It'* overheating because the thermostat is out. Put the correct t-stat in, continue diagnosis.

If you are just doing a cylinder compression test, you do not need to disconnect the ignition module. All of your spark plugs will be out for the test anyway.

Just pull the injector fuse, or disconnect all the injectors.

I requested the info about the ignition module due to the instructions included with my compression tester. " ...to disable electronic ignition systems disconnect the electronic ignition module or remove the primary battery terminal from the ignition coil". Agreed, the plugs'll all be out anyways.....but I've found that, for me, following any written instructions is usually the right thing to do. Just tryin' to cover my ***-etts.
Thank you for taking the time to reply.

Thank you also to dpieroni3 for the comments and CathedralClub for the help/edit.

FTR I will be installing the correct t-stat in addition to some other parts before I leave for home in the hope that that will forestall immediate future issues with the cooling system. etc. My mom lives 60 miles from Reno and any friend or family help is at least that far away. She'* disabled......and in poor health. I worry-and do what I can. But it'* never enough-I don't trust the car, the maintenance it'* been given is completely inadequate. THAT is why I so appreciate this website, the information available here, and the people (YOU) who are so willing to share their experience and time.

chops to you all: Thank you. !!!!

Curious:

How many miles are on this car?

How many miles per year is this car driven?

How many miles per trip is this car driven?

How many miles before each oil change?

CathedralClub:

odo: just under 125k
the last 2 years less than 1k/yr
maybe 2-3 miles per trip
oil change- last one 1 1/2 yrs ago - I paid neighbor to do it b/c it was in dire need.

Poor car.

So it never gets warmed up. You could do it a huge favor by taking it out on the highway for a half hour every six months or so. Or more often if possible.

. . . would more likely be transmission fluid leaking into the radiator in my experience. These don't blow head gaskets easily.

More questions to assist diagnosis:

Is it limping on a cylinder?

Does the engine oil look like chocolate milkshake after it has been running at least a few minutes?

How is the transmission fluid level, perhaps too full?

Does the transmission fluid smell like sweet sweet antifreeze at all? . . . or just stinky Dexron?

While we're here, does the transmission fluid smell burnt?

If there is a leaking head gasket leak that is allowing oil into the coolant, generally it will also allow coolant into the oil the whole time the car is cooling down after being shut off, because the cooling system stays at 16PSI until temperature loss causes the coolant to contract . . . or until a leak allows coolant out of the system.

If the in-radiator transmission cooler has a leak between the cooler and the coolant in the tank, the coolant pressure will push coolant into the transmission cooler and it will get to the transmission.