I have a ’69 Mustang with a 302. I've had this car for about 5 years and had the engine rebuilt about 3 years ago. The rebuild included a new radiator, water pump,and electric fan (in addition to the engine driven fan). </P>


There is one problem that I've always had with it. When the engine is fully warmed up and I'm sitting in traffic the temp gauge will sometimes climball the way up to the line just before the H on the gauge, hold there for about 10-20 seconds, and then go back down to normal. (It normally holds steady just over the left leg of the "M" in the word "TEMP" on the gauge) The movement of the needle from normal to high, and vice-versa, occurs in the space of about 3-4 seconds.</P>


I've replaced the thermostat several times, and the sending unit once; both to no avail. I don't think the engine is actually overheating as I tend to think that the quick movement of the needle would indicate otherwise; in addition the engine runs fine. There is no burned oil, or other signs of overheating.</P>


Does anyone know what may be going on here? Are temperature gauges prone to erratic behavior like this?</P><edited><editID>automan25</editID><editDate>37911.8771180556</editDate></edited>

 

If you replaced everything else, all I can think of is the gauge itself... or air pockets in your cooling system

 

I would replace the gauge..also have you run the heater to see if it cools down on the gauge..also look at your rad cap

 

This may be a dumb question is the electric fan installed correctly? So are made to push air and others pull the air thru the radiator. If the fan is ok then I would hook up a secondary temp gauge that is known to read correctly and compare the readings. This will determain if gauge is ok. Check radiator cap as stated above. I also noticed this only happens while sitting in traffic which sounds like a air flow concern. I would also check and make sure the stock fan is not on backwards. This will cause a real air flow problem. If problem is still there i would flush cooling system it maybe restricted some where.