Surely someone with a '68-'71 has run into this....... When I first pulled the original engine out and had another built, there was no problem reusing the temp. sending unit on the early GM 487 heads that were on it. Second rebuild was with new aluminum heads. The hole in the heads was for a 3/8" sending unit and the original was a 1/2".  I couldn't find a 3/8 sending unit that would register accurately so we put original in the thermostat housing neck. The engine ran hotter, 210 degrees no matter if it was 25* or 100*  outside, unless I turned the a/c on then it would climb to 220*...... The question is...... can the Dart Iron Eagle head be safely bored out from 3/8" to 1/2" so the sending unit can be put back in the head where it belongs? It would look better, too.

longhorn2942010-09-05 16:24:15

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   I know the voices aren't real, but they have some pretty cool ideas...

You should be able to find an adapter that the sending unit threads into and the adapter threads into the head.  Check with some aftermarket gauge suppliers...I've seen them come with the adapter since they don't always know what engine the gauge and sending unit will be used in.

Trying to stick a 1/2" unit into a 3/8" hole is definitely not easy. I'm not aware of any adapters that go that way, that would fit in the area of the head that the sender unit goes, and still have room for the exhaust/headers.
I don't see why you couldn't drill/tap the 3/8" hole in the head out to 1/2", and re-thread it...just remember that it is a 1/2" pipe thread, not a regular SAE(nuts & bolts) type thread.
IF the area looks like there is enough "meat" there to make the hole larger without weakening the head there, I'd say go for it. What does your engine builder say?
Perhaps a call to Dart would help?
I know most of the aftermarket performance heads these days use the 3/8" fitting because most senders are that size. They ain't interested in whether or not your old style, original, mechanical sender will fit...


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Joel Adams
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  Thanks Gunslinger and Joel.  If the hole was larger than the sender, an adapter would probably work but the other way around would mount it up out of the head, seems to me. Think I'll try giving Dart a call tomorrow and see what they say. Joel, the builder is leary of enlarging the hole. He's never done that before. Dart should be able to tell me. I just figgered somebody had run into that before. I'll let you know what I find out. I guess it just depends on how thick the boss is around the hole. Worse comes to worse, I can just put it back in the thermostat neck. I just had the radiator rodded out and cleaned all the bugs and dirt out of the fins so it should run cooler anyway.

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   I know the voices aren't real, but they have some pretty cool ideas...

i ran into the same problem when I changed the heads on mine during the rebuild.  I purchased a sending unit at NAPA part # TS6641. Fits 89 - 91 camaros and firebirds. The calibration is the smae and the unit works great. I think the cost is around 25 - 30 bucks. Saved a lot of fustration trying to change to something different. Hope this helps.
Rodney


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 Thanks Rod7515. I wonder if it will work the same on my '71 tho. They changed sending unit part #'s in '72. Your's was still 1/2" in '74? Mine has a 'button' on top and the '72 up had a spade connector. The gauge #'s are different, too..... If it can't be retapped, it would be worth a shot, although I tried several in the past with no luck. I'll keep the #...... Thanks.

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   I know the voices aren't real, but they have some pretty cool ideas...

Yes, mine was a 1/2" and my new heads had a 3/8".  I was told that GM used the same calibration on all there sending units.  Not sure if that is correct but I do know that the new sensor worked great and seems to be very accurate according to an infro red temp meter. It also looked cleaner without a sensor on the thermostat housing. Let us know what you do. I have a 72 also that I may end up with the same issue if I do a rebuild in it. Oh, another option is to have a machine shop turn down your old sensor and put 3/8 threads on it. I had a friend that was going to try that for me but then I found the other sensor.
Good Luck
Rodney   

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