Welcome to the North American Subaru Impreza Owners Club Wednesday August 5, 2015
Home Forums WikiNASIOC Products Store Modifications Upgrade Garage
NASIOC
Here you can view your subscribed threads, work with private messages and edit your profile and preferences Home Registration is free! Visit the NASIOC Store NASIOC Rules Search Find other members Frequently Asked Questions Calendar Archive NASIOC Upgrade Garage Logout
Go Back   NASIOC > NASIOC Technical > Service & Maintenance

Welcome to NASIOC - The world's largest online community for Subaru enthusiasts!
Welcome to the NASIOC.com Subaru forum.

You are currently viewing our forum as a guest, which gives you limited access to view most discussions and access our other features. By joining our community, free of charge, you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is free, fast and simple, so please join our community today!

If you have any problems with the registration process or your account login, please contact us.
* Registered users of the site do not see these ads.
Reply
 
Thread Tools Display Modes
Old 11-16-2005, 09:33 AM   #1
Jon Bogert
Scooby Specialist
 
Member#: 1133
Join Date: Mar 2000
Location: SE PA
Vehicle:
09 GTR, 02 996 C4S
95 993 C4, 71 911, 04 STI

Default Let's talk about fuel dilution (of oil).

This has come up recently, and it's a concern for people running somewhat thicker oils, especially as weather gets colder in many parts of the country.

As I understand it (and I may be worng): The basic idea is that a heavier weight oil--say a 5w40 as opposed to a 0w30--will allow more blowby when cold and therefore some gasoline gets into the oil. The ECU richens the mixture for cold starts also. This happens with every car to some extent and the fuel burns off once the car has been brought up to temperature and is driven around for a while. The more time the engine spends cold, such as in winter driving or short trips that don't get the engine hot enough, the more fuel gets into the oil.

Fuel dilution is also a problem in racing engines because with larger tolerances and richer mixtures there is more room for the fuel to sneak by the rings (and valve guides?)

But, there's a Catch-22: Lighter weight oil degrades quickly with any fuel dilution, lowering the flash point and reducing it's (already meager) ability to protect your high performance engine. Heavier weight oil has much more headroom in both viscosity and flash point. A little fuel doesn't affect it's performance at all.

So what to do? As a datapoint, I used my STI for about 80% short trips and commuting. My Motul 5W40 had .8% fuel dilution after 5k miles. <2% is considered acceptable, but that <2% is a general number, not specific to the quality of the oil or it's ability to handle fuel dilution without a loss in performance.

Anyone with higher fuel dilution than that running an Xw40 or heavier oil? Anyone running Xw30 (which should have lower numbers) have data?

Personally, I've been thinking about trying the 0w30 German Castrol for winter, just to see what's what.
* Registered users of the site do not see these ads.
Jon Bogert is offline   Reply With Quote
Sponsored Links
* Registered users of the site do not see these ads.
Old 11-17-2005, 02:13 PM   #2
bluesubie
Scooby Guru
 
Member#: 767
Join Date: Jan 2000
Chapter/Region: Tri-State
Location: N.J.
Vehicle:
04 FXT

Default

Here's my last GC UOA . Since it's such a thick 30 weight and my daily trips are 5 miles each way, my dilution was .5% on this UOA and 1% on 2004 GC during this past winter. Both UOA's were at just over 6k miles.

Notice how my flashpoint was at the minimum. The viscosity barely budged though. After I saw this analysis, I was wishing that I tried a Motul 30 weight to see if that would help the dilution.

I think it's something that I can live with though. I've looked around at WRX dilultion levels and thinner oils don't always mean less dilution (my percentage was higher than yours). Even with the guys running additives (do a bitog search for Ed Hackett WRX running RP). There's also a comment on the bitog link (in my link above) about higher dilution on WRX's in general.

-Dennis

Last edited by bluesubie; 11-17-2005 at 02:21 PM.
bluesubie is offline   Reply With Quote
Old 11-17-2005, 02:23 PM   #3
hondaeater69
Scooby Guru
 
Member#: 60324
Join Date: Apr 2004
Location: a pillow.
Default

i've been using a 10-40 (RP) and my latest UOA showed a dillution of <.5%. this was 7.5K interval. prior to this i was running a 10-30 and dillution was the same. I use a lot less oil with the 10-40 however, down to about 1qtper interval as opposed to 2-3.
hondaeater69 is offline   Reply With Quote
Old 11-19-2005, 08:23 AM   #4
bluesubie
Scooby Guru
 
Member#: 767
Join Date: Jan 2000
Chapter/Region: Tri-State
Location: N.J.
Vehicle:
04 FXT

Default

Quote:
Originally Posted by hondaeater69
i've been using a 10-40 (RP) and my latest UOA showed a dillution of <.5%. this was 7.5K interval. prior to this i was running a 10-30 and dillution was the same. I use a lot less oil with the 10-40 however, down to about 1qtper interval as opposed to 2-3.
Do you make many short trips?

