Oil pressure after engine rebuild 5 bar+ ??
07-17-2008, 03:07 PM
#16
Chronic Tool Dropper
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The last new car I bought made it alll the way home from the dealer before it's first change, and it was dosed immediately with Mobil-1. Changed at 100, 500, 1000, then 3-6k intervals for the rest of the time I owned it. (290k) Car before that sold with over 300k on the meter.
Modern engines are built to such great tolerances that the old practice of "break in" is unnecessary. For everything but rings, "break in" can also be described as the early stages of "wear out".
Rings are a separate discussion, or better yet lets talk about "seating the rings". That's a poor name for the process of wearing the bore to the point that you can get a good seal without leaving a film of oil on the cylinder wall above the top ring. So spikes and high spots, the tops of those hone crowns, etc, need to be ground off by the rings until they are worn together ebnough to get that desired seal. On the 928, it is actually the rings that get all the wear, since they ride on the silica exposed during the paste-honing process in the bore. The wearing faces of the silica are quite smooth from the initial boring process when they are supported by the aluminum, and only after the paste honing do they stand proud of the aluminum enough to carry the piston and rings clear of the metal. Bottom line, there's nothing in the bore to "break in".
Meanwhile, everything else in the engine expects oil flow earlier than cold straight 30wt will usually flow, and there are places where the cold viscosity of 30wt may prevent or limit flow. Lifters come to mind, and I'm sure there are more places. It may be that straight 30wt is OK for the first fill if it happens to be a very hot day, but why risk early but unintentional "break in"... I meant "wear out" of engine bits with oil that doesn't flow adequately?
Detergent vs. non-detergent discussion has been going around social circles of the old wives for years. Some engines are particularly prone to foaming the oil (older Harley-Davidson, early 356/912 and the air-cooled VW motors) so folks use non-detergent thinking that the detergent is 'causing' the aerating. Isn't at all related, but the myths die hard. The detergents in the oils allow it to carry diluents and contaminants safely without breaking down. The stand-by generator here at at the house had a spec for 30wt non-detergent from the supplier. I called the engine mfr directly to make sure I could use M-1 without voiding any warranties and they said heck yes. Seems the generator guys had come up with the ND oil recommendation on their own; the engine supplier didn't know. Kinda makes you go Hmmmm.
Soooo, IMHO, it's never too early to go to synthetic. Modern engines should break in on the same viscosity they will live with forever. A few changes very early will get any stray fuel/carbon/contaminant bits out before they do a lot of damage. I also don't believe you get your value out of a car until you've put at least 250k miles on it.
Modern engines are built to such great tolerances that the old practice of "break in" is unnecessary. For everything but rings, "break in" can also be described as the early stages of "wear out".
Rings are a separate discussion, or better yet lets talk about "seating the rings". That's a poor name for the process of wearing the bore to the point that you can get a good seal without leaving a film of oil on the cylinder wall above the top ring. So spikes and high spots, the tops of those hone crowns, etc, need to be ground off by the rings until they are worn together ebnough to get that desired seal. On the 928, it is actually the rings that get all the wear, since they ride on the silica exposed during the paste-honing process in the bore. The wearing faces of the silica are quite smooth from the initial boring process when they are supported by the aluminum, and only after the paste honing do they stand proud of the aluminum enough to carry the piston and rings clear of the metal. Bottom line, there's nothing in the bore to "break in".
Meanwhile, everything else in the engine expects oil flow earlier than cold straight 30wt will usually flow, and there are places where the cold viscosity of 30wt may prevent or limit flow. Lifters come to mind, and I'm sure there are more places. It may be that straight 30wt is OK for the first fill if it happens to be a very hot day, but why risk early but unintentional "break in"... I meant "wear out" of engine bits with oil that doesn't flow adequately?
Detergent vs. non-detergent discussion has been going around social circles of the old wives for years. Some engines are particularly prone to foaming the oil (older Harley-Davidson, early 356/912 and the air-cooled VW motors) so folks use non-detergent thinking that the detergent is 'causing' the aerating. Isn't at all related, but the myths die hard. The detergents in the oils allow it to carry diluents and contaminants safely without breaking down. The stand-by generator here at at the house had a spec for 30wt non-detergent from the supplier. I called the engine mfr directly to make sure I could use M-1 without voiding any warranties and they said heck yes. Seems the generator guys had come up with the ND oil recommendation on their own; the engine supplier didn't know. Kinda makes you go Hmmmm.
Soooo, IMHO, it's never too early to go to synthetic. Modern engines should break in on the same viscosity they will live with forever. A few changes very early will get any stray fuel/carbon/contaminant bits out before they do a lot of damage. I also don't believe you get your value out of a car until you've put at least 250k miles on it.
07-17-2008, 04:16 PM
#17
Burning Brakes
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Thanks for all the input. For a 1st timer this "break in" type of oil is a little confusing. Specifically, Valvoline 10W-40 Premium Conventional oil is now in the engine. I had 10w-30 on hand, but read somewhere it was too thin to set the rings?? So I went with 10-40. I ran Mobil 1 before the tear down and now am planning to go with Amsoil. 
I am trying to get the car road ready. For some weird reason I have ending up with no brake fluid and the breaks are about the only part of the car I did not fix or replace. I will give it 50 miles or so on the 10w-40 and change the oil using. . . stay tuned!
I am trying to get the car road ready. For some weird reason I have ending up with no brake fluid and the breaks are about the only part of the car I did not fix or replace. I will give it 50 miles or so on the 10w-40 and change the oil using. . . stay tuned!
07-17-2008, 04:36 PM
#19
Range Master
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Delvac 15w 40. Sweet stuff, diesel grade, and on sale at NAPA for $9.53 a GALLON!
07-17-2008, 06:05 PM
#20
Drifting
07-17-2008, 06:37 PM
#21
Burning Brakes
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Hi,
this link will give a perspective on "normal" oil pressure on 928 engines;
http://928.landsharkoz.com/Blogs/tab...4/Default.aspx
Never us a non detergent lubricant in a 928 engine - all lubricants (including SAE30 as suggested by Ryan) are "detergent" type if they have an API Quality rating above SC (current is SM). The SC rating was adopted in 1964
this link will give a perspective on "normal" oil pressure on 928 engines;
http://928.landsharkoz.com/Blogs/tab...4/Default.aspx
Never us a non detergent lubricant in a 928 engine - all lubricants (including SAE30 as suggested by Ryan) are "detergent" type if they have an API Quality rating above SC (current is SM). The SC rating was adopted in 1964
