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Grot
07-14-2012, 07:24 PM
First off, this is on my truck. An 03 Merc Mountaineer, with the 4.6 v8.

So starting yesterday, when the engine would hit idle speed i would lose all oil pressure. the Gauge and the oh shit light confirm. A slight throttle blip would bring pressure back.

so i think it is probably one of 4 things. Low oil, bad belt, bad pump, bad OP sending unit.
Had not heard any belt squealing, and it doesnt look frayed or dry rotted.
Checked the oil, it was a little low, but still above the L mark. went ahead and put an extra quart of 1 weight thicker oil in it. 5w30 instead of 5w20)

Drove the truck, the issue seemed to be resolved.

Starting today, losing pressure at idle speed just like yesterday. and now it completely loses pressure randomly, and now it wont come back.

Have not check the Sending unit, but its probably fine...

Anyone think of anything else it could be? or should i just go ahead and replace the oil pump?

klapa
07-14-2012, 08:04 PM
Bad bearings? The OP will be lowest at idle - the pressure switch ("sending unit") that drives the "idiot light" usually is set for ~ 5PSI (really low OP).

It would seem that you have an engine about to break - but if you think it is a bad indication - just get a cheap mechanical OP gauge and a brass tee fitting to connect the gauge to where your pressure switch is located - usually on the upper valve oil galley.

Did the idiot light indication first blink and then later come on solid at idle? That would be another indicator that you have something BAD going on that is about to destroy your engine - probably a main or big-end rod bearing but it could be a cam bearing too (though less likely to cause such low OP).

For an American V-8 or V-6 the oil pump is rarely the culprit - it is the most lubricated part in the engine. In rare cases - the oil pressure relief valve in the oil pump might fail - usually due to a broken spring.

Most likely is what you don't want to hear - BAD BEARING.

Grot
07-14-2012, 08:22 PM
The light is off when you first start the car. the driving it will turn on, and my info screen will read low OP; with the OEM Dummy gauge falling completely down.

Im getting no noise out of it, and it drives fine when this is happening.

After a little research, it sseems the Sending unit is a common Failure point on these engines, so i guess the mechanical gauge would be the next test to see whats going on.

93celicaconv
07-14-2012, 08:47 PM
So you have both a gauge and an idiot light? If so, normally, the gauge and idiot light are not coming off of a common source. Usually the gauge is from a sending unit, and the light from a switch. If both are telling you the same thing, then I think you have a true indication of poor oil pressure. You might not be hearing much of anything in your engine if one of the mains on the crank is giving way. If a rod, you should be hearing some knocking sound when the idiot light is on.

I would check first to see if you have a single unit sending data to both the switch and the gauge, or if you have separate sources to them.

klapa
07-14-2012, 09:49 PM
Grot,

Ditto above - plus I don't know what an "info screen" is?

When I had my Mopar V8's I just had four hoses - two radiator hoses and two heater hoses - I didn't even have a single vacuum hose - I used to think that vacuum hoses were just for "pansies". :)

That being said - I did have a 1965 Plymouth Valiant with a 170 CI slant six that had exactly the symptoms you have with the oil light - and no noise - and then one day on the highway - KABOOM!

The oil pressure will be better when the engine is cold - when you put a load on it and everything expands is when the pressure will go low.

If you do actually have BOTH an idiot light AND a gauge - with separate "sending units" - you should not start the thing up again until you check the bottom end.

Grot
07-18-2012, 10:22 PM
Traced the sending unit. there is a singular sending unit for both the dummy gauge and the idiot light.

Decided to install a mechanical gauge, so i put a large T where the original was affixed. and now have both running from the same source.
Not sure that was a great idea in afterthought.

Low pressure has been confirmed, but it isnt as low as i assumed it would be.

Standard idle pressures are 25-30 PSI. when im getting a, idiot light, pressue is has only dropped to 20-22 PSI. not a total loss of pressure.

Still no idea whats causeing this though.

93celicaconv
07-19-2012, 03:27 AM
Traced the sending unit. there is a singular sending unit for both the dummy gauge and the idiot light.

Decided to install a mechanical gauge, so i put a large T where the original was affixed. and now have both running from the same source.
Not sure that was a great idea in afterthought.

Low pressure has been confirmed, but it isnt as low as i assumed it would be.

Standard idle pressures are 25-30 PSI. when im getting a, idiot light, pressue is has only dropped to 20-22 PSI. not a total loss of pressure.

Still no idea whats causeing this though.

