Best/common oil sensor locations for gauges?


I’ve had an SPA digital oil temp/pressure gauge ( for the last 7 or 8 years on my E36 M3. Since I’m probably selling that car soon, I’d like to pull the sensors and the gauge and put it on my SE30 car.

Can’t seem to find a consensus on where to place the sensors, though, and some of the threads discussing it are 3+ years old. I’m liking the idea of the sandwich plate before the oil filter, as this appears to be very easy to get to. Is there a common brand/place to get this from? Any major issues with using this or should I try for the oil distribution block instead?

I have an oil distribution block on the E36 M3 (replaced some oil sender, don’t remember where) – is there a chance this could work on the M20 motor?

Thanks, in advance, for the help!



Get OP from the OEM location. Temp is harder. You can experiment with sandwich filters and see how they work for you. I tried 2 different ones and they read very high. I never figured out for certain why. I was able to rule out radiant heat from the manifold. My favorite theory was that the region of the block below the water jacket becomes quite hot.

Best place to get oil temp, IMO, is by putting a bung in the oil pan on the driver’s side. Can be done with JBWeld if you use a bung with a flange that gives lots of surface area for the epoxy to bond.

In the old days I was pretty obsessed by everything. These days, not so much. I’d be willing to drill the darn hole w/o even removing the pan. Then clean out the AL shavings as best you can thru the hole as best you can, and figure the filter will get the rest. If you miss an AL shaving or two, they should make it thru the pump ok. The pump gears are a lot harder then an AL shaving.

If someone had suggested I do that years ago I’d have thought them a nutjob. “Metal shavings in the oil no problem???”


two sensors, right? OP at stock OP fitting under the oil filter. Just be sure to use a length of -4 line and mount the sensor on the inner fender…it will die from vibration if mounted on the motor. Oil temp I like to take from the pan…lets you know the temps of your bearings. You’ll have to weld a bung on the pan, but that is easy with the pan off.


Thanks guys.

That’s a bummer – I just finished reinstalled my oil pan after putting a scraper/baffle on it. For some reason I thought oil temp in the pan would be cooler than what you care to read because, at speed, the air going by the aluminum could create a slightly cool layer of oil around the sides of the pan. I’m probably over thinking it, though. How far off would the oil filter temperature be from the oil pan? Few degrees or are we talking like 20+ degrees?

What about replacing the oil level sensor with something? It’s not like I care about that sensor anyway. I guess you’d need a temp sensor that would extend a few inches down so it stayed submerged. Maybe I’ll try a simple heat shield on the temp sensor if I go the sandwich route. Not sure I want to take the chance on drilling a hole in my oil pan at this point – my luck, I’m sure I’ll jack something up. I’ll wait till I need to rebuild the motor and then add the bung then – 200k motor and doing first season of racing starting in March… who knows how long the thing will last.

Regarding using the OEM location for the OP – what kind of plug/threading is this? Do I need the pressure sensor that’s there? As in – do I need a distribution block so I can keep the OEM sensor and add my new sensor? Or do I just need to get a 1/8 NPT converter and put in the new OP sensor and just discard the OEM one? What is a “-4 line”?




Sandwich plates will likely differ, so the ~50deg too high reading I got probably won’t be the same for another. 50 is just a guess. I was doing a lot of temp and pressure experiments back then. Altho I had 2 temp sensors in the sandwich, I did not have them anywhere else during that experiment so I don’t know for certain what the temp was in the oil pan, or anywhere else, at the same time. Also, I went off scale on my gauge. So maybe 50-70deg too high is a better #. You should try it tho. Get another datapoint. Maybe something crazy was going on when I did it.

RE putting temp sensor at oil level sensor locaiton. The oil level in the pan varies wildly. It would not be easy to rig something up such that the sensor ended up <1" from the bottom of the pan.

If you want 2 oil pressure sensors, or maybe a sensor and a switch, then you will need to use a manifold. You won’t want to use the OEM pressure switch because it’s 12mm and you manifold will be 1/8NPT. If you want separate sensors, just buy a little 1/8NPT manifold, common at places that sell nitrous parts, and then plumb it to the block with a short length of SS hose and adapters. Use a -4 AN hose because AN fittings are far more tolerant of disassembly/reassembly then NPT.

Chuck’s -4 is a reference to hose dia. Look up AN hose and fittings.

For clarity, no you don’t need the OEM oil pressure switch. The smart thing to do with it is to turn it into a coolant pressure switch. To do this, remove the 2 small hoses at the throttlebody. Plug one at the thermostat body. Follow the other to the block. It goes into the block near the starter. With some liquid wrench and a breakerbar or big impact wrench, remove the hosebarb from the block. A 24mm deep socket will do.

