Thread: Flathead dual temp sender-good idea?

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So, Have had quite a few calls about checking the temp on both sides of a flathead since our gauges were in Classic Trucks magazine. I didn't have a real good answer besides running 2 gauges.

We had a few ideas, some better than others, just wanted to see what you guys thought about them.

The first idea, really didn't have any legs from a business point of view. We were looking at a 2-2/16" temp gauge with dual readings, kind of like a dual air gauge. The business case fell apart with unrealistic volumes and maybe a break even after 5 years. We have built 3-3/8" dual temp gauges, but still a big package.

What we can do, that is cost effective are these to things:

Dual senders, similar to early flathead V-8s a temp sender in each side of the head, running to one gauge, give you the average of both sides. While some argue that will not tell you much, its basically what you have with a sender in a non-flathead installed in the intake. An average of both sides. While this is not by any means perfect, it will give some information about both sides.

Dual sender with warning: Similar to the later flathead gauges. Run a regular temp sender on one side of the engine, and a warning sender on the other side. You get the the temperature of one side and when the other gets too warm, say around 220F, it will peg the gauge. While not perfect either, the gauge will tell you which side of the engine is having cooling issues.

So, a couple of ideas, just wanted to see what you guys thought.
Thanks in advance for your input.
Mark

A better idea. Individual senders in the heads, wired to a two way toggle switch and then from the two way to the gauge. I have this in my T with a flathead. Works real good. This way, all you do is flip the switch to see each heads' temp.

Originally Posted by paul274854

A better idea. Individual senders in the heads, wired to a two way toggle switch and then from the two way to the gauge. I have this in my T with a flathead. Works real good. This way, all you do is flip the switch to see each heads' temp.

Yes, I have reccomended that and it seems to not be good enough for most, I thought it was pretty good, but I guess you can't please them all

Mark

Originally Posted by marks914

Yes, I have reccomended that and it seems to not be good enough for most, I thought it was pretty good, but I guess you can't please them all
Mark

I like the idea. Once you've determined which cylinder bank runs hotter than the other, make that the "default" selection on the switch, and then check the cooler running side as needed.

Bob

Two senders hooked to one dial gives the reading for the hottest head, not an average of the two.

Originally Posted by R Pope

Two senders hooked to one dial gives the reading for the hottest head, not an average of the two.

That would constitute resistance in a parallel circuit, right? When resistors are connected in parallel their combined resistance is less than any of the individual resistances. Since electrical temp gauges measure voltage, the reading wouldn't accurately represent either side.

Bob

Guys,
the senders are designed with half the resistance, therefore the gauge reads the total, these are not run in parallel.
If you ran two standard senders, and split the wire, I think you would get the highest resistance value, which would be the lower temperature of the heads.
Mark

The dual reading gauge would be way kewl, but easy to see where it would never work on a biz deal...kind of like any one off type part, limited market for resale and high cost to build... Would it be feasible to have a single gauge with the dual senders that the reading would alternate between left and right automatically? No idea how you would do it, just a thought.

I think the 2 small gauges would work, side by side reading left and right temperature? If I were to ever bother running a flattie again, the 2 gauge deal would be the way I'd go. Don't understand why people wouldn't go with one gauge and flipping a switch, but then I still don't understand why people run automatic trannies in everything......

now if it was me---I'd put a motor minder in the rad cap

then if i wanted more info ---a temp sender each head, one at top and bottom of radiator, egt and o2 sensor for each port( only 6 of them(don't want to make this too complicated), a ----

Originally Posted by marks914

Guys,
the senders are designed with half the resistance, therefore the gauge reads the total, these are not run in parallel.
Mark

Then in series? So the body of the sensor doesn't ground to the block?

Bob

Electricity follows the path of least resistance. A temp sender varies the resistance according to temperature, hotter temp=less resistance, therefore more power flow through the gauge. Which ever sender has the least resistance controls the reading. Just try disconnecting one of the two, the meter still works fine, no half readings.
BTW, the senders are run in parallel, they are both grounded.

Temp senders go higher temp with less resistance.
if you run 2 senders of the "regular" value, 180 degF turns into 210F, if you remove one of the senders it reads 180 again.
We have made a few senders as a test with the correct range to split the difference and give the average of the two sides.
Ill run more tests on the new senders this week and report the results.
Mark

When I bought the digital gauges for my car I asked the manufacturer if I could put a temp sensor in the trans and one in the motor and use a toggle switch to switch between the 2. I was told no, unless I put in a VERY expensive special low restance switch, because the gauge wouldn't read correctly. I guess paul274854 has found otherwise.

Why not have 2 needle pointers in the same gauge working off the same pivot point like clock hands? Red for the Right head, Lime green for the Left head?

heres my idea.. use 1 single gauge, an adjustable temp warning light setup and 2 real senders, a special relay ( can't think of the type/ name ) that will switch off 1 power source when another is switched on, and otherwise work just like a normal relay.. this way, if your 'second side' starts getting hot enough to turn your adjustable warning light setup on, that circuit will close the relay and it will switch senders, so ither way, it can be seen if it is getting hot