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  #1   IP: 66.135.239.139
Old 04-03-2017, 05:14 PM
Nickelrw87 Nickelrw87 is offline
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Temp Gauge & Sensor thread size

Hi!

I need to replace my gauges (2 of 3 dont work, and all have cracked faces).In the catalog, i see the ISSPRO gauges, which i want to purchase - but i noticed the thread for the sending units are 1/8" and 1/2". Product number GAUG_10.1_451 and GAUG_10_179. Besides measuring (which would prob be the easiest) how can i tell which thread size to get?
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Old 04-03-2017, 07:15 PM
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ndutton ndutton is offline
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It depends on where you're installing the sender. The typical location on the late model engine is in the front of the head (above the flywheel) and for that the 1/2" pipe thread sender is correct.

Welcome to the best boating related forum on the web.
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Nickelrw87 (04-03-2017)
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Old 04-03-2017, 07:31 PM
JOHN COOKSON JOHN COOKSON is online now
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The senders are sized in NPT threads. You can't measure the sender hole size to find the right sender size. This happens because a 1/2" pipe is greater than 1/2" outside diameter where the threads are.
When I went through this drill I took my best shot then went to the hardware store and bought a short iron nipple to confirm my best guess\measurement before I ordered the sending unit. It was 3/8" for my temp sending unit.

TRUE GRIT
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Old 04-03-2017, 08:47 PM
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NPT Thread Size

John's suggestion is good, and you can measure the largest diameter of the hole in the block, or the largest diameter of the threaded part of the fitting, and determine the NPT size from the column labeled "Nominal Outside Pipe Diameter OD", from this:

http://www.engineeringtoolbox.com/np...ads-d_750.html

For example, the O.D. of 1/2" NPT is .840", or almost 7/8". A 3/8" NPT has an O.D. of .675", or 5/8". So, it's difficult to confuse a 1/2" with a 3/8" fitting and a good ruler or tape will do.

See Wikipedia National Pipe Thread article for more info.
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Old 04-03-2017, 09:54 PM
Nickelrw87 Nickelrw87 is offline
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awesome! I been lurking a while on here and its honestly one of the most informative forums ive ever been on and the amount of comradery is amazing! I see very very little "beefs" or trolls.

I have a late model A4, and the current sensor is above the flywheel on the head. Id like to just use that same spot if can.

Thank you guys!
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Old 04-04-2017, 12:37 AM
JOHN COOKSON JOHN COOKSON is online now
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87
Here's some more stuff.
Do not go after the sending unit with an open end wrench. You will only round the soft brass. I used a closed end wrench and a hammer and had good luck. A decent socket should work also.
If the sending unit does not want to loosen start the engine and let it get good and warm then while the engine is still running see if you can persuade the sending unit to loosen. The heat + vibration will help to loosen.
When I did my temp sending unit the last time I threaded a plumbing nipple into the hole, attached a tube to it, got the end down in the bilge, started the engine briefly and blew a bunch of KRAP out of the cooling jacket and passages.
A belated welcome to the forum.

TRUE GRIT

Last edited by JOHN COOKSON; 04-04-2017 at 12:44 AM.
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Nickelrw87 (04-04-2017)
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Old 04-04-2017, 07:16 AM
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87 - Another welcome to the Forum....

As John says, use the best fitting tool to start: a closed end wrench, or a big socket and breaker bar if you have one that fits.

That said, depending on how long ago and how tightly it was installed (and given that you're replacing it anyway), if you end up having to use a longer pipe wrench to break it free it's no big deal.

P.S. I replaced all my gauges with MMI ISPRO several years ago - they still look good after being in the weather for 8 years. Great value.
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Last edited by BunnyPlanet169; 04-04-2017 at 07:19 AM. Reason: PS
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Old 04-04-2017, 08:38 PM
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Al Schober Al Schober is offline
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Nick..
Getting the sender out of the head can be a bear - not a casual undertaking. Measure your sender across the flats, then equip yourself with a 1/2" drive breaker bar and the right size SIX point socket. If the sender is already damaged, you may have to install the socket with a hammer. Don't be surprised if you have to stand on the breaker bar!
An option (that I went with) is to leave the old sender there and install a new one elsewhere. My new temp sender is in a tee in the outlet from the manifold.
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