Then thread your OEM oil pressure switch into the block. It’s a 7psi switch. Reusing it’s connector, wire it to a great big warning light on your dash. Needs to be big and bright and right in your face. The kind of thing that will stab your retinas out.

I know this thread has been mostly about oil temp, but IMO the important thing is oil and coolant pressure. Then coolant temp and last, oil temp.

A final note. I’ve gone thru a lot of gauges and sensors. There was a time when I had 4 oil temp sensors, 4 oil pressure sensors, and 2 oil pressure switches. It was kinda crazy but I was curious about everything and playing around with the car at night was my hobby. One thing I learned is that the most elegant way to do gauges is to get the high end ones like Stack and Autometer that have programmable colors and a data-out for a datalogger. They are more accurate then normal electric gauges, you don’t need to add switches because the programmable backlight colors will get your attention as long as you place the gauge in your face, and the data-out is by far the best way to get gauge info to a datalogger, at least that’s the case for Traqmate.


Oil temp in the pan is a direct reflection of the temp of your bearings…something that is good to know. The stock OP sender is a standard bolt thread (10 x 1.5??). I drill and tap them for a 1/8" pipe tap and use a -3 or -4 line to the pressure sensor. You don’t need the stock unit. Multiple connections at that fitting will, over time, break. KISS principle.

Oil level sensor can be cut off just below the “O” ring for extra oil capacity. You can also weld a cylinder to hold the OT sensor…done it, but requires a good aluminum welder.

Hate to tell you this, but the addition of a windage tray will not prevent oil starvation in left hand corners. The correct way to fix this has tow solutions. First a Paul Poore pan. Second, remove the PRV from the oil rail and plug the hole. Modify the oil pump, then add a plate to the right side of the oil pan to prevent oil from going up the side of the motor.

Use the search function and you can find a great deal of information on these subjects.


In the engine subforum there is a thread for each crankscraper and baffle solution available to us. The baffle solutions that Chuck stated are, IMO, the best available to us. However the PP pan is expensive and you’ll need an oil pump with a modified pressure relief valve to do his second suggestion. The modification, as I understand it, smooths the action of the valve making it more reliable for analog pressure relief vs. the clumsy “open” or “closed” that I think it would do otherwise. Chuck can do that mod for you.

I’m sticking with 12mm for the OEM OP sensor. My recollection is that it’s the ports in the thermostat housing that are 14mm. The reason the difference is significant is that 14mm is a fair amount bigger than 1/8NMPT so adapters are common. A 12mm hole, however, is only a little bit bigger than 1/8NPT so adapting is harder. Usually people just use a hose and remote the sensor when faced with a 12mm hole. There are a couple 12mm to 1/8NPT adapters available if you look hard enough tho.

The reason for the focus on 1/8NPT is that fits most sensors. Some oddball temp switches are bigger tho.


More helpful information, thanks guys! I’m liking this rare feeling of not being the only one that types long forum posts. :slight_smile:

Think I’m figuring this out. Really wish I’d known about this before I reassembled the oil pan, but oh well. :slight_smile: I actually really like the idea of cutting off the oil level sensor and replacing it with a cylinder that has an NPT port, though that’s certainly a project for another day.

Regarding the oil pan, do NPT bungs need to be welded from the inside? It sounds like a better idea to do it that way, but is there a major downside to welding the outside flange to the outside of the pan? I imagine, if you’re not careful, it could easily leak. Or maybe it can’t handle the pressure that way?

While I’ve disassembled/rebuilt/assembled everything on this car from the subframes to the wheels, I haven’t really touched the engine (beyond the oil pan) – so I didn’t realize there were coolant lines running to the throttle body. Is this an emissions thing? I can’t imagine the throttle body gets hotter than the coolant, right? So I’m guessing it’s attempting to warm up the incoming charge to get more thorough combustion?

Either way, I dig the pressure switch switch idea (see what I did there?). :slight_smile: I think I’m going to do that – sounds like an easy and elegant approach to that problem (which was next on my list after figuring out how to reuse my SPA OT/OP gauge). I believe the SPA gauge will allow me to drive a “retina stabbing” light if the OP drops below a certain level.

For the OP, I’m thinking of doing this now:

OEM OP Switch hole
== to ==
10x1.5 ( or 12x1.5 ( (whichever is the right threading) to -4 AN male adapter
== to ==
2’ of -4 AN hose ( to ==>
== to ==
-4 AN male to 1/8 NPT female (
== to ==
SPA OP 1/8 NPT sensor (which, from photos, doesn’t appear to have anything stick out past the threads, so I’m guessing shouldn’t have a problem fitting into the female-to-female converter)

Then would just need to have something to mount the pressure sensor to on the fender (I imagine zip tying to something that’s there would work, too). Another option would be to make my own -4 AN female to 1/8 NPT female hose.

