erp52

ZDDP additive for an old slant six

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On some other Dodge forums, people suggested using a ZDDP additive to the engine oil.  Is this a good idea?  Ed

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Waste of money. Just use a diesel oil, API CI-4 or CJ-4. These have plenty of zinc. If you want to minimise wear, use a synthetic oil such as 5W-30 and forget about zinc. Any synthetic oil is better at minimising wear than ALL mineral oils.

 

Read Richard Widman's paper on oil at http://www.widman.biz/Corvair/English/Links/Oil.html

 

but here is the paper to save you the trouble of looking it up.

Corvair_oil.pdf

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Spinneyhill is absolutely correct.  The new diesel engine oil specification is now API CK-4, which is usually paired with the passenger car motor oil (PCMO) specification of API SN.  A dual-rated heavy duty engine oil would therefore carry the API CK-4/SN (or API CJ-4/SM, etc) designation.  The concern with API SN is that it requires 30-grade oils to also have a maximum phosphorus (the antiwear component of ZDDP) level of 800 ppm.  That is why now it is now more difficult to find a 30-grade HDEO with an API CK-4/SN rating.

 

I've been using Petro Canada Duron SHP 10W-30 in the 225 in my 65 Barracuda.  Duron SHP is approved for API CK-4/SN for the 15W-40 grade while the 10W-30 grade is approved for API CK-4 and SUITABLE FOR API SN because it uses the 15W-40's additive package but cannot be approved for API CK-4 because of its 1200 ppm phosphorus content.  I have not been able to get other HDEOs (like Shell Rotella) to confirm that their 10W-30 grades use the same additive package as their 15W-40 grades.  See Heavy Duty Engine Oils.

 

My 1965 owners manual recommends the 20W-40 grade for ambient temperatures are consistently above 32°F (see Chrysler Oil Recommendations).  I've upgraded to a 75 psi hemi oil relief valve spring and I've found that my original oil pump has no problem generating 75 psi above 2000 RPM in hot weather with 10W-30.  Using a thicker oil (like 15W-40) just means that more oil blows off back to the sump without reaching the bearings.

 

If you're looking for a good engine oil for your slant six, there is no need to use anything heavier than a 30-grade oil (ie, 0W-30, 5W-30. 10W-30).  If it has low oil consumption, a synthetic would be a good choice (eg Mobil Delvac Elite 222 0W-30).  Excessively thick oils tend to run hotter and could cause unnecessary engine wear in colder weather.  I believe HDEOs generally have higher HTHS ratings than PCMOs and would therefore offer better bearing protection.

 

See Engine Wear.

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