Low oil pressure after extended highway run

Hey guys, I found a thread from Sept. where David was having some oil pressure issues.  you all answered most of my questions in it. I had a few more but I didn't want to revive an old thread... so:  

I bought new gauges (not installed yet), oil pressure is one reason.  Elaine just has a light so I can't tell what the pressure is.  If I do a highway run, anything for an extended period over 55 mph, when I come off the highway and to a stop, in gear at low idle, the light flickers.  At what PSI do the lights typically trigger?  If I cruise around at lower speed for a few minutes it stops doing this.  Someone (Gary, I think) mentioned drain back issues in a dirty engine, maybe that's the issue?

I'm probably going to try to install my new gauges this weekend or next (might do yard work this weekend) so I can get a better read on the dynamics of the oil pressure.  Nevertheless, I thought you all might know what's going on just from the highway example.  

I guess I have one other question/clue too.  If the truck sits for more than a couple hours, it always takes a couple seconds to smooth out on start up, there's no pressure for a bit and it's noisy.  It seems more excessive than the lifters pumping up in other vehicles I've owned, really it sounds like a washing machine and when the pressure builds up after a second or two it goes away completely.  It doesn't seem normal to me but maybe it is?  Would worn bearings cause knock on startup but then smooth out?

I am not sure on this specific application but most lights turn on around 5 psi.  The flickering could be a faulty pressure switch or it could be you are dropping to 5 psi.

Honestly you should try hooking a gauge up and verifying the pressure but since you have plans to install oil pressure gauges you can also use that for verification.  You could also pull the oil pressure log off the block and carefully drill a new hole and tap it so you can make your mechanical pressure gauge installation there and retain the OE pressure switch for the light that way you can see when the light flickers see what your mechanical gauge is actually showing and if its the switch you could replace the switch and use the switch as a warning light to check your gauge if need be.

Some what like what I did on a 5.0 coyote swap at work, we had to drill and tap the log for the 5.0 coyote oil pressure sensor for the computer and retained the OE pressure sensor for the OE pressure gauge.  Im going to be hooking a actual pressure tester when I spin my oil pump over via drill to see what pressure I am getting to check it against my OE gauge which works to try and estimate what pressure is where on the OE gauge.

I'd also want both the gauge and the light to be hooked up.  But on oil pressure you should be able to go to the hardware store and get the right fittings to put a tee or wye in and have both.

As for the problem on startup, what filter are you running?  I've heard that some filters don't have the drain-back valve in them and that allows all the oil in the system to drain back into the sump, so when the engine starts you have to refill that before pressure comes up.  I don't know if that is true, but it is a consideration.

David's issue was caused by gunk that was all over the inside of the engine from the PO, and his religious changing of oil finally got it to break loose.  But when it did it clogged the pickup on the oil pump, starving the system of oil.

Yours sounds more like either a bad sender or, more likely, the oil pressure in the engine is such that after a trip where the oil gets good and warm it thins out and the pressure drops down enough to light the light.  So what oil are you running?

I've got a high mileage 351w that does something similar. I have a gauge but no light.
Reading the gauge goes something like this:
When the engine is cold, oil pressure is in the upper half of the gauge range at idle.
When the engine is warm and at working RPMs, oil pressure is in the lower half of the gauge range.
When the engine is warm and RPMs drop off to idle, oil pressure drops off to the bottom of the gauge range.

I figure it's like Gary suggested in his post, that once the engine warms up and the oil thins out, it takes some RPM and more flow to keep the pressure up through these old bearings.

For years now, I've been using "Lucas" brand heavy-duty oil stabilizer with each oil change, and it makes a difference. Obviously it doesn't fix the underlying issue, but I'm sure it's helped me squeeze more useful life out of the engine.

Gary Lewis wrote

I'd also want both the gauge and the light to be hooked up.  But on oil pressure you should be able to go to the hardware store and get the right fittings to put a tee or wye in and have both.

As for the problem on startup, what filter are you running?  I've heard that some filters don't have the drain-back valve in them and that allows all the oil in the system to drain back into the sump, so when the engine starts you have to refill that before pressure comes up.  I don't know if that is true, but it is a consideration.

David's issue was caused by gunk that was all over the inside of the engine from the PO, and his religious changing of oil finally got it to break loose.  But when it did it clogged the pickup on the oil pump, starving the system of oil.

Yours sounds more like either a bad sender or, more likely, the oil pressure in the engine is such that after a trip where the oil gets good and warm it thins out and the pressure drops down enough to light the light.  So what oil are you running?

Many filters have anti drainback check valves some real cheap ones dont have it and some I found the anti drainback check valve doesnt really do that good of a job at preventing drain back.

You can run a tee to run both sensors but it could pose a problem in getting them bolted in place properly.  I would consider drilling and tapping but for me I wont be doing that, if Dakota Digital ever releases the XTM retro cluster for our trucks I will bin the OE fuel pressure gauge sensor and install the Dakota Digital sensor in its place and place a warning for 20 psi on the oil pressure to flash and activate a buzzer/light when oil pressure hits 20 psi.

Lima Delta wrote

I've got a high mileage 351w that does something similar. I have a gauge but no light.
Reading the gauge goes something like this:
When the engine is cold, oil pressure is in the upper half of the gauge range at idle.
When the engine is warm and at working RPMs, oil pressure is in the lower half of the gauge range.
When the engine is warm and RPMs drop off to idle, oil pressure drops off to the bottom of the gauge range.

