. Direct compressed air from the inside of the filter out to avoid lodging debris deeper into the media.

Use soap and water to wash foam filters. If it’s been a few years, simply replace the filter; they’re inexpensive and mark the only line of defense against wear-causing debris entering your engine and wearing the cylinder and piston rings.

Check the spark plug

A dirty or bad spark plug may also be to blame. Remove the plug and inspect condition. A spark plug in a properly running four-stroke engine should last for years and never appear oily or burned. If so, replace it.

Use a spark-plug tester to check for spark. If you don’t have one, clip the spark-plug boot onto the plug, hold the plug against the metal cylinder head and slowly pull the starter cord. You should see a strong, blue spark. It helps to test the plug in a darkened garage. Replace the plug if you don’t see a spark or it appears weak.

While you’re at it, check the spark-plug gap and set it to the factory specifications noted in the lawnmower owner’s manual.

If you know the plug is good, but you still don’t have spark, the coil likely has failed and requires replacement.

Did you hit a rock or other obstacle?

We’ve all killed a lawnmower engine after hitting a rock or big tree root.

If your lawnmower won’t start in this scenario, you probably sheared the flywheel key. It’s a tiny piece of metal that aligns the flywheel correctly to set the proper engine timing. Hitting an immovable obstacle can immediately stop the mower blade (and crankshaft) while the flywheel keeps spinning, shearing the key.

In this case, the engine timing is off and the mower won’t start until you pull the flywheel and replace the key. It’s an easy enough job IF you have a set of gear pullers lying around the garage. If not, rent a set from a parts store (or buy one…there’s never a bad reason to buy a new tool) or visit the dealer.

My lawnmower starts, but runs poorly

If you finally get the lawnmower started, but it runs like a three-legged dog, try cleaning the carburetor with AMSOIL Power Foam. It’s a potent cleaning agent designed to remove performance-robbing carbon, varnish and other gunk from carburetors and engines.

AMSOIL Power Foam Carb Cleaner

Add gasoline stabilizer to avoid most of these problems

Which sounds better? Completing all these steps each year when your lawnmower won’t start? Or pouring a little gasoline stabilizer into your fuel tank?

Simply using a good gasoline stabilizer can help avoid most of the problems with a lawnmower that won’t start. AMSOIL Gasoline Stabilizer, for example, keeps fuel fresh up to 12 months. It helps prevent the lighter hydrocarbons from evaporating to reduce gum and varnish and keep the fuel flowing. It also contains corrosion inhibitors for additional protection.

AMSOIL Gasoline Stabilizer

I have a five-gallon gas can in my garage from which I fuel two lawnmowers, two chainsaws, two snowblowers, a string trimmer, an ATV and the occasional brush fire. I treat the fuel with Gasoline Stabilizer every time I fill it so I never have to worry about the gas going bad and causing problems.

You can also use AMSOIL Quickshot. It’s designed primarily to clean carburetors and combustion chambers while addressing problems with ethanol. But it also provides short-term gasoline stabilization of up to six months.