I have had the same problem with my 65 289 c code. It seems that only the OE will read corect. I have gotten over it. As long as it doesnt boil over its not over heating. I do check the rad before I drive and it seems ok.

 

AFIK, all current "replacement" temp senders for For cars are crap. Find a used one, clean it up, and use it.

 

Is there some way to add a second gauge (aftermarket) to get an accurate temp reading? Don't want to give up on the original style dash gauge but would like to get as accurate a reading on the water temp as possible.

 

IF you want an accurate temp reading, you'll need to install a mechanical temp gauge, period. The factory type "electrical" gauge setup is hit or miss for being accurate. I hung a mechanical gauge under dash using tye-wrap so if I wanna flip it up out of site I can. But an accurate reading was much more important that looks in this case.

 

Not so long ago I found my truck's oil pressure sensor to be leaking from the center. Bought a new one and was shortly blown away by my gauge reading 10 psi lower. Worried me that possibly either gauge was wrong so I used my mechanical gauge to see what I really had. Dug up an original sender, cleaned it, and put it on. Back to the original reading which was pretty close to the reality I measured.
Just as 22GT says, I've had about the same luck with temp senders and have been collecting a few used originals of both for some time.

 

Is there some place on the engine I can hookup a mechanical gauge AND keep my original sending unit?

 

I had a 29 Model A that i installed one in the upper rad hose
looked ugly,, but served it purpose

 

OKAY.....heres what ya do........get yourself a 2.7, 3.5, 4.0 and a 5.0 ohm resistors
1/2 or 1/4 watt, start your car, get it to temp, start with the lowest value resistor,
put it between the sender and the gauge feed wire. When your car is at temp,
see what your gauge reads, you want mid scale ideally. This will give you a correct reading and IF you overheat, your gauge will go higher. I know this works as this
is the setup I have been using for 2 years. It is almost IMPOSSIBLE to get the correct sender nowadays to read correctly on your gauge. The revered 22GT did a test a few years ago on senders, and said almost all of them dont read correctly.That post is here on VMF somewhere. Try this setups it is real easy to do and works! Good luck.

 

OKAY.....heres what ya do........get yourself a 2.7, 3.5, 4.0 and a 5.0 ohm resistors
1/2 or 1/4 watt, start your car, get it to temp, start with the lowest value resistor,
put it between the sender and the gauge feed wire. When your car is at temp,
see what your gauge reads, you want mid scale ideally. This will give you a correct reading and IF you overheat, your gauge will go higher. I know this works as this
is the setup I have been using for 2 years. It is almost IMPOSSIBLE to get the correct sender nowadays to read correctly on your gauge. The revered 22GT did a test a few years ago on senders, and said almost all of them dont read correctly.That post is here on VMF somewhere. Try this setups it is real easy to do and works! Good luck.

Okay, this I can do. The only question now is to figure out what the temperature truely is when the car is all warmed up. Guess I will get me a mechanical gauge, put it in place of the sender to determine what the temp is and then use your technique to get the gauge to read correctly. Any tips on what you did to permanently put the resistoer in place to make it durable and visually normal?

 

If you decide to upgrade to an aftermarket manifold, many of them have an extra bung. You can also try and find a thermostat housing for a later model that used a thermostatic vacuum control valve and use THAT bung.

Option #2 is to "calibrate" the gauge to the sender by measuring the resistance of the sending unit at different temperatures (saucepan on the stove with the candy thermometer method) and then adding an appropriate-sized resistor.

 

After completely re-wiring my 65 FB w/289...I can't seem to find the correct tempurature sending unit. I re-wired the car as a 66...harnesses and all new gauges. Everything works great except the temperature gauge. I tried a brand new Napa sending unit that was listed for a 66...TS6153. With this sensor, once the car started warming up the gauge would go all the way to H in relatively short order. Then, after reading many threads here, I went back to Napa and got a TS6628 which many people on this forum have had luck with. With this sending unit, once the car started warming up, the gauge would go almost all the way to H but would fall a little shorter than the first one...and then it would stay there. It would move to H slower than the first one. With the TS6628, when the needle was just short of H I would measure the temp with an electronic laser gauge at the bung the sending unit is screwed in to and it would read right around 160 degrees.

HELP...almost no hair left.

Instrument voltage regulator (IVR) bad. Common problem...HTH

 

Normally I might agree with you but I installed a brand new one as part of the conversion (not to say the new could not be bad) and it is not effecting any of the other gauges...everything but the temp gauge seems to be working fine.

 

Let me tell you a story about my temp gauge readding slightly head. I hadn't had the car long before I realized the temp gauge was running slightly warm, not in the red just above the center line. So I replaced the thermostat, still ran the same. So I replaced the waterpump, and it was bad by all means -the shaft pulled off the impellor when I took the belts off. Then I flushed the radiator still ran slightly hot. Was going to live with it. Till I pulled one of the valve covers off and didn't see any oil on the rockers. Long story short my oil pump was gummed up and not pumping much oil at all. 0 psi at idle using an aftermarket manual gauge under the hood. I replaced the oil pump, and yes checked the rod bearings. And low and behold the temp now reads in the center. Never heard of this one before but just might want to check everything before you say bad gauge.

 

Let me tell you a story about my temp gauge readding slightly head. I hadn't had the car long before I realized the temp gauge was running slightly warm, not in the red just above the center line. So I replaced the thermostat, still ran the same. So I replaced the waterpump, and it was bad by all means -the shaft pulled off the impellor when I took the belts off. Then I flushed the radiator still ran slightly hot. Was going to live with it. Till I pulled one of the valve covers off and didn't see any oil on the rockers. Long story short my oil pump was gummed up and not pumping much oil at all. 0 psi at idle using an aftermarket manual gauge under the hood. I replaced the oil pump, and yes checked the rod bearings. And low and behold the temp now reads in the center. Never heard of this one before but just might want to check everything before you say bad gauge.

Thanks for sharing that interesting (and almost really painful) story. I have had the valve covers off about a month ago and everything was fine...everything well oiled.

 

Phydeauxman.....Easiest way, go to a hobby shop or Harbor Freight and get an IR
thermometer, tells the temp by just pointing it at a surface, I have one to check
temps of my electric airplane motors. Point it at the thermostat housing, water pump
or anywhere on the engine, you should be around 180 or so at temp.
I cut my sender wire, SOLDERED the resistor in the line and put black shrink wrap over the whole affair, cant even see it as the resistor is pretty small. Good luck!