Oil changes on a rarely driven car

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Staff member
May 27, 2002
Guelph, Ontario
A good friend of mine has a 96 Mustang GT with an aftermarket Vortech supercharger on it
and he doesn't drive the car all that much, it's a weekend summer car only. As a result, he has
only driven it about 1000 miles since his last oil change, which was more than a year ago now!
I keep bugging him to change the oil (it's Mobil 1) but I wanted to know if there really would
be anything wrong with his oil? He never starts the car unless he's going to drive it (I told him
that if he started and idled the engine it would just put moisture into the oil that would
not burn off since the oil wouldn't get above 200F unless the engine was under load)
Also, whenever he does drive the car he takes longer trips with it, driving it a half hour or more

So if his oil were analyzed at this point, what would it show? Would it still be suitable for
continued use?
Patman, I have a similiar situation with a Bronco. I drive it on the weekends only, and it accumulates about 1-2K miles a year. I run Castrol GTX 10w-30 in it, and change the oil once a year. I have heard that you should change oil every 3 months in a seldom driven vehicle.....something about acidic buildup?
Patman, TheLoneRanger is correct. It should be changed every 3 months, and I would not go more than 4 months. Nasty things happen to oil once they start to set. If I had either one of these vehicles I would change it. Just cheap insurance. I would say this even applies to good synthetics.
Any opinions on applying the three month oil change rule to a car that is stored during the winter? For example, oil and filter are changed prior to storing a vehicle. Four months later the vehicle is removed from storage. Would you change the oil and filter again with zero miles but four months of the oil sittign in the crankcase?
That is an excellent question, and something I have always wondered. When I used to store my sports cars in the winter I would always change the oil before storage, but I never changed it right away afterwards, since I would never start the engine during that storage period. I figured the oil was going to be pretty much as good as it was when it came out of the bottle, since it was simply sitting there in the bottom of the oil pan.
He's a good friend of mine so with a little bit of convincing I think I can get him to have his oil analyzed, it'll definitely be good to know!
Test the oil to find out for sure.
Then you'll have more than a look at the dipstick to decide. I do think it is important to periodically start and run the engine(to normal temp) and circulate everything to keep seals wetted, bearings covered etc. That goes for the whole car not just the engine.
Terry, in your opinion, if someone is going to store a car for 4 months, for the winter, are they better off not starting the engine at all (if they cannot drive it) or should they start and idle the engine for a while. Won't starting and idling an engine simply introduce more moisture that won't be burned off without the engine under load? I always figured starting and not driving the car does more harm than good, as it also puts moisture into the exhaust that won't be burned off.

I see Bob added some new smilies too!
Gee Whiz Patman... I don't have an answer from analysis to help you.... I'd stick with my theory of starting it and running it at a high idle until I get normal temp of the oil,not just coolant.
I didn't think oil got up to proper operating temperature just by idling it though. I once was doing an oil change on my mom's Probe GT and it was snowing so I just started her car in the garage, ran it for 15-20min, and then revved the engine to about 5000rpm for 10-15 seconds and drained the oil. It was not hot at all. Usually with her car, I can drive it a couple of miles and the oil is burning hot.
Patman, When I say high idle I mean to approximate the rpm you would get cruising down the road at 45 or 50 mph. If your normal idle is say 750 run it up (smoothly) to 1500-1800 for 5 minutes or so. It'll warm up and will not fuel soak the engine like you can revving it while its still cold. Then smoothly bring the idle down to normal idle.
It's worse than I thought, my friend sent me an email just now and told me his last oil change on his Mustang was September 1999!

He only put 1200 miles on the car though. I've convinced him to get an oil analysis done, so he'll be sending you a check soon Terry. He feels like this for forgetting to change his oil so often:


He's very particular about the maintenance on his daily drivers though. I'm very interested to see his oil analysis results on the Mustang's oil!
Tell your friend to change that oil or his Mustang will start running like a Chevrolet. HA!

[ May 31, 2002, 08:51 PM: Message edited by: Johnny ]
I’m gonna go out on a limb here and say that letting a car sit for more than 3 months with the same oil in the crankcase may not be that bad for it.

Having said that, I’ll agree that the guy who starts up his classic/rarely driven vehicle and lets it run for 10 minutes once each month is NOT doing his pride and joy any favors, especially if he leaves that oil in his car for an entire year.

BUT as long as the few times that vehicle is started it is driven long enough to get the engine up to full temperature and keep it there for at least 15-20 minutes and the PCV system is working properly, any accumulated moisture and some of the byproducts of combustion should boil off.

The big question is how the oil fights off corrosion over time just sitting still, with only a normal amount of contaminants in the oil. This could be tested by a TBN analysis.

I spoke to a guy about a year ago who had a Toyota Celica which had sat for around a year with the same oil in it (Mobil 1 if memory serves) and when he finally tested it, with about 5,000 miles on the oil, the results looked fine.

Can you get that blown ‘Stang owner to change his oil, have it tested (including the all-important TBN in this case) and then get back to us? More data is (usually) a good thing.
My 1st rule of thumb is change oil minimum twice per year. Only a problem on my wife's BMW and my father-in-law's 1971 Toyota Land Cruiser (has 25,000 miles on it). He drives 6 blocks at a time, 4 times a day, and 20 miles on Sundays.
2nd Rule: Change oil when it is hot, and before storing the vehicle for the winter or whatever period of time. It will be fine when you start it up later (this is a common practice with harvesters)
-You may see a little lead in the analisis. Show me a bearing and I will tell you whether it has been stored with dirty oil. It doesn't matter so much how much of the TBN is still in the oil as a whole, The dirty oil in the bearings sits without changing or circulating, corroding small areas.
The very first post on BITOG under Car and Truck Gas Engine oil.
Just felt like doing that. I don't like going back and reading all the stupid things I've said though.
I doubt there is any harm done leaving oil in your car for a year or more. Didn't we see a Porsche just recently with the original oil in the crankcase for 5 years? The UOA was fine. What about all these engines that junk yards have sitting around for years, and then are sold as used replacement engines? Probably some are duds, but more than likely because of mechanical problems, not because oil sat in the crankcase for a few years. Anyways, it will be interesting to see the results on the Mustang if it's analysed.
I just put 0-40 XD3 Esso syn oil in my 92 Dodge Cummins diesel, I will start this diesel about every one to two weeks throughout the winter, anytime I do start it is will get a full hour minimum highway driving, if short trip required the engine will aways get fully warmed up to operating temp on a drive.

I will put on few kms in winter and bulk of kms in April/May, can I go full 6 month OCI to 6k kms with these conditions and change oil in June without damaging my diesel?

My opinion is that oil in a properly sealed-up engine (air filter and breather elements/filters in place) should pretty much last indefinitely.

My recommendation for the original poster would be a 5-year fill of the appropriate grade of Mobil-1 or synthetic XD-3. This whole 'acid eating away at the inside of the engine' stuff is just BS -- corrosion is generally greatly accelerated by heat, and the acid neutralization properties of motor oil do exactly that -- neutralize acids.

As others have pointed out, there are UOA's with oil in for up to 5 years. At work, we did UOA's on oil that was *40* years old, and it was still fine.
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