Which leaves the oil temp sensor. I guess I have a few options there. Sort of in order of preference.

  1. Go with Scott’s JB weld approach with something like this Seems kinda risky to me because I’d probably end up with a leaking oil pan. Scott, does that option seem to have the “large enough flange” you were referring to?

  2. Add a sandwich plate and block the unused ports (

  3. Skip the oil temp altogether for now.

  4. Attempt to rig something in place of the oil level sensor. Seems like an easy item to make as a single piece to replace the entire OEM level sensor though – basically a hollow cylinder with an NPT port at the bottom and a flange at the top to bolt into the pan. Though – since the oil sensors usually have the wire integrated, I imagine tightening this sensor inside a hollow cylinder wouldn’t be super easy.

  5. If I had a place to route the oil back to the block to ensure movement of oil, I could use the setup above with a manifold. Though it would be a crapshoot at that point as to whether the distance away from the exhaust would accurately offset the extra heat added by the exhaust.

  6. Add a manifold inline out to the oil cooler. Though, given the placement, this would probably have the same “running too hot” problem as the sandwich route.



Weld the bung on the outside, not the inside. The one in your Jeg link will work. Be advised that NPT thread are not cylindrical but tapered. This means that sometimes it matters how things go together. Imagine, for example a big bolt and how the diameter of the bolt is unchanging. Call that a cylindrical thread. Now, however, imagine that the bolt tapers such that it’s wider at the head and more narrow at it’s tip. That’s a tapered thread and that’s how NPT threads work. As you thread one into another they will tighten up at some point because the “bolt” is getting increasingly wider and the threaded hole in the nut is getting more narrow.

There’s consequences to this. if you were to fasten the bung to the oil pan backwards, you’d be trying to thread your tapered bolt into something that has it’s taper backwards. The bolt starts narrow and gets wider and the bung would also start narrow and get wider. Therefore the bolt (sensor) would never tighten down into the bung.

The bung you linked to will work fine. You drill a hole in the pan the dia of the narrow part of the bung and put the bung in. The wider dia part of the bung would be outside. That’s plenty of surface to weld or epoxy.

Re. wouldn’t a weld leak. Not if the welder knows his business.

Don’t make your own hose. Too hard. Get extra adapters and fittings that look interesting. Having a grab bag of extra adapters will come in handy eventually.

Fastening your sensor at the end of your AL cylinder. Well, if it was good thick AL you could just tap NPT threads into it. But since the threads are tapered, you have to be careful how far your tap goes into the metal. Still seems over-complicated tho.

With some careful searches you can find all this info and more already here. Be sure to set the search period to anydate. Search words like bung, sensor and baffle will turn up all sorts of old info.


Yeah, I did a bunch of reading up on the NPT threading and how they work. It’s clear to me that the flange would be on the outside no matter what… I guess what I was wondering was if you’d instead drill a hole the size of the wider part of the bung, and then stick the whole bung through so the flange sits flush against the outside of the pan. Doing it this way, the bung would stick into the inside of the pan, but you’d also have a nice gap between the drilled hole and bung to facilitate a nice weld (on the inside). That said, the more I think about it, you’re trying to keep the hole low, which would make welding the bottom of the bung a huge pain if it was inside the pan.

I was also trying to reconcile why Chuck mentioned it’s easier to do while the pan is off the car. :slight_smile: Seems like, if you’re going to weld on the outside with just the narrow tip of the bung (man, so many double entendres trying to talk about this!) sticking into the oil pan, then having oil pan off the car isn’t that much of a help – beyond what you mentioned about getting shavings into the pan. But even that, it seems, can be solved with a vacuum, or even just pouring in a couple quarts and draining it.

Minor question – where’s a good spot to do the drilling where it’s less susceptible to being knock off by random shit I might drive over? Can’t be too high… I’m guessing the reservoir that sticks out into the driver’s side where the oil level sensor sticks in? Facing the back of the car? Of course, that would explain why this would be a pain while on the car – I bet I can’t get a drill at that point given the steering rack.

Also, I found a thread from a while back (almost 10 years ago) suggesting that someone ran had run both sensors (pan and oil cooler, though at different times) and found them to be the same measurement. One data point isn’t exactly a lot, but maybe others have tried this?



Pan needs to be off so you can take it to a welder that does aluminum. Put the temp sensor about an inch from the bottom on the driver’s side. Cut the bottom off the level sensor to increase capacity.