i have a bit of concern with my 84 6.9. my truck only has the stock "normal" oil pressure gauge. and at full operating temp it idles at the bottom of the "normal" range. mostly wondering if that truly is "normal" and what the range equates to in PSI.

 

Unfortunately these aren't really anything more than an oil pressure indicator, and are best taken very little notice of. Buy a good quality electric actuated guage and install it on a convinient location. Often a combo set is available giving you temp, oil pressure. These are a good choice.

 

you cannot equate the PSI to the stock gauge.
they are a glorified idiot light.
im a fan of mechanical gauges.
but electric gauges arnt bad either.
these engines have a low pressure high volume oiling system.
if this is something that just happened, you may wanna check your oil and make sure youre good.

 

The '83-'86 are an actual gauge, NOT a "switch with a needle". Still very imprecise.

 

Yup, you won't get much useful data out of the stock gauge. That being said, my 88 I converted to a proper oil sender and that's about where it sits. I end up in the 17-19 PSI range at hot idle, no more than 35 PSI at high revs.
This is with a totally rebuilt engine with new oil pump.

Remember that International says that the service limit for hot oil pressure is 12 PSI. It doesn't take much to keep this engine running just fine.

Just remember to change the oil regularly and use good filters and the pressure isn't something you really need to worry about... Unless it drops to 0, in which case you've got a problem

 

Ah. Thought it might be something like that. I was just worried due to the cruise control related troubles that caused the engine to go to wide open throttle in park about 40 seconds after it had stared on a cold morning . I will probably still get an oil analisis done next oil change just to make sure everything is still fine.

 

I wouldnt worry these engines are built tough and can handle reving at high rpms for a longggg time. I regulary ran my last idi at 3200-3600 lots, I wasnt very nice to it, but she ran strong every day.

 

Unlike an old gasser, these engines are governed. So WOT will only net you 3600 RPM or less, no matter what you do. And this RPM is fine for the engine for long periods.

 

Just wanted to share this cause i founded it and thought it should make it into the appropriate thread.

Cheers,
Devin



https://www.ford-trucks.com/forums/1...er-thread.html

more good info here to btw

 

YES! I want to jump in here and dispel this many years ongoing myth that these gauges are oil pressure switches, idiot lights, etc. and not true pressure gauges. That is 100% misinformation and FALSE.

The oil pressure senders are variable pressure senders that send a variable voltage depending upon the oil pressure to an OIL GAUGE that responds to that voltage just like every other electrical oil pressure gauge with with a variable pressure/variable voltage sender.

There is nothing imprecise about that unless you THINK that you need an oil pressure gauge that measures pressure directly from an oil pressure line to the gauge and that it must have number spread as weal rather than a 'NORMAL' spread - the needle would indicate the same no mater what is printed on the gauge.

If the oil pressure sender is working properly and not defective and the gauge is working and not defective then you will see an accurate indication of the oil pressure.

The only legitimate complaint is that SOME people want to see a NUMBER spread instead of -NORMAL- range. However, consider that MOST people would not know what the numbers indicate or what is a 'normal' range when they are looking at numbers, even most of those who prefer to see the 'number' spread don't even know what the numbers are supposed to be in an IDI diesel. Again MOST people would be completely lost in understanding what numbers on an oil pressure gauge mean.

Unless a numbered gauge was explained in the owners manual and they possessed and read the owner's manual, eventually, practically every owner and subsequent owner would be calling the dealerships or auto repair mechanics to ask if the numbers they see are normal. Most common mechanics would not know what the normal oil pressure 'number' readings should be unless they were trained to work on Ford IDI diesels - they wopuld have to look it up somewhere, another big waste of time compared to a gaue that tells you that IT IS NORMAL. With the 'NORMAL' spread shown on the gauge, it's like "Hey, if the needle is pointing in the 'NORMAL' range, don't worry about it!" So the vast majority of drivers go on their way with no worrys about what numbers mean - they can see if it is normal or not.

