Good oil change interval?

[gr8shot]

Wondering what's the norm for you guys? I was thinking about going 4-5k per change.

Its a 96 cutlass, with a great running 3.1. Just had HG and intake gaskets done a few thousand miles ago right before I bought it. I changed the oil right after I bought it after running less than 1k miles just in case there was any coolant mixed in that was left over, and I just changed it again about 400 miles ago.

The miles I put on it are 99% highway so I figure I should be ok going a little longer than 3k. I use Valvoline conventional oil in all my vehicles so it'll have regular 5w-30 in it.

Any thoughts? Should I go longer, shorter?

Also is 28-29mpg about normal for these cars? My dad always has cars with the 3.8 and they'll regularly get over 30mpg.

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[tornado_735]

I too drive 95-96% highway, and have been going about 6k miles between oil changes.

Make sure you're using a good quality filter. I use Fram Tough Guard, but others recommend Wix.

[White93z34]

28-29mpg sounds pretty good for it.

I'll usually go around 3-5,000 miles.

[ptcfast2]

When I sent my oil in for analysis to Blackstone Laboratories it was when my old engine had 180,000 miles on it. They said that with the GM 3.1 engines they recommended to OCIs of 4,000 miles per on conventional from what they've seen from the other oil analysis of 3.1 engines. They said that the higer the miles the shorter your OCIs should be, but they said 4,000 OCIs were fine up until 200,000 where the recommended reverting to 3,000 on conventional to be safe.

I currently run a 10,000 mile OCI with Mobile 1 Extended + a Bosch Distance Plus filter + Magnetic drain plug. I'm also running a new engine with an oil cooler so 10,000 miles would be a lot for an older one or one without an oil cooler.

[urbex]

Personally, I go 3,000 on it. But this winter that may change since I'm pretty much only driving in the city and my car never warms up.

[xtremerevolution]

Personally, I go 3,000 on it. But this winter that may change since I'm pretty much only driving in the city and my car never warms up.

That could be argued as a reason to change it just as often, not at longer intervals. Oil is designed to hold contaminants. Whether the engine is hot or cold, it will keep getting and holding contaminants.

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[xtremerevolution]

When I sent my oil in for analysis to Blackstone Laboratories it was when my old engine had 180,000 miles on it. They said that with the GM 3.1 engines they recommended to OCIs of 4,000 miles per on conventional from what they've seen from the other oil analysis of 3.1 engines. They said that the higer the miles the shorter your OCIs should be, but they said 4,000 OCIs were fine up until 200,000 where the recommended reverting to 3,000 on conventional to be safe.

I currently run a 10,000 mile OCI with Mobile 1 Extended + a Bosch Distance Plus filter + Magnetic drain plug. I'm also running a new engine with an oil cooler so 10,000 miles would be a lot for an older one or one without an oil cooler.

That assumes that oil degrades due to heat. An evidence to support that an oil cooler has any benefit at all in our cars? In fact, its a bad idea because your engine is designed to run at a specific oil weight, and cooling the oil causes that viscocity to change.

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[White93z34]

I would guess that depends on the type of oil cooler, If adding a factory cooler I cannot imagine it causing any ill effects, especially since the police impala 3800's have liquid to air oil coolers, some Bonnevilles have liquid to liquid oil coolers and both my 3.4 and 3.1 have factory coolers.

Now say you were over-cooling it by some aftermarket means then you might have problems.

[urbex]

That could be argued as a reason to change it just as often, not at longer intervals. Oil is designed to hold contaminants. Whether the engine is hot or cold, it will keep getting and holding contaminants.

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No, I'm planning on changing more frequently in the winter because I don't drive as much anymore, so 3,000 may be all winter long, and since it never warms up there's always condensation in the oil.

[gr8shot]

Thanks for all the input guys. I normally run an ac delco filter or pretty much something better than fram lol. Whatever is available that's less than $10.

I think ill stick with the original idea of 4k miles. It'd be nice to go longer but oil is cheap. A lot cheaper to change this car than 10qts in my duramax and a lot better mileage too! My drive is 116 miles round trip Monday thru Friday so I rack up the miles in a hurry. Been a great car so far. Couldn't ask for more for $1500!!

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[ptcfast2]

That assumes that oil degrades due to heat. An evidence to support that an oil cooler has any benefit at all in our cars? In fact, its a bad idea because your engine is designed to run at a specific oil weight, and cooling the oil causes that viscocity to change.

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GM included it by default on some 3.1 engines. The crate LG8 3.1 I got had it from the factory....so apparently GM thought it was needed for some models. Now I'd be crazy if I added an additional cooler to the factory one!

[Schurkey]

I did oil sampling on my first 3.4 back in the Nineties. Changed it at 6K, oil sample always came back "Oil fit for further use". There was one exception at around 70--80K, the thermostat failed, engine wouldn't warm up properly, and the oil sample taken then showed moisture contamination.

Back then, I would drain the oil from my 3.4 into a clean drain pan...and then pour it INTO my work truck or the lawn mower, or whatever engine was low at the time. I did this with complete confidence because the oil sample proved it was still usable oil.

I have every expectation that when used for longer-distance trips, dumping the oil at 10,000 miles would not be pushing it. There is ONE way to find out what your oil change interval should be...have the oil analyzed; not one time but several.





My Trailblazer typically goes 13K between changes; based on the oil life indicator built into the dashboard display.

[xtremerevolution]

I did oil sampling on my first 3.4 back in the Nineties. Changed it at 6K, oil sample always came back "Oil fit for further use". There was one exception at around 70--80K, the thermostat failed, engine wouldn't warm up properly, and the oil sample taken then showed moisture contamination.

Back then, I would drain the oil from my 3.4 into a clean drain pan...and then pour it INTO my work truck or the lawn mower, or whatever engine was low at the time. I did this with complete confidence because the oil sample proved it was still usable oil.

I have every expectation that when used for longer-distance trips, dumping the oil at 10,000 miles would not be pushing it. There is ONE way to find out what your oil change interval should be...have the oil analyzed; not one time but several.





My Trailblazer typically goes 13K between changes; based on the oil life indicator built into the dashboard display.

Those oil life indicators are such garbage. I haven't yet seen one that's accurate or a good depiction of when to change your oil. I and many other people ignore them altogether.

If the cooler is necessary, I suppose it may make sense to use it, but as Chris pointed out earlier, care must be taken to ensure that the oil cooler isn't too large.

For the record, there was always a noticeable difference in the way the engine felt on acceleration in my 95 Regal with the L27 if I ever let it go past 3500 miles on an oil change. It was repeatable, every time, regardless of what type of oil I used. It just felt rougher, so I stopped trying to get more out of my oil and just replaced it every 3k.

[gr8shot]

My lmm duramax used to barely make it 3k on the dic when it had the dpf and stock exhaust. Now that I got rid of the emissions garbage I change it around 7500 miles and it still reads between 20-30% oil life. Its amazing.

Once I get a few bucks ahead I'd like to send in a sample for the car at 4k and one from the truck at 7000+ and see how they fair.

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[xtremerevolution]

Where is it that all of you guys send these samples?