What oil weight do I use for a 1986 300zx Turbo?
Synthetic or regular?

 

Depends on how many miles it has, and the type of oil already in there...

Click: information:basic_z31_info [Z31.com]

 

Thanks

 

I use mobil one. it is in all the vehicles I own. I had a friend that actually worked for Mobil and was involved in testing and evaluating oils. He used it and praised it highly.

 

Given the stock VG30ET in the Z31 is such a mild application of turbocharging technology (light boost with relatively low compression ratios) and conventional oils have been dramatically improved the last 25-30 years, it probably doesn't matter if you use conventional, blends or full synthetic oil. Stick with an API certified product. Synthetics do resist oxidation (aka, burning) much better, but this advantage is usually lost where the oil is changed on a routine basis at intervals of 3,000 to 5,000. Yes most, if not all, of the newer engine designs using turbocharging require the use of blends or synthetics, but those are much more aggressive uses of the technology. Look up "Bob is the Oil Guy" forum if you wish a definitive (bordering on maniacal) source of opinions on this topic.

 

What weight oil is best?

 

It's not a question of what is "best", but what weight was the engine designed to use based on the bearing manufacturing tolerances and the conditions under which it is running. The original owner's manual indicates 10W-30 for most situations. If you live in a place where the car is expected to start at temps below zero, use 5W-30. If you drive across Death Valley on a routine basis (especially during the summer), use 15W-40. I think it would take some pretty extreme driving conditions to justify using 20W-50. I like the previous advice of using the same weight that has used in the engine in the past, as experience is hard to argue against.

Do not use the lighter weight oils (e.g. 5W-20, 0W-20) recommended for new cars. Nissan has always built some pretty tight engines, but a 25+ year old one still would not have been manufactured to tight enough standards for these oils.

 

Thanks