Oil Pressure Gauge adapter for 2000 Tacoma 2.4L 2RZ-FE

Ready for a first start after working on the engine for months, without pulling it from the truck. Bought an “Engine Oil Pressure Test Kit” (Item 62621) from Harbor Freight, hoping to be able to monitor oil pressure during startup, to see if the Vaseline I stuffed into the oil pump cavities to prime it works properly, prior to ignition.

That test kit has many adapters, but it seems that none of them fit the threaded hole in the block from which my oil pressure switch was taken.

Two adapters in their kit come close to fitting into the threaded hole. One of them, the 1/8” - 27 NPT M appears to have a taper that looks right, but that one is too large, suggesting that a smaller version, with the same taper, might be the correct fitting:


1/8" - 27 NPT M X 1/8" - 27 NPT F - 90 Degree elbow

1/8" - 28 BSPT M X 1/8" - 27 NPT F - 90 Degree elbow


I have highlighted the end of these adapter that are supposed to screw into a block. The description of the fitting on the other end of the adaptors is the non-highlighted part above, and all of the adapters in the kit have that same fitting, so the single hose leading to the gauge can screw into any one of them.


My problem is that I do not know, with any certainty, what thread is in the oil pressure port, and I have been unable to screw in any adaptor from the pressure test kit.


I know the following about the oil pressure switch taken out:


The threads are tapered, and approximately 10 mm in diameter. On my metric thread gauge they come out 0.9 mm per thread (unusual for Toyota); on my SAE thread gauge they are 27 TPI. I have to assume the threads going into the block are tapered the same as the switch threads, since they have to seal against high oil pressures. Further, interestingly, the switch can be easily screwed into the gauge end of each adapter in the set (i.e., it can be screwed into the 1/8” – 27 NPT F), and it seems pretty close to a perfect fit, which makes me think that the 1st fitting above ought to work, but I cannot get it screwed in. The leading edge of the threads on the switch provides an amount of screw length that doesn’t have threads, so it first fits into the hole before any screwing is required. That isn’t true of the adapters in this kit.


Finally, the kit has one adapter that is a short length of tubing that has the same fitting on both ends (1/8” – 27 NPT M). That tubing was easier to get a grip on, so I tried to get it to screw into the hole. Disappointingly negative. Several times, I could get it to seem like it was starting, but almost immediately it got hung up as if it were being asked to cross-thread itself.


Does anyone know what thread is in the port where the Oil Pressure Switch screws in? Or does anyone know where I can go to find out?

 

https://www.tacomaworld.com/threads/re-threading-oil-pressure-sender-on-3rz-fe.616082/

 

If you do a Google search for “toyota 2ZR oil pressure port thread”, there are multiple sources that report it to be 1/8 BSPT.

This is was I was expecting, as I (at work), buy pneumatic parts from SMC (a Japanese company), and their standard threads are BSPT.

Note: BSPT are sometimes called Rc threads.

 

Thank you both for the help, James and Jake.

First, I made a mistake in my statement of my problem above. The oil pressure switch has 28 TPI, not the 27 I wrote. That was a critical error!

The following is not an advertisement; it's simply evidence that my oil pressure port thread is 1/8" - 28 BSPT.

At www.yotashop.com you can find a 1/8" National Pipe Thread to 1/8" British Standard Pipe (Found on most Toyotas) Toyota to Aftermarket Oil Pressure Gauge Adapter (SKU: 265220; UPC: 21597-60480), and under its description they say:

"This adapter threads into Toyota blocks that have a 1/8" - BSPT thread for oil pressure sending units. If you are installing an aftermarket oil pressure gauge that has a 1/8" NPT thread into a Toyota engine block you need this adapter.

The threads are close but not the same. Trying to screw an aftermarket gauge into your block will do damage or leak. We use this adapter on Toyota 20R, 22R, 22RE, 22RET, 3VZ-E, 2RZ-FE, 3RZ-FE, 5VZ-FE and many more Toyota engine blocks that have the factory 1/8" - 28 BSP thread pitch."

From that statement saying that my engine, the 2RZ-FE, has a factory 1/8" - 28 BSPT I can assume that the threaded hole for the oil pressure switch in my block is (highly likely to be) 1/8" - 28 BSPT F in my engine, so I should use the 1/8" - 28 BSPT M fitting from my test kit. It's the only BSPT fitting out of the 11 adapters that came with my oil pressure test kit, so it should be the one that ought to screw into the oil pressure port.

The trouble is it hasn't yet. Btw, the number 28 represents 28 TPI, and is widely understood as THE TPI for 1/8" BSPT threads. For the oil pressure switch I have taken out, its fitting measured an averaged 9.73 mm outer diameter, and also has 28 TPI, so the desired fitting must be an 1/8" - 28 BSPT M. And, the 1/8" is the nominal ID of the threaded pipe.

Since the engine has been fully reassembled, getting to the oil pressure hole is a bit difficult for my fat hands combined with an adapter that is, in effect, a brass cube. That's one impediment to getting the correct adapter screwed in. Another piece of the difficulty is the fact that the switch's fitting starts with a small length of non-threaded metal before the threads begin, and when they do, they start off short and grow over about a full thread length of turning. In effect, that design gives the fitting a chance to drop itself into the hole before it starts being screwed into the threads of the hole. The fittings in the test kit all start off with full sized threads right at the start, with no unthreaded metal for dropping into the hole first before starting to screw, making it a bit more difficult to catch the first thread.

When I was attempting to screw in the NPT adapter, I found there was a nice round 1/8" pipe-like adapter that made it easy to try to screw it in, but as soon as the threads began to bite, the adapter would seize in the hole and no further turning was possible by hand. Subsequent to that attempt, given all that I have learned from your help, now I know it was a good thing that I didn't get that NPT fitting screwed into the BSPT hole.

Another approach might be to find an NPT to BSPT adapter and use one of the NPT fittings that might be easier for me to handle than the cubic brass one I am currently trying to get screwed in. Not too warm about that, but it's an option. Ya'll gave me good information about where I could get one.

That's all I know for now. Plan to next do some work on the threads in the hole directed at cleaning off any interfering materials that might be inside the hole threads, to give the adapter a chance to start, and keep trying to get the BSPT fitting to screw in. Also, when I next attempt to get the fitting to screw in, I will use some lubricant to see if that helps. Will keep you posted.

As usual, any tips from you experts would be appreciated.