looking or good engine oil
- Thread starter gosnell
- Start date
redrover
Well-Known Member
:? The correct oil grade for both 4-cylinders and V8 engines in P6s is a high quality 20/50 mineral oil, ideally with a high ZDDP content for V8s.
See this:
viewtopic.php?f=2&t=18317&start=0
and this
viewtopic.php?f=5&t=5488&hilit=egine+oil
There is probably much wincing and botty-clenching in the Rover world at the thought of 10/40!
The 4-cyl particularly is prone to low oil pressure at a hot idle due to the unusually rapid manner in which it wears big end bearings (40k - 60k in some instances). Putting a lower viscosity oil in will make it easier for the oil to escape out of all of the tolerances (which are designed to retain 20/50) and potentially insufficiently lubricate the crank. I'm sure there are a number of people out there who will testify to having run an oil like this (even a synthetic oil) for many moons without issue, but it is very much not the club's recommendation. We ran a fairly comprehensive technical article on the 4-cyl bottom end a few months ago in Driving Force, and a more general article on suitable engine oils about 2 years ago. RP6C members can email us for a digital copy of those articles if they want to read them.
The first number in a multigrade designation is the viscosity of the oil when cold, the second is the viscosity at 100 degrees C. So the second number makes the difference when the engine is running, the first is how thick it is on start up (in basic terms). I'd use (and did use) 20/60 in an engine that was very tired at the bottom end and didn't hold good oil pressure at a hot idle. It's difficult to get hold of, but a 10/50 oil might make cold starting easier in very cold climes, but I wouldn't feel too happy about losing any hot viscosity with a 4-cyl. It's designed to run at a constant 50 psi at all times (ie, idle through to red line), which is achieved with a combination of a massive oil pump and a progressive pressure release valve and finely calibrated spring. So losing some viscosity might cause hot idling pressure to drop.
Michael
See this:
viewtopic.php?f=2&t=18317&start=0
and this
viewtopic.php?f=5&t=5488&hilit=egine+oil
There is probably much wincing and botty-clenching in the Rover world at the thought of 10/40!
The 4-cyl particularly is prone to low oil pressure at a hot idle due to the unusually rapid manner in which it wears big end bearings (40k - 60k in some instances). Putting a lower viscosity oil in will make it easier for the oil to escape out of all of the tolerances (which are designed to retain 20/50) and potentially insufficiently lubricate the crank. I'm sure there are a number of people out there who will testify to having run an oil like this (even a synthetic oil) for many moons without issue, but it is very much not the club's recommendation. We ran a fairly comprehensive technical article on the 4-cyl bottom end a few months ago in Driving Force, and a more general article on suitable engine oils about 2 years ago. RP6C members can email us for a digital copy of those articles if they want to read them.
The first number in a multigrade designation is the viscosity of the oil when cold, the second is the viscosity at 100 degrees C. So the second number makes the difference when the engine is running, the first is how thick it is on start up (in basic terms). I'd use (and did use) 20/60 in an engine that was very tired at the bottom end and didn't hold good oil pressure at a hot idle. It's difficult to get hold of, but a 10/50 oil might make cold starting easier in very cold climes, but I wouldn't feel too happy about losing any hot viscosity with a 4-cyl. It's designed to run at a constant 50 psi at all times (ie, idle through to red line), which is achieved with a combination of a massive oil pump and a progressive pressure release valve and finely calibrated spring. So losing some viscosity might cause hot idling pressure to drop.
Michael