So, back to sending units:)

M

Mike B

Well-known member
Does anyone know what the oil pressure sending unit ohm range is?

I'd like to test the one I have out now to compare.

Jack led me to a sending unit on Amazon for water temp, but I have a box of gauges and sending units I can test...some SW, Some Ford, some GM, some Peterbilt, etc..obviously I don't have to be spot on, as there are no number on things really, but would like to make things appear "normal" on the gauge panel.

Thanks.
 
It'll be interesting to see what sort of answers you get. If you are asking about flathead-era FORD senders, I believe you might find they do not work strictly on 'ohms'. I'm referencing a pictorial in an old Motor Manual. I'm guessing an ohm value might have little meaning?? What do the experts say?
 
I'm not sure Bob, I took a sending unit I had, measure 14-.xx ohms, and placed it boiling water...it didn't change...I'm sure the modern one Jack led me to, would change resistance...so I just assumed the original ones would as well.

I guess it can't hurt to try what I have around anyways...and if they are resistance specific I'd at least have a starting point.
 
None of the instruments in flatties use resistance. You can measure a resistance, but it's of the heating element in the sender or head unit. See below.
 

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Ross, would you happen to have a diagram of just a single unit system?...the 59 I pulled from my '42, only had a sending unit in the left (drivers) side...I noticed the "heater" filament in your literature...and am assuming (of course;) ) that it is a resistance changing device..so allow the gauge to "swing"...then the other unit when reaches 212 degrees, makes the gauge go full hot?
 
I really am not familiar with the exact system used in the 42, from the other thread I assume it was a capillary tube? The King-Seeley system used on the ones I'm familiar with has a heater on a bimetallic strip that cycles a set of contacts open/closed, sending pulse of 6v to the gauge. The second sender on 8BA's is a simple switch that opens at 212 and sends the gauge to full hot.

Oil pressure gauges use the same system (minus the excess temperature switch). Bimetallic strip with heater, that sends pulses.
 
The senders are current devices. They use contacts, heating coils and bimetal strips. For an Oil Senders, when there is no pressure, the contacts in the sender are just touching and the gauge registers "0". As pressure increases a diaphragm bends which increases the tension on the bimetal arm. More heat is need to cause the contacts to open which results in an increase in the average current flow to supply the heat to the bimetal strip. The same current flow change occurs in the gauge heating it's bimetal arm and moving the pointer.
The fuel senders and temperature senders work in a similar fashion.
 
Now I am confused more:)

The sending unit that was in the engine I am using was a mechanical one (I think, it was clipped way short and metal braiding was around it a bit), but my gauges in my '42 are electrical...

On the 59 block I pulled from the '42, it just had a sending unit-single wire- in the driver side head...nothing on the pass side head..so am I missing a sending unit?

It appears via Jacks link, a fellow ran just the single wire unit to his gauge and it worked okay...
 
Mike B said:
I'm not sure Bob, I took a sending unit I had, measure 14-.xx ohms, and placed it boiling water...it didn't change...I'm sure the modern one Jack led me to, would change resistance...so I just assumed the original ones would as well.

I guess it can't hurt to try what I have around anyways...and if they are resistance specific I'd at least have a starting point.
Click to expand...

Yup, the old original units measure the same resistance hot or cold. They need to be powered and connected to the same resistance as the gauge heating element to measure the current. The new senders use a thermister that changes resistance in relation to temperature. The resistance to temp curve of these newer senders sort of works with the older gauges. In my experience they tend to read on the high side.

I am using resistance senders on oil pressure and fuel level with good results.

Standard Auto Products PS 60 for the oil pressure and a Tanks Inc. fuel sender for early Ford.
 
Great info Jseery, Jack E/NJ and Blown49, if he's still on - I don't know what a "member emeritus" is.

I'm pretty thick headed so I don't understand how opening contacts INCREASES current flow?

Sounds like oil pressure changes moves the contacts and changes the current in sort of an analog manner - unlike the digital - or 0 we normally think of for contacts?

You'd think after working in a power plant for 30 yrs, i'd understand a simple circuit....but I AM recovering from the experience.

Thanks,
Gordon
 
>>>I don't understand how opening contacts INCREASES current flow?>>>

Opening the contacts DECREASES the flow as you suspect. That's why the needle goes to HOT when the contacts are open or when you shut off the ignition.

Jack E/NJ
 
malpais said:
Great info Jseery, Jack E/NJ and Blown49, if he's still on - I don't know what a "member emeritus" is.

I'm pretty thick headed so I don't understand how opening contacts INCREASES current flow?

Sounds like oil pressure changes moves the contacts and changes the current in sort of an analog manner - unlike the digital - or 0 we normally think of for contacts?

You'd think after working in a power plant for 30 yrs, i'd understand a simple circuit....but I AM recovering from the experience.

Thanks,
Gordon
Click to expand...

LOL, it is fairly simple, the bimetal strips are heated until they break the contact points (stopping the current and thus the heat). As the strip cools it remakes contact and reheats the bimetal strip. A mechanical device (such a the diaphragm in the oil sender) changes the "stiffness" of the strip and thus changes the heat (current) required to break the contact points. It is going to somewhat vibrate as it heats and cools, but it is the average that gives you the reading.
 
Nope, not quite that simple.

As Mike noted above, >>>On the 59 block I pulled from the '42, it just had a sending unit-single wire- in the driver side head...nothing on the pass side head..so am I missing a sending unit?>>>

With no bimetal strip. The temperature is sensed by the heater wire. As the block heats up the heater wire heats up more and conducts less due to increased resistance. The guage then moves toward hot.

The pressure guage is really just an on off switch due to the diaphragm switch. Hi or No pressure. The intermediate pressure is really a fake intermediate measurement due only to the heater wire heated up more as the block oil heats. That's why I use a mechanical oil guage.

Jack E/NJ
 
This is probably getting into more detail than most people are interested in and may be different for different years. For the 49 thru 52 the temperature sender consist of two units, one basically an on-off unit and the other one variable. The variable unit works somewhat backwards to the oil pressure senders. When the engine is cold the bimetal arm has maximum tension holding the contacts points closed. It required maximum current to heat the bimetal strip to open the points. As engine temperature increases less current is required to keep the contacts at the break point. This is because the engine heat is added to the current heat, as engine temperature increases the current heat required is decreased.
The on-off sender has a bimetal strip that is set to open around the boiling point. Both senders are connected in series so that an over-heat condition on ether head is indicated on the temperature gauge but only one head is providing a variable reading. So, on the temperature senders a high current is related to low coolant temperature and low current is related to high coolant temperature.
 

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>>>This is probably getting into more detail than most people are interested in and may be different for different years. >>>

Agreed!!

I just can't help feeling that lawyers were somehow involved in the bimetal strip being added to the temp sensing system in later years. Why? Well, it's prolly more detail that would bore most folks.

And I also just can't help feeling that bean counters were somehow involved in the use of a cheap oil pressure idiot light instead of a more expensive lying guage in later years. Why? Another boring detail. 8^)

Jack E/NJ
 
Jack E/NJ said:
>>>
I just can't help feeling that lawyers were somehow involved in the bimetal strip being added to the temp sensing system in later years. Why? Well, it's prolly more detail that would bore most folks.



Jack E/NJ
Click to expand...

please explain?

i know that in later years years, owners manuals called out "Temp indicator" oil pressure indicator"...as oposed to OP gauge, temp gauge, etc......but would like to hear your thoughts.
 
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