Castol brew of 10 w40 $ 5w50?

[Russell]

I am using brew of 3 quarts castrol syntec 10w40 and 3 quarts of 5w50 in my 95 bmw 525i with the M50TU 6 cylinder engine.

Reason? Older BMWs like thicker oil when warm, yet seem to like thinner oil on start up as there is a cold start "winter" rattle on thicker oil such 15w40.

Thinner oils like 0w40to 5w40 are just nosier and seem to have a warm idle rattle after prolonged idling that goes away when engine is reved. Like the hydralic lifters drainout on thin oil. So the brew seems to be a good winter compromise here in central KY. In summer I have used 10w40 or 5w50.

Anyway, just my experience.

 

[tackleberry625]

The 5w-50 Syntec covers all the ranges and more of the 10w-40. The 5w-50 Syntec is thinner at start-up than the 10w-40 and it's thicker when it's hot because of the 50wt. Have you ever tried 6qts of the 5w-50 by itself to see how it does?

 

[Russell]

yes, it seems there is a warm idle rattle that goes away when I use slightly heavier oil than 5w. Yet heavier oil around 10 weight and up seems to rattle on a cold winter start for a few seconds until it pumps up. So a brew of 7.5w40/45 seems to work fine.

 

[tackleberry625]

lol nice weight oil 7.5w..........as long as it works for you then stick with it. Good luck with it.

 

[beanoil]

You have to be careful when making assumptions. The US site for Castrol has conveniently left out the 40c spec for each of their oils, but the SUS is listed. Converting those to cst, and plugging the whole mess into the Shell calculator, I come up with an actual cst at 40c of 67.1, and a 100c cst of 15.7 . This falls into a 20w40 range as I see it, looking at the viscosity chart on the opening page of BITOG. BUT, I admit to a little confusion when reading the chart also... for example, Mobil conventional 10-30 is 70cst at 40c, and 10.4 at 100c. If the mobil is graded a 10-30, there must be more to the equasion than reading the line on the chart. As stated before, if it's working for you, leave it. But I do think you are a little thicker than you believe when cold, and pretty thick over all.

 

[Russell]

Looks like you are looking at this is a more logical/detailed way than I am. Still hard to this a 5w and 10w oil is actually a 20w oil. Not questioning. Just think, as you said, there is more to it than we can see.

If you are correct, perhaps I should use Castrol 0w30 as the lower part of the brew.

However, old BMWs seem to really like thicker oil. At least mine does severa; UOA back this up. My 0w40 mobil 1 and 0w30 Castrol UOA were high lead. When I went to my castrol brew the lead has dropped.

 

[mechtech2]

5-50 by itself seems appropriate for your needs.
I'll take the better cold flow every time.

 

[bmwtechguy]

I would like to try the Schaeffer 5W-50 as it looks like a very good oil for these motors. Has anyone else tried it? I wish it was available in quarts or gallons instead of 5 gallon pails only.