I've got a nicely rebuilt 3.5 Factory MGB-GT V-8 engine on a test stand,
sorting out any problems before reinstalling it in the car. The engine has
had all new parts installed, the crank has miked out at standard/standard
after nitriding, and the oil pump gears are new with a new MG BHH 1348 oil
pressure relief spring. Here are my pressures, taken using a Smiths 0-60
PSI dual gauge (original gauge from car with 90,000 miles on it):
Cold at startup: Idle (800RPM) - 40PSI 2,000 RPM - 50 PSI
Hot (~200 deg F): Idle (800RPM) - 10-12PSI 2,000 RPM - 40 PSI
After years of running 4-cylinder engines, the hot idle pressure on this V-8
is a little disconcerting, but after reviewing all the previous posts and
David Hardcastle's information I believe these are OK numbers. I think we
are just not used to seeing these low idle pressures, since most big
American V-8s have idiot lights and not pressure gauges.
The one thing I don't understand is why 20/50 oil would be detrimental to
road engines, as mentioned below. I have used 20/50 as the standard oil in
most of my MG and older Toyota engines, with no ill effects. This is the
grade that is recommended by the manual. It is only recently (last 15 years
or so) that the lighter viscosity multigrades have been specified,
culminating in 5W-30 for my wife's 96 Camry V-6. I still believe in 20/50
for my older engines, particularly here in California where the temperatures
can get over 100 deg F.
Here's my other question. When we rebuilt the MG V-8, we torqued the lower
row of head bolts to ~30 foot pounds, to prevent the recently identified
issue of blow-by into the valley. Now I have two very minor oil seeps out
of the gasket below the rear RH and front LH head bolts! It would appear
that in attempting to correct one anomaly, we have caused another. Any
ideas? I am tempted to just re-torque the lower rows of bolts back to the
originally specified torque and be done with it.
Cheers,
Paul Kile
1974 Factory MGB-GT V-8
(wishing he could make the Convention this year, but maybe next year)
-----Original Message-----
From: trevor_easton@dofasco.ca [mailto:trevor_easton@dofasco.ca]
Sent: Tuesday, September 05, 2000 4:52 AM
To: buick-rover-v8@autox.team.net
Subject: RE: Muddying the waters?????
So David Hardcastle says
> . ... The Rover V8 does not like modern
> lightweight oils, in fact 5W-50 oil could, under certain circumstancs
> be detrimental to the engine. Thin oil cannot be pumped in volume in
> the same way as heavier oils, although the pressure will be
> maintained.
>
How can it maintain the pressure against what would appear to be the same
(Or lower due to thinner oil) system restrictions if it isn't pumping the
same or greater volume?
Heavy (20/50) oils are fine for worn engines and "fast and loose" racing
engines but unnecessary for and detrimental to most road engines. Even tuned
ones. If you are making adequate (per the manual) oil pressures at working
rpm's then your engine is receiving adequate lubrication. If your oil
pressure is low at idle but normal at higher revs even this is OK, just
means that your lube system is low restriction (worn maybe) but adequate
volume is coming from the pump because when the revs rise so does the
pressure. Another question is of course what is idle. My 3.9 will idle at
350 rpm with 5 psi or less oil pressure when hot (190F, 10/30 GTX) at a more
reasonable 700 rpm the oil pressure is 15 psi rising to 35 psi at 2500 and
not going any higher because the relief valve has opened. It reaches maybe
45 psi when cold.
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