Dumb question about oil
Thread Starter
Burning Brakes
Joined: Oct 2000
Posts: 878
Likes: 60
From: Minneapolis, MN USA
Dumb question about oil
I change my oil every summer, even though the car barely gets a couple hundred miles over the summer. Because, well, I think I should because oil ages or something.
I have two quarts, unopened, on my shelf. Can I use these when I change the oil, or has this oil aged/degraded the same way as what is in my engine and I need to change? Or do I need to buy/use all brand new, freshly purchased oil?
I have two quarts, unopened, on my shelf. Can I use these when I change the oil, or has this oil aged/degraded the same way as what is in my engine and I need to change? Or do I need to buy/use all brand new, freshly purchased oil?
Racer
Joined: Nov 2008
Posts: 442
Likes: 6
From: jacksonville Florida
you will be fine, especially with it even unopened, who knows how long some oil sits on the shelves at the store till it is bought. Good on you for keeping the oil fresh in your engine though, the difference there is even though you dont use the car that much, you still get moisture and other particulates that work their way into your oil while sitting in the pan.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
Once exposed to air, regular oil will begin to oxidize and age...even in your oil pan. Since you drive the car so little, you may want to consider going to a full synthetic oil. Then regardless of age, you can schedule oil changes every 2500-3000 miles. That may be several years of use on your time scale.
Pro
Joined: May 2013
Posts: 672
Likes: 31
From: Rapid City South Dakota
I've asked Amsoil's tech line a similar question. I change the oil at the end of the season, and don't start it until the spring. Oil change intervals have a time and mileage lifespan which starts ticking as soon as the oil becomes contaminated with water and other combustion by products. Oil filter components are the same. That being said, 7T1vette is correct that synthetics are much better and may not need to be changed every year, but that should be verified by oil analysis. I'll mention that I've gone years and over 30k miles on my Ford Powerstroke between oil changes, but I verify oil suitability yearly. The vehicle has over 180k on it.
Thread Starter
Burning Brakes
Joined: Oct 2000
Posts: 878
Likes: 60
From: Minneapolis, MN USA
Thank you all for the advice.
Regarding switching to synthetic - do I need to do a complete drain? I mean, if I do a "typical oil change" I assume there is some small amount of traditional oil in the system...I don't get it all out. What happens when that small amount of conventional oil mixes with the synthetic?
Regarding switching to synthetic - do I need to do a complete drain? I mean, if I do a "typical oil change" I assume there is some small amount of traditional oil in the system...I don't get it all out. What happens when that small amount of conventional oil mixes with the synthetic?
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
There is no 'compatibility' problem with mixing organic oil and full synthetic oils. Many oils are mixtures of both when sold (they don't say "Full" synthetic...so they are blended oils). So, a little residual organic oil left in the system is no big deal.
Now, be aware that the size of a full synthetic oil molecule is substantially smaller than an organic oil molecule. So what? Well, small molecules can ooze around and thru holes that larger molecules can't. That means that if you have an older engine [with older seals/gaskets that are partially worn], synthetic oils might leak from worn areas sooner than organic molecules would. It's not the fact that you have synthetic oil in your engine that leaks are noticed sooner; it's that a smaller particle can fit through an area that a larger particle can't. It would not be unusual for some small leak[s] to show up when switching to synthetic oil IN A WELL USED ENGINE. The leak PATH is there now; but the organic oil molecule can't fit through it!
Anyway, hope that info is of some use to you. IMO, full synthetic oil is the way to go in your situation. But, either type of oil will protect your engine (synthetic oil just does it better
).
Now, be aware that the size of a full synthetic oil molecule is substantially smaller than an organic oil molecule. So what? Well, small molecules can ooze around and thru holes that larger molecules can't. That means that if you have an older engine [with older seals/gaskets that are partially worn], synthetic oils might leak from worn areas sooner than organic molecules would. It's not the fact that you have synthetic oil in your engine that leaks are noticed sooner; it's that a smaller particle can fit through an area that a larger particle can't. It would not be unusual for some small leak[s] to show up when switching to synthetic oil IN A WELL USED ENGINE. The leak PATH is there now; but the organic oil molecule can't fit through it!