I had a similar situation on my convertible. After installing an electronic gauge set (one being oil pressure), I also put in a tee for the existing oil pressure switch. I had an oil light come on when the oil pressure gauge was reading 10 psig. The BGB said oil pressures as low as 2.5 psig are still considered OK, so I was thinking the oil light should not come on. I took the oil pressure switch out and the part number did not match a Toyota oil pressure switch for this application. I got a new oil pressure switch from Toyota for this engine, installed it, and the oil pressure light has never come on. I don't have a dummy gauge (don't even know what such a thing is), but only an oil pressure light. But I'm pretty sure a previous owner replaced the oil pressure switch with one that had a higher pressure trigger, which was causing a false output to the oil pressure light. Get a correct oil pressure switch from Toyota and replace the one you have, you should not have an oil pressure light on at the pressures you gauge is telling you that you have.

Grot
07-19-2012, 04:11 AM
i will see about replacing the sender.

The dummy gauge, in this situation, just reads on or off basically. if the pressure is fine it is right at half. if the pressure is bad it falls all the way to zero.

93celicaconv
07-19-2012, 12:55 PM
If that is what your dummy gauge is, then it operates with an input that is either on or off, just like your oil pressure light, so the same oil pressure switch can operate both. Not sure what the purpose is of the dummy gauge when you already have a working oil idiot light. As long as you are comfortable that your mechanical oil pressure gauge was displaying relatively accurate oil pressure readings, then I would recommend getting a correct Toyota part number oil pressure switch and installing that, getting rid of your existing one, and see if that solves your oil pressure warning light issue. If your engine doesn't make any unusual noise (typical of very low oil flow conditions), then I think your oil pressure switch is either defective or not the right application for the pressure range of your engine.

Grot
07-19-2012, 05:49 PM
Im not quite sure a toyota sender would work. lol This is on my ford truck.

Linking this here (http://www.explorerforum.com/forums/showthread.php?t=287097) so i dont lose it mainly. thinking it may fix my problem.

93celicaconv
07-19-2012, 06:36 PM
Im not quite sure a toyota sender would work. lol This is on my ford truck.

Linking this here (http://www.explorerforum.com/forums/showthread.php?t=287097) so i dont lose it mainly. thinking it may fix my problem.

LOL. No, I don't suppose a Toyota oil pressure switch will help you on your Ford truck. Looks like you may have found another possible explanation for your situation, from the link you provided, that last of which identifying a chaffed wire involving the oil pressure switch. That would be a prime item to take a good look at, before replacing any parts. Sounds like wiring on that specific engine wasn't routed the best way to avoid rubbing on surfaces and causing problems down the road.

Grot
07-19-2012, 07:55 PM
i definatly have at least 1 wire with copper showing through. im working on pulling the harness right now. this is a huge pain in the ass without a jack. plus it being 90 with 60%+ humidity i want to die.

93celicaconv
07-19-2012, 08:38 PM
i definatly have at least 1 wire with copper showing through. im working on pulling the harness right now. this is a huge pain in the ass without a jack. plus it being 90 with 60%+ humidity i want to die.

Pretty much typical temperatures/humidities where I am also. That copper showing through, is the copper broken (open)? I think the oil pressure switch grounds at acceptable oil pressures to turn the oil dummy light out, and opens to turn it on (so if you forget to connect the wiring harness to the oil pressure switch, your oil pressure dummy light is on). I think that is how most work, but not sure. So if the copper is open circuited in that harness, and if the wire is from the oil pressure switch, you likely have culprit.

klapa
07-20-2012, 02:58 AM
Just get a standard mechanical Oil Pressure gauge - there is a guy here who sells them here for cheap - if he still has any:

http://www.celicatech.com/forums/showthread.php?53235-AutoMeter-Gauges-For-Sale

Mechanical oil pressure gauges are not specific to any car at all - they just read pressure. They don't care if you are "Metric or Standard" - or Asian, American, Eastern or Western European - they just measure pressure - you can pick your own units.

Grot
07-20-2012, 04:31 AM
I have one installed as of yesterday. I think I may have it fixed. Didn't get to check today. Was already late for work when I stopped.

klapa
07-21-2012, 02:46 AM
I think the oil pressure switch grounds at acceptable oil pressures to turn the oil dummy light out, and opens to turn it on (so if you forget to connect the wiring harness to the oil pressure switch, your oil pressure dummy light is on). I think that is how most work, but not sure.

That is NOT my experience - albeit with older American cars. The oil pressure switch is in series with the idiot light - which has it's high side connected to a voltage source and the low side connected to the pressure switch. When there is no pressure, the pressure switch is closed and a short to ground - thus the light is on. When there is enough pressure to actuate the switch it is open - and there is no path for the current through the idiot light - thus the light is off.

