Since replacing the center section on my 1994 7.3l, I lose oil pressure when the turbo spools up. I can't say for certain that it didn't happen before replacing the center section but I didn't notice it. I thought maybe main bearings -- but that usually makes oil pressure drop when lugging the engine and this only happens when the turbo spools up. Any ideas?

 

You need a real pressure gauge first. See what sort of PSI you are getting. The stock one is just a switch, which turns on the "low" at like 5 PSI. So, 6 PSI will be mid-range "normal", but 5 psi will be "low".

Chances are you've got other problems, like a clogged line somewhere, or a shorting wire, or failed switch.

 

Thanks for the reply. Yea, I need to get a pressure gauge on it to see what it's really doing.

 

There is nothing wrong with the factory gauges. They work exactly the same as every other electric oil pressure gauge having the same sweep. It just doesn't have numbers on it for those who must see numbers. The "normal range" is the complete sweep between the LOW line and above. anywhere above the low line on the gauge is "normal range" The ISSUE with all of these complaints about the gauge being a 'glorified idiot light' is the sender, not the gauge.

Unless the gauge is going bad it sounds like the problem is in the sender and wire to it
I think that MacRobb's characterization of that 'LOW' line being 5-6 lbs is an exaggeration. It actually represents whatever IH/Navistar determined is the oil pressure that is 'LOW' and needs to be checked for the cause. I thought that pressure was much higher than 5-6 lbs. Even Macrobb has stated that it's much higher- around 9 to 11 psi? Whatever, above that 'Low' line is still in the 'Normal Range' and that's what the sweep of the gauge and sender switch actually represents.

Most people who buy vehicles wouldn't have a clue to what the numbers on gauges mean, especially with diesels which is why most vehicles don't have gauges with numbers.

I have personally witnessed my oil pressure gauge with the sender SWITCH running consistently at the vertical line in the letter 'R' in 'NORMAL' AND when the oil got old and dirty and the engine was hot it was reading consistently at the Left Edge of the letter 'N.' <---HOW do you explain THAT if it's simply an ON-OFF switch? <<<--- If that was the case it would only have TWO possible readings. Middle of normal and pegged all the way to the left below the 'low line'. It's OBVIOUSLY more than a simple on-off switch "idiot light" mechanism. It has also given me readings below the 'N' and considerably above the "Low" line when I was nearly 2 quarts low on oil <<-- HOW could it do that if is is simply an ON-OFF switch? Still I think the sender switch leaves much to be desired, so I changed it out for the "real" oil pressure sender

I don't like misinformation in automotive forums (Like here at FTE) and there is always a LOT of misinformation.

Anyone can replace the sender (switch) (notoriously regarded as a bad idea from Ford and I certainly agree. I was very angry about this when I first learned that it is true) [REPLACE] with a REAL oil pressure sender and the gauge will work as a real oil pressure gauge because that is exactly what it is, but there is a resister in the line that has to be removed. The resister on my 87 was right next to the sender and it simply unplugged right there from the wire, leaving a 90 deg. connector on the wire to go right on the [real] OP sender that I put in. VERY CONVENIENT. On other trucks it might be a resister on the instrument cluster circuit board right next to the oil pressure gauge.
The instructions for doing that are easy to find.

Judging from the description and use of your truck (VAN) you might want to install an after-market oil gauge with numbers.

I can tell you that the electric/electronic gauges and senders are VERY ACCURATE. MORE ACCURATE than the oil pressure tube gauges. (called analog gauges if I remember correctly).

