Friend has been advised to used Vauxhaul Semi-Synth 15/40 oil in his 95 WRX, on the basis that fully synth oils thin out too much when they heat up......this seemed a little strange to me

Personaly I use the fully synth Motul300v 15/50 in my 99 STI, I would have expected to use the same for his engine?

Thanks

Paul

 

I've been using fully synth since importing my MY95 WRX 3 years ago. I use Mobil 1 5w50 and have had no probs (touch wood). Subaru UK used Mobil 1 5w40 for years, all engines come from Japan, just the ECUs are different depending on global location AFAIK