Oil Light Flickering

[Lil Mike]

i get this once in a while my oil light flickers on and off. it does it for like 1-2 mins at start up then goes away. it doesnt happen at every start up. my oil level is good. is it something to do with the pump?

[Ichiban]

I would check the wiring to the sending unit, located directly above the oil filter mount on the engine block. It is a single wire pressure switch, but I can't remember if it grounds the light on or off. If it is a ground on system like I think it is, a faulty switch, or a short somewhere will activate the light. My 83 for some reason had the light on since I did an engine swap, and I drove like that for years.

Your best bet is to get a mechanical oil pressure gauge and ditch the dummy light, or add a T fitting and run both. At least, borrow a gauge to check the actual oil pressure. Normally, cold engines have the highest oil pressure, as the oil is thick and provides more resistance to flow. Running 15w40, my accord put out 60-85 psi cold, and 20-25 hot, at idle. At 3000 rpm hot, pressure is usually ~60 psi.

Getting an accurate reading of oil pressure will be able to give you an idea of what is actually going on, or what may be wrong. Until then, it is impossible to tell.

[lostforawhile]

I would check the wiring to the sending unit, located directly above the oil filter mount on the engine block. It is a single wire pressure switch, but I can't remember if it grounds the light on or off. If it is a ground on system like I think it is, a faulty switch, or a short somewhere will activate the light. My 83 for some reason had the light on since I did an engine swap, and I drove like that for years.

Your best bet is to get a mechanical oil pressure gauge and ditch the dummy light, or add a T fitting and run both. At least, borrow a gauge to check the actual oil pressure. Normally, cold engines have the highest oil pressure, as the oil is thick and provides more resistance to flow. Running 15w40, my accord put out 60-85 psi cold, and 20-25 hot, at idle. At 3000 rpm hot, pressure is usually ~60 psi.

Getting an accurate reading of oil pressure will be able to give you an idea of what is actually going on, or what may be wrong. Until then, it is impossible to tell.

you will need an adaptor to convert the bsp threads to npt to hook up the gauge correctly
the thread on the factory sender is 1/8 bsp which is an oddball thread and most everything else is 1/8 npt. all aftermarket gauges and the fittings with them are npt. the sender grounds by the way. my books says also that low oil pressure on startup in a high mileage engine isn't a huge concern if it's good at speed. honda doesn't even list an idle oil pressure only a pressure at a specific rpm.

[Ichiban]

you will need an adaptor to convert the bsp threads to npt to hook up the gauge correctly
the thread on the factory sender is 1/8 bsp which is an oddball thread and most everything else is 1/8 npt. all aftermarket gauges and the fittings with them are npt. the sender grounds by the way. my books says also that low oil pressure on startup in a high mileage engine isn't a huge concern if it's good at speed. honda doesn't even list an idle oil pressure only a pressure at a specific rpm.

I used teflon pipe tape on my sunpro oil pressure gauge fitting and it worked fine. This was before I knew about BSP threads. Do you know anything about the pitch, taper, angle and thread depth about BSP in comparison to NPT? I'd like to know.

The sender grounds, obviously. Does the switch closing turn the light on, or off? I've seen some that simply ground, completing the circuit and lighting up the light, and others that break the path to ground, closing a power open relay, and activating the light. The purpose of the second system is that if the circuit is broken anywhere, the light comes on and let's you know the monitoring system is buggered.


Also, I posted up my typical gauge readings for comparison. I wasn't claiming them to be factory spec, or even normal for that matter. However, low pressure at cold startup for more than a few seconds is worth investigating, as oil pressure at hot idle is always less than at cold idle.

Hell, my car cold builds over 20 psi of gauge pressure while rolling on the starter before it even fires. That's way more than enough to satisfy the pressure warning switch.

[Ichiban]

Some good info on BSP and NPT incompatability.

http://www.colder.com/Portals/0/pdfs/NPT.pdf

Specifically;


BSP NPT

Nominal 1/8 1/8
TPI 28 27
Pitch 0.0357 0.03704
Major Dia 0.383 0.39531
Minor 0.3372 0.35189
Tap drill size 11/32 inch R
Thread angle (deg) 55 60
Taper 3/4" per foot
(NPT dimensions are at notch point of gage plug)


Seems like I can mash them together but really not all that well.

[Lil Mike]

thanks everyone i borrowed a gauge from my teacher at school. right now my car is torn apart. i cant even start the engine, so when i get it back together ill fire it up and check the pressure.

[lostforawhile]

I used teflon pipe tape on my sunpro oil pressure gauge fitting and it worked fine. This was before I knew about BSP threads. Do you know anything about the pitch, taper, angle and thread depth about BSP in comparison to NPT? I'd like to know.