Some people here will right away disagree. Where did I get the information? I researched it and I read a lot of highly technical documents. That statement is based on what Gauge EXPERTS have stated. People (engineers) who are responsible for designing and maintaining gauges in Nuclear Power Plants, Petroleum refineries, Natural Gas refineries etc. They use a lot of pressure gauges and if you research the subject you'll find that they have changed out the old analog (tube pressure) gauges for electric gauges and senders precisely because they are more accurate and more dependable. Also, someone who works for one of the top gauge manufacturers, frequently mentioned in guage topics (I forgot which company) did a write-up on their website comparing all the types of gauges (pressure gauges specifically) and they sell ALL of those types of gauges so I don't think the report was biased. The same thing as the experts I referred to above was stated in that write-up, the electric gauges and senders being the most accurate and dependable.

In fact if you look up pressure gauge subjects on Wikipedia you will find the same. I read one there about Oil Refineries or maybe it was about Natural Gas refneries while I was searching and reading about the profession associated with gauges (I forgot what that profession is called) The wikipedia article mentioned why such refineries and processing plants had changed over from anolog pressure gauges to electric gauges and senders = more accurate and more dependable.
(probably 'solid state' electronic gauges and senders is the proper terminology)

Electronic measurements are extremely accurate compared to analog measurements, plain and simple.

Compare all of that with the perceptions and expertise of some of the a backyard mechanics who would argue about this.

Personally I think that the best use for the old pressure-tube style gauges is if you are restoring an old vehicle that originally used them.

I can understand why some hot-rodders like them. It gives you a simpler and more direct feel for what is happening at the main bearings where the back pressure from the oil pump (oil pressure) is measured. It is however, not as accurate of a perception as the measurement from a good electric gauge and sender. That difference in accuracy probably doesn't matter because it's the feel of being closer connected to the engine that matters more. Those gauges are pretty cool in that frame of reference.

I am HOPING that I can get some work done now after spending too much time on this forum last night and today. (lack of sleep.) So that's it for me, I am shutting this computer OFF.

 

What sender did you use?

 

I'm talking about what pressure the /switch/ turns off at. Which I'd guess to be 5-6 lbs, considering that 11 PSI at hot idle is the service limit... and still OK.
Therefor, the "LOW" reading of the /switch/ has to be below that by a bit.

With a /gauge sender/ installed, I recall that 11 PSI would occasionally trip the "low oil pressure" dash light, and it would read pretty low on the gauge.
I don't recall that truck *ever* getting more than 1/4 way into the normal range, even when hitting 35-40 PSI(generally cold).
(I had a stock and aftermarket sender right next to each other on the same line, so they should read the exact same pressure. Which also might have been a little low overall, because I used that same line to feed the turbo... so the pressure drop from that flow along about 6' of 3/16" ID line)

 

FIRST, it's the Standard Motor Parts PS-60. From all of the information I had, that's the one I chose. I bought it probably a year ago and I just did the changeover some days ago after I had removed my GP controller, GP harness, alternator, etc. to do some replacement and repair work. Easy access to the OP sender. I haven't tested how well it will work. I won't have the truck back together until later this coming week.

The "real" "pressure "gauge senders" are the 'can' type, look like brushed aluminum but I believe they are steel. The gauge "switches" are considerably smaller in diameter and height and have a plastic outer cover, usually grey or black. (mine was grey). Parts dealers were often listing these switches as pressure senders for gauges which made it very confusing for anyone ordering parts but that's what Ford was specifying for these trucks with gauges (since they changed to the switch). You would probably remember these can type senders if you worked on some older vehicles, like 1960s, more often trucks. Or on ford trucks going up to the early to mid 1980s before they made the change to switches. All or most of them should have had the 'can' type. I'll show you in a minute what they look like.

FIRST, I looked into this subject extensively when I first learned about it. From parts numbers for various years I was able to determine that in these IDI trucks and vans Ford changed from the real sender to the sender switch in about 1987 in the F series to as late as 1988 and 1989 for some of the E series Vans. On the medium to heavy duty trucks I think they stayed with the real oil pressure senders instead of the switch. I can't say that's an exact determination because it's based on a comparison of parts listings from numerous manufacturers listed at Rock Auto Parts.

