Okay, I'm stumped. I have an 82 F100 (300) w/AC. This is my "first" spring/summer with this truck and it seems to be running hotter than normal. Drove the truck to Florida (from GA) this weekend and the temp. needle fluctuated the whole way (AC on). Sometimes it would go between the "A" and "L" of the normal band and the back to the "M". Yesterday I installed a new (not rebuilt) water pump, new thermostat (180), new flex fan, new temp sending unit, new radiator cap, and coolant. I installed a new radiator about 3,000 miles ago. Drove the truck today on the highway (80 mph +) with AC on and temp. needle stayed between "R" and "M". However, after driving on side roads (diff. speeds) and idleing, the temp. needle would rise to the "A" and back to the "R" or "M". This truck does not have a fan clutch and the only other thing that I did was add a trans. cooler between the fan and radiator. There is about 1 (maybe a little more)inch of space between the two. My questions are: 1. What is a "normal" temp. reading for this engine and is it okay to drive at highway speeds with the needle on high end of the normal band? 2. Have I missed something that could be wrong with the cooling sytem? 3. I have read several articles regarding an air damn inside the fan shroud. Could this be happening since I installed the trans. cooler? Any suggestions will be much appreciated!

 

jessbass:

How's the condition of your radiator upper and lower hoses?

When your temp guage was floating were the other guages doing the same thing?

Through the years i have noticed that all my guages will float slowly to the top-end then after a second or two they will slowly drift back to their normal positions. Since i know that everything under the hood is OK i just ignore this when it happens.

Summer highway driving my temp guage will read between "O" and "R" on the word NORMAL...sometimes on 90 degree days it will go up to the "M".

Winter highway driving readings are on the "N" barely reaching the "O".

1981 F-150 2WD STYLESIDE P/U
4.9L 1 BBL CARB
C6 AUTO
2.73:1 LIMITED SLIP REAR AXLE
STABILIZER BARS FRONT & REAR
6100 LB GVWR PACKAGE
ORIGINAL OWNER
195,000 PLUS MILES
100% STOCK & UNREBUILT
BUILT FORD TOUGH!!!

 

All hose are new (less than 1,000 miles). Driving back to GA on Sunday I noticed that all guages were acting up especially the fuel and temp gauge. Everything was fine with the radiator. I suspect it may be the voltage regulator behind the instrument cluster. Will proceed to replace this as my next step.

 

Another thing that can cause this anomoly is buildup or crud breaking continuity at the sender itself remove the wire at the sender and lightly wire brush the threaded contact and do what you can to similarly clean up the wire inside the slip on boot.