BMW M30 Oil and Water Temperature Sender Installation

This how-to covers installation of 1/8"NPT senders into the oil filter housing and thermostat housing for a BMW "Big Six" M30 engine, as performed on a US-spec '86 E28 535i (many other M30-engined BMWs will be similar, particularly E23s and E24s), and discusses fitting terminology, cutting fluids, tools/supplies, and the procedure. Thanks to Devinder Grewal for pointing out a good oil temperature gauge location.

What Does "NPT" mean?

For those who are not familiar with the terminology, "NPT" stands for National Pipe Thread. NPT fittings are tapered, and tighten as they are screwed into the hole, performing both joining and sealing in the process; in contrast, a straight fitting requires an o-ring or metal seal ring (i.e. the 12mmx1.5 oil pressure sender on an E28). The size of an NPT fitting doesn't correspond to any logical dimension. For NPT fitting measurements and drill-size charts, see this page from the A&J Fittings website. Don't be confused by references to "NPTF" - this is the "Dryseal" thread, and it is compatible with NPT. The only thing you need to know is that any combination other than an NPTF-to-NPTF connection will require sealer, whereas NPTF-to-NPTF does not. In fact, I bought an NPTF tap even though the Auto Meter senders are NPT; this way, I'll have the Dryseal base covered if I ever use an NPTF fitting.

Precious Bodily Fluids (?)

Tapping is made much easier and you get better results if you use cutting fluid. Oil/WD-40/??? can be used, but I decided never to use them again after I used Tap Magic cutting fluids at a job I once had. I've used their fluids in lots of automotive & house projects, and my consumable tools last noticeably longer; for hacksaw blades, I'd say the useable life is increased by a factor of three. The stuff smells pretty good too!

Tools and Supplies

The list of tools and supplies for this procedure are below, with part numbers and prices as from McMaster-Carr Supply Company. Both NPT and NPTF taps are listed, but you can choose either, and will only need one of them. Both "All Metal" and "Aluminum" cutting fluids are listed and I'd suggest you get both (you will end up using them more than you think), but if you get only one, get the "All Metals" for overall usefulness.
1/8"NPT tap 2525A169 $12.94
1/8"NPTF tap 2525A213 $12.94
"R" size drill bit 3069A69 $6.76
Tap handle 25605A63 $5.25
"All Metal" cutting fluid 1413K31 $1.88
"Aluminum" cutting fluid1413K42 $1.88
Teflon tape 6802K33 $2.02

Tapping Procedure for Pipe Fittings

Tapping isn't a difficult procedure if you're patient and can drill a hole fairly straight. It's important to use ample cutting fluid during all of the steps.
1)Drill the proper-sized hole for the tap.
2)Insert the tip of the tap in the hole, making sure it's straight.
3)Start the tapping in a continuous motion, turning the tap from 3/4 to 1 turn on the initial cut.
4)Back the tap out 1/4 turn. This breaks the chips and allows the cutting fluid to flow into the grooves, and not doing so can result in galled threads and/or a broken tap.
5)Continue to tap, turning the tap forward 1/2 to 3/4 turn, then backing out 1/4 turn, doing this until the tap is about 1/3 of the way down its cutting length.
6)Remove tap and clean threads. Carb/brake cleaner and q-tips work well, but avoid compressed air as it can move metal chips to places where you don't want it.
7)Test-fit the fitting. If the threads don't engage or don't pass through the thickness of the piece, continue incrementally with steps 5 and 6. If the hole is too small, the threads will not engage properly or seal well, or they might strip; if the hole is too big, the fitting will not tighten adequately and thus will not seal.
8)Clean out the housing really well!

M30 Oil Filter Housing (w/o Oil-Cooler)

The oil filter housing is quite easy to drill & tap. The hole is centered 1/2" behind the reinforcing rib, and 1/2" below the top edge of that part of the housing. I used a drill press, but you can clamp the housing to a 2x4 just as easily. You might notice the piece of coat hanger wire in the chuck, extending into the tap handle; I devised this technique to help me get the tap started straight.

(click on any picture for a large version)

M30 Thermostat Housing

The thermostat housing is moderately difficult to drill & tap due to the peculiar placement required for the sender. I chose a position under the housing, angled 15° forward (relative to in-car position) to avoid both the intake manifold and the lower thermostat housing nut. It's also important to choose the proper distance from the head/housing interface due to possible interference with a large sensor in the top of the housing. In my installation shown here, a combination of placing the hole a bit too far from the head and tapping the hole a bit too much caused the temperature sender to barely contact the large sensor; 1/8" closer to the head and there would have been no interference. I suggest that you attach the sender wire before you put your hoses on.


Installing the Sender in The Hole

Wrap the threads of the sender twice with the teflon tape, in the direction that tightening the sender will tighten the tape - you have a 50/50 chance of getting it right if you just guess which way to do it, and if you get it wrong, it'll be self-critiquing. Pull the tape taut as you put it on, but not so taut so that the threads cut through it. Install the sender hand-tight, then give it about 1/2 to 3/4 turn past that point. Check continuity between the sender body and the part; if resistance isn't zero, the temperature readings will be affected; if continuity is bad, try tightening the sender about 1/8 turn. Once the vehicle is running, check for leaks at the joint and if there are any, tighten the sender no more than 1/4 turn at a time to correct them.

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