Anyway, hope that info is of some use to you. IMO, full synthetic oil is the way to go in your situation. But, either type of oil will protect your engine (synthetic oil just does it better
).
Last edited by 7T1vette; Jul 5, 2016 at 11:31 PM.
Thread Starter
Burning Brakes
Joined: Oct 2000
Posts: 878
Likes: 60
From: Minneapolis, MN USA
Thanks 7T1...makes sense to me. I have been wanting to pull my engine and "refresh it" (not quite a full rebuild) as I do have some various seal leaks here and there. So I wanted to get those fixed/cleaned up and then paint the engine. Maybe I'll wait to switch to full synthetic once I do that...
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Pro
Joined: May 2013
Posts: 672
Likes: 31
From: Rapid City South Dakota
I would not worry about the residual oil left in the engine when switching over to synthetics. There is quite a bit of talk about why synthetics seems to cause leaks, and there are 2 main reasons. Poly Alpha Olefins (PAO) and synthetic esters (PE) are blended in todays true synthetics, and balanced proportionally to limit oil leaks. Pure synthetic esters shrink seals while PAO's swell seals, so blending them is important. You need both because additive packages such as ZDDP do not stay in suspension in pure PAO's. Early pure synthetic ester based oils caused engine leaks due to seal shrinkage.
Molecule size isn't a player because mineral oils are a mix of different length aliphatic hydrocarbons or different "sizes" if you will. The mix of different molecules are what makes mineral oil inferior: synthetics are uniform and engineered for maximum resistance to fracture, volatilization etc. However, if the gaskets are plugged up with carbon the natural detergents capability of synthetics will suspend the carbon in the oil and "unplug" the leak. Hope this helps.
Molecule size isn't a player because mineral oils are a mix of different length aliphatic hydrocarbons or different "sizes" if you will. The mix of different molecules are what makes mineral oil inferior: synthetics are uniform and engineered for maximum resistance to fracture, volatilization etc. However, if the gaskets are plugged up with carbon the natural detergents capability of synthetics will suspend the carbon in the oil and "unplug" the leak. Hope this helps.
Pro
Joined: May 2013
Posts: 672
Likes: 31
From: Rapid City South Dakota
Well, yes I am agreeing and perhaps I was a bit unclear. Some early synthetics which were pure esters were noted for seal/gasket shrinkage and subsequent oil leakage, so the rumors persist about synthetics causing oil leaks. There are no pure synthetic esters available for motor oil today. The swelling and shrinkage issues are cancelled out by proper blending of the synthetics.
Burning Brakes
Joined: Mar 2006
Posts: 829
Likes: 131
From: Spartanburg SC
If your engine has some age, and some leaks, I would suggest a high mileage oil. It has helped my leaks some. It will take some time, due to the minimal miles you drive, but, it will help.
Advanced
Joined: Oct 2015
Posts: 60
Likes: 5
From: Sandy Lake, PA
I got this tip from my local Harley dealership. My '98 engine is air-cooled but the premise still applies. Don't let the used engine oil sit there over winter because it has become acidic from combustion by-products. Do your usual oil change procedure at the end of the driving season; driving until the engine comes up to operating temp, then draining. Refill with new oil, change filter, then start long enough to circulate that new oil throughout the engine's internals. In that way the new oil will not have any acids to 'eat' away at the bearing material.
Same thing when using an over-wintering fuel stabilizer. If you simply dump the required amount into the fuel tank without starting the engine and running it for awhile, the treatment never gets into the carb. And don't forget to operate the secondary accelerator pump if so equipped. Untreated fuel will still be sitting in the secondary fuel bowl if isn't squirted into the carb so treated fuel can take its place.
Same thing when using an over-wintering fuel stabilizer. If you simply dump the required amount into the fuel tank without starting the engine and running it for awhile, the treatment never gets into the carb. And don't forget to operate the secondary accelerator pump if so equipped. Untreated fuel will still be sitting in the secondary fuel bowl if isn't squirted into the carb so treated fuel can take its place.
Advanced
Joined: Mar 2014
Posts: 76
Likes: 2
The big issue with synthetics isn't that they break down, rather, all the additives (Friction modifiers, viscosity, anti foam, ect) deplete due to oxidation. So while the motor may be "oiled" it'll wear quicker from the lack of additives.