In article <9506242349.AA25959@locke.MIT.EDU>,
Jacob ben-David Zimmerman <zimerman@mit.edu> wrote:
>
> Okay, here's my current predicament...
>
> I was enroute to NY from Boston on Fri, when I noticed that my oil
> pressure has dipped. Here's the scoop:
>
> -I had always, up to this point, gotten ~50pso at idle and ~90psi at highway
> speed. Now, suddenly, I was getting 55-60psi at highway and ~20psi at idle.
[...]
> As long as I had anything over 1750rpm, I had opver 50psi pressure; the gauge
> acted just as if I had shifted my noraml operating range down by 20psi.
I am a bit confused about the 50/90 readings you are getting. Would that
be on a cold or warm engine? If not on a stone cold engine, 90psi is *very*
high, and would indicate there is something wrong with the oil pressure
relief valve. Perhaps the control spring was shimmed, or a too strong
spring fitted?
For a hot engine, your 20/55-60 pressure readings look perfectly normal. In
fear of repeating myself too many times: The factory spec is between 40
and 60 psi at 2000 rpm, when hot. Remember also that it takes much longer
for the oil to become really warm than for the coolant.
> 1) Oil breakdown. I had been pushing it a little hard for about an hour prior
> to the drop being noticed, although the temp hadn't gone over halfway
>through
> the normal range.
The oil temperature does not match coolant temperature.
When pressing hard for an hour, the oil temperature will be *much* higher
than for, say, 10-15 minutes of commuting. When hot, the oil will be thinner,
and oil pressure lower. Simply the laws of physics/chemistry at play.
> I reason this because when I put a quart of fresh oil in
> pressure went up slightly, although just the added volume might have done
> this.
Not the volume (unless the oil level was too low - you checked that?)
By adding extra oil, you cooled the oil down - enough to increase
pressure slightly for a while.
> 2) Oil Pressure sending unit gone bad...small leak through sensor?
> 3) Oil pump going. Engine sounded dead normal all the way; but maybe the pump
> is in trouble?
> 4) Dropped the thrust washers...I remember someone saying that this was
> accompanied by a drop in oil pressure, but can't remember how much. I would
> think more than 20psi, though.
I really wouldn't think if it was any of the above. One hour of "pushing it"
will make the oil pretty hot, especially on a warn summer day. No worries
about that, but if you still feel concerned you could always fit an oil
cooler w/thermostat.
> 5) Did someone speak earlier of a pressure relief valve? I used to get right
> up around 90psi pressure at speed, and I was pushing it...could I have
> tripped some kind of valve that lowered my pressure?
IMHO, a warm pressure of 90 psi would indicate your pressure relief valve was
not working as it should. A pressure of 55/60 psi would indicate it is working.
Egil
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