Best oil weight for 1977 Chevy Monte Carlo 305

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Hey Everyone,

Trying to get some insight on the best weight oil for my car. Its a 1977 Chevy Monte Carlo with the 5.0/305 2bbl carbuerator with 66,000 original miles. It is the original engine that was supposedly freshened about 15,000 miles ago, but not sure exactly what was done to it. I have a feeling its just new seals. Completely stock minus headers.

The car does not appear to leak or burn any oil. It does sit in a garage for periods of time as its not a daily driver. I was thinking a 10w-40 or 20w-50. I run 20w-50 in my other vehicle which has an older Chevy 350 that has worn valve seals and does burn a tad of oil. It likes it, but feel that may be too heavy for the 305.

What do you all think? And this is non-synthetic oil.

Thanks for the help in advance!
 
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It doesn't need anything other than the 10w40 the manual calls for. 20w50 is too heavy for a non-DD in Jersey's climate. Hopefully whoever rebuilt it replaced the soft factory cam.

T6 may not be a bad choice at all.
 
I'd go for a heavy duty 30 ,such as Rotella T5 10w30. With low miles and what sounds like a non-leaker, you can go with a nice Mobil 1 in 0w40 flavor.The ZDDP is what you're after with this engine,not just a thicker grade.

Edit:beat me to it mrsilv04
 
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Originally Posted By: FL_Rob
I'd go for a heavy duty 30 ,such as Rotella T5 10w30. With low miles and what sounds like a non-leaker, you can go with a nice Mobil 1 in 0w40 flavor.The ZDDP is what you're after with this engine,not just a thicker grade.


Nope. Myth's never die on the internets.
 
I had an 85 Monte SS with the L69 and it ran just fine on normal 10w30. Good oil pressure, no burnoff.
 
Originally Posted By: Falcon_LS
Maybe consider a 5W-40 like Rotella T6?

That's what I would use. Great stuff.
 
Originally Posted By: dave1251
Originally Posted By: FL_Rob
I'd go for a heavy duty 30 ,such as Rotella T5 10w30. With low miles and what sounds like a non-leaker, you can go with a nice Mobil 1 in 0w40 flavor.The ZDDP is what you're after with this engine,not just a thicker grade.


Nope. Myth's never die on the internets.

Ha. No kidding. 1100 posts and you'd think he woulda absorbed something.
 
Any 5w30 you have less start up wear and the same thickness on the top end its a no brainer to me. I would use Defy myself It has higher zinc.
 
Get some modern 10W-30 (hopefully FAR) and she'll probably only last another 35 years (or 66K)...

I'd hit Rock Auto and grab a couple carb rebuild kits, rotor & distributor caps, etc. while they are still available and CHEAP!

Any other intere$ting tranny/engine/electrical $pare$, rebuild kits for master cylinder, etc. while you still can: someday they may turn out to be helpful. When they close out this kinda' stuff it can really be INEXPEN$IVE!

Cheers!
 
To the OP:

The answer depends partially on how the car will be used.

If I were to assume that it will sit un-driven a lot;
The HDEO recommendations made by previous posters make a lot of sense.
Rotella 10W30 and 5W40 for example.

HDEO formulations take into account that some engines may not be cranked for extended periods of time.
If I remember correctly; additional additives that address rusting and corrosion of internal engine components are present in HDEO formulations for this reason.

That 305 will have very mild cam action and low valve spring pressures.
The concerns regarding ZDDP and flat tappets are minimized with that configuration.

Still it has flat tappets:
Quaker State Defy 10W40 comes to mind for me on this one due to the "boosted" ZDDP level.

Good luck sir.

Rickey,
 
Any HDEO 15W-40 at a minimum, and evne at that, I'd add a zinc additive.

That engine is garbage and will eat the cam sooner rather than later...
 
Run any modern 10w30. Carbs will lead to some fuel dilution. Modern fuel has ethanol. Modern oils are equipped to counter ethanol's negative effects, and they have alternative anti-wear agents to make up for ZDDP reduction. Mobil Super 5000 10w30 will treat your motor well.
 
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