getting hot. help?

I have a bone stock 48 cj2a with 180 thermostat and when first started it gets hot and maxes out the gauge, then immediately temp plummets to 180 and stays there without getting hot until next time it's started cold. And this all happens again.

I'm assuming everything is basically fine just thermostat is taking its time opening. Maybe I just need to remove new thermostat and drill small holes in it for coolant to get to both sides of thermostat to open it quicker. Is there something else you guys think?

New thermostat 3 months ago and new riser piece for it. But I don't remember if I drilled hole in thermostat or not.

 

Installed backwards?

 

Nickmil may have it.

if not... My old Willys truck couldn't tolerate any thermostat higher than the spec 165ºF. When I went to a higher temp unit, in cold weather the engine block would boil before the thermostat opened - maybe because it is housed up in the cold air behind the fan. Possibly a hole or two would circulate the heat better...

Your symptoms also remind me of a cooling system that may need to be burped. But I doubt that would persist over very many cycles.

 

I pulled the thermostat and there were no holes drilled in the thermostat so I drilled two 1/8 holes. It was installed correctly. Test drove and it seemed to fix my problem. But now it takes longer to reach operating temperature so soon or next time I will use same 180 degree but drill only 1 hole. But problems fixed

 

Based on my experience with F-Heads, my 55 CJ5 would show a very quick warm up on the gauge and continue rising to about 10 to 15 degrees above thermostat before it would drop to thermostat temp. This only happened on initial start ups after the engine had cooled.
I first suspected the t-stat but changing it not not help, no matter what temp t-stat I put in it would rise 10 to 15 degrees above rating before coming down to proper temp.
Upon replacing the water pump and bypass hose I noticed that there was considerable corrosion/crud build up inside the steel bypass hose fitting, resulting in a nearly plugged condition. I removed the fitting from the block and cleaned it out with an appropriate size drill bit, after that the warm up was slower on the gauge but gauge stops dead on at the rated t-stat temp.
You may have a plugged water pump bypass hose/fitting, drilling a hole in the t-stat would increase bypass so you may have a plugged fitting as I did.
As I understand it enough bypass volume/velocity is needed to prevent nucleate boiling witch can create hot spots during engine warm up and give a high temp on the gauge if the head and block has little or no coolant circulation during warm up...the block is getting hot but the coolant is not moving so the t-stat does not get hot enough to open until the block is nearly overheated...

 

When I installed my thermostat in the 51 3a, I drilled at least two, maybe three 1/8" holes in the flange......if one is good, more is better, right?...well, next time it'll have one hole...slow warm-up as you mentioned....