My mechanic is partial to 20-50 Castrol GTX. I put it in my newly rebuilt SL6 for the first 3000 miles, but I noticed when I was using Penzoil 30 wt for the break-in the engine seemed to like it better. Is that my imagination working? What does everyone else use?

bwhitejr

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'72 Duster (Performance 360)
'83 Ramcharger (Performance 318)
'80 TrailDuster (360)
'80 D-150 Truck (See Below)
CompCams 252S, Holley 390cfm, Offy manifold
Ported, Polished and Gasket Matched
P4286813 Springs,0.040 Overbore,
0.090 Shaved Head

20W-50 is a bit thick for a new engine, isn't it? I've usually been using 10W-40, but mine is an older engine that burns a bit of oil so I didn't want to go any thinner.

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"Mad Scientist" Matt Cramer
'66 Dart - turbocharged 225
My blog - Mad Scientist Matt's Lair

20-50 is way too thick on a just rebuilt engine.

Use 10w-30 (synthetic if you want, but not necessary)

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

20W50 is too thick for any engine unless it is virtually worn out and you're just trying to extend it for a few thousand. 10W30 is recommended by all manufacturers that I know of and is the original fill in all of them. You'll get better performance and better fuel economy with 10W30.

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David Kight
'62 Valiant Signet, White
'98 Dodge Dakota
'06 Jeep Liberty

Growing older is unavoidable but growing up is strictly optional.

SAE 30 - religiously.

D/W

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If it ain't broke, fix it!

Your mechanic needs to get some education; he's doing it wrong. 20w50 is far too thick for a newly-rebuilt engine, and definitely too thick for an engine in good condition. All it'll do is accelerate wear and cost power and mileage. Straight #30 would also not be the most appropriate pick for break-in of a new engine.

My pick would be 5w30 for break-in, 10w30 for routine use. Straight #30 if I lived someplace where the ambient temperature never dropped below 40°F.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Texas, for instance?

D/W

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If it ain't broke, fix it!

Well.....Down here on the Texas Gulf Coast it stays above 40*F between March and November. Actually there will only be a handfull of days where the temperature actually dips to 40*F or below. So should I use 30 wt during the months it is above 40*F?

I could use better mileage.


bwhitejr

_________________
'72 Duster (Performance 360)
'83 Ramcharger (Performance 318)
'80 TrailDuster (360)
'80 D-150 Truck (See Below)
CompCams 252S, Holley 390cfm, Offy manifold
Ported, Polished and Gasket Matched
P4286813 Springs,0.040 Overbore,
0.090 Shaved Head

For Coastal Texas I'd suspect that straight 30wt in the Winter months and straight 40wt for the other seasons would be about right. On those really cold (35 degree ) days just let the engine idle another 30 seconds or so at cold startup and you'll be fine with the straight 30wt.

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"Former Owner" of '65 Barracuda, 225, Auto, MP 2bbl intake, MP cam, Dutra Duals. Presently Moparless.

#40 is unnecessarily thick. Reduced economy, reduced power, increased wear at startup.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Then...10w30 assuming your engine's in good mechanical condition!

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Well, there might be places in Texas that don't go below 40F, but I've never lived in any of them. I've plowed snow with the airdam on my '84 Shelby Charger in Killeen (Central Texas), and seen a lot of sub-zero days in Wichita Falls and Lubbock.

As I recall from my readings, it snowed on Santa Ana's army on the way to the Alamo ...

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"When you find a big kettle of crazy, it's best not to stir it." - Pointy-haired Boss

1964 Valiant V200, 225/Pushbutton 904
BBD, CAI, HEI, LBP, AC, AM/FM/USB, EIEIO

Reduced economy? - Insignificant. What 14.1 mpg instead of 14.3? Get a modern car if you're worried about fuel economy.

Unecessarily thick? - Not for Texas in August it ain't. Give me a few pounds extra psi of oil pressure when it's unbelieveably hot in Houston.

Increased wear at start up? - Maybe if you are the type that nails the throttle immediately before pressure is up, otherwise no significant difference in lubricity or film strength that would lead to increased wear.

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"Former Owner" of '65 Barracuda, 225, Auto, MP 2bbl intake, MP cam, Dutra Duals. Presently Moparless.

Speaking of snow. It snowed and stayed on the ground on CHRISTMAS EVE last year!!!!!!!!!!. I am in my mid 50's and have lived here all my life and have seen snow on the ground three times. It was very special for it to snow on Christmas Eve, believe me.

bwhitejr

_________________
'72 Duster (Performance 360)
'83 Ramcharger (Performance 318)
'80 TrailDuster (360)
'80 D-150 Truck (See Below)
CompCams 252S, Holley 390cfm, Offy manifold
Ported, Polished and Gasket Matched
P4286813 Springs,0.040 Overbore,
0.090 Shaved Head

I used 5-30 in my last oil change and my engine didn't seem to like it. Noisy valvetrain, just a tad more of oil consumption (still less than a quart on 2kmile trip) I'm using 10-40 and thing's better.

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Juan Ignacio Caino

Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.