I've got a dumb question: My 90 xj has a 195 degree thermostat, but it never gets anywhere near 210. I rebuilt the cooling system 2 years ago. When I bought it, the temp gauge stayed pegged, lol. During the Christmas cold spell, I put cardboard in front of the radiator and it still didn't get above 195. I know there are a wealth of xj owners who wish they had my problem, I just think if it would get to 210 I might get more from the heater. Do they make a 200 degree thermostat?

Sounds to me like you have a different issue, and if a 200 degree thermostat is available, it won't fix what is actually your issue and could cause a bigger issue of overheating.

I would suspect you have a thermostat that is stuck open. You also can't 100% rely on any gauge, so even though you are seeing a dash gauge show under temp, doesn't mean the engine is actually below full operating temp. You'll want to use a IR temp gun on the thermostat housing and see what it shows after the engine is good and warm.

Also, since you're saying you want to get more from the heater have you looked into a restricted heater core? Are both hoses connected to the heater core the same temp? If not, then you have a restriction in the heater core.

I'll check the heater hoses. The thermostat is fine, besides, I'm used to it by now. Thanks

Just because a thermostat is new doesn't mean it's any good. Parts can fail right out of the box. Even thermostats where you have a sliding part and sometimes it can get hung-up on the shaft and not close all the way, or just get stuck. You may consider removing it and putting in a pan of water and bring to a boil. That would be one way to test it. But it doesn't factor in rushing fluid though. Good Y/T videos how to do it. (or try another one)

Like advised above, put an IR temp gun on the thermostat housing and see what the temp is. It could also be the temp sensor too (if the engine is operating at the right temp but gauge not reading right.

If you have a 195 in it, it should be close to 195 degrees.
Does your Jeep have a working heater valve? Or has it been removed?
Have you tried back-flushing the heater core? That might be worthwhile to perform. I did my 95 Grand Cherokee year ago and I got a rush off terrible crud out of the heater core. Better heat instantly. Just youtube how to do it.

X2 on checking with an IR gun. The temp sensor for a 1990 is in the back top corner of the head under the fuel rail.

what is the approximate ambient air temp ?

My XJ runs cool 180-190F, but will run up to 210 after idling for a few minutes at standstill, if the ambient air temp is say 75F

It rarely gets below 50F around here, but at that temp, it will not get to 210

I use ONLY MOPAR thermostats. Yes, they're pricey. Worth it.

Only thing I ever bought from the dealer.

Here's my story.

I bought 3 Stant SuperStats in 195* for 3 of my Jeeps.
Installed all 3. The Jeeps took forever to warm up, but would eventually get to 195*.
But, when the stats opened, the temp dipped to 180*
I swapped them all out with MOPAR.
At 22*F outside, I can start and drive any of these vehicles down the road and have heat from the vents in under 5 minutes.
On hot days, the needle stays at 195ish and only moves a needle's width up and then the fan kicks on.

I always boil new thermostats with a thermometer in the water to make sure they work correctly out of the box.

While I don't believe my dash gauge is very accurate, My '88 runs around 200ish (looking straight down on it) on all but the hottest days while moving even at slow speeds. Just remember you get a bit of parallax error reading the temp gauge from your normal driving position. From here mine appears to be about 195ish. I run a STANT.

Make sure that dang heater valve is working, or better yet, bypass and chuck it (assuming you still have it). Check the hose temps on either side if you do. Also make sure your blend door is fully opening.

Once up to operating temp, full heat out the dash vents, 45F outside, still cold inside, my "instant" read thermometer stuck in the center vent reads about 120F. Once the cabin warms up it will peak around 140F.

Thanks all, I will get a Napa thermostat when I decide to change it. Yes, I boil my thermostats and this one is good at 195. I'll just bundle up when driving until the weather warms.

Napa is where I got my Stant SuperStats FWIW

Napa is where I got the cheapest thermostat they sell and has been fine for over 10 years now.
LOL.
This is before I joined the forums and read all the bad out of the box threads about thermostats.
MLOL.

Yep. 10 years. replacement parts quality has nose dived.