Low oil pressure after overheat and low oil condition

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.

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

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

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.

--scott

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.

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.

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.

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.

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

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

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.