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In earlier articles related to oil maintenance on your car, we've addressed several issues about the type of oil you should use, whether it is okay to switch oil brands and types, and even some secrets motor oil companies do not want you to know.
Upset Owner Worries Dealership Damaged Her Car's Engine
Today, however, we will learn something focused on not just the hazards of adding too little oil or not monitoring your car's oil levels but what happens if too much oil is added.
This question was raised on a recent Toyota Rav4 forum, where one Rav4 owner noted that for the past 15,000 miles, the dealership had been overfilling her engine with motor oil with each change.
The owner is worried that it might have damaged her car to the point that she is considering suing the dealership.
Is she overreacting? Or is there cause for alarm?
With little room for doubt, too much oil can harm your car's engine. Your engine oil lubricates various moving parts and helps regulate engine temperature. However, an excess of motor oil can lead to several potential issues:
- Aeration and foaming: When there's too much oil in the crankcase, the crankshaft can dip into the oil reservoir and whip it up. This whipping action can lead to air bubbles forming in the oil, which reduces its effectiveness in lubricating engine components.
- Increased pressure: Excess oil can cause higher pressure within the engine. Excessive pressure can lead to oil leaks, damaging engine components, and/or creating a mess under the hood.
- Increased oil consumption and loss of power: In some cases, having too much oil can cause the engine to consume more oil than usual. This happens because the excess oil can be pushed past the piston rings into the combustion chamber, where it gets burned along with the fuel and leads to fouling of the spark plugs.
To avoid these issues, it's essential to maintain the proper oil level in your car's engine. Refer to your owner's manual for the recommended oil level and follow it carefully during oil changes.
What The Motor Oil Experts Say
When it comes to the operation of your car's engine, proper lubrication is defined by the four R's:
- Right Oil
- Right Place
- Right Time
- Right Amount
If the first three "Rs" are ignored for this article, what happens when the right amount is not correct?
To find a clear answer to the problem of dealership service techs filling the engine with motor oil past the recommended marks on the oil dipstick, let's examine what some experts have to say about the effects of oil on an engine.
How Your Motor Oil Level Can Affect Your Car
A general answer to this oil level worry is possible through an episode of The Motor Oil Geek YouTube channel, where the host and co-host demonstrate the effects too little and too much oil have on an engine, as per their tests with an engine measured on a dyno. If you prefer, however, a summary of the video is provided below for your convenience as well.
How MUCH OIL is TOO MUCH? Dyno Results!
Video Dyno Summary
In the video, the host and his guest run a thoroughly tuned and tested engine on a dyno and compare the results when the engine is run with a little less oil than recommended, the correct amount of oil, and when an excess of motor oil is added to it.
What they found is the following:
- Too little oil gave the engine more horsepower but with lower oil pressure. In contrast, the engine ran the risk of not having enough lubrication to protect the moving parts from excessive premature wear.
- The correct amount of motor out caused a small drop in horsepower but raised the motor oil pressure to the specifications needed to keep the engine running optimally with normal wear.
- Extra oil added significantly decreased horsepower; however, the engine oil pressure stayed constant over a wide range of RPMs, meaning that the engine was presumably optimally protected even more wear-wise.
Caveats to This Video
Bear in mind, however, that this was a race engine, not one you would typically find in a stock car bought off the lot. In other words, the engine components and any modifications made to the oil passages can affect the results, but at least it provides a good idea of what goes on when relative oil amounts are poured into a motor and then run.
The video did not discuss whether too much oil can result in frothing of the oil, which is expected to lead to decreased lubrication of the engine. Or, that increased oil pressure from excessive oil added puts an engine at risk of developing an oil leakage problem.
The consensus of both questions can be found from additional similar videos, such as this informative motor oil video addressing the question of "Is my engine damaged when too much oil is added to it by a service center?" The answer is "Yes." Too much oil and oil pressure can adversely affect a car's engine.
However, the actual level of damage can only be determined by either an obvious outright engine failure or an in-depth analysis on an engine-by-engine basis, where all factors are considered and adjusted to ensure equivalent comparisons.
What the Rav4 Owner Can Expect
As noted in several comments from the Rav4 thread, the owner should be reassured that since the oil overfilling they noted was just a little above the recommended marks on the oil level dipstick, they should not be overly worried about their engine having been significantly damaged.
Possibly the most "damage" is done to the Rav4's fuel efficiency, which likely decreased due to the extra oil, which would have placed a heavier load on the moving parts of the engine and thereby required the burning of extra fuel to achieve normal driving for the owner.
When To Suspect Too Much Oil Without Checking The Dipstick
The plus to this fact is that should you have your oil changed and notice that your mileage has decreased some, it could indicate that the oil level was too high during the oil and filter change and, therefore, bears investigation.
If your engine oil is overfilled, you can either return to the service center and have them drain the excess or do it yourself and avoid any further problems with the garage.
If you decide to DIY and want to make any future engine oil overfill incidences easier to take care of, here is an informative article titled "Toyota Tundra Oil Sample Analysis After First 1,000 Miles" that shows a handy and affordable accessory you will want to add to your engine's oil pan.
For additional motor oil-related articles, here are two more titled "Walmart Engine Oil Showdown You Do Not Want to Miss" and "Silent Engine Killer Revealed by Oil Experts."
Timothy Boyer is an automotive reporter based in Cincinnati who currently researches and works on restoring older vehicles with engine modifications for improved performance. He also reports on modern cars (including EVs) with a focus on DIY mechanics, buying and using tools, and other related topical automotive repair news. Follow Tim on Twitter at @TimBoyerWrites as well as on Facebook and his automotive blog "Zen and the Art of DIY Car Repair" for useful daily news and topics related to new and used cars and trucks.
COMING UP NEXT: I Think My Mechanic Destroyed My Car –Ford Owner Catches a Bad Fix on Video
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