Oil Choices

[.RJ]

too much change for your catalytic converter

If you are not burning excessive amounts of oil, how is this going to affect your cat converter?

[Apoc]

i wouldn't go 10k on an oil change, but plenty of people do (i think some cars actually have that as their stock interval?). i do about 6k miles every 6 months so i just do it then. the s calls for 7500...

A vast majority of the late model eurocars have a 10k mile interval. Some techs (like Pat Goss, who I don't like) says there's no way that's good for a car but he conceeds that people don't keep cars long enough these days for it to catch up to them. Both my E36 and B5 had/have 10k mile service intervals.

[.RJ]

If you want to get picky about the oil change interval, you can have the oil analyzed every 3k or so (blackstone labs, napa, few others) and they can tell you how much longer the oil is good for. IMHO, changing the filter is more important than the oil if you are using a good synthetic - oils are pretty damn good these days and will hold up just fine at 300 deg in track conditions.

[Mike]

too much change for your catalytic converter

If you are not burning excessive amounts of oil, how is this going to affect your cat converter?

my s burns a good amount of oil (1qt every 3k), that is just how it is... i suppose if you don't burn that much, it wouldn't effect it.

[.RJ]

Even if you are burning that much oil (within the mfr specifications) how does changing it often affect the cat's life or operation?

[Mike]

My subies manual says 3000 miles in it

only reasons to follow that:
a) you use dino
b) it has also been 6 months since your last oil change
c) you like throwing money away

[Ginger]

I read that the frequent change intervals are bad because the Ph of the oil changes while it's in the car. I don't know how much truth there is to it. It goes in slightly acidic and during the course of running changes to slightly basic (or was it vice versa?) and neither condition is good for the motor - but there's a relatively long, stable period during the metamorphosis where it's a neutral balance fluid and that's what's ideal. Could be BS... just throwing it out.

[Apoc]

That's 'cause you're always at WOT.

My Prelude used to burn oil like that, but the H22A is known for that.

[Mike]

Even if you are burning that much oil (within the mfr specifications) how does changing it often affect the cat's life or operation?

you're changing the composition of your exhaust fumes.

[Mike]

That's 'cause you're always at WOT.

or because when cruising the car is still at 4k rpms.

[.RJ]

you're changing the composition of your exhaust fumes.

How?

[Andy]

Why are we debating this? I assume the majority of our respective "knowledge" comes from Bob Oil Guy or interweb conjecture so we'll just end up in circles. Dept of Engergy has a datasheet with flash point/ash content etc etc and once coupled with actual oil testing in your car should provide enough evidence for you to keep using whatever it is you're used to using.

[Ginger]

you're changing the composition of your exhaust fumes.

How?

Well, when you mix oil and gas... oh, wait!

[Mike]

you're changing the composition of your exhaust fumes.

How?

burning oil = oil combusted
burning fuel = fuel combusted
combusted materials become gas
gas leaves the engine through exhaust
exhaust has a catalytic converter

[.RJ]

How does this:

burning oil = oil combusted
burning fuel = fuel combusted
combusted materials become gas
gas leaves the engine through exhaust
exhaust has a catalytic converter

Get affected by this:

changing too often actually does more harm than good

You dont burn any more or less oil by changing it more or less often.

[Mike]

How does this:

burning oil = oil combusted
burning fuel = fuel combusted
combusted materials become gas
gas leaves the engine through exhaust
exhaust has a catalytic converter

Get affected by this:

changing too often actually does more harm than good

You dont burn any more or less oil by changing it more or less often.

the composition of the burnt oil is different. when you trow in fresh oil, the cat is more or less shocked by the "new" fumes. shocking it too often is bad for it.

[.RJ]

the composition of the burnt oil is different. when you trow in fresh oil, the cat is more or less shocked by the "new" fumes. shocking it too often is bad for it.

Thats the most bogus explanation ive ever heard.

Cats dont have memory, they just provide a medium to react with the unburnt fuel and NOx and reduce emissions.

[Mike]

hrug: just going by what this guy says: <!-- m --><a class="postlink" href="http://forums.s2ki.com/forums/index.php?showtopic=169852">http://forums.s2ki.com/forums/index.php ... pic=169852</a><!-- m --> - he's far more knowledgeable regarding oil than anyone i know. his comment about the cat thing was not in that thread... just wanted to give an example of his credibility. then again, he could just be some guy spouting off from everything he reads like nsxtasy.

[BLINGMW]

sounds pretty wild to me.... that'd be the craziest f'in thing I've heard if it's true. I imagine you'd have to be burning a lot of oil for the cat to "care" if it's fresh. I mean really, if you burn a qt or two between every oil change, what % of the exhaust is from that oil? .001? I have no idea.

Shock the cat. Honestly. :lol:

*edit*
wow, did I actually ballpark that dead on? hock:
if you burned a qt every 5k miles, and got 30MPG, you burn 167 gal of fuel, and .25 gal oil. ~0.0015 by volume. Or 0.15%.

....right?

[.RJ]

his comment about the cat thing was not in that thread...

So where is it?

All of the info that is posted in that thread is easily available many places on the interweb. All I can see about his credibility extends to copying, pasting, and formating into a forum post.

Nothing in that post is wrong and its great info, but it doesnt look like there is any original thought going on in there and i'd take any "advice" with a grain of salt and some objective research. The only thing frequent oil change intervals affect is your wallet.