Reg 30W oil versus diesel oil

[Timothy B.]

Based on recommendation on this forum (Duke and others) I switched during my last oil change on my 67 SB from regular Quaker State 30W oil to 15W-40 Chevron Delo diesel engine oil. Since that time I quickly noticed two differences that I can notice.

>> Oil pressure now runs a bit higher than it did before. Used to run during warmup around 45 psi, idle at 30, and hot idling down to 15 or 20 psi, hot running around 35psi. Now during warmup pressures run up to 55 range and even hot idling stays up at almost 30 psi.

>> This may seem odd, but I can hear a difference in the sound of the engine. Sounds to me like the lifters are noisier now then they were before. Little more "clicking" now and then that I hadn't noticed with the 30W oil.

From the experts I wonder if either of these two things should concern me? Are these differences expected? Thanks for the great advice guys!!

[Duke W.]

Re: Reg 30W oil versus diesel oil

I think you're reading too much into this, and the differences would not be noticable to even senstive owners, but we tend to get a little over-obsessive.

The wider viscosity range of 15W-40 shoule tend to reduce oil pressure slightly when cold and increase it a bit when hot relative to a straight 30.

The base stock except for the viscosity range of the two is essentially the same, but the CI-4 oil has a higher dose of detergent, dispersent, anti-wear, and anti-corrosion additives, all of which will be beneficial, and CI-4 oils will tend to clean out dirty lifters, which could make them either noisier or quieter depending on how dirty and worn they are.

If you think the lifter noise change is significant you should consider going through the hydraulic lifter adjustment procedure.

You can also buy CI-4 oils in straight 30 weights and GM owner's manuals of the era usually say that SAE 30 is okay if ambient cold start temperatures will not fall below 40 degrees, but I prefer the more consistent absolute viscosity of a multi-grade.

Duke

Duke

[Timothy B.]

Re: Reg 30W oil versus diesel oil

Thanks Duke!

[Terry F.]

You may need to recalibrate your ears also: ) *NM*

[Joe L.]

Re: Reg 30W oil versus diesel oil

Tim-----

Also, the traditionally HD diesel oils like Chevron Delo and Shell Rotella are "dual rated" and fully rated for gasoline engines. The "current edition" of these products is rated at, in addition to its diesel engine ratings, API "SL", the highest current rating for motor oils for use in gasoline engines.

[Scott Marzahl]

Re: Reg 30W oil versus diesel oil

Joe,
Is there any problem using diesel oils in modern cars with Catalytic converters?
The goal would be to help clean up the internals of an engine during use.

Thanks.

[Tom S.]

Re: Reg 30W oil versus diesel oil

Scott
Absolutelty no promlem running it in newer cars.I have an s-10 with 250,000 on a 4cyl. and a v-6 version with 489,000.Both run on the Chevron delo 400.P.S THE NEWEST DIESLS coming out have or will have convertors or some type of gas recircultion system on them.
P.S. how about a 1994 1500 6.5 diesel with 749,000 again on delo 400.

Tom

[Joe L.]

Re: Reg 30W oil versus diesel oil

Scott-----

Personally, I would not use a diesel oil which was not "dual rated" for gasoline engine service. However, if the oil is dual-rated with a gasoline engine service rating, then I see no problem in using it in an engine with a catalytic converter.

The problem with the diesel engine oils is that, generally, they are not available in a viscosity which is approved by most automotive manufacturers for modern passenger car or light truck engines. So, for the purposes of conforming to warranty requirements, I would not recommend using one of these oils.

[Jon #40768]

Re: Reg 30W oil versus diesel oil

I havent worked as a mechanic in about 25 years, but back then, diesel oil had a lot more detergent than normal oil. It could be that the detergent cleaned the lifters. I would also readjust the lifters.
Jon