Is diesel- or just gasoline-rated syn. oil better for gasoline engines?

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250
Location
Phoenix, AZ USA
I've stayed away from the diesel-rated oils ('bout all the 15W-40s and now some 5W-40s) because of the additional detergent/dispersant required for the diesel soot. Also, Red Line recommends against using their diesel-rated 15W-40 oil in gasoline engines "...since it could increase the tendency for spark plug fouling". However, lots of you, and Mobil, too, recommend Mobil's Delvac 1 for gasoline engines. Can some oil-technology-educated participant discuss the trade-offs here?
 
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34,473
Location
NJ
I'm no expert but I think as long as your car is buring oil, you should be fine. In a high mileage car or one that uses a lot of oil, I'd be less likely to use a diesel oil. I do think they are among the best at keeping your engine clean. S3k and Delvac 1 are the strongest oils from each company. Redline is also against using synthetic right away and wants people to wait 3k miles yet many cars come factory filled with synthetics. I think Redline's tech staff is weak and misinformed many times.
 

Jeffrey Behr

Thread starter
Messages
250
Location
Phoenix, AZ USA
quote:
Originally posted by buster: ...as long as your car is buring oil, you should be fine. In a high mileage car or one that uses a lot of oil, I'd be less likely to use a diesel oil.
Did you mean to say 'as long as your car is NOT burning much oil'? Mine consumes about a half-quart per 10,000 miles.
 
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2,569
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College Dorm...
Jeff, This is just my "edumacated" opinion, but I believe that the HDEO sulfated ash issue is way overblown. I do believe that in laboratory tests that the ash that accumulates in the combustion chamber and valve area is measurably higher, but in REAL WORLD driving and operating conditions, any higher accumulation doesn't matter, and I've never seen nor heard of any problems with the use of HDEO oil in gasoline engines. Sure, the SA in HDEO oils is higher, but when you consider modern synthetic PCEO oils come in around 1.2 or so, and with HDEO's at 1.3-1.5, I see no reason to worry. Trade-off's (in comparison to passenger-car synthetics): Up: Super-clean, very well-protected engine that can deal with very hard driving conditions, high heat/turbos, and can be ran for long drain intervals. Down: Higher HT/HS and thicker viscosity can slightly reduce fuel economy and maximum power output.
 
Messages
526
Location
Manitoba Canada
quote:
Originally posted by Jeffrey Behr: I've stayed away from the diesel-rated oils ('bout all the 15W-40s and now some 5W-40s) because of the additional detergent/dispersant required for the diesel soot. Also, Red Line recommends against using their diesel-rated 15W-40 oil in gasoline engines "...since it could increase the tendency for spark plug fouling". However, lots of you, and Mobil, too, recommend Mobil's Delvac 1 for gasoline engines. Can some oil-technology-educated participant discuss the trade-offs here?
Hello Jeffrey: Good question! First, I have to confess I started using Delvac 1 5W-40 in my personal equipment simply because I already had pails of the stuff for my commercial equipment. So why stock all these different brands and grades of oils? Diesel motor oils, especially the new CI-x oils, are designed for high soot environments. It's doubtful you'd find that in a car. There are also heavy loads placed on high compression diesels, and from large truck turbo's. Almost always, large HD diesels require exclusivly a xW-40 rating. Locomotive diesel-electrics made by GM usually run straight 40 grades. These motors need a HTHS that only a 40 grade oil can provide. Comparing Mobil 1 0W-40 to Delvac 1 5W-40 you'd think they would be the same. They're not. We'll also contrast a 50 oil, Mobil 1 15W-50. Let's look at some typical ratings: Kinematic Viscosity @ 100 C: M1 0W-40 14.3 cSt Delvac 1 14.8 cSt 15W-50 17.4 cSt BPT for yield stress of 60,000 cP at absolute temp: M1 0W-40 -47 C / -53 F Delvac 1 -42 C / -44 F 15W-50 -37 C / -35 F HTHS at high shear (One million shear per second): M1 0W-40 3.6 mPa s @ 150 C Delvac 1 3.9 mPa s @ 150 C 15W-50 5.11 mPa s @ 150 C Flash Point: M1 0W-40 232 C / 450 F Delvac 1 226 C / 439 F 15W-50 255 C / 491 F The Mobil 1 15W-50 is superior except in cold pumping. It also doesn't have the additive package to handle high soot loads in HD diesel engines. It's far cheaper than Delvac 1 or 0W-40, which should be surprising. You can have cross-graded oils too. Let's compare Mobil 1 15W-50: in Europe the same exact formulation you can buy here at AutoZone exceeds the European ACEA A3, B3, and B4-02 specs. I think I already covered the A3 spec in a previous reply to your Cayenne question. The B3 and especially B4-02 spec covers extreme use and extreme extended oil change intervals in LD diesels. This would be like a VW TDI. Due to additive chemistries required for large turbos and extra soot loads, a "B" rated oil cannot be used in large HD equipment, which needs "E" rated oil. Delvac 1 carries ACEA E3, E4, and E5, which is VERY impressive. It's also API certified to SJ and SL, so any motor that would benefit from a xW-40 will have excellent results with Delvac 1. I think the issue of "ash deposits" and ruining catalytic converters running HD diesel engine oils is overblown. Usually, a HD diesel engine oil will DECREASE oil consumption. So will running 15W-50. Remember: European car makers are free to set their own standards for the exact brand and type of oil to use in your vehicle. Such as the endless VW 500.x, 502.x, 503.x, 505.x, and 506.x specs. Porsche has their Approval List and it's very short indeed. BMW has the LL-01 spec, MB the 228.x and 229.x specs. The Euro car makers don't buy the argument that a "low bidder" or "lowest common denominator" oil can meet all needs. They carefully design their motors to work with their recommended oils. Sometimes they even have to design new oils, such as VW with the new PD turbodiesel: Castrol SLX LongLife II 0W-30. So it's very important to follow the advice, especially of respected engine builders and engineers at MB or Porsche. They do you a favor by subjecting the tested oils to very grueling procedures before passing judgement. Jerry
 
Messages
526
Location
Manitoba Canada
Jeffrey: As a follow-up, I stopped using Delvac 1 5W-40 when I purchased new my 1992 Honda Prelude. Honda was adament I NOT USE a xW-40 or heavier oil in the motor. They were really insistent, so who was I to argue? They wanted only a 5W-30, so I ran Mobil 1 5W-30 year round, changing the oil once a year and the filter every 3 months. When Mobil 1 0W-30 came out, I ran that too in the Honda. So it appears every maker has their little eccentricities and needs.
 
Messages
526
Location
Manitoba Canada
quote:
Originally posted by Jeffrey Behr: heyjay, you write as if you've seen the Porsche list of approved engine oils. I can't find it. Where have you seen it?
I've been looking at a 2004 VW Jetta Wagon with PD turbodiesel. The same dealer also sells Porsche (Several Cayene's on display). I was asking the Service Manager about oils and he had a sheet of "approved" oils for VW. I noticed, from upside down, there was also a Porsche Approval List. Ask your local dealer, especially the Service Manager, or Porsche Of America about the Approval List. They should be willing to share this information with you. Jerry
 
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