Choosing the right motor oil is critical for your engine’s health and performance. If you’re considering a thicker oil, it’s important to understand the potential 20w50 oil disadvantages. Using 20w50 motor oil in modern engines can lead to poor cold-weather starting and reduced fuel efficiency.
This viscosity was once common in older, high-mileage vehicles. However, engine technology has advanced significantly. Modern engines are built with tighter tolerances and rely on oil flowing quickly at startup.
This article explains the key drawbacks of using 20W50 oil where it isn’t recommended. We’ll cover how it affects starting, fuel economy, and engine protection. You’ll learn when it might be appropriate and when you should definitely avoid it.
20W50 Oil Disadvantages
The primary 20W50 oil disadvantages stem from its high viscosity. The “20W” refers to its winter (cold) flow rating, and the “50” refers to its viscosity at operating temperature. Both numbers are high compared to oils like 5W-30 or 0W-20.
This thickness can create several problems in engines designed for thinner oils. The issues range from immediate starting troubles to long-term wear and increased operating costs. Let’s break down the main disadvantages in detail.
Poor Cold-Weather Engine Starting
This is the most immediate and noticeable disadvantage. In cold temperatures, 20W50 oil becomes very thick and sluggish. It resists flowing freely through your engine’s oil passages.
When you turn the key, your starter motor and battery must work much harder to crank the engine against this thick fluid. This can lead to several specific problems:
- Slow Cranking: The engine turns over slowly, which may prevent it from starting at all in freezing conditions.
- Battery Drain: The starter draws excessive current, which can quickly drain your battery, leaving you stranded.
- Starter Motor Failure: The added strain can overheat and prematurely wear out the starter motor.
- Inadequate Initial Lubrication: The oil is so slow to reach the top of the engine that critical components like valve train parts run dry for several seconds, causing wear.
Reduced Fuel Efficiency And MPG
Thicker oil creates more internal friction and drag within the engine. The oil pump must work harder to push the viscous oil throughout the system. This parasitic drag directly translates to a loss of fuel economy.
Your engine uses more energy just to circulate the oil itself, energy that could otherwise be used to propel the vehicle. The difference might seem small per trip, but over the life of the vehicle, it adds up to a significant amount of wasted fuel and money.
- Increased mechanical resistance on moving parts like pistons and bearings.
- Higher load on the oil pump, requiring more engine power.
- Overall engine operates less efficiently, burning more fuel for the same output.
Potential For Inadequate Lubrication At Startup
Modern engine protection relies on oil reaching components almost instantly. The period between starting the engine and oil pressure building is when most wear occurs. 20W50 oil exacerbates this vulnerable period.
Key areas like the camshaft, timing chain tensioners, and variable valve timing actuators may not get oil quickly enough. This can lead to accelerated wear, noisy operation, and even catastrophic failure in some interference engines if the timing system is compromised.
Strain On The Engine’s Oil Pump
The oil pump is designed to move oil of a specific viscosity range. Forcing it to pump a much thicker fluid like 20W50 puts it under constant, excessive strain.
This can lead to premature pump wear, reduced oil pressure over time, or even pump failure. A failing oil pump will not deliver adequate oil pressure, leading to widespread engine damage from lack of lubrication.
Not Suitable For Most Modern Engines
This is perhaps the most critical disadvantage. Car manufacturers spend millions determining the optimal oil viscosity for their engines. Using 20W50 in an engine designed for 5W-30 is ignoring this engineering.
Modern engines have extremely tight clearances between moving parts. They depend on lower-viscosity oils to flow into these microscopic spaces. Thick oil simply cannot properly lubricate these areas, leading to overheating and wear.
May Void New Car Warranties
If your new vehicle is under warranty, using an oil viscosity not listed in the owner’s manual can void the powertrain warranty. Dealerships and manufacturers can perform oil analysis in the event of an engine failure.
If they find oil that does not meet their specifications, they can legally deny your warranty claim. This leaves you responsible for very expensive engine repairs. Always follow the viscosity grade listed on your oil cap or in the manual.
Increased Exhaust Emissions
Poor cold starts and reduced combustion efficiency caused by thick oil can lead to higher emissions. During a difficult cold start, the engine’s computer may inject extra fuel to help it catch, which doesn’t fully burn.
This results in increased hydrocarbon (HC) and carbon monoxide (CO) emissions. In areas with strict emissions testing, this could cause your vehicle to fail its inspection.
When Might 20W50 Oil Be Acceptable?
Despite its many disadvantages for modern engines, 20W50 oil still has specific, legitimate uses. It is not inherently a “bad” oil; it is simply the wrong tool for most jobs today. Here are scenarios where its use might be considered.
Older Engines With Worn Components
In classic cars or older engines with significant mileage, internal clearances have widened due to wear. A thicker oil like 20W50 can help fill these larger gaps and maintain oil pressure.
It can reduce oil consumption (burning or leaking) in a tired engine. However, this is often a temporary fix for an engine that needs mechanical attention. It’s crucial to check the original manufacturer specifications first.
High-Performance Or Air-Cooled Engines In Hot Climates
Some high-performance engines, particularly older V8s or air-cooled engines like those in classic Porsches or motorcycles, were designed for thicker oils. When operated in consistently hot climates or under heavy track use, 20W50 can provide a more stable film strength.
Always refer to the specific recommendations for your performance engine, as many modern high-performance engines now use thinner oils.