93celicaconv
07-21-2012, 03:12 AM
Yeah, after checking the BGB, it looks like Toyota's are set up the same way (low pressure closes the switch and activates the oil pressure dummy light). So if the wire is disconnected from the oil pressure switch, the oil pressure light will always be out. The telltale is that the oil pressure light will also be out when the ignition key is turned on as well.

klapa
08-05-2012, 09:26 PM
Yeah, after checking the BGB, it looks like Toyota's are set up the same way (low pressure closes the switch and activates the oil pressure dummy light). So if the wire is disconnected from the oil pressure switch, the oil pressure light will always be out. The telltale is that the oil pressure light will also be out when the ignition key is turned on as well.

Yea - if the wire is bad from the gauge cluster to the OP switch the light would never be on regardless of the open or closed state of the switch.

Aside from all that - in my experience - and I am sure this varies with engines a bit - if you have better than 5PSI OP with a hot engine at normal idle you don't have a bad bearing problem. Still - the mechanical gauge responds FAST - and gives quantitative feedback - not just some on-off indicator.

As an example - perhaps you might only have a problem with a main bearing - particularly the thrust bearing. it would be fine at idle in a parking lot - but if you gunned on the highway at speed under load you might see a momentary dip on the mechanical gauge - something to give a heads up on an impending problem. You might never see that with a light or an electrical transducer type gauge because of the response time.

Of course the mechanical oil gauge, once installed, IS an integral part of you engine oiling system. You've got to watch out routing the oil line to the gauge, as unless you are spending the bucks on braided steel line, this will be a cheap plastic tube subject to melting and/or chaffing. When such happens to break the line - you both both lose oil pressure and spray your car's interior with hot engine oil!

For my money, a mechanical oil gauge, properly installed, is just cheap insurance - don't leave home without it.

93celicaconv
08-05-2012, 10:12 PM
I personally have an electronic oil pressure gauge with a sender on my 5S-FE, with the original oil pressure switch for the dummy light also installed (in a tee). A little more money, I suspect, but I didn't want to risk an oil line blowout inside the cabin.

4.7 psi is the safe low limit on a hot engine at idle for oil pressure. I suspect the oil pressure switch is set to trigger somewhere at or slightly below 4.7 psi. I know my engine gets down to 7 psi on low idle when hot. I don't think I have a "bad" bearing issue, but I think I have worn bearings that should be tended to soon, as I have the cold start chatter until oil fills the gallies. This is telling me my oil is draining out of a bearing with too much clearance (as it should hold oil for a long time with no oil pressure at normal clearances).

klapa
08-05-2012, 11:00 PM
I personally have an electronic oil pressure gauge with a sender on my 5S-FE, with the original oil pressure switch for the dummy light also installed (in a tee). A little more money, I suspect, but I didn't want to risk an oil line blowout inside the cabin.

Understood - and perhaps there is no difference between the response times of a mechanical gauge and an electrical transducer type gauge - as they both use a diaphragm to indicate the pressure. I trust a mechanical gauge more just because it IS SIMPLE - it does not rely on wires or voltage levels for operation or accuracy - it just is a part of the engine oiling system itselfnd relies solely on the PRESSURE - the parameter of interest.

Yet it is true - the routing for the mechanical gauge piping is all-important to prevent a possible catastrophic accident on the road.


I have the cold start chatter until oil fills the gallies. This is telling me my oil is draining out of a bearing with too much clearance (as it should hold oil for a long time with no oil pressure at normal clearances).

I think that is the nature of a 5SFE - as far as I know, they all do it with a little age on them. Certainly mine did, even if it had a rebuilt bottom end. After resealing with a new head gasket the thing runs fine - but it still will rattle in the morning - unless I use SAE30W50 oil (Castrol GTX) which seems to minimize the time of the clattering.

Of course - it does not get as cold here as it does where you are - yet my clattering would seem to occur more often when it was warmer than when it was colder weather - thus the heavier oil helps.

93celicaconv
08-06-2012, 02:25 AM
I think that is the nature of a 5SFE - as far as I know, they all do it with a little age on them. Certainly mine did, even if it had a rebuilt bottom end. After resealing with a new head gasket the thing runs fine - but it still will rattle in the morning - unless I use SAE30W50 oil (Castrol GTX) which seems to minimize the time of the clattering. Of course - it does not get as cold here as it does where you are - yet my clattering would seem to occur more often when it was warmer than when it was colder weather - thus the heavier oil helps.

Well, I'm going to see if my bearing clearances with within spec our outside of it. If outside, I'm really hoping the crank journals are OK. I have a post in the Maintenance section on how one changes main bearing shells with the engine installed. I've heard folks say they do it, but I'm not clear on how to get the upper main bearing shells out if the crankshaft remains installed on both ends. If you have done this before, let me know - I don't want to destroy something trying & then be in a lot worse shape for trying.