Problem: temp gauge jumps up, then goes back to normal

[resq302]

Ok, I was on the way to a car show yesterday and was glancing at my gauges on my 69 Charger when I noticed the temp gauge jump to the right (get hotter) and then slowly return down to where it it should have been.  The other gauuges (oil and fuel) might have done this also but I was looking at the coolant temp mainly.  What would cause this?  Is it a bad voltage reducer on the back of the instrument cluster?  It does not do it all the time and seems to be one of those once in a great while type of deals. 

On another note, I have a 180 degree stat in the engine.  On the highway going to the show in the AM it was nice and cool out, probably 60s or low 70s, low humidity, and it was running 180 all the way.  I got off the exit ramp and it went up to about 190.  Now on the way home it was really hot and humid out and the temp was running about the 12 o'clock position on the coolant gauge which is (estimating half way between the 170-230 range) I would have to say it was probably running at around 200 degrees.  My car is a 383 HP 4 bbl bored 30 over with a mild cam, 4 spd manual trans, 3.55 gears (most of the trip was running at around 3000 RPMs and 65 mph) and the fan is a direct drive fan with a 22" rad and no shroud, exactly as Mopar designed it.  With the high humidity and temps yesterday, is 200 degrees on the open highway too excessive or is that an acceptable temp.  When I got off the highway coming home, it went up to mabye 210 tops but nothing over it.

Just looking for the groups opinion as to what theirs run at or what they should run at.

[Hemidoug]

Thermostat opening??? I know I can spot mine opening on the gauge. Was the engine running when it happens?

[Just 6T9 CHGR]

The gauges "spike" like that sometimes when the regulator on the cluster overheats, opens up (like a circuit breaker) & resets....does that on my car as well.

On Saturday afternoon, temps were around 85º-88º.  Took my car out to the Whiskey Cafe show.   Car hovered around 180º-190º on the highway & off.....never went higher than that.  My new rad works nicely
This reading was on my new Autometer gauge, although the reading on my factory gauge was pretty accurate as well

[resq302]

Doug,

The engine was running when this happened.  Happened on I-80 on the way to a show in Hackettstown, NJ at the M&M/Mars Plant.   I do notice the temp gauge go down when the stat opens so I know the stat is not the problem.

Chris,

Your car will probably always run cooler than mine due to the 26" rad and it also having a factory fan shroud.  It still baffles me as to why Ma Mopar never installed one on the 22" rads with manual trannys.  I guess they figured that the 200 degree range was acceptable.  Correct me if I am wrong but wasn't the factory stat rated at 195 degrees?

[OttawaCharger]

I had this happen on a Dodge van with a 360 once.  The thermostat was sticking and wouldn't open slowly like it it is supposed to.  Instead, it would pop open when the temp made the spring pressure high enough to overcome the static friction of the sticking thermostat.
I fixed it by replacing the thermostat.

[resq302]

I could see that if the temp was fairly cool but this was doing it when the gauge was at the 12 o clock position, it would jump up to about the 1 o clock position and then slowly return to the 12 o clock position.  Just was wondering if it was a normal occurance as I have never seen that happen before.  Maybe I have been lucky up till now.

[Just 6T9 CHGR]

Its the voltage regulator overheating.......

[resq302]

Could that have been caused by the warm day? Worse yet, could something have been shorting out or could it be from old age?

[Just 6T9 CHGR]

Quite possibly both....try a new regulator.  To me its not that big of a deal......inherent to the design if you will

[resq302]

Ok,  I do have an NOS one that I picked up off of ebay a couple years ago so I will try that and see.  It doesn't do it all the time and that was really the first I noticed it so it might have just been the day.

[Rolling_Thunder]

Its the voltage regulator overheating.......