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Explanation of zddp content from AFAB forum


Tonto Papadapolous
This is a pretty good take on the zddp controversy that I quoted from an Alfa Romeo forum. I am not saying I subscribe to this theory, but it is food for thought.

oil and zinc


Let's go back to basics to settle this for good.

The basic principle of lubrication is to maintain an oil film between moving surfaces. As long as an oil film is present, wear is not possible. On a properly designed engine (there are exceptions!) fed with oil of appropriate viscosity, the oil film will only be absent under one of these two circumstances:

-during start up, before oil has had enough time to reach every moving part;
-under extreme pressure, when oil starts breaking up (which implies that the oil wasn’t appropriate to start with).

If these circumstances didn’t exist, anti wear additives wouldn’t be required. Whenever the oil film is broken, the moving surfaces rub against each other and heat up; ZDDP reacts to heat and sticks to the heated surfaces, building up a protective film. Until then, zinc stays in suspension. This film stays there until more contact occurs. “Anti wear” does not entirely prevent wear, it mostly prevents the contact surfaces from welding together and ripping little pieces away.

One of the key areas where metal to metal contact is likely to occur at start up is at the cam/follower interface. It is a high pressure contact, and far away from the oil pump on an overhead cam engine. Single overhead cams are actually worse than our DOHC Alfa engines, as the cam lobes have little puddles of oil to dip in.

API’s requirements for oil certification are based on performance, not chemistry (other than limiting zinc contents due to catalyst requirements). In the current SM standard for gasoline engine oils, sequence IV-A test addresses anti wear performance at the cam/follower interface. This test is run on a Nissan 2.4 SOHC engine (240SX); it replaced the V-E test based on the Ford 2.3 (Pinto) engine. The anti wear requirements of SM motor oils are actually more stringent than SM specs, which were more severe than SL. This is in spite of the reduction in zinc contents: SM oils use other anti-wear chemistries that work, and some have been around for quite a while - for example in locomotive lubricants.

Also worth mentioning: diesel engine oils such as Shell Rotella or Chevron Delo are not such a good idea on anything but a new engine. They have a much higher detergent contents than gasoline engine oils. Especially if your engine has been fed a regular diet of motor oil with a weak detergent (and I’m finding several evidences that Castrol GTX is such an oil) the diesel stuff will clean out a lot of sludge which may lead to a clogged filter. All this for nothing, as current CJ-4 diesel oils are also on a zinc reduction diet.

Personally I am happy with any SM 10W40 or 20W50 in my Alfa 4. Engine and transmission oils have been submitted to enormous advances over the past 20years.

Hope this helps.

1985 Ford F-150

Country Boys Can Survive
Tooele, Utah
I know for a fact what a low zinc oil does to a flat tappet hydraulic cam and it aint cheap or fun to replace a set of lifters and a cam. Read my build up of my 410 and youll see the evidence.


Tonto Papadapolous
You're welcome. I bought some Valvoline VR-1 Racing oil today. The box says it meets SH guidelines, and has .14% Zinc, and a little less phosphorous.


Oilfield Trash
Stigler, OK
In a flat tappet engine, this is totally revelant. In anything roller, your wasting time and money trying to find oil with high zddp content. Also note that there are plenty of Diesel oils that are higher in zddp than gas oils. You may have to look as hard, but for break in of say a FE, the look is worth it. Doug, it is good info, but only relevant for older builds or maintains.


Licensed to Represent!
Good write up, thanks for the info!'hippie'

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