C1 temperature sending unit

[Roger Z.]

I know this issue has been posted alot,but if memory serves me correctly,There was an article posted awhile back about what to look for in a correct unit.
I looked in my past issues and can't seem to locate it.
Does anyone know what issue it was in?
Regards
Roger

[Jack H.]

Re: C1 temperature sending unit

Don't bother to look--the issue is all over the map!

Basically, there are four variations: (A) Is the stamped sequence upright or inverted, and (B) Does the sequence terminate with '12V' or '12 Volt'.

Different JG books describe what's 'right/correct/factory original' differently. So, if you're chasing judging points, read your copy of the JG book and go with what it says.

BTW, none of the descriptive text passages address specific font or leading/trailing characters of the neck band's identifying sequence.

Personally, I've walked the scrap yards for many years and harvested 100's of these AC senders. I've seen all four variations in stamped ID sequence and can't say that there's any correlation between the differences based on what year the donor vehicle was...

My take is there was more than ONE temp sender stamping machine at work within AC/GM and our textual descriptions of what's right/factory original are based on small sample myth...

[David L.]

Re: C1 temperature sending unit

Roger,

Back in Sept. 1991 I did some research on GM # 1513321 temperature sending units.
The articles that I used are in the following:
Vol. II, No. 1, pg. 24
Vol 16, No. 4, pg.14
Vol. 16, No. 4, pg. 37
I also collected 28 temp. sending units from various 1959-1968 Chevrolets & Chevrolet trucks. Pictured are 3 pages of my research. I could not really come to any conclusions about the vaious stampings.

Dave

[Jack H.]

Re: C1 temperature sending unit

The key to construction (where you draw the line at F) relates to a running change. The early units have the smaller diameter bottom section (barrel) with a 'punt' in the end.

Later era units are larger in diameter with a flush/square bottom to the barrel. That relates to improved coolant penetration resistance.

If you take an early unit and look up inside the hex body, you'll see there's a 'gap' between the bottom barrel and the hex body. That's a potential path for coolant migration into the sender.

Take one apart and you'll find a 'pellet' which is the variable resistor forced against the bottom of the barrel by a conductive spring. If coolant invades the cavity, corrosion begins to attack the ohmic contact surfaces causing overall resistance to climb.

Plus, should there be a conduction path between the conductive spring and the walls of the barrel, you essentially 'short circuit' the variable resistor resulting in lower overall resistance. Those are the two failure mechanisms for the sender and it's a 'race' condition once the barrel cavity loses its water tight integrity...

BUT, when a sender is installed, we can't see the bottom barrel geometry and therefore can't distinguish early vs. late design characteristics. So, we go by what we can see and that's the emboss line.

Like I said, and your research confirms, this aspect of the part is all over the map. Probably the result of there being more than ONE set of production tooling for a part that was churned out in the millions of units per annum level.

Increase your sample size by 50X and you'll see more permutations on the body emboss...