When the oil pressure is only coming up to the 'N' then they might begin to wonder if something might be wrong.

As Macrobb has pointed out many times, these engines run on high volume oil with low relative oil pressure and the normal range readings on a numbered gauge will be different than for a gas engine - which is again why a numbered gauge would be MORE confusing to the vast majority of people.

For all of those reasons I think the gauge with 'NORMAL' range printed on it is better than a gauge with numbers and that is probably what Ford Motor company thought as well. It was a GOOD decision.

You can argue as much as you want about whether or not a gauge with the word 'NORMAL' printed on it to show the normal range is imprecise compared to a gauge with numbers printed on it but that is a superficial and meaningless argument.

Finally, there is a saying that goes, "If you lie to someone enough times they will believe it." That is exactly what I have seen happen in diesel forums going back for decades! This FALSE information about the oil pressure sender and gauge just became like a huge tsunami wave of misinformation.

You can waste your time arguing with that until doomsday if you chose to waste your time.

Senders and sensors that screw into the head or block need a good ground to the engine through the mating surface of the threads so don't use teflon tape or thread compounds that are not approved on the label for electrical conductivity / sensors. There is one teflon tape formulation manufactured to be electrically conductive but I haven't seen it yet. New thread compound that are copper colored rather than silver color have better conductivity than the old silver type.

 

I was sure grumpy and harsh when I wrote that this morning - in a rush to get out to a Dr. appointment and hadn't taken a morning pain pill yet. I didn't notice that while I was writing it other very interesting posts had been made or my post would have been different. I've been waiting a long time for an opportunity to dispel the pressure gauge myth and I felt like it was me and a few others up against maybe a hundred thousand+ people who have read the misinformation and continue to pass it on so that's why I was harsh.

It appears now in this topic that the stock or aftermarket electrical pressure sender style gauges really isn't an issue as long as they are working.

In fact I did a little bit of searching to find out how accurate these electrical style pressure gauges are and I was a bit surprised myself to learn from several sources that they are very accurate and just as accurate as a mechanical gauge that works from direct pressure from the oil in an oil line to the gauge. So there is another old myth that needs to be busted -> that mechanical gauges are more accurate.

The following is what the differences in accuracy of oil pressure gauges really amounts to:

That is from an article at a muscle car website discussing gauges for Mustangs:

What is The Difference between Electric and Mechanical Gauges? | AmericanMuscle

I don't know the qualifications of the writer, nothing special was shown but there is not much in that quote that can be argued. I think that what he meant by mechanical gauges being more accurate was simply that they have a very broad 270 degree sweep to allow much finer reading of the precise location of the needle on the number sweep.

Elsewhere he wrote this: I very highly doubt that there is any truth in that statement. So, where did he get that information? What about the disinformation I've been discussing in the diesel forums? Was he reading the Ford diesel forums? BUT WAIT! There is another big clue in the second sentence! That website SELLS Gauges- all sorts of them!

Would such sites present disinformation in order to sell more gauges (or products of any sort) and make more profits? My vote is resoundingly YES and this is so common for websites marketing and selling products on the web or through other advertising now days that it has become the rule rather than the exception. I will say that reputable manufacturers and reputable professional sales persons will not present such blatant disinformation to sell products because their reputations and large volumes of sales are at stake. What they do mostly is just twist and bend the information by arranging it and presenting it in such a way that can be and often is quite misleading to the untrained and unprofessional eye (the Consumer) without being an outright lie but it will give them an advertising advantage over competitors who are less shrewd or simply more honest.

I SUSPECT that this is where all of this NONSENSE about these gauges, eg: being operated by pressure switches instead of variable pressure senders (aka idiot lights of some sort) has originated. From unscrupulous sellers who wanted to mislead consumers into buying their products.

If that was true about Mustang gauges or IDI gauges, they would only stay in one position while running under all circumstances and never move until the engine was shut off.

Sorry this post was so long, I really want to get back to the original post and the image from a 7.3L shop manual manual that was posted.

 

I went as far as to install a digital precise oil pressure gauge. I was seeing 3 to 4psi pressure at hot idle, 26 to 28psi hot cruise. My supposedly sufficient factory oil pressure gauge always read in the middle of normal, and no check gauges light ever came on. I tried two different brands of gauges too. In the end when I upgraded my turbo last my oil pressure went up to 10psi hot oil pressure at idle, 35 to 38 cruising. Gauge are extremely important in my opinion. I actually have one on my turbo inlet, post turbo, and post water intercooler to monitor the efficient of my intercooler

 

That's a very good question and you've started a good topic that a lot of people will be looking for. I would ask the same question in that circumstance but there is no indication of an oil pressure problem in my truck. (gauge readings further below). I was very lucky and fortunate to buy a 1987 truck (sight unseen) that allegedly was a low mileage truck with 114k original miles (183,500km). There are indications that this claim could be true and some doubtful indications but after tracing the title and mileage history at the times when the truck was sold it was not possible to confirm either way and then I realized it doesn't make much difference because the truck runs great and I don't care if it has 214k miles on it instead of 114k.

Here is what my oil pressure gauge reads but FIRST: I just went out to start it to confirm what follows and I noticed something very interesting about markings on the gauge which I had somehow been overlooking before. All of the time that I have had this truck (16 months), I was thinking that the "normal" oil pressure range started at the beginning of the 'N' in 'NORMAL' and ended with the last letter 'L'. Looking at the gauge more closely now I realized that the normal range starts way below the 'N' = way down where the White Line is! Zero is below that at the RED LINE. The other end of the NORMAL range is the White Line at the top end!

That is quite a comfortable margin below the 'N' to the lower White Line and that is NOT the Zero Mark. If that White Line is indeed at the lower critical oil pressure on a fully warmed up engine being 12 psi at idle, as Macrobb has posted, then a lot of people will feel relieved if their gauge is reading below the 'N" but appreciably above that White Line. Later I will look up what it says in the 1987 factory shop manuals. I do know that the oil pressure sender is a variable pressure/variable voltage sender and it is definitely connected to a real gauge because I've looked that up and carefully read it before but I didn't see any psi information. Maybe there is something in there.

Macrobb, if you read this do you have a source for that information?

I also think that it is not possible to install a temperature switch for an idiot light by mistake because the threads are two different sizes in order to prevent such mistakes.

I am running 'Shell Rotella T' Triple Protection oil, 15W40 with about 800 miles since an oil and filter change. With ambient outdoor temperatures at 12*C to 26*C (~54*F to 79*F): At start up, warm or cold after a moment of oil pumping the needle moves quickly to the center of the R in 'NORMAL' if I am looking at the gauge directly which is approximately the vertical center-line of the gauge, or at the vertical line in the 'R' looking at it from the driving position.

It barely moves at all from that position after the engine is completely warmed up and the temperature gauge is pointing straight up at the 'R' in 'NORMAL' whether it's at slow idle of 650-700 RPM or driving at a highway speeds of 60-70 mph (~96-113 km/h) at ~ 2350 to 2700 RPM. I don't remember where the oil pressure gauge was during the colder Winter months, I suspect that it was very close to the same but the Winter temperatures here were not very cold - I think the lowest outdoor temperature for me while starting the truck was probably +28*F (-2.2*C) temperature.

So, what could cause the oil pressure to be reading low? As far as I know it could be an oil leak somewhere in the system but probably just lots of miles/km on the engine and resulting wear in the oil pump. Especially if the truck was routinely driven with longer than recommended oil change intervals or under extreme conditions without proper oil changes at recommended intervals.

