HD oil adds, cat. converters and delvac 1 / M1 SUV

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Staff member
Dec 14, 2002
New Jersey
Hi, I have heard that some compounds (zinc?) in HD engine oils can be bad for catalytic converter function. I am curious about the use of delvac 1/mobil1 truck & SUV in my light duty truck... I have a 98 Chevy S10 with the 4.3L engine.I think that this oil would be a good coandidate for use, but dont want to ruin my converters or degrade their performance. Does anyone know if this oil has those specific catalyst harming compounds? I knwo that just ecause an oil is rated SL doesnt mean that it doesnt have these compounds in it (rotella, for example). Any info would be great. Thanks, JMH
The phosphorus, which is part of the zinc phosphate antiwear and antioxidant additive compound, may eventually poison the catalytic converter. A very small amount gets to the cat from volatilzation of the oil or oil burning. Your '98 was probably designed for an oil of that day that has about as much phosphorus as modern diesel engine oils. The current crop of ILSAC GF-3 oils (5W-20, 5W-30, and 10W-30 with the "Energy Conserving" Starburst symbol) has a max limit of 0.1% phosphorus. The new ILSAC GF-4 oils due out this summer will have a max of 0.08% P. Don't worry about the Mobil 1 Truck & SUV 5W-40 harming your cat. Ken
It will only harm the cat converter if it burns oil. And if your burning enough oil to damage the converter, then the phosphorus in your oil is the least of your worries!
Don't fall for the politically correct BS on P in a well designed oil poisoning your cat. Ken2 and Jason8691 summed it up perfectly. Use the Delvac/M1 with confidence.
Does Delaware have a emissions monitoring program? If not, I wouldn't even worry about it.
I only live in DE part time, Im really from NJ, which dynos cars (at least until recently). JMH
Let's assume just for fun that phos in the amounts acceptable in API-SH CAN harm the catalytic converter in 100k miles. Now let's also assume just for fun that the reduced level of ZDDP in an API-SL oil are not completely made up by replacement Anti-wear additives in SL. Which do you think is going to be more expensive to correct in the long run? A cat, or an engine re-build? That is why I have not been "anal" about using only SL-rated oils in my high-po cars (2004 Honda S2000 and 2003 SVT SC'd Cobra). It is also why I can recommend certain Amsoil and RL formulations by looking at the name n the bottle, rather than thre fine print.
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