Has Anyone Gone From 5/10W-30 To 10W-40?

Joined
May 25, 2005
Messages
143
Location
DC
On one car I owned, I switched to 10w40 because with 10w30, my oil pressure dropped <i>very</i> low on hot summer days when idling in traffic. The 10w40 cured the problem, and gave me a few extra psi of safety margin under the same conditions.
 
Joined
May 27, 2002
Messages
3,202
Location
Far North East Texas
For several OCI's, I went from 5/10w30 synthetic blends to Lubro-Moly synthetic 0w40(Full PAO German oil, SJ)- does that count? It held up well, after a long interval it had *barely* sheared into the 30W range. To see the analysis report try a "way-back" search under my membership number in the UOA section. Seemed to cause some "drag", maybe reduce power a little- but I have nothing but the ol' b*tt-dyno to base that on. Gas mileage did drop by a fairly consistent 1 mpg as I recall, about 3% on my car. Conventional wisdom says that if all else is equal, a 10w30 should be more shear-stable than a 5w30. That may make less difference now than it once did. Remember that oil shears & thins first, & then eventually begins to thicken with further use. If you're concerned with keeping a conventional oil at a 30W for as long as possible, then using a 10w40 is at least worth a try. But to *really know* what's going on with shearing & viscosity, you'd need to have a sample analyzed every 500 miles or so. It would be expensive- but it sure would be interesting!
 
Joined
Jun 28, 2005
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1,627
Location
Timberline
Yep, even did it when the vehicle was new. Have a '97 Rodeo that calls for nothing less then 10w-30 in summer heat; but when I lived in Las Vegas, NV - hot desert and did vast amounts of highway driving, that 10w-30 would thin out to nothing. So I started running 10w-40 at barely 12k miles in the summer. Currently have 155k miles, still likes 10w-40 in the summer.
 
Joined
Oct 22, 2003
Messages
13,132
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By Detroit
I was running 5w30 in my '95 F150 4.9L and a few years ago installed an oil pressure gauge. When I saw the pressure was running below the spec range, I switched to 10w40 which put the pressure in the lower end of the spec range. During winter I can still run 10w30, but in summer the pressure can drop a lot. I did not notice any performance/power difference.
 
Joined
May 9, 2003
Messages
9,283
Location
Fayetteville, NC
yes. I didn't really use a 10-40, but the HM 10/30's i used had equal or higher viscosities, I assume. I didn't notice any added power, but the engine idled smoother, quieter, and used less oil, and helped to stop usage completely (coupled with VSOT)
 
Joined
Nov 15, 2004
Messages
107
Location
Ohio
Used Chevron 10W-40 in the summer for Auto-Rx rinse cycle because it was cheap. Could not tell any difference from the recommended 5/10W-30.
 
Joined
Feb 9, 2006
Messages
6,902
Location
Louisiana
In the past several years I've bounced around all over the spectrum. I've never really noticed anything either way.
 
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