I have not as yet seen a complete comparison of the 'NORMAL' range on a stock gauge to psi numbers or a comparison to an aftermarket gauge. I also don't know if the calibration and needle sweep of a stock factory gauge is going to match clalibration, the needle sweep and numbers on an aftermarket gauge, so without those calibration facts a simple comparison between the two different gauges doesn't prove anything about accuracy between the two respective gauges. One is only assuming that the gauges have the same calibration and amount of needle movement through a normal range of pressures and it seems very unlikely to me that all oil pressure gauges are manufactured identically with the same amount of variable resistance in the gauge.

I'll be keeping my gauge and using the specified senders until the gauge starts misbehaving or completely quits working.

"Sorry this post is so long" I am always thinking and analysing to make sure that I understand things down to minutest details and make clear and correct statements for readers but those days of intense high tech concentration (and knowledge) are long gone due to the lingering impact from a long term medical illness I had to go through. While having some current additional cognitive impairments from pain medicines, sometimes my mind goes in circles and I write too much. Sometimes I do make a stupid mistake when I am very tired. I should put that in my signature.

 

I always respect your knowledgeable posts in these forums, Shawn and that is an interesting account but I can't help but perceive a big hole somewhere in that account and I'll have to try to figure out what it could be. (??)

1) I have previously thought that when a gauge like this fails that it will just quit working completely OR it will act very erratic(but that is usually a wiring problem). I'll have to go back to the shop manual and start from there to study exactly how this oil pressure gauge works again (my long term memory is not good) to see what kind of failures could occur and what would cause it to behave as your account describes, reading center of normal under all running conditions is what your statement suggests.

I don't suspect that you tested the original gauge with varying voltage to see how it responds because it was obviously not working properly. I would have suggested a wiring problem somewhere which is not uncommon in these old trucks but from what you wrote about trying new gauges, the stock gauge was obviously defective. I have never heard of this specific complaint with an oil pressure gauge before but I haven't lived my life immersed in the automotive mechanics world. I will be testing the function of my gauge with variable voltage applied to it at some point because my gauge is performing in virtually the same way as you described.

However, after at least 800 miles and possibly 1000 miles of combined driving since my last oil and filter change the truck has only used about 1/4 of a quart of oil so I have no reason to think that the oil pressure would be low.

2) I have thought that the pressure sender itself either works or it does not work - provided the wiring and ground is good. I'll have to confirm that now too.

3) You wrote: >'In the end when I upgraded my turbo last my oil pressure went up to 10psi hot oil pressure at idle, 35 to 38 cruising.'<

(I am trying to think while I am mentally worn out and should not be writing but everything in this topic is very important to correctly understand for everyone concerned)

OK: My question: Is the measured oil pressure in these IDI diesels produced in the same way as oil pressure in a gasoline engine?

I'll proceed by assuming that the answer is yes.

Correct me if I am mistaken here but in gas engines the oil pressure is a function of the main bearing clearance to the main crankshaft journals (and the viscosity or 'weight' of the oil). The oil is pumped through the main bearing journals directly into those narrow main bearing clearance spaces and that creates the back pressure to the oil pressure sensor/sender which determines the oil pressure and gauge reading.

I have a feeling that these diesel engines don't measure pressure the same way but to make a longer story shorter this is what I am getting at: is going to be different

As the main bearings wear, the main bearing clearances or spaces increase and the oil pressure drops. So, if I'm not mistaken that increase in oil pressure that you described, starting with hot idle from 3-4 psi then up to 10 psi after installing the upgraded turbo is only due to the added restrictions of the upgraded turbo (better condition with closer oil tolerances) and is not going to increase the oil pressure and flow through the main bearing clearances at the crankshaft.

So, from a viewpoint taken exclusively at the main bearings to crankshaft journal clearances the engine is still operating in a low oil pressure condition. I don't think that the volume of the oil flow going through the bearing clearances is going to increase any more than the oil flow was before installing the upgraded turbo. That is, if the bearings are that worn, then installing a new better turbo that raised the oil pressure reading at the gauge is not going to remedy that condition at the main bearings.