This is part of the description of the 'real' pressure sender from a Ford Motorcraft part listing :
Listing is for 1960-1998 F250s

In spite of that description it's listed with this part number: MOTORCRAFT SW1547B. 'SW' indicates 'Switch' which helps to keep everyone confused. I've found that lots of parts suppliers use the terms 'sender' and 'switch' interchangeably which seems to be the source of the confusion.

"...proper output curve..." definitely suggests that it sends a variable signal (the curve) to the gauge from zero to high, depending upon the pressure. If I remember correctly these are called "pressure "transducers." Early today I looked up some high perfomance ones used in professional racing like NASCAR. Very expensive. Those are Electric 2 wire senders, not oil pressure tubes.

I have been under the impression that ALL of the 'can' types are real pressure senders that send a variable signal to the gauge in a curve that matches the pressure. They wouldn't have a reason to conceal a small switch in a much larger can, so unless I learn otherwise I'll think that all of these can types are "real pressure senders" and not switches.

I looked up the year of your F250 and there are NO 'can' type senders listed. All switches. That is probably because your truck has the resister on the instrument cluster circuit board and it's not a simple 'unplug the resister from the wire' like mine was. You have to remove that resister for these sender to give the correct readings. From memory I think the resistor is 5 ohms. I have mine here on my desk, the resister is inside of a rubber cover 5/8 in x 1-1/2. I'll probably cut open the plastic cover later to confirm what little resistor is inside and anything else that's in there. I'll wait until I know that my new sender is working properly.

I also looked at various years back to 1988 and aside from that one Motorcraft listing for an 89 F250 All the years I looked at (I think) were all switches.

For 1987, they used to list both the can type sender and the switch type. Now all of the listings for 1987 F250 F350 are the can type. I think that all of the earlier trucks will also be the can type. Sometimes people bought the wrong ones so some trucks might have the wrong ones in them.

By the way, while I was studying the sweep on these factory gauges, I think I determined that the center of the sweep, needle straight up is 35 psi. It's pretty easy to figure out the rest of the sweep from that reference point. The LOW line is whatever the IH/Navistar spec. is for the low pressure limit = "time to check for a problem." I think I used 9 PSI for that line, Maybe it was 5 psi I don't recall right now. Not much difference and with this gauge showing proper readings with the real sender and no resistor, knowing that the center of the sweep is 35 psi it should serve it's purpose well even without numbers.

As has been mentioned many times in topics here, these IDI diesel oil systems are high volume low pressure, so they're safe at lower pressures than gas engines. I've picked that up from discussions rather than reading any technical documents.

OK here is the URL to the 1987 senders, all 'can' type. All of these type should fit all of the IDI trucks (and many many other cars and trucks). They are 3/8" NPT (National Pipe Thread). I've only seen one (somewhere) that was 5/8" NPT. This style goes at least as far back as the late 1950's in Ford trucks. I don't know for certain that they are all set to read the same pressure curve though. It seems very likely but could be different for some gas engines- those that might run higher pressure ranges if there are any like that.

1987 Oil Pressure senders:

1987 FORD F-250 6.9L 420cid V8 DIESEL Oil Pressure Sender / Switch | RockAuto

Here is the url (link) to the 89 F250 OP sender/switch list with the Motorcraft sender at the bottom:

1989 FORD F-250 7.3L 445cid V8 DIESEL Oil Pressure Sender / Switch | RockAuto


You can scroll up on either page and you'll see where to navigate to other years/models. Click on the 'Rock Auto Parts' Logo upper left to go to the Home page and start from scratch for any car or truck.

By the way, Rock Auto Parts started as a family owned business (still are) many decades ago specializing in hard to find parts. They have an excellent reputation including a write-up in Fortune Magazine as being among the top 500 companies. It's in the 'About Us' section linked somewhere on the Home Page.

Sorry this post was so long!!!!
Always happens when I don't get enough sleep, combined with the effects of pain meds that I have to take.

