I just found this post over on another forum, but it may explain why my gauge was reading high, and dropping when I tapped at it while driving down the road. Their gauge shows 3/4 at 180F in the pic they posted (at the link below), which I know is basically nothing on these IDIs.
My F250 runs that at low cruising RPMs on a level highway. It typically runs between 180-192 at highway speeds, sometimes as high as 200F before it drops from the thermostat opening. But that's usually from high RPMs from getting up to speed and merging onto the freeway.
I figured it was worth reposting this here, in case anyone runs across this thread and has a similar issue. Try tapping the gauge with your finger, if it immediately drops, you know it's sticking. Better yet, get a real gauge like I am about to do. I am going to install the mechanical temp gauge to the factory gauge sensor location. The reason being, it's much easier to reach on a van. The dummy light sensor is seriously hiding, while the gauge sensor is right out in the open with nothing blocking it.
Source:
https://www.ford-trucks.com/forums/1134528-cooling-issues-87-e350-motorhome.html#post11353957
My F250 runs that at low cruising RPMs on a level highway. It typically runs between 180-192 at highway speeds, sometimes as high as 200F before it drops from the thermostat opening. But that's usually from high RPMs from getting up to speed and merging onto the freeway.
I figured it was worth reposting this here, in case anyone runs across this thread and has a similar issue. Try tapping the gauge with your finger, if it immediately drops, you know it's sticking. Better yet, get a real gauge like I am about to do. I am going to install the mechanical temp gauge to the factory gauge sensor location. The reason being, it's much easier to reach on a van. The dummy light sensor is seriously hiding, while the gauge sensor is right out in the open with nothing blocking it.
My '87 Diesel motorhome, the dash gauge runs right in the middle on the R-M, and my real gauge reads 180*F cruising....
Never been over 210* under the most extreme conditions, and the dash gauge has pegged out many times.
And these older dashs, there is a solenoid behind the cluster, witch often sticks, causing all the gauges to read high.
Source:
https://www.ford-trucks.com/forums/1134528-cooling-issues-87-e350-motorhome.html#post11353957