Originally Posted By: chevrofreak
Originally Posted By: cronk
"A 75W-90 gear oil is actually thinner than a 20W-50 engine oil is."
By that logic is 0w20 thicker than 85w140.
I dont see your logic.
Try pouring 15w40 out of a can and try to pour 75w90, see which bottle pours out first.
Compare the viscosity of these two if you don't believe me.
http://www.amsoil.com/storefront/svg.aspx
Amsoil Severe Gear 75W-90
Kinematic Viscosity @ 100°C, cSt (ASTM D-445) 16.7
Kinematic Viscosity @ 40°C, cst (ASTM D-445) 109.1
http://www.amsoil.com/storefront/aro.aspx
Amsoil 20W-50 engine oil.
Kinematic Viscosity @ 100°C, cSt (ASTM D-445) 18.9
Kinematic Viscosity @ 40°C, cSt (ASTM D-445) 123.8
Ok there is some truth to your point, but you are comparing 20w50 not 15w40 that the poster is asking about.
My point is that many of these engines run a 10w30 their whole lives with no issues. A 15w40 is not that much thicker to cause issues. especially in an older high mileage engine, I'm sure the clearances have opened up some and a little thicker oil film may actually benefit the engine.
If it were a new engine with VVT I would be more nervous to try it, due to the viscosity requirements of the various solenoids another parts related to VVT.
BTW, my grandmother has an 89 Toyota pickup with a 2.4 with 280,000miles. It started consuming and leaking about 2 qts between changes. I started using 15w40 Valvoline in it about 3 years ago, it runs much quieter and smother, and consumes/leaks only about 1 qt between changes now.