Oilpressure sending unit autopsy

[DutchBlackNsx]

Replaced the damn thing allready for the second time now, and wanted to know why this sensor has to be so huge.
Understanding how the internals work, might also shed a light for me on the reason why these things start mallfunctioning after a while, or better, why there is some speculation that engine vibration might have an influence on the device (read on other topics s.a. survey: oilpressure@8K rpm).

So here's the device by itself:

At the front there is a tiny tiny hole, where the oil goes into the sensor:

This is what the inside looks like. Notice on the top a wire wound resistor, and the two contacts which slide on both sides. The two sliders are mounted on the vertical bar which goes over the middle of the base, from whereunder a pin is pushed by the oilpressure.

Here you can see what happens if the pressure comes on (now used an aid to show)

I was a little disappointed with how easy this works.
Though it seems very well made, its not a very hightech solution.
Seeing the simplicity of the wirewound variable resistor, i wont be suprised if this is very sensitive for engine vibrations, to which this whole device is exposed to big style.

Just another NSX part never shown here on prime :wink:

 

[Aero]

Thanks for sharing. It seems too big too me too. Especially when trying to replace it I realized it was supposed to be made to only be replaced by a 5'0 tall Japanese woman with tiny hands. My hands were too big...took forever to finally thread it on there.

 

[DutchBlackNsx]

Took forever to finally thread it on there.

yeah, seems you have to be sorta lucky to get the angle right.
Removing the cables and wireharensses around the spot helps a lot though.

 

[rbirling]

Were you able to determine what failed?

 

[jond]

Would a slightly stronger spring at the very top(not the long one) fix the problem?
Either that or maybe some electrical contact grease along the top?

 

[DutchBlackNsx]

Any modifications are not aplicapable here. Opening up this device is destructive to its housing.

 

[whrdnsx]

I would recommend making up a stainless aeroquipe -3 line. To move the sensor to be soft mounted in the engine compartment. Somewhere to isolate it from Engine Vibrations.

This is a common problem in racing & generally most sensors have to be remotely mounted away from the engine.

 

[ATERPAK]

This is exactly what I did when I mounted another oil sending unit with a modification I made to the original block that mounts to the front engine head. I have both the stock and an a -3 stainless line mounted to that block and then I've mounted the sending unit on the engine firewall to isolate it from the vibration for the new unit. The stock unit has been designed for the vibration, but as you can see by the construction, it's not meant to be a very fast responding partly due to the vibration issues. Since our gauges don't really give accurate readings in lbs. or bars, then this works adequately enough for street use. Although it does seem to register to almost 0 (zero) during idle when the engine is warmed up and my newer gauge is showing over 20 psi. Basically this design is very similar for the gas tank gauge except that it uses a float mechanism to move the arm on a wound resister. Cheap but effective.

 

[Mac Attack]

My daily-drivers' sending unit is leaking a little.

While I've got some time over New Years, I was hoping to take this out and replace it with some other sending unit. The OEM is $200 and I can get a decent aftermarket sending unit for $50

Does anyone know what the thread is for the sending unit? The service manual is clear on the oil pressure unit on the oil filter base (1/8" BSPT), but I don't know what this sending unit is without taking it out or having another one in hand! Obviously I would like to order something in advance to do this while I also replace the spool valve gaskets.

If it is 1/8" BSPT, I'll just go ahead and run a 1/8" NPT tap through it so I can run a hose to a remote sending unit on the firewall.

Thank you!

Dave

 

[ATERPAK]

I've got a complete setup for this which allows you to keep the original sending unit, and also add a second unit as a spare and thus you will have a stock oil pressure setup in the dash and a secondary setup (which should be more responsive and accurate) in some other location. The setup includes the original block, a tapped area on the opposite side which already has a AN-3 male fitting in it and a 12" -3 stainless steel line and a -3 to 1/8 pipe female fitting for the new sending unit. Then plug the original unit back in, as long as it's not leaking and you will now have two sending units. Stock and aftermarket. You could plug the original opening using a 10mmx1.0 with a gasket. If you don't have bolt for that, the stock NSX caliper banjo fitting will fit in there and with some JB weld as a sealant. However that's a permanent fix. Be aware that the original sending unit has an o-ring seal and does not use a pipe thread for sealing. If you need more info, private email me and we'll talk.

Al

 

[Mac Attack]

Thank you Al, I was hoping you'd see this and respond.

The OEM sending unit puzzled me since there is an o-ring to seal it in there. I thought it wouldn't be a tapered fitting for that reason, but it seems like all Hondas use BSPT threads for their sending units.

Thanks for the 10x1mm info, it's the same thread then as used on the front bank oil pressure port test connection (page 6-18 of the SM)! From your response, do you sell this relocation setup?

