I have a 1969 Dart Swinger, which is only driven about 500 miles a year. It also often goes for several months without being driven (it's in a garage in one part of the state, in a moderate climate, I'm in another part of the state most of the time). It runs great and has 150K miles on the original engine. I assume it's a 170 (how do I tell?).

I'm wondering how often I should change the oil and filter. Obviously if I went by mileage, I could wait years, which seems odd. But doing it once a year seems a little odd also, since that's after only 500 miles.

Also, if it's relevant, after reading around a lot on this forum (thanks especially to SlantSixDan for his informative posts) and reading around at Bob is the Oil Guy, I figured out that my mechanic's recommendation to use 20w-50 Brad Penn oil and Lucas Oil Stabilizer, didn't seem like the right choice. I just changed the oil and went with Mobil 1 High Mileage 10w-30 and a Wix filter (I opted not to use the 1806 filter with the standpipe, since the housing on my Dart already has a long standpipe in it).

Thanks for any thoughts.

Describe "moderate climate."

How much variation in temperature, and what is the range of relative humidity?

The general rule is to change the oil annually if your not driving more than the recommended mileage. If temperatures don't vary much, and Humidity levels aren't high, then you can get away with longer intervals.

I.C. engines produce combustion byproducts that can create acids that will attack metal and other compounds when left in the engine for prolonged periods. When a car has been sitting for a long period, the oil may look perfect, clear and clean, but some of the additives may have settled out, and those combustion byproducts may have leached into the oil.

If your keeping the car as a collectable, or just as a neat old car, change the oil, and run it in your lawn mower if you feel it's still good stuff.

Change annually to avoid future issues. Parts are disappearing, The parts we used to see for free are now expensive. Don't take a chance. Set a date, and take care of it. Every couple of years have the coolant system flushed out and have fresh coolant put in.

Doesn't apply to you, but anyone with an aluminum slant should be maintaining the coolant annually at minimum, along with zincs. If an aluminum slant doesn't have zinc's they should be installed. Give the system a noble metal to destroy, rather than the block itself. It's hard enough to keep the head gasket intact with these engines.

2¢
CJ

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Part of Tyrde-Browne Racing

My thought: Drive your car more.

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1964 Dart GT

that's what I do,,

What CJ says is all true, but there are oils that stand time better than others. The TBN (total base number) of an oil is an indication of how well the oil will handle acidic byproducts of combustion. Thankfully with low sulfur (and other contaminants) in the fuel there are much less acidic combustion byproducts created.

I wouldn't hesitate to keep the Mobile 1 High Mileage oil in service for 2 years. The Mobile 1 Extended Performance will do even better.

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Joshua

Almost never gets down to freezing. In the 40s at night generally the coldest in the winter. No snow, onlly rains some in the winter. Rarely warmer than the 70s in the summer. Maybe ten miles from the coast, five miles from other bodies of water, so a bit of a marine environment--average humidity maybe 75%, but less in the winter. For what it's worth, the car has been in this environment since it was new and as far as I can tell has no rust. (It has always been garaged, was used daily until about seven years ago).
How much acids are going to really build up in the oil after 500 miles of driving? Or are there other factors that produce acids and other contaminants?

Thanks for the thoughts.

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Sadly, not an option right now.

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What's the difference between the High Mileage and the Extended Performance? I thought the High Mileage had more additives to prevent wear, in lieu of ZDDP and all that. Thanks.

There is a short hose that connects from the water pump to the bottom of the head. If it is about an inch long then you have a 170, if it's about 3 inches you have a 225, or someone replaced a 225 with a 198.

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ifyoubegintothinkyou'relosingcontrol...it'salreadygone

With the humidity that high, use caution storing the vehicle for long periods, and with maintaining the same oil for long periods. You will pull moisture into the bottom end of the engine, and it will impact longevity.

Just based on that, I would change the oil annually. The oil Josh recommends would be a great choice. If you are willing to run oil of this price range, you should be OK. Most won't. Walmart Synthetic isn't the same stuff.

The small number of miles concern me more than anything else when it comes to building acids up. Do you drive it once a year for 500 miles, or 125 times for 4 miles? If the engine doesn't come fully up to temperature, and stay there for at least 15 minutes, you can't cook the moisture out of the engine, the exhaust, or maintain your sealing surfaces. The number of heat cycles becomes important if your not maintaining temperature for a couple of hours. You must cook the water out of the system to minimize damage. When the engine is running under temperature, you will experience much higher contamination both into the oil pan, and into the environment.

How many hours does the engine run when you start it? Or is that minutes? Minutes is a big problem.

CJ

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Part of Tyrde-Browne Racing

Thanks. I'll have to go check it. My recollection (since the water pump was replaced recently, is that it's about an inch long--I know it's pretty short).

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Yes, I mentioned in the OP that I'm using the Mobil 1 High Mileage 10w-30. I was just asking Joshua Skinner what's the difference between the High Mileage and the Extended Performance, since he mentioned both. From my research here and at Bob is the Oil Guy, it sounds like the Mobil 1 High Mileage is the most highly regarded of the Mobil 1 oils and also specifically has more additives for wear protection. So I'm just wondering in what sense he was suggesting the Extended Performance is better. A lot of the people at Bob is the Oil Guy seem to think the Extended Performance is a bit of a marketing gimmick and not a whole lot different from the regular Mobil 1.
Thanks for the thoughts.

I was just basing the humidity off of what the averages were reported as on a weather website. It seems kind of high to me. Right at this moment the humidity is 48%. I think it tends to be high in the morning and then a lot less as the day goes on and at night.

As I said, the car has been here since it was new and I don't see any rust on it. How humid can it be? Also, again, it's always garaged, to the extent that makes a difference.

The car was driven regularly until about seven years ago. Now I drive it when I'm in town. That works out to being in town for a week or two, three or four times a year. When I'm in town it's driven every day, around town mostly, for ten to twenty minutes at a time, two or three times a day, but I try to get it out on the freeway at least once. Seems like that ought to be enough to get the moisture out of the oil. No?

It is kind of leaking from a lot of the seals. But that's been true for a long time, even when the car was driven regularly. The exterior of the engine is gunked up with a fair amount of oil. Although, it's not leaking enough that I actually see the oil level drop. My mechanic said all of the seals on the engine ought to be replaced, but I'm delaying because it's going to be expensive to do that and like I said, it's not losing enough oil for me to even see the difference on the dipstick.

On things like my plow truck or my mud bogger that see few miles a year I like to smell the oil each time I dip. An oil that is still good smells like when it came out the container. Really bad oil smells like poo. As soon as oil smells even a little off I change it.

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Yeah....Im the one who destroyed this rare, vintage automobile.....

Thanks. I'll take a whiff. Hopefully it will smell like roses.

It takes at least 20 minutes of driving under load to bring the oil to operating temperature in warm weather. You then have to drive another 15-20 minutes to boil out any condensation.

If you want to know the condition of the oil, send a sample to Blackstone for analysis. The cost is ~$35 for basic analysis, TBN and postage. Use the results to determine how often you need to change the oil. One of the oil/filter websites did a long term test and discovered that changing the oil often results in additional engine wear. This is likely due to the dry startup.

Ken