Retune engine after oil change?

JB

Messages
40
Location
KL, MY
Previously using 20W-50 dino oil and recently changed to 10W-30. Some people have advised me to retune the engine since I'm now using a lower vis oil. One reason being to lower the idle rpm. Previously, the idle was about 900 rpm now it's 1,000 rpm (probably due to the 10W-30). What do you guys think?
 
Messages
658
Location
EU
Why not? Unless you've modified the engine, manufacturer specs should give you best overall performance, in conjunction with your nice, fresh oil.
 
Messages
8,756
Location
RI
I wouldn't worry about it. If the extra idle RPM bothers you, then lower it. Retune for oil weight??? While you're at it, change the cam/crank/rod/ring clearances [Big Grin]
 
Messages
187
Location
California
I had it happen to me once.I changed my oil once in my BBC Chevelle and I bought a case of SAE30 WT.Well I goof up and really grabbed a case of SAE40 WT. It was at night and I totally missed it.I fired up the engine and it dropped my idle speed a bit over 200 RPM.This car idled right at 1000 RPM and it was just a tad under 800 RPM with the SAE 40WT.It stayed that way until I changed it and replaced it with SAE30WT again.I never touched the idle or timing and when I put the 30wt back in the idle went right back up about 980 RPM.The only change was the oil and filter.Even on a BBC it made a feelable difference. I have the spec's on these two oils and if this means anything to anyone to compare. --------------------------------------------------- .............................. 30 wt...... 40 wt... cSt @ 40C .................... 99.5....... 159.... cSt @ 100C.................... 11.5....... 15.1 .. SUS @ 100F.................... 518 ....... 837 ... SUS @ 210F.................... 65.8....... 80.1... VI............................ 101 ....... 96..... --------------------------------------------------- I dont honestly know how important these numbers are but since this was the same brand of oil and only differing in being 30 to 40 wt without question it made a difference in my engine.I dont homestly know if these numbers would suggest a larger load pumping the 40 wt but the engine felt the difference.
 
Messages
308
Location
Houston, TX
what type of a car are we talking about? if it's fuel injection, the idle should be controlled by the idle air bypass, thereby remaining the same regardless of the miniscule differences in oil drag. i'm very skeptical, btw, that a 100rpm difference can be attributed to differences in oil weight, even given a carbed car. -michael
 
Messages
18,449
Location
East of IGO
Thicker oil takes more horse power to to pump than a thinner oil. that is why the motor should be thick enough to keep the rod and crank berings apart but no thicker than necessary , it uses more power . [ April 23, 2003, 11:44 PM: Message edited by: Steve S ]
 
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