213 Green Diamond run temp

What temp does your 213 run at?
I have a 36 C-1 non-pressurized system running 50/50 mix coolant . I was missing the radiator so I bought a good used one, ( after I spent an hour cleaning the mouse nest out of it). Anyway it comes up to about 180* on the temp gauge pretty quick while driving. Then slowly goes up to about 200*. Is this normal? What temp should it run all the time at?

So today I drained the coolant and flushed with water for quite a while. I pulled the thermostat and cleaned up the gunk off of it. I had the drain plug out and circulated water through with it running and off until it ran clear out the block drain plug. I also used air to blow in the hole to help get gunk out. I just left water in it and tested it on the biggest hill around. It got a little above 200* maybe 210*. Is this too hot for this motor?

Have you verified the gauges are working accurately? You need to buy one of those laser temperature guns. I have seen them for as little as $15.
80 year old gauges may not be reliable. Buy a new thermostat. The ten bucks a thermostat costs is inexpensive insurance. If an old t'stat jams, the engine could overheat. The gauges may not be able to indicate the heat.
I do not know for sure, but, 180f - 195f does not seem unreasonable, to me.

A modern thermostat didn't seem to fit in the housing too well. I couldn't get it to not leak.This was with a t-stat gasket for a Small Block Chevy. I had one of them sitting around.I got the SBC gasket to seal with the old t-stat though.
My laser temp gun seems to run 10* cooler than the temp gauge. I'm going to borrow a buddy's temp gun and get a second opinion.

I don't have the exact answer for you as of yet. I just finished my rebuild and initial run-up. I haven't had it under load yet either. I'm sure you have noted that because our systems are not sealed. We can't raise the boiling point as done in a pressurized system. Most of these were run on straight water and as we all know (depending on altitude) water boils at 212 degrees. So at 200 degrees (if that is what you are truly reaching), you don't have much leeway. Using a 50/50 mix will take you to around 223 degrees (depending on the manufactures claim) and provides you a little more safety margin for boil over. I highly doubt you would be outside the original engineering design of the motor if it operates with a 50/50 mix under load and reaches a maximum of 200 degrees. Remember, we are only pushing something like 80 horse power and we weren't designed to get anywhere fast. Let us know how things check out.

Well not really sure which temp is right. I got the truck temp gauge to 200*. My temp gun said 182*, and my buddys temp gun said 190*. Both pointed directly at the same place on the tee where the temp sender is. So I figure at 200* on the gauge I am still fine. Not really a definitive answer but the one I am going with.

Your experience is why I don't trust non-contact thermometers. Drop a meat thermometer into the top of the radiator and get a true reading.

Laser temperature guns are most accurate at 90* to the surface. Flaking paint acts like insulation. The temperature reading can be different a quarter inch away from the last sample.
I have a Raetech. I have verified it with a proper lab contact gauge. Many multimeters come with a temp probe. Options for you.

So an update for you guys.
i have been running water in it since early August when I first posted. It has been getting to 200* on the gauge. I decided to put coolant back in it. FYI the gasket for a Small Block Chevy thermostat works on a Green Diamond. I flushed it again for an hour and a half. Running water in the radiator, out the drain hole in the block, out the radiator drain, out the top of the engine through the thermostat, with it running, with it off, blowing air back in the drain hole when it would plug off with gunk, you name it, I ran water in it. I then tried to seal the t-stat housing and had a leak. I didn't put silicone on the threads of the bolt that goes through the head. Then I proceeded to break the t-stat housing by over tightening it. Luckily I had a spare housing on a parts truck, which is a little different but close enough. I also dumped an extra gallon and a half of coolant on the floor, by filling it, fix leaks, refill etc. I never can catch all the coolant. I just siliconed everything and called it a night. The next day with coolant in it I drove it and it was staying at 185* on the gauge. So I am just going to keep driving it as is.

I don't remember the exact ratio, but I have read that a 1/16" of rust/scale is equal to more than an inch of solid cast iron in terms of heat transfer.
It is why heavy/ expensive engines use a coolant filter.
Any engine needs a clean cooling system. Pull core plugs and use air and water to displace the scale/rust/muck that has accumulated over the decades.