Oil breakdown with time?

[Tim Donahoe]

Does anyone know for sure that engine oil breaks down with time?

Let’s say you only put 1500 miles a year on your bug. That would take two years to get up to the maximum mileage before an oil change is due. However, most car manufacturers say to change your oil at least once a year—despite the mil age.

Does the oil age or chemically lose its effectiveness while in the engine somehow? Or is this a myth to sell more oil or oil changes?

I’m curious because VW stated that hypoid transmission oil didnt ever require changing—unless the weather called for a thinner oil (like if you lived in Alaska, Sweden, etc.).

Oil is oil. Why would engine oil break down over the period of a year, but not transmission oil?

Does anyone know of any facts on the matter?

Tim
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Let's do the Time Warp again!

Richard O'Brien

[ps2375]

It's not that it breaks down, it's that it get contaminated from the short trips and not getting hot enough to "burn" off the moisture and other contaminates.

[Frodge]

I change my oil once a year in the bug. It’s still clear when I change it even then. I would go longer if the bottom of the case didn’t rot out from moisture. That’s my only concern. When the magnesium rots out.

[Frodge]

As an example, I run synthetic Mobil Delvac 1 5w40 on my BW diesels. 10k intervals. The cars have over 200k. No oil usage or burning and no rot in the case. The older cases rot out with moisture more readily. (Oh, I used to do 10k a year no problem, sometimes double that, no more, and still no problem.) oil is so cheap for these cars that I just drain it once a year. Those rotted out cases make me sick just looking at hem.

[60ragtop]

a transmission is not an internal combustion engine so no by products of that is why the gear oil last longer.
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Rick
Certified Mechanic by the State of Michigan in 1977
ASA certified in 1987
Certified Hunter Wheel Alignment Master Technician 1986

[Tim Donahoe]

60, I understand that the engine provides combustion contaminants, as opposed to the transmission, but an engine driven as little as 1500 miles a year would seemingly not contain as many combustion by-products as compared to, say an engine that is driven, say 5000 miles a year.

Using that logic, I was just wondering why the oil would break down sooner, regardless of mileage.

Of course, short trips, especially in winter, would provide too much moisture inside the engine, and require frequent changes, regardless of mileage. But where I live in California, we get little to no rain for many months of the year. No humidity to speak of, and no moisture present whenever I change my oil; although, since I have a working thermostat system, my engine warms up quickly, and I rarely drive it without the oil getting to a nice temperature.

So, it seems moisture build up and combustion contaminants are the reasons for changing yearly, and the oil simply sitting in the motor has no correlation to oil breakdown.

Tim
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Let's do the Time Warp again!

Richard O'Brien

[Frodge]

Honestly. You could go two years or 3k. Just my opinion. If it’s always getting to operating temp and it’s under 3k, I don’t see why not.

[VW_Jimbo]

[VW_Jimbo]

[ricaroo]

Do you change the oil at the end of the season or the beginning?

I change it at the beginning of the season, every other year

Rick
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1971 Standard Beetle 2 dr Sedan 1600dp

[Frodge]

I’m not disputing what you learned, and I will defer to you with these older carbureted engines. They also run richer than new cars and it gets into the crank case. Go onto something like the vw diesel forums, vw recommends 10k oci. No way folks are doing this 4x a year. My Tdi is 17 years old and it’s fine. I do agree that the older engines benefit from more frequent changes, but a lot of these cars, like my own sit idle in the winter because they’re considered classic cars. Not being a wise guy but so I flush my oil 2x in the winter when rarely used because of salt on the road? On the east coast folks don’t take their old classics out.

[VW_Jimbo]

Every three months, wheter it is sitting doing nothing or being used.
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Jimbo

There is never enough time to do it right the first time, but all the time necessary the second time!

[Frodge]

I will also add that it’s kind of ironic that Valvoline gave the class on more frequent oil changes.

[VW_Jimbo]

[VW_Jimbo]

[Frodge]

I said I agree with older carbureted engines to a degree. My golf Tdi has 240k on it and runs like new. 10k intervals, Mobil delvac 1 esp 5w40. No oil usage or burning. Cam looks brand new.

[VW_Jimbo]

[Frodge]

[Tim Donahoe]

Jimbo, your explanations make sense to me.

Thanks,

Tim
_________________
Let's do the Time Warp again!

Richard O'Brien

[scrivyscriv]

I worked for Valvoline oil change during A&P school and the training we got there was that oil itself does not break down, which is why oil can be recycled and used again after processing. The official company training was that the oil additives - corrosion resistance, anti-wear, viscosity modifiers, etc - were the chemicals that broke down over time.
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Robert in Memphis
Dünkelgrügen 1967 Java Green bug thread
Engine rebuild thread
If you're ever in the Memphis area, you are welcome to stop by for advice and help.