Oil Pressure

[EricW]

I've noticed, a couple of times now, that when I start the 5 after it has sat
a couple of days the starting oil pressure is much higher than normal, around
6 kg/sq cm.

It does not seem to come down much after the car has warmed up, and sits at
just over 4, whereas it used to sit at about 3 at normal temp/speed.

I am not complaining about having good oil pressure, but it is a change and
there has to be a reason, is something bad going on?

Has anyone got any thoughts

Eric

[Colin Francis]

On Mon, 13 Sep 2004 09:54:36 +1200, you wrote:

I've noticed, a couple of times now, that when I start the 5 after it has sat a couple of days the starting oil pressure is much higher than normal, around 6 kg/sq cm.

It does not seem to come down much after the car has warmed up, and sits at just over 4, whereas it used to sit at about 3 at normal temp/speed.

I am not complaining about having good oil pressure, but it is a change and there has to be a reason, is something bad going on?

Has anyone got any thoughts

Eric

Have you had a recent oil change and used a different oil Eric ?

Colin Francis

[simple]

Eric said:

I've noticed, a couple of times now, that when I start the 5 after
it has sat a couple of days the starting oil pressure is much
higher than normal, around 6 kg/sq cm.

I'm not sure what my cold idle pressure is (maybe 4), but I find it
doesn't take much in the way of hard driving to get the pressure to 6
- this is a good reminder to me that I really should be taking it a
little more easily until the engine warms up

OK - I take that first bit back - I just went outside in the rain &
started the car - at cold idle (1400rpm today, ambient temperature
maybe about 14 deg C, car has been sitting for 9hrs) the oil pressure
gets to about 5 within a few seconds of starting the car. I'm using
Mobil-1 5W/50, and it's arguably due for change (and is also partly
cheaper/thicker oil, since I use cheaper oil for top-ups).

When the engine is warm, the idle oil pressure is 2. I'm told that
this is also the real test of when the engine is warm - your coolant
temperature gauge may look like it's up to temperature, but until the
oil is hot & thin (and therefore back-pressure has reduced), you
can't really consider that the engine is up to temperature yet.

I am not complaining about having good oil pressure, but it is a
change and there has to be a reason, is something bad going on?

Unless you can think of a good explanation, a sudden change like this
would have me concerned (bearing in mind that I know next to nothing
about cars, and may be prone to paranoia - it's a good thing that I
live with a psychologist who is able to rub my back & offer gentle
words of support when the world gets scary


Side note 1:
If your oil temperature is hot (ie. idle pressure is 2) before your
water temperature has got to its normal place (about middle of the
gauge), then this suggests a faulty (stuck open) thermostat. Your
car will still go almost normally, but fuel economy is likely to be
impaired, and that's a good reason to get it fixed! Normally the
water is up to temperature before the oil is.

Side note 2:
Later MX5 model years (about '94 onwards) don't have a real oil gauge
- it just looks like a real one. The needle just indicates that you
have *some* pressure, but not how much. If the needle doesn't vary
over a range from about 2 to 6 during normal sort of activities then
you have the pretend gauge & it won't provide you with much in the
way of interesting information. There's some info here:
http://www.miata.net/garage/opg.html

Obviously, neither of these side notes are likely to be relevant to
Eric's problems


Karl.

[EricW]

Thanks Karl,
Interesting stuff. When I come to think of it, I have not driven the 5 much
in the last three months, mostly due to the weather and if I can't drive it
with the top down then there isn't a lot of point, the BMW is a nice drive
in the wet. Ann, however, drives it almost daily and had it serviced about a
couple of months ago, so it might just be that the oil is thicker and better
than when I last used the car regularly.

My car is a 94 but the oil pressure gauge appears to be quite active in
response to temperature and RPM. The water warms up quickly, so no problems
with the thermostat and the fuel economy, judging from the recent list
discusion, seems to be what everyone else is getting, so maybe I am being
paranoid as well.

Roll on the summer so I can get the lid down and go for a blast, the BMW
sunroof just isn't the same!

On the subject of going for a blast, I recently drove to Wellington in the
Bimmer and was told of a good route, which I have never driven before and am
definitely going to drive again in summer, in the 5. Turn opposite the Star
Hotel in Kihikihi, just South of Te Awamutu, and, about 8km on, turn right
to Mangakino, then through Whakamaru to Turangi. It is flat and fast, with
sweeping bends and an odd section or two of hairpins, there was also a
marked lack of local constabulary (just as well really!). It was a great
drive in the BM, it will be a fantastic drive in the MX5. If you have never
driven this route I can thoroughly recommend it, those who have will know
how good it is!


Eric