Overheating problem, any advice??

[71 RT]

I really don't know if this is a motor problem, or an electrical issue.  Any advice or help is much appreciated. 
The temp gauge on my rally dash show that my 440 is running hot.  When I drive 30-40 MPH it heats up SLOWLY to the top of the normal range, and then just keeps going very slowly to the "H".  It never goes past the H, just right up to it.  I assume it is running hot, but thought it might be the temp gauge is going bad.  Occasionally, after it warms up to near the "H", it will spike up, past the H.  This "Spike happens in about 1 second, and then comes back down to the H slowly (in about 3-4 seconds).  Here is my question.  Can the temperature really spike that fast, or is that a sign that the gauge is not working properly?  Is it possible that really hot water is suddenly hitting the temperature sending unit, causing it to spike like that?  I always thought these gauges were slow to changes.  All other gauges appear to be working properly.  I have replaced the sending unit.  I want to find out if it really is that hot.  I have a 22 inch radiator that was rebuilt, and have a shroud.  I also have a clutch style fan.  It is not spitting water on the floor when I stop the car.  I obviously do not want to hurt the motor or heads.  If I want to hook up an aftermarket temp gauge, what is the easiest way to do it, without hurting the water pump, radiator, etc?  I just want to confirm that it really is running as hot as it appears. 
I have even thought that maybe I could get a voltage meter reading on the back if the temp gauge, but have no idea how much it is supposed to read.  Could it be a radiator hose collapsing?  Is there supposed to be a spring inside the lower radiator hose to keep it from doing this?  Any thoughts or advice is appreciated.

[Charger-Bodie]

have someone check it with a lazer temp gun. just point it right at were the sending unit screws in and find out what its really running for temp.

[Rolling_Thunder]

check the temp at the thermostat housing with a laser temp and clarify what the actual temp is...      if it really is hot then you got an issue --- if it is not hot - you have a GM style replacement temp sender....    which makes the gauge rear high...    get a sender from your local dodge dealership or put a 15 ohm resistor inline with your sender's wire...    this will drop the reading on the gauge to read almost exactly 1/2 up the operating temp scale at 180*

If you are indeed running hot, check engine timing, and if you are running lean...   

If the car is not puking fluid then it doesnt seem to be running hot...     I bet you have the wrong sender....

Spiking issue...    check for a cut in your wire...    spiking is a grounding issue...    if all your gauges spike then it is the voltage regulator on the back side of your dash.

Good luck   

[71 RT]

Thanks Rolling Thunder.  You have been very helpful.  I got an after market temp gauge yesterday, and took the rad cap off the motor.  I started it cold, to see if the thermostat appeared to be working.  I let it idle.  There was no movement in the radiator and the water was cool.  The gauge was over the 1/2 way point, and still nothing.  When it neared the top of the normal scale, the thermostat opened, and the water measured 160.  As it neared the H for hot, it was still only 180.  I know this is not exactly the same temp as the front of the water pump, but just sitting there idling, it has to be close.  I have come to the conclusion that the temp gauge shows it to be hotter than it actually is.  What temp range should the "normal" range be, and what is the HOT temperature?  Any help is appreciated.  Thanks for your help!

[Rolling_Thunder]

normal on operating temp range should be between 170 and 230 (see stock gauge)

I usually just add a 15 ohm resistor in the wire going to the sender...    this drops the reading on the gauge to where it should be...    (160 is exactly half scale on the gauge)

otherwise go to a dealership and get the correct sender...     sorry - not sure on the ohms reading on the correct sender

[71 RT]

Once again, I have to say how great this site is!  I have had an overheating problem, for many months.  I posted a question, and Rolling_Thunder and others posted solutions.  Rolling_Thunder said that the new temperature sending unit I had bought from a parts house might actually be for a GM unit, which appear to send a higher signal to the gauge.  He suggested I get a MOPAR part, and to measure to see if the car is actually as hot as the gauge said it was.  He was EXACTLY right.  The car never got very hot, but the gage said it was.  I called a mopar dealer, who gave me the original part number.  He searched and said that a dealership in a town 25 miles away showed to have an original temperature sending unit.  I called the small dealership and asked to confirm it was really there, AND IT WAS.  I asked him if he could hold it for me, he said "I DON'T KNOW ABOUT THAT, IT HAS ONLY BEEN ON THE SHELF SINCE 1984 WHEN SOMEONE SPECIAL ORDERED IT AND NEVER PICKED IT UP."  I got the part, and Rolling_Thunder was right on the nose!  The gauge never got over the halfway point when idling in the driveway.  I took it for a drive, and it stayed in the normal range.  I appreciate the help, and I take my hat off to Rolling_Thunder!  I owe you one.  Who knew that the new Temperature sending units can act differently than the mopar ones??
I love this site!
71 RT

[Rolling_Thunder]

Hey man - glad to see you got your issue sorted out