Thanks to all those who responded to my enquiry about using 5W50
Mobil 1 in my TR6 (54,000 miles and 25 psi oil pressure at hot idle)
instead of 20W50 Castrol GTX.
The opinions were:
Emphatic No: 1
Emphatic Yes: 2
Qualified Yes: 3
The qualifications were:
5W50 may be too low viscosity, use 15W50 or 20W50.
Oil seals may leak.
Apart from the fact that Mobil 1 appears to be available in Australia
only in 5W50, the viscosity issue puzzles me. The 5 represents the
cold viscosity and I have plenty of oil pressure when cold (about 80
psi, appears to be the bypass valve pressure). The cold oil pressure
may be lower with Mobil 1, but the flow should be greater.
It seems to me that even though we measure oil pressure, it is the
flow that really matters. I could put 240 weight oil (grease?) in
the engine to get good pressure but there would not be much flow.
The pressure that is being bled off by the bypass valve on cold start
is wasted and I would be better with a lower viscosity oil which
produces better flow, even with a lower pressure.
As a consequence, I intend to change to Mobil 1 later in the year
when I have the time for a controlled changeover with proper
measurements before and after, under reasonably comparable
conditions. I shall report back with the results.
Trevor Jordan
74 TR6 CF29281U
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