I'm trying to figure out where to locate a coolant temperature sending unit so I can read a "real" temperature instead of the dummy gauge in the instrument cluster. On the back of each head on my DOHC 2.5L there's a plug that looks identical to the ones that tap into the oil gallery on top of the engine block. Do those plugs on the back of the heads go into the water jacket, or do they go into the head's oil passages?

Thanks,
Pat Olsen
'97 Legacy 2.5GT sedan

Tap into the feed line going to your heater core with a T. It flows through there whether you have the heat on or not. Much easer than the head.

Fitz

Except I don't have a T with a 1/8" BSPT hole in it for a sending unit, whereas I can go to the dealer and buy the hex plug to install the sending unit in the head. Assuming, of course, that it taps into the water jacket. :)

Pat

Why not just back the plug out a bit and see what comes out? :)

Actually, the engine is empty right now, as I just installed it yesterday. :) Hence I figured this would be a good time to pull one of the plugs out to install the sending unit.

Pat

I just removed one of the plugs from the engine that I just pulled. Although I can't say with 100% certainty, it appears those plugs do go into the water jacket. There was definitely no oil residue on the plug or inside the cavity that it provided access to. All the oil was drained on Friday, but I would still expect there to be some residual oil film somewhere in there, and there wasn't as far as I could tell.

However, my cursory glance at the plugs misled me - they're not the same as the ones that go into the oil gallery on top of the block. The hex in the middle is 12mm vice 8mm, and the plug itself is bigger. I don't have any way to check metric thread sizes that big, but I'd guess these are 19mm and the oil gallery plugs are 17mm? So the idea is pretty much a bust. :( And I'm not sure there's enough room under the plug for the sending unit to stick out.

Pat

Aren't those holes so you can get the wrist pins out?

those are coolant plugs from casting the heads, the small ones are oil plugs.

my motor is out and apart i had those plugs out for cleaning.

Correct. The larger ones are coolant, much smaller ones oil (oil line is drilled only not cast and has te be blocked after machining).

Except I don't have a T with a 1/8" BSPT hole in it for a sending unit, whereas I can go to the dealer and buy the hex plug to install the sending unit in the head. Assuming, of course, that it taps into the water jacket. :)

Pat

http://www.egauges.com/vdo_acce.asp?Subgroup=Hose_Adaptors


;)

http://www.egauges.com/vdo_acce.asp?Subgroup=Hose_Adaptors


;)
Nice find. True to your name, too. :lol:

Those are pretty nice. Two problems, though: (1) I want to get the engine together and started today or tomorrow, and (2) although some would argue the difference isn't enough to matter, those are NPT vice BSPT.

Pat

You can get a simple adapter from McMaster-Carr for NPT -> BSPT, although I suppose drilling and retapping the other side and plugging the NPT is an option as well. Perhaps if that shop custom makes them, they can thread one for you properly.

I guess if you really wanted, you could unscrew the stock CTS and replace it with your aftermarket one. I would guess that the stock one is BSPT since everything else is on the motor, and I doubt you'd throw a CEL if you just left the stock one plugged in and zip tied it secure somewhere.

There are two items tapped into the coolant cross-over log - a larger sensor with a brownish electrical connector, and a smaller sensor with just a simple spade connector on it:
http://www.submariner.org/thepno95/Pictures/Subaru/Engine%20build/coolant%20temp%20sensors.jpg

I'm assuming that, as on my Mustang, the "real" connector feeds the ECU, while the spade connector (which you can hardly see in the picture, as its color blends with the mung on the engine block) feeds the gauge? If that's the case, then I guess for the short term I'll go with 8Complex' approach. In the long term I don't want to have a "dead" gauge in the instrument cluster (even if it is just a dummy gauge), but I'll survive with that for now.

Pat

***disclaimer: i like ghetto fixes****

couldn't you just get a small piece of pipe/conduit and a tap and make your own "t" for the heater core line? then you can do it tomorrow, err today.

josh

Not sure, I thought that the ECU fed the cluster, but I've been known to be wrong before.

Speaking of which, that "real" sensor looks like it's 1/4 NPT/BSPT, and the "dummy" one looks to be 1/8 NPT/BSPT. You could get lucky on that one.


spongejosh - I would do the same, but I don't think I've ever even seen a BSPT tap. :lol:

I've actually got a 1/8" BSPT tap that I bought online specifically to do my initial install early last year. I bought a sandwich adapter, which has (as I recall) 3/8" NPT ports on it, and then bought two 3/8" NPT plugs that I drilled out and tapped for 1/8" BSPT.