 

Thanks for the reply, very interesting! See my comments
So, I interpret that to mean that 11 psi at hot idle is the LOW end or 'Service Limit' that IH/Navistar determined is the point at which that pressure, 11 psi (or below) warrants checking to see what the problem is. Could be low on oil, could be something else. Is my perception of the term 'Service Limit' correct? eg: the lower limit that is telling you, "you need to check this to see what's going one- like low on oil or whatever?" That seems like what you meant.

Why would that be? It should be the same as the oil pressure specifications for the engine. That's how they would design the switch.

The oil pressure dash light is operated by a pressure switch isn't it? (I was just relating it in my mind to the temperature switch and the separate temperature gauge sender) Or at least the oil pressure light was designed to operate off of the original oil pressure switch that was in the truck. THAT might illustrate that the original oil pressure switch-to-gauge WAS IN FACT designed to reduce the pressure shown on the gauge to 'LOW' when the actual oil pressure got down to 11 PSI (according to your gauge). That makes straight logical sense to me.

Hmmm. Possibly: #1- more resistance in that switch-to-gauge wire than it is supposed to have... old wiring from the switch, broken strands somewhere in the wire, corroded connection somewhere or a gauge that was somehow aged and not working well, or that resistor in the circuit beginning to fail and creating more resistance? More resistance in that circuit would cause that according to my understanding. With a real temperature sender if that resistor remains in the circuit I think the gauge readings will be reduced by 1/2. (that's my understanding at this point from what I have read in related topics).

There is such a thread here at FTE from 2009 about using a 'T' fitting to hook up a gauge sender (can type) and a pressure switch for a dash light, at the same time. Ford did that on some trucks with gas engines and FTE member Parts Dummy (a former Ford Parts Manager) posted the Ford drawings and part numbers showing that fitting, the part number and the sender and switch part numbers, plus as usual lots of different places (not just dealerships) that still listed having that part in stock. Maybe you remember that topic. Very interesting information in it relating to tested gauge and switch pressure measurements.

#2: An affective pressure drop in the pressure switch due to a pressure sender in the same line maybe?

Two separate gauges and senders in other words...

I agree, they should read the same or very close to the same.



Now THAT is very interesting! I don't quite see where that 6 feet of 3/16 line goes, that's a long line.... but... Could THIS be the cause for slideman1955's gauge problem when the turbo spools up? A pressure drop in line or the port where he has the pressure switch connected?
He did mention that it might have been occurring before he did the work. Otherwise it's still an unsolved mystery to me.

Thanks for your input Macrobb. Your experience is always interesting to read about and I like your videos too!

BTW, off this topic but I still need to reply to an email from you about 2 years ago re: Linux and I want to ask you a very important question about CNC machining, as I know you work at a CNC machine shop. That question has very much to do with IDI diesels and is a very important question. (it's also simple to answer but you're the only person I know who hangs out in a quality CNC machine shop and who would know the answer). I'll get to that one of these days very soon because just recently it has gone from an important question to very very important and the time clock started ticking a few days ago. It is as intriguing as it sounds and it will come up here in a topic at FTE one of these days.

I'm too tired to write that email &question now though. Sometime in the next few days I hope.

That's it for me, [burnt out] I'm getting off of here.

 

Man, you are as bad as I am about making massive wall-of-text posts! :P

I recall reading that in the Ford service manual for the IDI. That 11 PSI at hot idle is OK, anything less than that means rebuild or fix whatever is wrong.

Because of tolerances - You have to assume that a pressure switch(which involves a spring and contacts) has both tolerance in manufacturing, tolerance in temperature(at a higher temperature, the spring may be a little weaker?)
It's also got hysteresis - it might turn on at 10 psi and off at 12 psi, or on at 5 and off at 7. Otherwise, when you got to that level, you'd just see the gauge flickering instead of staying "on" or "off" as the spring contacts "bounce".

