best type of oil for 71 340 engine

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matthew110366

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whats the the best type and grade of oil for a 340 small block , 20W50, 10W40 etc.
thanks
kevin
 
Depends. Is the motor freshly rebuilt? How many miles on it
 
I'm running a 70, 318. It has all new gaskets and seals and is basically extremely low mileage. It was beautiful inside. I've run 5-30 Mobil 1, it seeped a drop or two. I switched to 10-30 for a while and had no problems. I use 15-40 Rotella now, I had a case given to me. I think the Rotella works fine and it has zinc so the new cam has given me no problems. Just make sure it has ZDDP (zinc) and 10-40 should be about right unless you have large clearances on the rods.
 
The motor was rebuilt about 4 years ago, has appox. 10,000 on it , slightly heavy cam , been running 10-40 in it
 
What suddenly calls your attention to oil weight?

If you google oil viscosity you'll find it starts based on climate/temperatures.

Start with the recommended weight according to your climate, then based on bearing clearances 'if you know them' use your best judgment to determine wether you need more viscosity.
For ex. typical california car never see's/operates below 20*, so no need to run less than a 20 wt , now in the summer it can get into the 90's-100's in most of the state..so more viscosity-50wt=20/50wt oil, however if you spend most/all of the driving in the cold parts, 10/40wt is fine.

jmo
 
I live in Kentucky , during the summer months it can get to 90 degree plus , but it stays in to mid to high 80s , I only drive the car in the spring and summer mnths only to cruises and shows ... I didn't rebuild the motor and Im unaware of the specs ... So I'm looking for the best combination for the motor.
Regards
 
matthew110366 said:
I live in Kentucky , during the summer months it can get to 90 degree plus , but it stays in to mid to high 80s , I only drive the car in the spring and summer mnths only to cruises and shows ... I didn't rebuild the motor and Im unaware of the specs ... So I'm looking for the best combination for the motor.
Regards
Click to expand...

THE most important aspect of modern oil is the removal of zink and other mineral additives. Any flat tappet engine needs those additives to live, wether it is a fresh rebuild or has 100k miles on it and especially if you are running a high lift cam with high seat/spring pressures. I use 10/30 Mobil 5000 and a bottle of ZDDP. You can buy special oils with the additives but it gets spendy in a hurry. I buy the Mobil at Wal-Mart in a 5 quart jug for $11 and a bottle of ZDDP is another $8-10. I currently have 3 classics running on this combo with zero cam wear issues........so far.

Robbie running the Rotella.........they took the zink out of that too because of the particulate filters on the new diesels. Might wanna see if yours is the older stuff that still had it. I run Mobil Super 1300 in my Pete and was told of this a couple years ago by my distributor. He said if I was using the oil in any flat tappet car engines to use an additive or get the special oil...:sad3:
 
Valvoline VR-1 10w-30. It's got a high zinc content for your flat tappet cam.
Or, if you want a thicker oil, it also comes in 20w-50.
 
5w/40 HDEO's (diesel) best thing for the old V8s, anywhere in North America. Shell, Chevron, Mobil, doesn't matter - all have marque blends in this grade, just choose your price range.
 
The reason I'm question oil viscosity , about ever 2 yrs I strip the engine down of all of it's accessories , hoses, wiring , radiator , etc and do a repaint and cleaning of the engine for car show season , I've noticed that there is a slight seepage of oil from were the heads meet the block , I was courious if my oil was too thin and if it should be thicker for start up porpose
 
I use mobil 1 5w30 full syn. I don't have to worry about the zinc problem because my motor has a roller cam in it.
 
matthew110366 said:
Why a diesel oil because of zinc content ?
Click to expand...
Contrary to popular myth, most of the current API spec'd HDEO's contain on average just a little less ZDDP than their predecessors. The emphasis in the last round was supporting diesel emissions for particulate traps and things like that. But even the ones using other anti-wear formulas have shown improved wear rates over the old ZDDP-laden varieties. But that's another topic.

The best reason for using the 5W/40 grades now is because modern viscosity index enhancers and other contemporary blending additives and processes give the new multi-grades all the benefits and none of the drawbacks of years past. It used to be the viscosity spread sheared down more or less quickly in alot of those multi-grade oils, whereas today they are stable and hold up to extendend change intervals in the most extreme conditions.

No need to worry about the weather, it ain't your daddy's oil any more.
 
I run 20w50 in the hot summer most of the time and 10w30 for the best ET with the cold fall air at the track.

It's about how tight the engine is and how it was built ** BUT **

I would have to question why and how a 340 could ever be built to tight for 20w50.

Modern engines that use 5w30 oil or 5w20 oil *ONLY* are made very different then a typical American old school v8.

I run a heavy oil if in the hot summer or in a very hot climate.20w50.

If in a cold climate, i would run the lightest oil.10w30 in your 340.
 
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