-Dennis
bluesubie is offline   Reply With Quote
Old 11-20-2005, 03:00 PM   #5
hondaeater69
Scooby Guru
 
Member#: 60324
Join Date: Apr 2004
Location: a pillow.
Default

Quote:
Originally Posted by bluesubie
Do you make many short trips?

-Dennis

not really, most of my driving is highway. I'd say 90% highway, 10% city.
hondaeater69 is offline   Reply With Quote
Old 11-20-2005, 03:46 PM   #6
othon
Scooby Newbie
 
Member#: 18440
Join Date: May 2002
Chapter/Region: SCIC
Location: so cal
Vehicle:
2004 WRX Wagon STG 2
big things coming...

Default

let me help to make sure this dosent get out of hand.

When your living in a cold area use a lighter oil.

When living in a hotter area use a thicker oil.

if you look in your manual it will have a temp to weight chart for where you live.

i live in southern california so i dont go any lower then a straight 40 weight in my motor and my car loves it. in the summer time i run 20w 50
oh and Dyno by the way as well i only use synthetics in my trans and rear diff (Royal Purple)

as far as dilution from gas not much can be done about that, its a normal thing but you can make sure to warm up the car for a short period not to long cause you can introduce more gas into the oil if letting the car warm up to long. just wait till the temp gauge hits the "C" then take off.
an then take it easy till the temp reaches normal operating temps.

even during the summer in the more temperate areas i wouldnt go to a 20w 50 but a straight 40 weight would be great for the motor....well unless your auto crossing or racing then whole new ball game.

The main point to all this is to just keep an eye on the oil make sure your level always stays full and to change it every 2500 - 3000 miles dont wait any longer. also if you run it harder the sooner you'll want to change it cause the oil will burn faster and be all dirty and nasty.

As far as blow buy you'll have more of that with a thiner oil cause it will break down faster and burn off faster as well. so thicker will be better.
othon is offline   Reply With Quote
Old 11-20-2005, 04:38 PM   #7
volkl23
Scooby Specialist
 
Member#: 39092
Join Date: Jun 2003
Chapter/Region: MWSOC
Location: St. Louis MO
Vehicle:
2004 WRX STi
Java Black Pearl

Default

I'm curious to see your UOA since we both have 04 STis and have similar driving patterns. The last UOA I did, I had a fuel dilution of 0.5% using M1 5w30 with 7000 miles on it. I just sent out for another UOA using M1 10w30. I should get that early next week. Here is my last UOA:

[/IMG]http://img.photobucket.com/albums/v146/ezandfast/3-5UOA.gif[IMG]
volkl23 is offline   Reply With Quote
Old 11-20-2005, 04:38 PM   #8
volkl23
Scooby Specialist
 
Member#: 39092
Join Date: Jun 2003
Chapter/Region: MWSOC
Location: St. Louis MO
Vehicle:
2004 WRX STi
Java Black Pearl

Default

I'm curious to see your UOA since we both have 04 STis and have similar driving patterns. The last UOA I did, I had a fuel dilution of 0.5% using M1 5w30 with 7000 miles on it. I just sent out for another UOA using M1 10w30. I should get that early next week. Here is my last UOA:

volkl23 is offline   Reply With Quote
Old 11-21-2005, 09:33 AM   #9
Jon Bogert
Scooby Specialist
 
Member#: 1133
Join Date: Mar 2000
Location: SE PA
Vehicle:
09 GTR, 02 996 C4S
95 993 C4, 71 911, 04 STI

Default

Here's mine. Breaking in sloooowly...

Jon Bogert is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
speaknig of lisa loeb... let's talk about really cool eyewear! Disoriental Off-Topic 41 11-18-2005 01:25 AM
Let's talk about short blocks Red Rocket Factory 2.0L Turbo Powertrain (EJ Series Factory 2.0L Turbo) 29 06-14-2002 08:58 AM
Let's talk about clutches... Prairie Dawg Texas Impreza Club Forum -- TXIC 12 06-12-2002 07:49 PM
Let's talk about when to change out the rods. Andrew Normally Aspirated with bolt-on Forced Induction Powertrain 10 03-04-2002 11:44 AM
Let's talk about the Rimmer Supercharger rao General Forum Archive 88 09-21-2000 07:56 AM


All times are GMT -4. The time now is 09:06 AM.


Powered by vBulletin® Version 3.7.0
Copyright ©2000 - 2015, Jelsoft Enterprises Ltd.
Powered by Searchlight © 2015 Axivo Inc.
Copyright ©1999 - 2015, North American Subaru Impreza Owners Club, Inc.