I am running royal purple now. Am decently pleased, but started using it after I read of Jake's experience with lower oil temps.

I was running 230-240 on hot days with moderately-spirited driving (pre oil cooler).

After the cooler install I can't get above 200' - I think I am going back to dino due to the high cost of the RP and how much I need.

QUOTE (BMartin914 @ Feb 6 2006, 06:38 PM)

I am running royal purple now. Am decently pleased, but started using it after I read of Jake's experience with lower oil temps. I was running 230-240 on hot days with moderately-spirited driving (pre oil cooler). After the cooler install I can't get above 200' - I think I am going back to dino due to the high cost of the RP and how much I need.

what was the cost?

what is class III class IV stand for?

I had to use several quarts of the stuff to fill the system with the new cooler. IIRC, I paid about $70 for a case of the stuff at Pep Boys. After I did the calculation it was the same amount for 12 qts in a case as it would have been had I bought 12 individual quarts. So, about $6 a quart.

I can't answer the Class III vs. Class IV question.

Yeah. Someone should explain the characteristics in each oil group. I was always told to use group IIIs in my porsches, but I missed out on why.

Motor oil used for vehicle engines is commonly called engine oil in American Petroleum Institute (API) documentation. Engine oil is used for the lubrication, cooling, and cleaning of internal combustion engines. Motor oil may be composed of a lubricant base stock only in the case of non-detergent oil, or a lubricant base stock plus additives to improve the oil's detergency, extreme pressure performance, and ability to inhibit corrosion of engine parts. Lubricant base stocks are categorized into five groups by the API. Groups I are composed of fractionally distilled petroleum normally via solvent extration process to improve certain properties such as anti-oxidation. Group II base stock is composed of fractionally distilled petroleum with much lower impurites than Group I, the refining process is more severe which can remove more impurities than solvent extraction. This refining process is called hydrocracking or hydrotreating. Group III base stock has similar characteristics to Group II but with higher viscosity index, produced by further process Group II or slax wax, from dewaxing process, by hydroisomerization. Group IV base stock is polyalphaolefins (PAOs). Group V is a catch all group for other synthetic and mineral base stocks. Examples of group V include polyol esters, polyalkylene glycols (PAG oils), and perfluoropolyalkylethers (PFPAEs). Groups I, II, and III are conventionally referred to as mineral oils and groups IV and V as synthetic oils. However, some manufacturers (e.g., Castrol) have recently labeled their group III based oils as synthetic in the US.

SOOO. What are the advantages to each group, or is this classification system useless in the sense that similar performing oils are not in the same groups and that oils in groups don't share characteristics with oils in the same group?

The whole debate of Group III vs. Group IV,V is an old one. I'm not sure if we've had a discussion here about it, but the Group III is a hydrocracked dino oil with synthetic additives, whereas the Group IV and V oils are fully synthetic and made in a lab. Now I'm going to overgeneralize. Group IV,V oils tend to have higher TBNs, meaning they last longer than Group III and other dino oils. Royal purple has a base number from 6 to 8ish depending on which product you test. Group IIIs also won't 'make' leaks since it's actually a dino oil. Personally, I think that RP is one of the best Group IIIs out there. Amsoil, which is a group V, has the highest base numbers of 30+ oils I tested, 13-15 base number. There are other favorites like diesel oils which are also excellent in their 15w40 weights, like Rotella and Delvac 1300 Super (Chevron Delo also falls into this class). I don't however care for the Delvac 1 synthetic (it has a lower base number than the Delvac 1300 Super) and has less ZDDP. Rotella Syn on the other hand is an exellent product, but the 5w40 weight limits it's usability in our engines. Motorcycle oils tend to have higher base numbers and more ZDDP and other anti-wear additives which is very good for our engines. Mobil 1 V-Twin comes to mind, but at $9-10/qt, I'd stick to regular Mobil 1 Extended Life and add ZDDP to the oil if it's all that important. I personally believe that the reason we see higher temps with the Group IV and V synthetics are that they can hold quite a bit more heat and pulls that heat into the oil, so more oil cooling is needed to make the best use of those oils. Group IV and V oils also tend to give better protection at higher temps and have higher film strength at those higher temperatures, so who know. I go solely by base numbers and additives, and use a damn good filter.