Do not read too much into this. There is no way to know the exact condition of the device. It really comes down to how long it was operated and how low the voltage was. The worst case scenario is sitting still headlights on, heater running full blast with your foot on the brakes and the wipers running. That can actually cause the car to stall because the voltage drops so much. Conversely if you have a newer high output alternator and you seldom run a big electrical draw it might be barely impaired.
The switch is a type of transistor. You have to understand that when a switch is closed it has essentially zero resistance. That means no heat when a switch is open it has essentially infinite resistance, no current is flowing and no heat. So switches are happiest open or closed. The speed at which a transistor can open and close is effected by voltage. Less than optimum voltage makes switching slower. A partially open switch has resistance and that means heat. A lot of heat. If you ever moved the light switch on the wall slowly you probably heard some snap crackle pop and maybe smelled something burning. Thatās an extreme example but you get the idea.
Just my 2 centsā¦the original Pertonix Ignitors were designed to run on lower voltage found when connecting the unit across a coil. The Pertronix II and III do require a full12 volts for proper operation. I have an original Pertrox in my car for over 12 years and has been great.
This is a commonly held misconception. And it is Pertronix fault. In the instructions they told you to do this on one page. And then showed how it was wrong on the next.
This really isnāt my hobby. Several years ago I was hired by Pertronix to write how to articles for installing the Ignitor on Ford vehicles. They were getting a bad reputation for so many failures due to low voltage.
I guess I got one of the good ones. LOL. When I was researching upgrading to the Pertronix III, I saw quite a few sites that stated only the II and III required the full 12 volts and sold a relay kit to go with them. The old internet is really great for the proliferation of wrong information.
Okay. I think Iāve got it. The red wire needs to be removed from the +coil and connected to 12 volts supplied by the relay I purchased. The red/green wire on the +coil should supply 9 volts when the engine is runningā¦
I took itās temperature at the sender. Itās 212 when the guage is at the mark like in the above pic. Iād like to see something closer to 165, which the thermostat is rated for.
So my 210 or better was a pretty good guess. See how big the radiator hoses are? That gives you an idea of how much water needs to move through the system. If you remove the radiator cap (when cool only) and rev the engine you should see a lot of water movement. If not most likely you need to have the radiator rodded out, re-cored, or replaced. Stay away from the aluminum boxy looking things. ACP makes a couple of excellent replacements that look and fit like the original.
These cooling systems never had enough capacity to hold the coolant temp where the thermostat first opens. 210 deg is about right for normal operating temp on my 70, and that is where the NOS sensor measures 22 ohms and the gauge is centered.
67 sensors might be different, but with the system pressurized at 13 psi, coolant doesnāt boil until almost 240 degrees. So the temp gauge shouldnāt peg at H until close to 240 deg. Ford would have had a lot of cars in line for service if the temp gauges showed H at 210 deg.
The problem is aftermarket temp sensors will peg the gage long before that temperature because they have the wrong value thermister. If you have an aftermarket temp sensor you will need to buy a infra red thermal gun so you know what temperature the engine is operating at.
Shurley did that, and measured 212 at the sender. Thats normal temp and centers the temp gauge on my 70 351C with NOS sensor. This agrees with the data you had measured on an original sensor too. But I think the original 67 temp sensor might have been calibrated closer to 195 to center the gauge?
Here is the thread with the temp sender data. Royce tested an OEM Motorcraft C6DZ 10884-B / SW552 NOS part (correct for a 67), Calicat and 70XR7Tom both tested an OEM Motorcraft D0WY-10884-A / SW924 NOS part (correct for a 70 351C). All three measured around 22 ohms at 212 degrees. Looks like Ford intended the temp gauge to be centered at around 212 degrees coolant temp. As Royce and Bill both suggested, Shurley might have an aftermarket sender that reads too high at normal operating temp.
