10W30 vs 10w40 engine oil
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Joined: Oct 2021
Posts: 747
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From: Windsor, On
Car: 1984 Trans AM
Engine: 305
Transmission: 700-4r
Axle/Gears: 3.23
10W30 vs 10w40 engine oil
Any of you fellows using 10W40 oil in your 395 ci as opposed to 10W30 as recommended in the 1984 owner's manual?
Supreme Member
Joined: Jan 2009
Posts: 2,317
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From: belle fourche,s.d.
Car: '82 z28
Engine: L83 5.7
Transmission: 700r4-1985
Axle/Gears: 3.42 posi
Re: 10W30 vs 10w40 engine oil
I think you meant 305, but yes i did use 10w40 in my 305 back in the day,and in 350 now 
Supreme Member
Joined: Oct 2000
Posts: 3,240
Likes: 810
From: Park City, UT
Car: '92 Corvette, '89 1/2-a-'Vette
Engine: LT1, L400
Transmission: ZF6, T5
Axle/Gears: 3.45, 3.31
Re: 10W30 vs 10w40 engine oil
It won't matter, other than 10w40 may give slightly lower fuel economy. Anyone who's run 10w40 and changed at proper intervals will have had "good luck" with that....just the same as anyone who's run 10w30 and changed at proper intervals. Either way, the engine will likely outlast the car.
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