Also, I'd assume you'd set it a couple PSI lower than the "service limit", so that you don't have the light come on randomly, only to get to the service center and find that it's still OK(just barely).



I assume that the oil pressure light was designed to operate off of a gauge sender like on the gas trucks(and earlier models). The problem was, the range that an IDI is in is lower than most other engines out there, and so it kept bouncing off the "low" limit.
Ford got tired of people complaining and just stuck a switch in there.
Because, why else would you go to all the trouble to have a fully-working gauge in there?

I think I got the resistor out of there back when I installed it; before that, it barely registered at all.
I'm just guessing that the gauge is designed for like 60-100 PSI full scale(which would work on a gas truck), so it always reads low with the lower pressures from an IDI.

Quote:

Originally Posted by Fixnstuff

Now THAT is very interesting!

When I got my Banks Sidewinder, it came with a 3' piece of braided hose which ran from the fitting on the driver's side of the block up to the turbo.
I had a local shop make me a duplicate of that hose, and then built a manifold block out of aluminum. The manifold block has 4 ports - oil in from the block, oil out to the turbo, and two ports for sensors.
So, now I have 1 3' hose that goes from the engine block to the "sensor block"(located on the driver's side fender well area), and the second goes from there to the turbo.

I'm doubting it's an actual pressure drop when the turbo spools up, though. I never noticed *any* difference in pressure with the turbo, though I notice a big difference upwards with RPM.

I suspect that he's got a grounding issue somewhere or a flaky switch or something. I'd like to see actual numbers(which is why I always go for a 'real' aftermarket gauge, even a cheap one).

Thanks!
I just wish I had more time these days to do stuff like this. Right now, most of my projects are in a holding pattern waiting for time.

I'm always willing to answer anything I can.

 

Thanks for the replies guys -- interesting stuff!
The only reason I can think of for the oil pressure drop when the turbo spools up would be the added stress on the main bearings. I had an old 460 gas engine that would lose oil pressure when loaded heavy and you stepped on the accelerator. I replaced main bearings and all was good.
I had an industrial pressure gauge around but no tubing so I just screwed it in in place of the sender on the IDI today. I obviously can't tell what it's doing under load going down the road but at idle I have 40 PSI cold and 25 PSI or so hot. This leads me to believe that you guys are right and I just have a sender/wiring problem.

 

I replaced the sender -- now it reads just above the center of the sweep at all times. I don't think that's accurate, but I'm going to leave it alone.

 

he is right especially when he said most people would not know the proper oil pressure anyway. That is why they have generic red and green line s usually.

 

I agree with Macrobb, bought my truck new and the oil gauge has always had a mind of its own. Ice cold engine first start in the dead of winter, gauge may barely move although oil is thicker. Hot engine towing for hours in 100° degrees, gauge needle may be at the half way mark. And as a wise man once said when a poster insisted on an overly long and involved answer to prove vastly superior knowledge, "HE ASKED WHAT TIME IT WAS, NOT HOW TO BUILD A CLOCK!"

 

I always thought that the factory gauge was just a fancy idiot light but when the gauge quit and the idiot light on my 87 came on i thought i had a big problem, so when i tore into it i first found it had a switch for an idiot light and the replacement was a sender for a gauge. When i installed the sender the idiot light went out but the gauge still didnt work so i found that resistor you guys spoke of and removed it and low and behold the gauge began to respond like a mechanical gauge, pressure changing with the speed and temperature of the engine. Jeez what a revolting development, i guess this was an 87 and up thing because all my pre 87 trucks gas or diesel have had oil pressure gauges that acted normally. I will also add that any one who adds a mechanical gauge to an idi will be severely disappointed as i have never seen one with more than 40psi oil pressure which is only about 1/4 sweep on most mechanical gauges

 

Mine hovers around 40-45psi driving and a fuzz under 20psi idling, i've yet to change the oil though so i expect that to lower by 5psi or so across the board.