The key ingredient is ZDDP (bacically zinc and phosphorous) they are high pressure additives necessary for flat tappet cams. Uncle Sam determined that these additives can clog up a catalytic converter IF your engine is burning oil. So the auto companies and the Government decided to force the oil makers into reducing the amount of ZDDP in modern oils to help maintain the mandated 125,000 mile emissions warranties in place (some parts are only 75,000 miles). Modern roller cam engines do not need as much of this additive (except for the crankshaft thrust bearings which still take a lot of load)
Old oil from the 1990's had 1600 ppm of ZDDP, while most new oils have 1/2 of that amount. The diesel engine oil has a higher percentage (1000-1200 ppm) because most large diesel engines and farm/industrial equipment still use flat tappet technology. I'm trying the Quaker State Defy, since it is supposed to have about the same amount of ZDDP as the diesel oils, ,but with a more friendly weight (10W-30 instead of 15W-40).
Joined: Thu Mar 22 2007, 08:13AM
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As regards engine oil for "our" engines. I would suggest that before choosing one, a copy of the SAE Automotive Lubricants Reference Book is bought, read, and understood.
It will tell you that diesel engine oil should not be used in gas engines, irrespective of how much zddp it has.
Joined: Sat Aug 19 2006, 05:03PM
Location: Ontario, Canada
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Uncle Joe wrote ...
It will tell you that diesel engine oil should not be used in gas engines, irrespective of how much zddp it has.
Is there a short answer why that is the case? There are lots of us running Shell Rotella-T 15W40 and similar diesel oils in our engines. Rotella is advertised as being suitable for "mixed fleets" i.e. gas and diesel engines, and has an API "S?" rating for gas engines as well as a CJ rating for diesel engines.
Joined: Thu Mar 22 2007, 08:13AM
Location: In the workshop
Posts: 1063
Mike66Chryslers wrote ...
Uncle Joe wrote ...
It will tell you that diesel engine oil should not be used in gas engines, irrespective of how much zddp it has.
Is there a short answer why that is the case? There are lots of us running Shell Rotella-T 15W40 and similar diesel oils in our engines. Rotella is advertised as being suitable for "mixed fleets" i.e. gas and diesel engines, and has an API "S?" rating for gas engines as well as a CJ rating for diesel engines.
Short answer: Flat tappet diesel engines need high zddp, high detergent oils. Flat tappet petrol engines need high zddp, low detergent oils. The reason being that high detergent levels in a petrol engine remove the zddp.
Fleet oils should be avoided in all kinds of performance engines.
Joined: Fri Jan 04 2008, 10:48PM
Location: NWPA
Posts: 9
I have read there are detergent differences in diesel- and gas-formulated oils. I can't find the article I was looking for but found something from www.cam-shield.com. I realize they're trying to sell us something but I think they explain the differences pretty well:
"Here are the differences between diesel engine oil and gasoline engine oil. In a modern diesel engine there is substantial exhaust soot contamination that the engine oil must contend with. Diesel oil is designed with much higher levels of detergency and dispersency to fight the soot contamination. Like ZDDP anti-wear chemistry, detergents are a surface active chemistry and compete directly for space on metal surfaces, such as the cam lobe and lifter face. So, in practice, the effective level of Zinc anti-wear is a bit lower than what we expect it to be based solely on chemical analysis. Additionally, the ZDDP that is generally used in diesel formulas is primary ZDDP (which activates at higher engine temperatures) since a diesel engine runs predominantly at operating temperature. In a gasoline engine, we must have both primary and secondary ZDDP (which activates at lower temperatures) since the engine will experience a significant number of cold starts. Also, the viscosity modifier polymers that are used in multi-viscosity engine oil to prevent viscosity loss at operating temperature (to protect the bearings) are different for diesel oil and gasoline oil. Diesels operate at essentially the same rpm all day long and need polymers that are shear stable to protect the bearings. Gasoline engines experience many large ranges of rpm during operation and require polymers that have both shear stability and thickening efficiency capability to protect the bearings."
Here's what i use and it works. I run reg. 10W-30 along with the Luca's high zinc additive and the Royal Purple lube for assembly.
Here's my take on this (and sorry to get in on this never ending oil discussion) is,if you run a high detergent oil and the detergents keep on washing the natural deposits off the walls on the inside of the block,they keep on going through the oil filter and keep cycling through the engine. Take a look at some of the old engines and look at the amount that there is on the inside of the block and you wonder how the engine ever ran. THROW in one oil change of diesel oil and it will smoke forever and the mosquito population will go down or the tree huggers will put you beside Hoffa. If it's a gasoline engine run oil made for it,if you got a diesel....run that oil....AIN'T ROCKET SCEINCE here!!!!
Joined: Sat Aug 19 2006, 05:03PM
Location: Ontario, Canada
Posts: 2919
Glen, I forget the actual amount, but that Lucas bottle is super concentrated ZDDP. How much of that do you throw in with the 10w30? I run Rotella 15w40 + 1/4 bottle of the Lucas ZDDP, since the CJ oils don't have as much ZDDP as the older formula, but you can have too much of a good thing.