Thanks again,

Dave

 

[davidf]

Wow, such simplicity and they cost so darn much.:frown:

 

[Mac Attack]

Well, instead of spending $200 for another OEM sender, I just placed an order with Summit Racing for $250 for hopefully a better setup that will relocate the sender off the engine:

(1) RUS-641431 - Fittings, Brake Adapter, Steel, -3 AN to 10mm x 1.0 Male
So i can get from the 10x1mm oil pressure sender fitting to a -3 AN hose

(1) EAR-63010118ERL - Brake Line, Speed-Flex, Braided Stainless Steel, 18 in., -3 AN Female, -3 AN Female
Should be plenty long enough

(1) AER-FBM2719 - Fitting, Straight, -3 AN Male to 1/8 in. NPT Female, Steel
Hose to the standard 1/8" NPT pressure gauge - Note that NOS makes a stainless braided hose that has a -3 AN female to a 1/8" NPT female to eliminate this fitting, but I would have had to wait.

(1) AVM-30-4407 - Oil Pressure Gauge
This is the AEM digital gauge. I like the combination of a digital readout and a kinda analog sweeping action so I can tell rate of change. Otherwise, I would have gone with the SPA gauges to save space.

(1) ARP-100-9904 - Sealant, ARP Thread Sealer, 1.69 fluid oz.

Also, I ordered one o-ring each from Honda (top left corner of page 8-3 in the SM) for the sender connection if I want to take it apart and try to rotate the fitting 180 degrees:

91319-PR3-003
91302-PR7-A00

Now for gauge placement....

Dave

 

[ATERPAK]

Not really Davidf. The cost for the adaptor parts are not that much if you modify the original sending unit mount or have the right fitting to go into the original stock connection. However after I had two after-market sending units fail on me twice while on the track, I decided that I wanted a little more safety in knowing whether I had oil pressure or not. That's why I decided to keep the stock setup and add an additional sending unit & gauge to a modified attachment block. Every since doing that I now have had no failures on either unit and I can get quick readings on oil pressure changes when in the heat of battle.

Al

 

[Mac Attack]

Al,

Do you sell your attachment block?

I hope it wasn't AEM senders that failed - do you mind sharing which two sending units failed (and if they were mounted in the stock sender location)? That certainly would be unnerving to see the gauge drop to zero on the track. I would have dual gauges now too!

Thank you,

Dave

 

[ATERPAK]

Yes I do sell the entire setup and I have one left. I PM you on this. Did you receive it? Let me know if you are interested in it.

The gauge setup I used was from Defi. The gauge has an almost identical look as the stock gauges including the lighting. Defi makes a good product and it wasn't their fault that things went bad twice. The first time we thought it might be a fluke. The second time I decided that it must have something to do with the vibration of the motor since the oil pressure died on the gauge during VTEC operation. Since I didn't loose VTEC when it dropped I knew I still had oil pressure. That's when I decided I wanted a backup so I modified a new attachment block to isolate the Defi unit and still keep my stock sending unit. Works great.

Al

 

[Mac Attack]

No, I didn't receive your PM. Unfortunately this morning I already ordered the parts listed a few posts above since I wanted to do everything (spool valve gaskets and this) while I had some time off the next few days (it's my daily driver and I don't get much time to work on it with little kids, etc)!

Defi is nice - glad to hear mounting the senders remotely and not on the head fixed the failures.

I appreciate your responses. There seems to be a resurgence of OEM oil pressure gauge issues recently so I'm sure some folks here will be interested in your setup!

Dave

 

[Mac Attack]

Using the parts listed above, I replaced the OEM sender and mounted my new AEM sender unit to the firewall. Now I need to remove the OEM gauge and find a place for the new gauge :frown: I plan on putting it on an A-pillar pod with oil temperature soon....

It helps to unmount the coolant tank and push it to the rear a few inches. Removing the spool valve is nice too (I replaced the gaskets on those). I removed the sender unit mounting block from the front head and threaded my 10x1mm to -3 AN steel adapter into it. It just seated perfectly inside the machined o-ring groove for the OEM sender unit sealing surface. I used Loctite red 27100 to seal the threads before getting the full 3/8" threads into the block. I was worried about this sealing sufficiently. With the 3/8" of threads and Loctite red, I knew it wouldn't be a big leak, but a major PITA if there was a minor leak. The 24 hour wait for the Loctite to cure was difficult!

Luckily, it hasn't leaked so far after a grueling test today :wink: Oil pressure on a cold startup at idle is 65 psi, hot idle is just less than 20 psi, and hot redline is around 80 psi (there's about a 5-8 psi drop when the spool valve opens). Amsoil 10W30 with a NAPA filter.


Overall, for $50 more than the OEM gauge and just a little more labor, I'm very pleased with the results (assuming it doesn't leak over time)!

Sorry, I should've taken pictures of the steel 10x1mm to -3 AN adapter threaded into the aluminum block. It's too late now - that thing is buried. The AEM sender is now located on the firewall with a rubber mount, you can see the braided line running to it near the coolant reservoir.

Dave