Personally it depends on the condition of the rest of the car, if the care is in generaly good shape and I plan on keeping it for a while, I put in synthetic, mostly for its cold flow properties (quick lubrication on the sub zero (down to -40) starts). Some people clain that it starts or worsens seal leaks, but I have not had a high milage (300,000Km or 186,000mi) car that does not leak from somewhere
I just put synthetic in my low (for me only 136,000mi
) milage SVX. just my $0.02
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current stable, subject to change without notice:
1995 Red SVX, 4.44 & Quick Change
2014 Nissan Titan S 4X4
1992 Teal SVX parts car