Low oil pressure after overheat and low oil condition

[muzician21]

89 Toyota Cressida, 7MGE inline 6. Recently experienced a brief
overheat after a blown hose concurrent with a low on oil situation.
Now finding the oil light goes on at stopped idle under load (~600 -
800 rpm) after the engine has gotten well warmed. This started
immediately after the overheat. No improvement after installing a new
oil pump. Going to 20W 50 oil with STP improves it marginally, it
lowers the RPM at which this happens but it still does it after
getting good and warmed up.

The car otherwise runs like a clock. What has likely happened?

Thanks

[jim beam]

low oil almost certainly means the journal bearings got smeared and you
now have bigger gaps between them and the crank. this bigger gap allows
more oil to pass, thus you lose pressure. if you're lucky, you could
drop the pan and replace the big end bearings with the motor still in
place. if you're not, you'll have to take the motor out, remove the
crank and check for tolerance, then replace the main bearings as well as
the ends - with sizes that depend on whether you had to re-grind or not.


--
nomina rutrum rutrum

[Nate Nagel]

First, hook up a mechanical oil pressure gauge to see what the pressure
really is. It's possible that you have a bad idiot light sender.

That said, you likely have a wore out engine, the overheat and
consequently thin oil having finally done it in. You may be able to put
in new rod and main bearings and nothing else and restore acceptable oil
pressure, but then again, maybe not. I don't recall if the Cressida has
replaceable cam bearings or not.

nate

--
replace "roosters" with "cox" to reply.
http://members.cox.net/njnagel

[Scott Dorsey]

You have wiped some bearings. Which ones? I don't know, but I'd
start looking at the easiest ones to get to like the camshaft.
On some Toyota engines they are the first to lose oil when the
pressure drops, and you might get lucky. More likely the crank
bearings are bad, but you might get lucky.

If the crank bearings are bad (which is pretty likely), a new engine
is probably the cheapest solution.

But hey, you _could_ have put a bad oil pump in there, if you got a
cheap rebuild.... probably not... but you might get lucky...
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[uncle_vito]

One other comment is to use straight 40 weight oil to compensate for your
damaged bearings. 20W50 is still on the thin side.


"Scott Dorsey" <klu...@panix.com> wrote in message
news:ja8arq$g8h$1...@panix2.panix.com...

[Scott Dorsey]

uncle_vito <uncle_v...@yahoo.com> wrote:
>One other comment is to use straight 40 weight oil to compensate for your
>damaged bearings. 20W50 is still on the thin side.

It's worth trying. The worst you can do is wreck the engine bearings
which are already wrecked.

"Just keep driving it, when it doesn't run anymore, that's when you need
a rebuild" -- My dad

Problem with the thick oil is that it doesn't flow as well through the pump.
I know folks who swear by Rislone for increasing viscosity at high temperatures
without increasing it at lower temperatures. I'm kind of skeptical, but you
can try it and it doesn't cost much.

[Jeff Strickland]

"muzician21" <muzic...@yahoo.com> wrote in message
news:100d049b-e462-4412...@l24g2000yqm.googlegroups.com...

BEFORE you go crazy on Low Oil Pressure indications, you need to ascertain
if the oil pressure really is low, or if the sensor that alerts you of this
is faulty. The sensor is essentially a diaphragm that moves in and out with
the pressure, if the diaphragm has a hole in it, then the pressure reading
will be false, and you can be told of a condition that does not exist.

You can connect a manual oil pressure gauge to an oil galley and read the
actual pressure, or you can replace the oil pressure sending unit and see if
this actually fixes anything. If the pressure is good, and you replace the
sending unit, then no-harm-no-foul. If the pressure is not good and you
replace the sending unit, then you will continue to get the warning. You
have to price a manual oil pressure gauge and a new sensor to see where the
cost-benefit situation falls. My guess is that the sending unit will cost
the same or less than the gauge, and if you use a gauge to check the
pressure, you will end up buying a sending unit if the pressure is okay. If
you have access to a gauge for free, then this is the way to go.

If the oil pressure really is low, then you have managed to destroy a
bearing somewhere... Sorry.

[uncle_vito]

The fact that he has more than ZERO oil pressure means that bearing damage
may be limited. He may as well drive it with the thick oil. If major
bearing damage, the engine would not even run, or would self destruct in a
few miles with bearings seizing.

I had some experience rebuilding a '69 427 engine in 1996. Oil pressure was
low and some metal was seen in the pan. Engine ran OK but I was a
perfectionist. All bearings were seen with wiped areas where the babbit was
removed and copper showed. No down to the steel yet but that case would be
only for catastrophic failure.

I also bought for cheap an 82 Camaro with the 2.8L V-6. Previous owner had
not changed the oil. All insides were jelled. I did not rebuild but
thoroughly flushed the engine and scraped out jelled oil from the rocker
area. Engine ran fine for years. Always had low oil pressure. Traded car
in when we were done.

"Scott Dorsey" <klu...@panix.com> wrote in message

news:jab9o3$cp5$1...@panix2.panix.com...

[jim beam]

On 11/20/2011 12:48 PM, uncle_vito wrote:
> The fact that he has more than ZERO oil pressure means that bearing damage
> may be limited. He may as well drive it with the thick oil. If major
> bearing damage, the engine would not even run, or would self destruct in a
> few miles with bearings seizing.

b.s. engines run real well with bearing damage. it's just that most
people stop driving because they can't stand the noise - but the motor
will continue to operate well beyond that point. and bearings rarely
actually seize. if an engine seizes, it's because lack of oil has
welded piston rings to the cylinder wall, not anything to do with bearings.

--
nomina rutrum rutrum

[uncle_vito]

I will seize real quick when the bearing hammers itself apart and the rod
separates from the crank. You know things will get jammed up real fast.


"jim beam" <m...@privacy.net> wrote in message
news:jacjj2$i3m$1...@speranza.aioe.org...

[Nate Nagel]

That's exactly what happened to an old BMW I had :( Bought it cheap as
a pig in a poke because it had an exhaust leak. Fixed the exhaust, oh
no, it's still making noise. A high speed road trip to Pittsburgh and
back finished it off - it spun a bearing the next morning when I tried
to go to work :( fortunately there was a junkyard that had a good used
BMW 3.5 for a semi-affordable price... ended up selling the car anyway
when I moved to VA because the suspension was a bit questionable (200K
miles) and while it theoretically was worth fixing, I couldn't afford it
- especially after laying out the cash for a new engine.

That's not meant as a knock on BMWs though - the thing had 200K miles on
it when I bought it; the appeal was the surprisingly rust free body,
nice interior, and low price - not many cars are worth anything at all
after that many miles. (I did however have an old VW with even more
miles that I regret selling to this day - that sucker was strong and
never let me down. And I did rebuild the suspension on that one,
because the parts were actually within the reach of your average car guy.)

nate

[jim beam]

On 11/22/2011 04:37 PM, uncle_vito wrote:
> I will seize real quick when the bearing hammers itself apart and the rod
> separates from the crank.

that may well be where it ends up, but not always.

> You know things will get jammed up real fast.

a thrown rod rarely seizes an engine - it just "misses". it's the oil
loss from the hole the rod punched through the block that seizes the
engine - after the remaining pistons have friction welded themselves to
the cylinder walls.

when a customer comes to you with the story of "it was making a
clattering noise, then it stopped. now i'm losing oil and the power is
down a bit, bit it seems to be running ok." you know it's a 6+ cylinder
- minus one.

--
nomina rutrum rutrum