non-standard size temp sender? Can't find right size replacement

[centuryhouse]

I can't seem to find a suitable replacement temperature sending unit.

I have a 72 GMC Sierra Grande 350 5.7 4brl 2wd - but from what others here have said, it appears the engine was replaced with a late 70s crate engine, which makes parts look-up difficult or impossible.

The 1/2" size threading on most replacements is way too big. Even Lectric's units are described as "they screw into the original size 1/2" pipe thread-size hole (not the smaller 3/8" hole)".

I also need the tab type connector, which appears not to be the type that comes on most.

I found this correct connector type at O'Reilly but the threading was too large:

http://www.oreillyauto.com/site/c/de...er+-+universal

Pics:

[leftybass209]

Just to be clear, where are you trying to put the temp sender?

The stock location is in the drivers side head. Its near impossible to go to an auto parts store and pick one up. I have a crate engine with the anemic design heads, and I purchased my sender from classic parts. My gauge reads correctly, no leaks, no issues.

[centuryhouse]

Originally Posted by leftybass209

Just to be clear, where are you trying to put the temp sender?

The stock location is in the drivers side head. Its near impossible to go to an auto parts store and pick one up. I have a crate engine with the anemic design heads, and I purchased my sender from classic parts. My gauge reads correctly, no leaks, no issues.

Mine is in the driver's side head.

If you happen to run across the part number you got, please pass it on. I'll peruse their site. I found this, but it doesn't specify the threading size, which is where I have my problem:

http://www.classicparts.com/1971-72-.../#.Va_Zh6RViko

[leftybass209]

Do you have the 3 gauge cluster, with just a temp warning light, or do you have the 7 gauge cluster with an actual temperature gauge?

[leftybass209]

This is the part number if you have the gauge....

(1956-72) Water Temp Sender-w/ Gauges Item Number:*53-811

[centuryhouse]

I do have the gauge, the full 7 cluster.

That part that you listed has a different connector than I have, and unfortunately doesn't specify the thread size either.

[leftybass209]

http://67-72chevytrucks.com/vboard/s...d.php?t=614092 read through this for part numbers for the 3/8 size temp sender.

[centuryhouse]

Originally Posted by leftybass209

http://67-72chevytrucks.com/vboard/s...d.php?t=614092 read through this for part numbers for the 3/8 size temp sender.

When we say it is a 3/8 or 1/2 size, what is that a measurement of - the threading, or the tip part below the threading?

I am having a problem with the threading being to large, so that the unit will not fit into the hole because the threaded part is too large.

As an example, here is a part. It describes it as 3/8", 14 thread:

http://www.rockauto.com/catalog/more...nid=455&jpid=4

[Bigdav160]

3/8 pipe has an external dimension close to 5/8 inch.

1/2 pipe has an external dimension of just over 3/4 inch

[centuryhouse]

Thanks! I was concerned because the one I just got today from RockAuto said 3/8 but measures nearly 5/8! I thought they sent the wrong one

[WIDESIDE72]

Here's the one I bought. http://www.ebay.com/itm/NEW-gauge-te...r#ht_364wt_840

I got hosed if the one from classis parts works.
http://www.classicparts.com/searchprods.asp

(The one from ebay cost more than 4 times what the one from classic parts does.)

[WIDESIDE72]

sorry, PN 53-811

[centuryhouse]

Originally Posted by WIDESIDE72

sorry, PN 53-811

This one didn't work out?

And the one on ebay did show the right temps, right?

[WIDESIDE72]

I have no idea if the one from classic parts works or not. The one from ebay does.

[Orange Crate]

Why not just change the gosh darn connector?

[Orange Crate]

There is a good reference on sensors here (Tread sizes and resistance and such like):


http://www.megamanual.com/v22manual/mwire.htm#clt

[centuryhouse]

Originally Posted by Orange Crate

Why not just change the gosh darn connector?

The real problem I have been having is with the thread size, more than the connector.

I just got one in tonight from RockAuto. It fits and has the flat connector type.

With the engine warmed up (95 degree heat, drove it around the parking lot twice then let it idle for 5 or 10 minutes) the gauge now shows a slight temp change instead of pegged all the way left - but still far cooler I'm guessing, than it should.

After warmed up:

[WIDESIDE72]

Nope. Still wrong resistance.

[Orange Crate]

What part number did you get from RA? Does it match either one below?

From the link I posted above:

"If you are looking for 3/8 NPT sensors with a standard “spade” type connector and a ground through the body of the sensor GM part number 25036135 is what you need "

"There is also a spade type GM sensor with a ¼" NPT thread available as GM part number 25036292. This part was originally used as an oil temperature sensor on 84-87 Corvettes, and has the same resistance curve as other GM sensors."

Just trying to help.....

[MagmaJct]

When I first got my truck from my late uncle when he died, the gauge didn't work.

I bought a replacement sender at O'Reilly's. It was too large, but they insisted it was correct. I kept it. I later discovered someone (my uncle?) had replaced the stock 195* thermostat with a 160* unit. Not sure if the cooler thermostat was put in to mask a problem, I replaced it with a 190* unit.

My gauge now reads where yours does. I highly suspect once I install a 195* thermostat, the gauge will read correctly.

Regards,
Mike

[centuryhouse]

Thanks for everybody's help here. One more question:

Where does your temp gauge normally sit once the engine is warmed up - say a 20 minute drive in 75 degree weather, in town driving but without much stop and start?

I purchased several senders including some recommended here for my '79 crate engine with 3/8" threaded sender, and all put out too much resistance to work with the 100 ohm gauge resistor. I end up with too much resistance and the needle stayed at the cold end.

As a temp fix, last night I replaced the 100 ohm resistor with a variable resistor (ie. a guitar volume pot I had laying around).

I did this and dialed in a lower amount of resistance, and the temp needle now responds appropriately - reads cold when the engine is first started, and warmer as the truck warms up until it comes to rest close to the middle. I will likely borrow & use an infrared temp reader to see what the actual temp is, and see how the gauge matches it. As a longer term fix I may have one of the 1/2" threaded senders turned down to see if that works. But for now...

Pic on the left is right after I started it, pic on the right is after a 20 minute drive: