I can see that being and older design with larger tolerances it would be happier with a thicker oil, a 50sae which is approx 18cst at 100degC20/50 is what is used in the older engines or engines with the cam driven oil pump as they wont pump the thinner oil as well unless they are in top condition. You can get 10/50 5/50 but its expensive and fully synthetic. These are also old design engines with a lot bigger clearances (even the last 4.6) than modern engines so the thicker oil isn't such a problem in fact it could be argued its a benefit. You pays your money at takes your chances. There are probably more oil related posts on this and other car forums than any other posts.
It's the 20w i'm trying to understand.
Oil is thicker when cold so at 0degC a 20w is over 2000cst in viscosity. A 5w is around 850cst which is still many times thicker than a 50sae at 100degC but if it's quite happy with a viscosity of 18cst than how is a 5w at 0degC too thin?
I've been reading up some articles on http://www.opieoils.co.uk/technicalinfo.aspx. Think i've been reading too much, just wanted to make sure the engine i've spent/ spending too much on has a well suited oil,
I know the cam runs at half engine speed but the cam driven oil pump uses a gear, doesn't it depend on the ratio of the gearing as to the speed of the pump? Maybe it's geared 1 to 1 in which case it would run at half engine speed. Just a thought.A big advantage of a crank driven pump is it runs twice as fast as a cam driven pump, this means starts producing pressure at half the engine revs of the cam driven pump
I thought one of the advantages was the crank driven pump is its self priming. If the oil pickup picks up air it would re-prime and you might be ok (don't know how long the engine could be run at low to 0 oil pressure?) If the dizzy driven pump picks up air it won't self prime so more chance of damaging the engine??