question about mixing of octane at the pump
Cadillac
 

Cadillac Forums | Help Us Help You | Advertise | Cadillac Parts | Cadillac News | Cadillac Classifieds / (Old System)

Cadillac Technical Archive | Cadillac Dealers | Cadillac Reviews | Cadillac Dealer Reviews | Cadillac Vendors

CadillacForums.com is the premier Cadillac Forum on the internet. Registered Users do not see the above ads.
+ Reply to Thread
Results 1 to 8 of 8
Northstar Engines and System Technical Discussion Discussion, question about mixing of octane at the pump in Cadillac Engine Technical Discussion; When I go to the pump I mix half 89 octane with half 93 octane to make 91 octane. I ...
  1. #1
    fpmesiIII's Avatar
    fpmesiIII is offline Cadillac Owners Fanatic
    Automobile(s): 1996 Cadillac Seville STS (167k)
    Join Date
    May 2005
    Location
    Western NY
    Posts
    473

    question about mixing of octane at the pump

    When I go to the pump I mix half 89 octane with half 93 octane to make 91 octane. I heard from a friend that this is not good, he said that it would mess up the emissions sensor. Anyone have any comments on mixing of octane when filling up at the pump? Is this bad or o.k.?

  2. Remove Advertisements
    CadillacForums.com
    Advertisements
     

  3. #2
    mcowden is offline Cadillac Owners Connoisseur
    Join Date
    Jun 2003
    Posts
    1,164

    Re: question about mixing of octane at the pump

    Well, what you're doing seems like a waste of time, but it won't hurt anything. You can put 87 octane in it if you want to. It won't have as much power, but the knock sensor will prevent any damage and you'll save a few dollars. A few members here have been using nothing but 87 octane for years with nothing bad happening. It works fine. Why are you mixing grades anyway?
    Mike

  4. #3
    fpmesiIII's Avatar
    fpmesiIII is offline Cadillac Owners Fanatic
    Automobile(s): 1996 Cadillac Seville STS (167k)
    Join Date
    May 2005
    Location
    Western NY
    Posts
    473

    Re: question about mixing of octane at the pump

    to make the recommended 91 octane in the owners manual. i also heard that you get better gas mileage with a higher octane, which will save you money in the long run from having the better gas mileage.

  5. #4
    mcowden is offline Cadillac Owners Connoisseur
    Join Date
    Jun 2003
    Posts
    1,164

    Re: question about mixing of octane at the pump

    The owner's manual recommends 91 or higher, so you can use 91, 92, 93, or 105 if you want. The performance benefits are negligible and probably not even noticeable by going with a higher octane like 105 race fuel (especially not at $4.00+ per gallon!). If you really want to know, try it for yourself. Fill up from empty with 87 octane and reset your average mileage. Drive it normally until it's empty, then fill up with 93 and do the same thing. My guess is you'll see very similar mileage and better performance with the 93. If I was you, I'd save the time of mixing grades and just stick with one or the other. Mixing doesn't hurt anything, but it doesn't help anything either. The few cents' savings at the pump doesn't seem worth the hassle. You can put regular, mid, or premium in it and have very similar performance and mileage, but the regular will cost you less. No damage will result from any of those choices.
    Mike

  6. #5
    fpmesiIII's Avatar
    fpmesiIII is offline Cadillac Owners Fanatic
    Automobile(s): 1996 Cadillac Seville STS (167k)
    Join Date
    May 2005
    Location
    Western NY
    Posts
    473

    Re: question about mixing of octane at the pump

    thanks mcowden, your information is very helpful. i will give the 87 a try. where i fill up they have their 87 octane a lot cheaper than their 89 and 93 because they buy the 87 in massive amounts. so that will help the old pocket book a lot. thanks again.

  7. #6
    mcowden is offline Cadillac Owners Connoisseur
    Join Date
    Jun 2003
    Posts
    1,164

    Re: question about mixing of octane at the pump

    No problem. Let us know what your mileage and performance results are. It will make for an interesting debate. This is the time of year when stations are rolling out their summer reformulated gasoline in the EPA mandated areas (June 1 if I remember right), so gasoline-related questions are in season right now.

    I want to clarify something also: the knock sensor prevents damage to your engine by telling the PCM to retard the timing when it detects the sound of detonation in the engine. Detonation can occur because of high compression and a number of other factors, but in the Northstars it's primarily the compression. 10 to 1 or more in most if not all of them, whereas most production road car engines are 9 to 1 or less. By retarding the timing, performance suffers a little, but no damage will result. Higher octane gasoline is recommended in the Northstars for maximum performance, which means that theoretically the knock sensor doesn't have to effect any retardation of the timing to account for detonation due to the lower octane rated gasoline.

    Gasoline is not a single product. There is no such thing as "straight gas" or "pure gas" sold at gas stations. It's a blend of lots of different stuff, and performance can vary slightly from tank to tank, even using the same grade from the same station. It's a common misconception that "race fuel" will make your car go faster. That's really not the case because theoretically the timing should be advanced to its maximum value using 91 octane gasoline in a Northstar. Therefore, the increased octane won't cause the timing to be advanced any further and no performance gains are seen. Also, they have to use some nasty stuff in race fuel to boost it up to those octane numbers. That stuff can degrade fuel system plastic components over time.

    More than you wanted to know, I'm sure, but thought I'd share a bit. I read too much about this stuff. :drinker
    Mike

  8. #7
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
    Automobile(s): White Diamond '03 DHS (with floor shift)
    Join Date
    Jun 2004
    Location
    Woodstock Ill.
    Age
    66
    Posts
    70,459

    Re: question about mixing of octane at the pump

    To confirm what Mcowden said, I have been using 87 for 3 years now and haven't noticed any difference in performance or milage, only in my wallet.

  9. #8
    caddydaddy's Avatar
    caddydaddy is offline Cadillac Owners Connoisseur
    Automobile(s): 2005 Escalade 6.0L 2WD, 2007 Jeep Grand Cherokee Limited CRD
    Join Date
    Jan 2003
    Location
    Belle Chasse, LA
    Age
    32
    Posts
    3,653

    Re: question about mixing of octane at the pump

    Some gas stations have two tanks, one of 89 and the other of 93. To get mid grade octane, it's a blend of the two.

Quick Reply Quick Reply

Register Now

Please enter the name by which you would like to log-in and be known on this site.
If you do not want to register, fill this field only and the name will be used as user name for your post.

Please enter a password for your user account. Note that passwords are case-sensitive.

Please enter a valid email address for yourself.

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Bookmarks

Cadillac Posting Rules

  • You may post new threads
  • You may post replies
  • You may not post attachments
  • You may not edit your posts
Read about Lincoln | Buick | Kia Forte Forum
Need products for your Cadillac? Check out your options at the links below:

custom floor mats | Cadillac Chrome and Black Chrome Wheels | window tinting