Hello. I have a question about the proper oil to use in my 71 225 cid engine. First let me say I purchased the car last year and I know nothing of it's history. The engine is original. The odometer reads 49,712 miles and doesn't smoke. A recent compression test confirmed that all 6 cylinders are still strong. I plan to re-gasket the engine while it is removed from the car during the restoration, and while the head is removed I will rebuild it. So far so good. I wasn't prepared when a friend asked me what oil I planned to use. Today's oils are formulated differently since this engine was engineered, and the zinc/sulfur compounds which are necessary for my flat tappets are no longer present. I did some research and my options are as follows:
1) add oil additives that contain ZZDP (zinc dithiophosphates???)
2) find specially formulated oil that contains zinc/sulfur compounds
3) use oil intended for diesel trucks

Does anyone have any advice, AND can anyone recommend a particular product? Has anyone had any bad experiences with any of these products? Thanks for your time.

You can use any modern oil displaying an API service category (currently API SM) as they are all backwards compatible with older categories. I would go with a dual rated (like API CJ-4/SM) heavy duty engine oil because slant sixes do not require the lower phosphorus levels for catalytic converter protection. HDEOs have higher levels of anti-wear and cleanliness additives than passenger car oils. Starburst oils have anti-friction additives for improved fuel economy.

• Engine Oil
• Heavy Duty Engine Oils
• Chrysler Oil Recommendations
• Engine Wear

Thanks for the wealth of information!

The "OMG modern oils will eat up our old engines because no ZDDP!" scare is largely baseless. You can spend many, many hours poring over a great deal of information of highly variable quality with a question like yours. The basic answer Frank Raso gives is correct -- use a reputable brand of an appropriate viscosity grade of off-the-shelf engine oil. It is not necessary to spend money on special boutique oils or additives. I don't agree with Frank's comments on dual-rated oils (such as SN/CJ-4). The "C" ratings are for diesel engines, and the CJ-4 category's limit of 1200 ppm Phosphorus is not of concern because that is more than ample for protection of engines like ours. See what the API has to say on the subject—they're the ones who devise the ratings.

Avoid making the common error of choosing too heavy a viscosity grade of oil. It is incorrect that heavier-weight oil gives better protection. Using the lightest viscosity grade your engine's mechanical condition will support will ensure quick lubrication of all parts at engine startup, thus reducing wear. With a low-miles engine such as yours, if it has not been abused and is in basically sound condition, 5w-30 is a completely justifiable good choice, 10w-30 is OK too, and there is no reason to use 10w-40 or 20w-50 or straight 30-weight, etc.

Be sure and use a good brand of filter -- no Frams!

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

Dual rated oils are rated for BOTH diesel and gasoline engines, which is why they have a gasoline engine rating (like SN). The fact that an HDEO also has an SN (or SM or SL etc) rating means that it also meets the performance requirements of API SN. HDEOs do not have friction modifiers (for slightly better fuel economy), which prevents them from getting an API Starburst. Energy conserving (Starburst) oils were never specified for Slant six engines.

API Motor Oil Guide

…because Energy Conserving (Starburst) oils didn't exist when slant-6 engines were being built. There is nothing about such oils that makes them unsuitable for use in a slant-6 engine.

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

True. There is no reason that a Starburst Oil (ie meeting the requirements of ILSAC GF-5) could not be used because it has additional performance requirements (for emission control life & CAFE) over API SN.

My point is that slant six engines do not benefit from the additional requirements of ILSAC GF-5. Although there would be a small fuel economy benefit, I think it would be very hard to measure. I think the base oil (with higher HTHS) and additive package in HDEOs are more beneficial to older flat tappet engines than the GF-5 additive package. For example, comparing Petro-Canada 0W-30 oils, Supreme Synthethic (PCMO) has an HTHS of 3.1 while Duron Synthetic (HDEO) has an HTHS of 3.3. Widman also does not recommend Starburst oils for flat tappet engines. See Selection of the Right Motor Oil for the Corvair and other Engines.

We seem to agree.
Agreed!
Agreed here, too.
I wish Petro-Canada's engine oil were easier to buy. You'd think they'd have it lined up by the double-aisle at Canadian Tire, but no.
Yeah...I'm not sure how sound that !recommendation is.

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

If you're looking for uncommon Petro-Canada (or Esso, Shell, or Chevron) lubricants, send me a PM. I'm using Esso XD-3 Extra 0W-30 but Shell Rotella T5 0W-30 and Chevron Delo 400 0W-30 are good too.
I think Widman's interest is in maximum flat tappet valve train protection. Starburst oils (ILSAC GF-4 and GF-5) are limited to 600-800 PPM of phosphorus (P), which is the anti-wear component of ZDDP. CJ-4 oils limit P to 1200 PPM while CI-4 & earlier oils do not have a P limit.