increasing viscosity

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I have two older cars that spec 10w-40 however I have a large stash of 10w-30. Can I just add a viscosity thickener like STP to the 10w-30 to get it closer to 10w-40 or is there a better alternative? I'm in So Cal so cold weather starts are not an issue
 
I would skip the STP. 10W-30 should work just fine. STP is a polymer that may affect cold cranking and pumping performance, even though you're in SoCal. I would just check the oil level more frequently for the first oil change or two.
 
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Perhaps some 20w-50 would provide a similar and friendlier viscosity improvement.

How much oil is going into the crank?
 
Originally Posted By: redhat
Perhaps some 20w-50 would provide a similar and friendlier viscosity improvement.

How much oil is going into the crank?


That's what I would do, blend it with a thicker oil, maybe even a 60 weight so that you have a lower ratio.
 
What older cars?

And no I wouldnt just use STP to water down and thicken up your oil.
 
66 barracuda holds approx 5 quarts
mid-90's Saab turbo 4 quarts (specs 10-40 or 15-40 if temp consistently above 60 degrees
 
Originally Posted By: VQLT
66 barracuda holds approx 5 quarts
mid-90's Saab turbo 4 quarts (specs 10-40 or 15-40 if temp consistently above 60 degrees


Does either vehicle allow a 30 weight?

What engine in the 'Cuda? Is it built or stock(ish)?


Reason I ask is that oils before [insert correct date] sheared much more than modern oils. A 1960s 10w40 might have sheared down quite a bit over 3-4000 miles, and your modern 10w30 will probably stay in grade. Another example is that 10w30 in the late 90s didn't shear but 5w30 did, so 10w30 was recommended then over 5w30 for warmer temperatures.

If that's not a comfortable response, then go with mixing a 50 grade with the 30 to approximate a 40.
 
barracuda is 273 V8 commando high compression stock engine I can probably get away with 10w30.
the saab specs 10w40 or 15w40
 
Yeah for the Saab you may want to get some 50 to add in with the 30. Turbo/shearing/etc. I'd get something from the same manufacturer (or additive package) as your stash.
 
If your stash of 10w30 is high quality oil, just run it. Modern oils are very good and I'm confident the engines will run fine. If you are really concerned, you can use equal parts 10w30 and 20w50 (as another post mentions), or just ignore the 10w30 and run what is spec for those engines.
 
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