Whether I really need to use BSPT can be debated. As I alluded to above, the thread pitch for 1/8" NPT and 1/8" BSPT is nearly the same - one is 27 TPI and the other is 28 TPI. There's also, I believe, some difference in the taper and shape of the threads. Nonetheless, there are plenty of people who have mixed and matched the two without issues, such as using an NPT Autometer sending unit in the OEM oil gallery adapter (which is BSPT). But I'm anal, so I bought the tap. :)

Pat

I have put an NPT fitting into a BSPT tapped hole (the oil pressure type -> oil feed line fittings) and the fitting was absolutely trashed when I pulled it out. IMO, either get an adapter or do it right the first time.

BTW Patrick - Have you considered tapping a hole in the center of the allen socket area on one of those head plugs? Not sure if you could get a socket for the fitting into the allen socket area, but it's worth a look, I suppose.

BTW Patrick - Have you considered tapping a hole in the center of the allen socket area on one of those head plugs? Not sure if you could get a socket for the fitting into the allen socket area, but it's worth a look, I suppose.
I haven't done exactly that, but you're right, it wouldn't be big enough. What I've done already is removed one of the big allen head plugs from the bottom of the passenger side head - it's got a 14mm allen head on it, and the plug is probably 22mm or more across. I drilled it out and tapped it, but even with the 14mm hex there's really not enough room for the sending unit (since it, too, has a 14mm hex to it). I've got the sending unit in there, but I'm not sure how good the thread engagement really is, because the hex portion of the sending unit contacts the plug.

The plugs on the back of the heads are only 12mm, so the issue would be even worse.

One thing I've though of is taking the big plug from the bottom of the head to a welding shop, have them open up the hex portion (so there's a nice hole there), then weld a nut or something on top. I could then drill out and tap the center of the nut to install the sending unit. The nut would obviously give me a way to drive the plug into the head. Basically, it would be like a giant version of the oil gallery plug/sending unit adapters on the top of the block, which have a 17mm head to them with a 1/8" BSPT hole through the center. Make sense?

It's around freezing out in my garage right now, so my motivation to finish the job this evening is pretty weak. Tomorrow it's going to be back up around 50F, which is a bit more comfortable. :) So I'm gonna visit the welding shop first thing in the morning and see if they can hook me up.

Pat

I confirmed in my Haynes manual (not sure why I didn't think to check there earlier :rolleyes: ) that the little single spade connector is for the factory gauge. So, for the short term, I'm just going to remove that sending unit from the cross-over log and install the aftermarket one there. In the long term, I'll do my bottom head plug welded adaptor trick. :)

Pat

Cool deal. You could probably zip tie the stock gauge sensor to the aluminum crossover pipe and get a vague reading. Would be funny if it was still "accurate". :lol:

I guess if you really wanted, you could unscrew the stock CTS and replace it with your aftermarket one. I would guess that the stock one is BSPT since everything else is on the motor, and I doubt you'd throw a CEL if you just left the stock one plugged in and zip tied it secure somewhere.

...OR you can get this adapter and fit both the stock CTS and the gauge sender sensor :)

http://www.egauges.com/vdo_acce.asp?Subgroup=BSP_OTOD&Manf=All

I use this one to connect my oil pressure and oil temperature sender units.

I also use this 1/8 NPT ---> 1/8 BSPT conversion adapter: http://www.egauges.com/vdo_acce.asp?Subgroup=BSP_Adapter_Bushings&Manf=All

That 2-into-1 adaptor is pretty nice, but I went another route.

I took the cross-over log off the engine I just pulled so I could take a better look at it. I noticed that the walls of the "legs" off the cross-over (where it goes down to mate to the block) were nice and thick, so I decided to drill and tap into one of the legs.

Here you can see the aftermarket sending unit installed a couple inches from the factory one...
http://www.submariner.org/thepno95/Pictures/Subaru/Engine%20build/cross-over%20tapped1.jpg
and here you can see that the threads are all completely engaged, so that's cool...
http://www.submariner.org/thepno95/Pictures/Subaru/Engine%20build/cross-over%20tapped2.jpg

So, mission accomplished. :)

Pat

Well done!!!!

Is that a Defi temperature sensor :) Looks similar to mine.

Question: would you have gone this route had the engine block was not removed? :)

Yeah, it's a DEFI sending unit. I have the DEFI DIN 3-gauge setup.

If I wasn't already taking everything apart, I probably would have figured out some way to put the sending unit into the heater hose, as Fitz originally suggested. You wouldn't even need to drain all the coolant to do that, as the heater lines are basically at the top of the coolant system.

Pat