How much engine temperature fluctuation?

The other way around.
TF1 is stable(Pan), TF2(TC) is fluctuating based on tc solenoid status
TF2 rises are not affecting the coolant temp and the coolant temp affecting TF2 temp

 

Thanks to those of you who have replied with response that included things such as: literally measured in the same manner with the same result.
I do understand the combustion cycle well as well as how a thermostat works. What I do not like is the swing of the temp. Knowing it is normal from others measured results is very helpful.

I did a mild build on the stock 20R for my first off-road truck. 1979. I had the below (or maybe a model or two older but the direct replacement) gauge. I had a whole suite of nice gauges in that truck... BUT, the first thermostat I had in it was too hot, maybe around 200. It would swing maybe 5-10 degrees. I switched out to a 180 and from then on, no matter what, it ran almost exactly 180. Needle barely moved out of the white line on 180. It was fun to watch the engine heat up and the thermostat open and it stable out to 180 and STAY. I know it had to cycle the thermostat open and closed to maintain this, but it did it so very well. This swing on the 3.5 seems dramatic compare to my one and only comparison. This is the only other engine I have had a quality gauge on that is high quality and accurate.

I know enough to know it is not getting too hot. I also know enough not to like its swing. Again, knowing it is normal vs. just dont worry about it is/was helpful.

Thanks!

 

I was driving when I wrote that...LOL. You are right...TF2 fluctuates and is the one I monitor.

Coolant affects TF2 (as coolant cycles, TF2 goes down).

 

You're weren't hurting anything up around 200 degs. Fuel atomizes a little better and doesn't stick to cylinder walls and the surrounding area. By going colder, all you did was lower the average mpg.

Again, there's a reason the manufacturers average this stuff out by the time it gets to the gauge cluster. They've been doing the same thing with fuel level readings forever. Can't have the fuel gauge bouncing around while driving..

 

I'm glad you brought this up. I just picked up a '16 TRD OR AC. I have never notice it fluctuate like that until this morning, driving to work. I just put the scan gauge in a couple hundred miles ago. This was also the coolest temps I've driven it in, since putting the scan gauge in. It kinda freaked me out, because my '13 only fluctuates between 190-197. I've actually never had a car that I ran a scan gauge in that would drop into the 180's, unless I was going down a steep hill and DFCO kicked in.

 

You were driving when you wrote that?

 

I'm a professional stunt driver who dabbles in writing.