How long does engine oil really stay good?

[symbolipoint]

TL;DR

If engine not used too often, can engine lubrication oil really stay good for most of that time? (few years)? I believed not but shop representative says, yes.

I though engine lubrication oil needs to be changed every few months or every 3 to 6 months, or every 3000 to 4000 miles, no matter what. Last time I had oil change was more than four years ago, and I have not driven the car for more than just a few miles per week, and not more than maybe two or three times per week. I thought the time was past due for an oil change.

Then the representative at the automotive repair and maintenance shop asked about how much driving I do, and checked the oil with the dip-stick, and told and showed me, the engine oil looks NEW and FRESH, and that I do not need to change the oil. To me, the oil on the stick appeared clear greenish with no sign of any dirt nor particles.

What's the best guidance here. How long can automotive engine oil stay in good condition, if a car is only used a couple times per week, not driven too far, through the months or years?

 

[Bystander]

Summary:: If engine not used too often, can engine lubrication oil really stay good for most of that time? (few years)? I believed not but shop representative says, yes.

What's the best guidance here. How long can automotive engine oil stay in good condition, if a car is only used a couple times per week, not driven too far, through the months or years?

Synthetic? No "leadfoot"/jackrabbit driving? Nearly forever.

 

[symbolipoint]

Synthetic? No "leadfoot"/jackrabbit driving? Nearly forever.

Not synthetic ;, ordinary engine lubrication oil; I was not too fond of the higher price for synthetic engine lubrication oil. My usual driving behavior is slow accelerations most of the time, and coast as much as possible before pressing the breaks for stopping. Occasional stop-n-go type driving.

 

[Baluncore]

How long can automotive engine oil stay in good condition, if a car is only used a couple times per week, not driven too far, through the months or years?

It will depend partly on temperature variations. Each day that the vehicle warms and cools, the engine volume will breath out, then breath in damp air. The water from the air will be neutralised by the detergents in the oil, until the detergent capacity is depleted.

 

[jack action]

I though engine lubrication oil needs to be changed every few months or every 3 to 6 months

This is the typical engine manufacturer's recommendation.

How long can automotive engine oil stay in good condition, if a car is only used a couple times per week, not driven too far, through the months or years?

You must first define "good condition".

Will your engine last 190 000 mi instead of 220 000 mi? Maybe.
Will your engine break down in the next 6 000 mi? Definitively not.

Car manufacturers have similar criteria for automatic transmission fluid (usually every 2 years) and I've seen many many cars that never had their transmission fluid changed in their entire lifetime. The same goes for manual transmissions or differentials.

If the oil is not dirty, then you don't have particles that will break down lubrification. Even if you change the oil, you would probably not need to change the oil filter. I know that gasoline will gunk up after a few months - a kind of sticky wax forms up - which can obstruct the passages it goes through. I wouldn't be surprised that oil does something similar and that has something to do with such a time-wise recommendation for changing it.

The most important thing is to always have enough oil.

The car I have presently had its last oil change done by the previous owner at 236 000 mi, about 2 or 3 years ago. When I bought it at 249 000 mi, there was 1 liter missing (right at the low-level limit on the dipstick). Before selling it to me, he added 1 liter of 5W30 (it's supposed to be 5W20) - the cheapest stuff bought at the local gas station - and I added 2 000 mi in the last year since then. (Yes, you read that right, 15 000 mi since the last oil change.)

My owner's manual specified every 5 000 mi or 6 months (severe conditions, which is always true when driving in Canada). Here is the definition of severe conditions according to my owner's manual:

• Driving less than 5 miles (8 km) per trip or, in freezing temperatures, driving less than 10 miles (16 km) per trip.
• Driving in extremely hot [over 90°F (32°C)] conditions.
• Extensive idling or long periods of stop-and-go driving.
• Driving with a roof rack, or driving in mountainous conditions.

If it wasn't for that, the oil change recommendation would be every 10 000 mi or 12 months, and the oil filter every 20 000 mi.

 

[symbolipoint]

The most important thing is to always have enough oil.

liquid level on the dipstick looked full. That means, I guess no burning oil and no leaking.

 

[Averagesupernova]

I think the main reason to change oil in your case is all the short trips make it likely that any moisture in the crankcase is likely not ever completely removed due to the engine not ever getting fully warmed up. Only you can know that for sure based on your driving habits.

 

[symbolipoint]

I think the main reason to change oil in your case is all the short trips make it likely that any moisture in the crankcase is likely not ever completely removed due to the engine not ever getting fully warmed up. Only you can know that for sure based on your driving habits.

I could not guess. I certainly do not know.

Not much else to say. The car works well. It runs well. Man at Garage said oil looks clean, new, and fresh, and I do not need the oil to be changed. I will return there in about 5 months.

 

[Vanadium 50]

I have a PHEV and the factory recommends synthetic and a 12 month/12000 change cycle.

In the last 12 months I've used more oil than gas.

 

[berkeman]

In the last 12 months I've used more oil than gas.

Yeah, but the electrons! Billions and billions of electrons!

 

[Vanadium 50]

I put back as many electrons as I take out.

 

[berkeman]

Aww, you're such an environmentally conscious Physicist.

 

[hutchphd]

Here is my method. When checking the oil level via the dipstick I examine the oil with my fingertips. If it looks dark or feels gritty I will change the oil and filter. Not complicated.