I figure it's like Gary suggested in his post, that once the engine warms up and the oil thins out, it takes some RPM and more flow to keep the pressure up through these old bearings.

For years now, I've been using "Lucas" brand heavy-duty oil stabilizer with each oil change, and it makes a difference. Obviously it doesn't fix the underlying issue, but I'm sure it's helped me squeeze more useful life out of the engine.

Old worn out oil can do that too.  My 175k mile 351W stays around 70 psi cold and 55 psi hot at idle but when I finally hit 2,000 miles with that last 1,000 miles before my oil change the oil thins to the point where oil pressure at idle is around 40 psi hot at idle but will return to 70 psi when you touch the throttle and bring rpm back up to around 1,000 rpm

Thanks everyone.  Lucas, it does sound a lot like your old 351w.  

I'm running Wix oil filters.  I've been extremely religious changing the oil as well, to try to get the piston rings to come back around (remember my blow by issues from several months ago), which seems to be working.  In fact, now my oil doesn't turn black immediately, which I am happy to see.  The oil I've been using is 15-40.  I suppose I can try throwing some snake oil down the hatch to see if it helps.  

I wish it was a little easier to get the oil pan off these, it would make it a little easier to check the screen.  In any case, I think what you guys are saying makes sense that she's probably just a little tired.  

I wasn't specific enough in the original post.  By new gauges I meant an entire new gauge cluster.  I bought the intellitronix set on sale.  I like the Dakota Digital look better but they're just so dang expensive.  I don't have a Tac on the stock gauges either, so this fixes two problems.  

If I pop it in park at a light, the light does go off when the RPMs rise a little.  

Rusty, since I'm putting a new gauge cluster in I'll probably use the OEM hole, but I am curious... when you drill and tap a new hole how do you keep shavings from going in the engine?  This question shows my inexperience, of course, but I'm genuinely curious.  

Just a word of warning, I have an Intellitronix universal digital dash installed in my Suzuki Samurai and even with the oil pressure sensor remote mounted I've had 3 failures in 4 years.  Their stuff is lifetime warranty, but it's a little distressing watching the oil pressure swing from 10psi to 50psi on the freeway at 3500rpm.  The first two were mounted to the block and the 3rd was remote.  I think their sending unit is sensitive to vibration.

I am in the process of finding a sender from an alternate manufacturer.  I am making the assumption that the code for the gauges is the same given that they only list the one sending unit on their website.

I have an aftermarket gauge Y'd in with my factory oil pressure gauge on my 460.  I bought the fittings at Home Depot and Amazon.



Note that this has seen zero road miles since install.

red1980F150 wrote

If I pop it in park at a light, the light does go off when the RPMs rise a little.  

Rusty, since I'm putting a new gauge cluster in I'll probably use the OEM hole, but I am curious... when you drill and tap a new hole how do you keep shavings from going in the engine?  This question shows my inexperience, of course, but I'm genuinely curious.

If you drill and tap a new opening you have two choices to do.  One you can remove the tube from the block and drill it on the bench and then flush it out before you reinstall it.  If you dont remove it only option you have is to coat your drill bit in grease to grab the metal shavings so they dont fall in.

Ive used this second technique with grease on aluminum intakes where I had to add a Sniper coolant temp sensor port the grease grabs the shavings and they dont fall into the engine.  Then when you tap it you dip the tap in grease as well and it grabs the shavings there as well.

Thanks for the intel Chris.  If you find a different sensor and think of it, let us know.  It sounds like I'll probably have the same issue, but at least now it won't be unexpected.  

Rusty, thanks for the tips.  They totally make sense.  I've used the trick of using grease to keep a nut in a socket many times, hadn't thought of it for drilling a hole.  

I just wanted to update this.

I just received the replacement sending unit from Intellitronix for my Suzuki.  They changed sensors at some point from a single post to a double post Here's their sending unit.  They also list the resistance range on the website now which they didn't the last time I looked.  The sensor is 0 to 100PSI and has a resistance range of:

PSI	Nominal Resistance	Resistance Range
0-2	242	227-257
3-7	182	155-210
50	103	92-114
100	33	22-49

This is from their website, I just formatted the table better.

From this it would seem that they have chosen a marine sensor to base theirs off of, at least as best I can tell.  All the 240-33 ohm range sensors that I have been able to find show op on marine websites.  It doesn't really matter since the fittings are the same, but the closest "automotive" one I could find is from Autometer and it 255 to 43.  This is within the tolerance range, but doesn't take into account the tolerance of the autometer sender.

red1980F150 wrote

Thanks for the intel Chris.  If you find a different sensor and think of it, let us know.  It sounds like I'll probably have the same issue, but at least now it won't be unexpected.  

Rusty, thanks for the tips.  They totally make sense.  I've used the trick of using grease to keep a nut in a socket many times, hadn't thought of it for drilling a hole.

Lucas,

I added a small STP oil treatment bottle and it helped the startup issue a little.  Today I added a quart of Lucas Oil Stabilizer, like you do, and the problem seems to be gone (though not "fixed" as you point out).  So I think you hit this on the nose.  

Hey John, I'm glad it worked out.
I'm not usually one for "solutions in a bottle" but that stuff seems to work pretty well. I'm using it as assembly lube in the replacement engine I'm currently building for my truck.
Hope you get many more miles - cheers!