Oil Change Interval? Modern oil in an old car...any difference?


#1

I have a 25 year old car 125K…I drive mostly 1-3 mile one way trips …at least twice a month I try to make a 30 min one way drive. I only drive 5k a year…I change the oil every 3 months…(severe service/manual)…after 25 years and improved oils can I extend this safely? I was thinking going to 4 months. The oil turns close to black after 90 days.


#2

I drive my 95 Nissan pickup under the same conditions about the same number of miles per year.

It’s just that the area has built up to where whatever store you need to go to is just a couple miles away.

And once in a while, you get to get it on the highway and let it cruise.

I use regular 5W-30 oil, and change the oil/filter every six months.

Tester

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#3

Re the oil turning black quickly, check the crankcase ventilation system and repair as needed.


#4

While checking the PCV system is wise, my guess would be that it’s turning black quickly due to blowby. That would suggest to me that the oil is being diluted with combustion gasses. The blowby is also probably carrying unburned fuel past the rings into the oil. I’d recommend that he stick with his current oil change schedule.


#5

If the oil is turning black after 90 days, then 90 days is a good time for the change-out interval. My Corolla of similar vintage but more miles on the clock, I change the oil every 4-5 K miles. And it isn’t black at that point. But getting on the dark brown side. If it turned black after 90 days, then I’d change it at 90 days.


#6

Tester


#7

That’s a toughie… I will assume you have no problems with the crankcase evap systems you can easily fix.

Given the amount of crud you are getting at just 90 days it seems you should change as often as you do. Normally I’d say put synthetic in it and change it once a year. Stretching to 4 months from 3 seems reasonable and reduces your workload a bit, not to mention the recycled oil volume. I’d stay with regular oil and try 4 months. If the oil seems noticeably worse after 4 than 3 months, go back to 3.


#8

Agree! The engine is probably partially worn and blow-by will quickly turn the oil black. This in itself is not serious; 40 years ago even new engines turned the oil black after a few thousand miles.

Your driving pattern ensures you are running a rich mixture very often, which enhances carbon formation in the oil.

If this was my car, I would change oil twice a year, use high mileage oil, and take the car for a fast 20 mile drive every month or so.

Other than the PCV system I would not bother with repairs on such an old vehicle. Just keep checking the oil level.


#9

If you are really bothered, you can get the oil tested to know what’s going on.


#10

Is this a car that is special to you? Like a Jaguar convertible, or a much-loved car of some special design? If so, do everything you can to make it last and keep on the oil changes every few months. If not, I’d stop messing with the oil and change it every 5K or annually. Just my two-cents. I would bet the engine will not be the part of a 25-year-old car that ends its life. I mean this with no malice.


#11

I fully agree with @gorehamj’s advice.

Make your decision in the context of how long you plan on keeping the car.
If it’s only for another 5 years or so, then change it every 5K or once per year.