So, either the engine was running at a critically low oil pressure at hot idle, way below the 12 psi critical limit previously posted by Macrobb, which could indicate several possible problems that a new turbo is not going to fix, OR your "New" pressure gauges were not calibrated properly for these old idi diesel engines with the specified senders that are in these trucks. You did not state that you changed the sender to one recommended by the gauge manufacturer (if they even have such a recommendation) - only the gauge and that was my FIRST perception of something suspect and a big hole of something important missing from your account. That is why DETAILS are so very important and why I strive to cover every relevant detail.

If all oil pressure gauge pressure senders are identical then the pressure sender would not matter and likewise of all oil pressure gauges are calibrated the same than what gauge you use wont matter either. The sensitivity of each manufacturer's gauge model should be in the Mfr. literature. Having not bought one since the 1960's , I can only guess-ti-mate that most automotive oil pressure gauges are in the sensitivity range + or - 2psi.

I'm at the end of my concentration stamina so I guess the OTHER possibility is that I do not understand exactly what restrictions produce the back pressure for oil pressure gauge senders in IDI diesel engines or I am missing something in my understanding of pressures and flows in this system. Specifically at the main bearings - pressure in the system can be increased by adding a restriction to oil flow somewhere else in the system and technically the pressures in the whole system will equalize art a higher pressure on the pressure side but that is not going to increase the FLOW rate from the pump through the main bearing clearances because the PUMP is still pumping at the SAME pressure and SAME volume through the same bearings that it was before adding a new turbo.

A higher flow rate through the bearing clearances would require a higher pressure from within the oil pump itself which would be necessary to compensate for increased bearing clearances (from wear or excessive wear).
Adding a restriction somewhere that increases the system pressure is not going to increase the pressure and flow capacity of the oil pump.

Sorry if I seem confused, I would definitely not deny that today.
Sometimes I can concentrate well.

If you really know enough about the oil pressure and oil flow system and how this relates to Shawn's experience and my perceptions or about oil pressure from senders and gauges in these engines I'd sure like to know your views. Even if you are just mildly confident that you understand the principles and have an opinion. I also certainly want to know if I am mistaken about anything I wrote. It's important to me to never make a mistake when trying to share knowledge with anyone but given the impairments that I have mentioned before I have to chose to take the risks of being wrong or not write anything at all.

Disclaimer: I'm not a professionally trained automotive technician nor have I ever been officially employed as an auto mechanic - just an occasionally backyard mechanic as needed on my own vehicles and to help friends etc. when needed = since the age of 12 and I'm now 66 but my chosen training and experience is in other areas with significant overlapping technical backgrounds. I think my objectives here are much the same as everyone else's, that we make the right decisions and get our trucks and Vans fixed in the best ways we can.

If you think that it is difficult to read a long post from me then you should be thankful that you are not sitting here in my chair writing it because I assure you that it is hundreds of times more difficult for me to write it than it is for you to read it. - unless you are struggling to learn American English in which case i wish the best.

 

I haven't had time to read the full topic, but I wanted to point out a couple of things:
1. 88+ trucks have a switch, not a gauge sender, unless it's been replaced. Ford got tired of people complaining about it "reading low".
2. Remember, if you are reading oil pressure off a line which is supplying something, you will have oil flow happening, which will result in pressure drop. So you are reading engine oil pressure - hose restriction, not the actual engine pressure.
(this is why I'm going to look at pulling a second plug out of the block to read pressure from, so I'm not reading from the same line supplying my turbo.
3. The stock gauge, even with a sender... is imprecise. The sender might be working perfectly, but by now the grounding and resistances in your dash unit are going to be sketchy.
This is why your switch-style sender, which should simply read in one place on the gauge(middle, approximately) tends to move around based on temperature.
If you really care about reading pressure... hook a mechanical gauge(or electrical gauge with separate ground wire going directly to it from the sender) up to a port you aren't also using for supplying something else.