My opinion is that the oil has improved over the years and the car builders now recomending thinner oils because of fuel economy reasons, not because oil clearances have changed. I keep reading people state that the newer cars NEED thinner oil because of tighter oil clearances, I don't agree and would like to prove or disprove this as I think this is a widespread falsehood. Here is another such statement where I gave oil clearance examples of a newer and older 350 Chevs. Sorry for the rant
Originally posted by JohnnyO:
Yeah, but I bet that was on a dyno in a very controlled environment. Some car from the 60's would be okay on straight 30 weight but modern cars have a lot tighter clearances and run hotter, so I think you need a good multi-grade now.
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I've lost count of how many people have said this, but I think your dead wrong. True they are able to hold tighter tolorences these days, but that doesn't mean they are using tighter oil clearances. I dug thru some Chiltons manuals to compare the recomended rod and main oil clearances for a 1969 Chev 350 (truck) and a 1994 Chev 350 TBI (truck), the figures below. If anybody can prove or disprove any of this, please do.
1969 350
.0008-.0024 main
.0007-.0028 rod
1994 350 TBI
#1 .0008-.002 main
#2/3 .0011-.0023 main
#4 .0017-.0032 main
.0013-.0035 rod