Engine Oil

Bill Molloy · Post by **Bill Molloy** » Fri May 29, 2009 1:29 pm

Which engine oils, manufacturer and specification eg; Castrol GTX 10/40, are suitable for your 4.2 ?

Post by **Heuer** » Fri May 29, 2009 2:55 pm

I use Penrite Classic 20w/50 mineral oil.

Bill Molloy · Post by **Bill Molloy** » Fri May 29, 2009 3:56 pm

Now I know that 10/40 is thinner than 20/50 and I'm sure I've seen it explained somewhere before, but other than thinner oil being better in a cold climate how do you/they decide which grade to use depending on the wear & tear / age of the engine ?

I'm assuming there's some logic behind it.

Post by **Heuer** » Fri May 29, 2009 4:13 pm

According to Wikipedia:

"Multi-grade

The temperature range the oil is exposed to in most vehicles can be wide, ranging from cold ambient temperatures in the winter before the vehicle is started up to hot operating temperatures when the vehicle is fully warmed up in hot summer weather. A specific oil will have high viscosity when cold and a low viscosity at the engine's operating temperature. The difference in viscosities for any single-grade oil is too large between the extremes of temperature. To bring the difference in viscosities closer together, special polymer additives called viscosity index improvers, or VIIs are added to the oil. These additives make the oil a multi-grade motor oil. The idea is to cause the multi-grade oil to have the viscosity of the base number when cold and the viscosity of second number when hot. This enables one type of oil to be generally used all year, and when multi-grades were initially developed, they were frequently described as all-season oil. The viscosity of a multi-grade oil still varies logarithmically with temperature, but the slope representing the change is lessened. This slope representing the change with temperature depends on the nature and amount of the additives to the base oil.

The SAE designation for multi-grade oils includes two grade numbers; for example, 10W-30 designates a common multi-grade oil. Historically, the first number associated with the W (again 'W' is for Winter, not Weight) is not rated at any single temperature. The "10W" means that this oil can be pumped by your engine as well as a single-grade SAE 10 oil can be pumped. "5W" can be pumped at a lower temperature than "10W" and "0W" can be pumped at a lower temperature than "5W". The second number, 30, means that the viscosity of this multi-grade oil at 100 ?C (212 ?F) operating temperature corresponds to the viscosity of a single-grade 30 oil at same temperature. The governing SAE standard is called SAE J300. This "classic" method of defining the "W" rating has since been replaced with a more technical test where a "cold crank simulator" is used at increasingly lowered temps. A 0W oil is tested at −35 ?C (−31 ?F), a 5W at −30 ?C (−22 ?F) and a 10W is tested at −25 ?C (−13 ?F). The real-world ability of an oil to crank in the cold is diminished soon after put into service. The motor oil grade and viscosity to be used in a given vehicle is specified by the manufacturer of the vehicle (although some modern European cars now make no viscosity requirement), but can vary from country to country when climatic or mpg constraints come into play."

Bottom line is to go with whatever Jaguar specified which is pretty broad going from 5W/20 to 20W/50. I change my oil every 3,000 miles anyway so longevity is not a prime requirement for me.

I stand corrected - my oil is Penrite HPR 20W/60 designed as a direct replacement for SAE30 oils.

Bill Molloy · Post by **Bill Molloy** » Sat May 30, 2009 8:50 am

Hi David

sound advice. I also found this article which makes good reading :
http://www.apicj-4.org/EngineOilGuide2006.pdf

I've posted it on JL site too - lets see the response there as well

Post by **Heuer** » Sat May 30, 2009 9:30 am

The Penrite site has a mine of information: http://www.penriteoil.com/uk/nextpage.php

For the E-Type they recommend Classic HPR30:

I like Penrite because they understand old cars and there is no marketing hype. Note the 'Operating Considerations'.

MarkE · Post by **MarkE** » Sat May 30, 2009 12:53 pm

I've always used Duckhams 20/50. I changed from Castrol GTX (back in the 70s!) as the Duckhams held much better oil pressure when hot, and the old Lotus twincam oil gets very hot.

The chap who rebuilt my 4.2 and 5.3 used Duckhams in both of those as well...a Jag apprentice in the 1950s, it was his oil of choice for the same reason.

Nothing more scientific than that really. Perhaps the real reason is that it's green and smells good!

Post by **Heuer** » Sat May 30, 2009 3:24 pm

I thought I was indecisive, but now I am not sure:

MarkE · Post by **MarkE** » Sat May 30, 2009 3:57 pm

Probably goes to show that if you buy good stuff and change it regularly, it doesn't make much difference.

Duckhams does smell good though!! Not up to burning Castrol R levels...but not bad.

Post by **Heuer** » Sat May 30, 2009 4:20 pm

I understand one trick is to add a few caps of Castrol R to the fuel tank. You get all the racing smells without the aggro.

As Zinc Phosphate seems to be the key to classic car engine oil this article explains things very well: http://www.penriteoil.com/uk/nextpage.p ... ine%20Oils

If you are worried about ZDP levels 20W/50 oil intended for diesels would be the one to use.

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