Well, I have similar problems with a fresh rebuild on a 72 engine. I went
ahead and replaced the pressure relief valve including the cap, spring, and
a metal space that fits in the cap (I noticed that was missing when I did
this). I used the up-rated spring and had a hell of a time getting it
pressed in. Once done, all that did was increase my max psi - the car still
can see 10-15 psi on a low (650 rpm) idle. That is hot. When cold, the car
now idles with a starting idle psi of 60-70, and 90 psi at speed. After
maybe 10-15 minutes of driving, I'm down to 10-15 psi at idle but still
running a solid 75 psi at 3000 rpm (but can drop to as low as 50 at 2000
rpm). So that low rpm psi is still troubling.
But the 72B uses a mechanical gauge so perhaps I have a restricted oil line
or maybe the gauge isn't that accurate. Or my only other theory is the oil
pump. One thought is close tolerance between oil pump inlet and bottom of
oil pan? I had a problem fitting it on, not sure why, so I had to pound out
the bottom of the oil pan to get it to fit (something I read on this list).
And to make matters worse, I think I tightened the oil pan bolts too tight
but I left that alone since I have no leaks.
I know the book states 10-25 psi for a warm idle and technically I'm within
spec but in all my previous MGBs, it was very rare that the psi would drop
below 40 at idle. So my low pressure at idle bothers me and I'm still
looking for a resolution, if there is one. So I'm with Thomas on this one,
at least on the low idle. But I'd be even more concerned if the psi was
below 50 when driving with rpms 2500 or higher. Perhaps the relief spring
is the place to start but it is a real bitch to get the nut pressed down in
order to get it in the threads. I made a little tool that was essentially a
bolt and a union that I could use to push against the body of the car and
the nut that finally made the job a bit easier.
David Councill
67 BGT
72 B
At 03:44 PM 3/28/2004 +0100, Paul Hunt wrote:
>Sound wrong on two counts - shouldn't be that low at idle and shouldn't rise
>linearly.
>
>Book states 10 to 25 at hot idle and I think this should be considered an
>absolute minimum, mine only gets as low as 25 if left to idle for a long
>time in ambients of 80F or so, normally it is around 35 to 40. Hot running
>is quoted as 50 to 80 (mine is about 60), but this should be achieved at
>quite low revs, say about 2000, and not rise very much after that as it
>should be controlled by the pressure relief valve. Sounds like your valve
>may be stuck open.
>
>Tip: When you remove it refit the cap *without* the spring, and mark the
>cap and block where the threads just start to engage. Then fit the spring,
>position the cap so its mark is just before the block mark, then you know
>you only have to turn the cap a few degrees whilst fighting spring pressure
>to get it started.
>
>PaulH.
>
>----- Original Message -----
>From: "Thomas J Pokrefke" <pokrefke1@comcast.net>
>To: <mgs@autox.team.net>
>Sent: Sunday, March 28, 2004 2:55 PM
>Subject: Oil Pressure Question
>
>
> > After warmed up (measurements taken after a 15 mile high speed tollway
> > trip), my MGB shows about 10psi for each 1,000 prm while driving. This
> > holds true for idling as well: i show about 10psi for an 950rpm idle.
|