The sender grounds, obviously. Does the switch closing turn the light on, or off? I've seen some that simply ground, completing the circuit and lighting up the light, and others that break the path to ground, closing a power open relay, and activating the light. The purpose of the second system is that if the circuit is broken anywhere, the light comes on and let's you know the monitoring system is buggered.


Also, I posted up my typical gauge readings for comparison. I wasn't claiming them to be factory spec, or even normal for that matter. However, low pressure at cold startup for more than a few seconds is worth investigating, as oil pressure at hot idle is always less than at cold idle.

Hell, my car cold builds over 20 psi of gauge pressure while rolling on the starter before it even fires. That's way more than enough to satisfy the pressure warning switch.

the factory oil pressure light comes on at something like 2 or 3 psi,so it's more of an OH SHIT! light. in theory the engine could blow up,and there be enough residual oil pressure to make the light come on AFTER it blew up. as fas as bsp,the threads are almost exactly like the standard NPT thread,except there is one more thread per inch. npt is 1/8-27 and bsp is 1/8-28,just enough to screw up your threads. the adaptors you need are available very cheaply through mscdirect.com also through aftermarket gauge suppliers such as autometer,and so on. this is a common sender thread used on hondas for many years,and is probably still being used. I ran a line from the oil filter adaptor up to the firewall,then it runs to an autometer pressure switch,that comes on at 20 psi, and then goes to the gauge. as far as the circuit,the sender complets the ground to the light making it come on,it's just a garden variety pressure sender,other then the wierd threads.

[lostforawhile]

here you go http://www1.mscdirect.com/CGI/NNSRIT...MT4NO=33052256

[lostforawhile]

this thread needs to be a sticky,i hear over and over i used NPT threads on the oil filter adaptor. that RUINS the threads. i've typed this info i bet 40 times before.

[Ichiban]

Are you telling me that using marginal torque on a brass fitting on an interference thread to begin with is going to hurt the cast iron threads? With approximately 35 thou/inch of difference in pitch, you are only engaging 5-6 threads max, which is .175 inches, the difference in pitch over that thread engagement is only 6 thou. (the width of my hair)

So what, you fuck a ten cent 1/8 NPT brass fitting. Who cares?

[lostforawhile]

Are you telling me that using marginal torque on a brass fitting on an interference thread to begin with is going to hurt the cast iron threads? With approximately 35 thou/inch of difference in pitch, you are only engaging 5-6 threads max, which is .175 inches, the difference in pitch over that thread engagement is only 6 thou. (the width of my hair)

So what, you fuck a ten cent 1/8 NPT brass fitting. Who cares?

you're not screwing something into cast iron,that part is aluminum,the oil filter adaptor is not part of the block,it unbolts. it's very soft threads. and i'm not talking about thread pitch,i'm talking about threads per inch. that means when you try to screw in a fitting with a different number of threads per inch,you are trying to cut threads with the fitting. in effect you are cross threading it. also NPT is not an interference fit, it's a tapered pipe thread. i make NPT fittings all the time,and i have all the good quality taps and tapered reamers for making the holes correct,NPT and BSP are not compatible.

[Ichiban]

Oh, they're not compatable, but you can get away with it. Also, the 2gen motors, the EK and EL do not have an oil filter adaptor, the filter screws directly to the block. I would not attempt to intermangle BSP and NPT on a 3gee!!

Tapered threads become an interference fit upon tightening.

But I'm not trying to argue with you.

PS: About 3 weeks ago I rethreaded about 200 joints of 8-round casing in a Modern NC lathe. Basically a 4-8'' pipe thread, it has the same 3/4 per foot taper. I've got a marginal understanding of threads.

[lostforawhile]

you got to use a modern lathe? lucky. the newest ones we have are close to 30 years old.
you would be suprised how many otherwise intelligent people on this board,have forced an NPT fitting into the bsp threads on the oil filter block.

[Ichiban]

you got to use a modern lathe? lucky. the newest ones we have are close to 30 years old.
you would be suprised how many otherwise intelligent people on this board,have forced an NPT fitting into the bsp threads on the oil filter block.

Modern is a machine tool distributer up here in Canada. We have a Modern CNC lathe with Fagor controls, and a small Modern vertical mill. Those are the two newest machines we have, the lathe I usually run is an Italian Morando that was built in 1962. It's a beast, we can swing 42" over the ways, and the ways themselves are about 14' long. It has a dual compound on it that can feed X as well as Z, and some sort of stupid pre-CNC copier device on it. It has 2 chucks, a 4 jaw on the front and a scroll 3 jaw on the rear of the spindle. Spindle bore is 10".

I should post a picture of this thing, do a joke photo with another, smaller lathe chucked up in it.

We also have a Csepel lathe that can swing about 40" and an even longer bed. The coolest part about the Csepel is that it has an electronic shift on the fly transmission. It sounds like a dying dinosaur when you shift.