what grade motor oil should i be using in my 89rs/305 tbi? thanks

 

Mobil 1 synthetic 10W-30

 

I have an 89RS/305TBI with about 155,000 miles on it, and it still runs killer. I use Valvoline 10w-40 synthetic blend in it. I noticed my oil consumption went down by about half after I switched from regular motor oil. Full synthetic is the best, but the blend only costs about half as much per quart. Most manuals will recommend 10w-30, but I think that's only because it's supposedly more energy conserving and emissions friendly than 10w-40. I prefer 10w-40 because it's a little thicker, which seems to protect your engine better, and doesn't experience viscosity breakdown quite as quickly, especially in a high mileage motor where your ring and bearing clearances are getting larger. It helps increase your oil pressure somewhat. 20w-50 or straight 30 weight are even better for that purpose, but they make for slow cranking during the winter sometimes. I've been running 10w-40 year round with no problems. I run 20w-50 racing blend in my 69 Camaro, but it hardly ever sees winter driving. Whatever grade you decide to use, I'd totally recommend a full synthetic or synthetic blend over conventional motor oil. Since synthetics are so much more resistant to viscosity breakdown, I've been going 6,000 miles between oil changes instead of the usual 3,000 miles, and haven't experienced any ill effects at all. Full synthetics really never break down, but any kind of oil gets dirty enough eventually. Hope this helps you out! Pat.



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89RS w/350 TPI; 69RS/SS w/450 HP 350/Muncie 4-Speed "Too weird to live, too rare to die."

 

I would go with 10w30... I use mobil 1 synthetic in cars after the engines second oil change... I have seen cars with minor seepage that ended up with a serious oil leek after switch to synthetic... I start w/ organic on a fresh motor and switch to synthetic after the second oil change...

zroc

 

oh yeah.......... castrol organic.... mobil 1 synthetic... (left that out... sorry)

zroc

 

I use synthetic in the Camaro I have now, but another 91 I used to have, I used Havoline 10W30. That engine had 170,000 mile on it and was still running a 14.2 in the 1/4. (Then it got totalled.)=(

 

Since many have sugested Mobil 1, and I also have it in my GTA, check out their FAQ page.
Mobil 1 FAQ

 

Your original question only asked what grade of oil to use, by which I assume you mean what weight or viscosity. To really answer that, we'd have to know more details, such as what climate you live in, what kind of driving you do, and what condition your engine is in.

If you live in an area that gets below 0 degrees, and are using conventional petroleum oil, then you want to use a 5W30 oil during the winter. Other times, or if the temp stays above zero, then 10W30 is fine. Avoid 10W40, since it has to use more viscosity index improvers to obtain the 40 rating, and the VI improvers are the first thing in an oil to break down.

Certainly, if you use synthetic, the 10W30 recommendations given are sound even in the extreme cold. However, if your RS is getting worn and using a quart of oil every 300 miles, then you probably don't want to throw a multi-dollar per quart oil in there that often. Otherwise, it's a good choice.

I would advise staying away from all of the major oil companies' synthetics except Mobil. The big guys don't really believe in synthetics, and only have them so they can say they have them (and to put them in their racers' cars, even though they say they're using the same oil you can get off the shelf). AMSOIL and Redline specialize in synthetics, so if you're looking for the best, go for AMSOIL, Mobil 1, or Redline. Of those, AMSOIL is the only one willing to show test results against other synthetics, rather than comparing their product to petroleum like most synthetic manufacturers do.

So, what did you really want to know?

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82 Berlinetta, orig V-6 car, now w/86 LG4/TH700R. 2.73 unlimited slip. Cat-back from '91 GTA, Accel HEI SuperCoil. AMSOIL syn lubes bumper-to-bumper. Daily driver, work-in-progress (LB9 w/ZZ3 cam, TBD heads, exhaust, paint, etc.).
57 Bel Air, my 1st car. 0.030 over 396, Weiand Action+, Edelbrock 1901 Q-Jet, Jacobs Omnipack, 1-3/4" headers, TH400 w/TCI Sat Night Special conv & shift kit, 3.08 10-bolt, AMSOIL syn lubes bumper-to-bumper. Best 15.1 @ 5800' Bandimere. Daily driver while Camaro was being put together.