Certain Small Engines And Equipment
Some lawn mowers, generators, and other small air-cooled engines may specify a thicker oil like SAE 30 or 20W50 for summer use. The operating conditions are different from a car engine—often simpler and running at constant high RPMs in hot environments.
Always check your equipment’s manual for the correct oil type for the season.
How To Choose The Correct Oil Viscosity
Selecting the right oil is easier than you think. You don’t need to guess or rely on old habits. Follow these steps to ensure you’re using the best oil for your engine’s protection and performance.
Consult Your Vehicle Owner’s Manual
This is the single most important step. The manufacturer’s recommendation in your manual is the definitive guide. It will list one or more approved viscosity grades (e.g., 5W-30, 0W-20) based on your climate.
It may also specify industry standards like API SP or ACEA ratings. Using an oil that meets these exact specifications is the safest choice for warranty, longevity, and efficiency.
Understand Viscosity Grade Numbers
The “W” stands for winter, not weight. The number before the W (e.g., 0W, 5W, 20W) indicates the oil’s flow at cold temperatures. A lower number flows better in the cold.
The number after the dash (e.g., 20, 30, 40, 50) indicates the oil’s viscosity at the engine’s normal operating temperature (212°F/100°C). A higher number is thicker when hot.
Consider Your Local Climate And Driving Conditions
Your manual often provides a temperature chart. If you live in a region with very cold winters, a lower “W” number (like 0W or 5W) is crucial. If you live in a extremely hot desert climate and do heavy towing, the manual might suggest a slightly higher hot viscosity.
Never deviate far from the recommendation. Modern multi-grade oils like 5W-30 are engineered to perform well across a broad temperature range.
The Risks Of Using Thicker Oil For High Mileage
A common misconception is that all high-mileage engines automatically need thicker oil. This is not always true and can be a risky assumption. Here’s what you should consider instead.
High Mileage Formulated Oils Are A Better Solution
Oil manufacturers produce “High Mileage” versions of common viscosities, like 5W-30 High Mileage. These oils contain specific additives to address the needs of older engines:
- Seal Conditioners: They help rejuvenate and swell hardened engine seals to reduce leaks, without needing thicker oil.
- Extra Detergents: To help clean out sludge that older engines may have accumulated.
- Additional Anti-Wear Agents: To protect worn components.
These formulations solve common high-mileage problems while maintaining the correct viscosity for proper flow and protection.
When Thickening Oil Is A Sign Of A Bigger Problem
If your engine is losing oil pressure or consuming excessive oil, switching to a thicker grade is a band-aid. The underlying issue—such as worn bearings, a failing oil pump, or stuck piston rings—will continue to worsen.
A better approach is to diagnose the root cause. An engine mechanic can perform a leak-down test or oil pressure test to determine the true heath of your engine before you make any changes to the oil type.
Step-By-Step Guide To Checking And Changing Your Oil Correctly
Step 1: Gather The Correct Materials
You will need the correct amount and type of oil (check your manual), a quality oil filter, a wrench for the drain plug, an oil filter wrench, a drain pan, funnel, and gloves.
Step 2: Drain The Old Oil
Run the engine for a few minutes to warm the oil slightly. This helps it drain more completely. Safely lift the vehicle, place the drain pan, and remove the drain plug. Allow all oil to drain. Then remove and discard the old oil filter.
Step 3: Install New Filter And Refill
Install the new oil filter, lubricating its gasket with a bit of new oil first. Reinstall and tighten the drain plug to the proper specification. Use a funnel to pour in the new, manufacturer-recommended oil. Do not overfill.
Step 4: Check For Proper Level And Leaks
Start the engine and let it run for a minute. Check for any leaks around the filter or drain plug. Turn the engine off, wait a minute for oil to settle, then check the dipstick. Add small amounts if needed to bring it to the “Full” mark.
Frequently Asked Questions (FAQ)
What Are The Main Disadvantages Of 20W50 Oil?
The main disadvantages of 20W50 oil include difficult cold-weather starting, reduced fuel economy, potential for inadequate lubrication at startup in modern engines, increased strain on the oil pump, and possible voiding of new car warranties. It is generally too thick for engines designed for thinner viscosities.
Can I Use 20W50 Oil In My High Mileage Car?
You should only use 20W50 oil in your high mileage car if your owner’s manual lists it as an acceptable viscosity. A better option is usually a “High Mileage” formula of the manufacturer’s recommended viscosity (e.g., 5W-30 High Mileage), which contains additives for older engines without the flow drawbacks of thicker oil.
Is 20W50 Oil Good For Hot Weather?
20W50 oil can be suitable for hot weather in engines specifically designed for it, such as some classic or air-cooled performance engines. For most modern passenger vehicles, the oil viscosity recommended in the manual is engineered to protect the engine in all climates, including extreme heat. Using a thicker oil than recommended can still cause flow issues at startup, even in hot weather.
What Is The Difference Between 20W50 And 5W30 Oil?
The primary difference is viscosity. 5W30 oil is much thinner when cold (5W vs. 20W), allowing for easier starts and faster lubrication. It is also thinner at operating temperature (30 vs. 50), reducing engine drag and improving fuel efficiency. 5W30 is the recommended oil for a vast majority of modern gasoline engines, while 20W50 is for specific, often older applications.
Will Thicker Oil Like 20W50 Stop My Engine From Burning Oil?
It may temporarily reduce the rate of oil consumption in a worn engine by slowing leakage past worn seals or rings. However, it does not fix the underlying mechanical problem and can cause other issues like poor startup lubrication. Addressing the root cause of the oil burning through repair is the only permanent solution.