Kinda like medicine, if you see the patient's chest move up and down he's showing some sign that he's alive. But, you have no idea if he's sick.

To calibrate the gauge, you could either use an infared thermometer pointed at the thermostat housing or remove the radiator cap and use a thermometer. Start the engine and let it warm up. (if you can manage to keep it running that long)
Make marks on where the gauge is reading throughout the process. I would go with something like:
"L"= 100deg
"N"=180-190deg
"H"=212deg if it even gets that hot
At the very least you'll have some idea of what's actually happening.

Folks on here are doing their best to share their experience with you. Sometimes you make that very difficult.

My experience? On my last Mini, a '59 FrankienMini with a 1380, I kept seeing the gauge go way up in the red. So, I proceded to "fix" it. Brand new 2 core radiator, added auxillary radiator, added auxillary fan, water wetter... Only to find out that when that gauge/sender combination was reading red, the coolant was actually at 185deg. Exactly where you want it. A huge ammount of time 'n money wasted just because I didn't listen to the advice of confirming the problem.

Check the timing with the vac line removed it should be around 8 degrees BTDC. When you hold the revs steady at around 2500 to 3000 RPM with the vac line connected you should have no more advance than 32 degrees, it should move up but not be erratic.

the only way you can test a temp sending unit is when the temp gauge arm rises as the engine heats up and lowers as you rev up, the motor fan blows air to the radiator which then cools down the coolant... the temp gauge should be responsive.

kinda like the medicine, you would know that the medicine is working if the patient is showing some sign that he is getting better.

mightymice, no i did not remove the vacuum tube,, oh that's probably why its dancing up and down, i shouldve pulled the vacuum tube, ill try your advice tomorrow as soon as i get back from work.  i'm gonna tell my other mini friends too,they have same issues. thanks much...

So, after replacing the sending unit, you say that it no longer shows overheating.... How have you confirmed what temperature the car is running at?
Using the search feature and typing "overheating" would likely give you hours of reading.

Kinda reminds me of flight training when the instructor would tap a few times on a gauge that he didn't like the reading on. I always thought, "Well, if it changes, is that a good thing or a bad thing..."

Answer this one question for me...

When you are checking your timing, are you removing the vacuum tube from the distributor and carb, then capping them off while you perform your timing check?

so i just recieved my new points today, and just installed it... now the car is revving really good, few adjustments here and there. and i replaced the temperature sending unit, now the gauge doesnt show overheating, the arm is steady at 50% and lowers as i rev.

the car is working ok little by little with just few dollars, $10 here, $5 there, not really spending too much for it because it's just my weekend starbux display car.,i have my own daily driver., i save money while others are throwing their dinero away.

i did my own body work, at least the welding part, the money i saved would cover some necessary upgrades, like probably buying a decent electronic distributor kit,high performance coil,high performance wire.  yah know, if i go to classic car exhibit and gatherings and open the front hood, at least there is something there that shines, not just rusts..lol

right now, the white dot is fairly steady ,maybe 70% steady,it moves down as i revv up but it dances a little, that's why i want to switch to electronic dizzy to have a real steady timing.

i took off all four brake pistons,the rear pistons are stuck,all rusted.  the rubber(inside,not the cover) is still intact, the outer rubber are all eaten out by old age. (ooops!)

i really wanna buy the short shifter, cost $240,,,hmmm a little pricey but it will make the car feel virgin,,,,i mean new.

I hate being mean, but someone find this person a clue. I have been reading these posts for a while and have been giggling at how this "person" is not taking any advise, but thinks he can fix a problem that he obviously has no experience with. I say let him spend his money, at least by the time he replaces everything on the car and still cant get it running and decides he gives up, it will be another project car for sale. 

Im with MtyMous on this guy.

Robster.

Instead of putzing around with you Iphone4, go to a REAL computer connected to a printer and search where I explained what 'dwell" is and why it needs to be set accurately. We can't do your homework for you.

Concerning the dancing white spot:

At idle, it should be relatively steady under the strobe of the timing light. With the vacuum advance disconnected and the carb port plugged (as previously explained) you set the initial advance according to the specific engine you have. (You DID confirn that did you?) The white dot sgould be somewhere before TDC anywhere from 6 degrees to 10 or 12 DEPENDING ON THE ENGINE! Do it wrong and you could wreck your engine. If you engine is worn or has an uneven idle, the dot will rattle around a wee bit.

When you "rev up" the engine, the dot is SUPPOSED to move - the mechanical advance (ALSO previously described by me) advances the timing anywhere from the intial setting to 28 degrees or more - it will go beyond the marks. If you are blipping the throttle, the dot will jump about. If you turn the idle screw to advance the timing slowly, pausing to look, you should see the dot move to a new realtively stable setting - you can't hold it steady by hand.

When you set your timing properly as instructed by the manual and the folks here, and discover it really can work well, I'll tell you what I think of the 123. ( Hint: I've already said it.)

Gotta go.

Nite all.

Hahaha. VVS. Love it. It's becoming a pandemic.

Yes. Yes it is. VVS stikes again. https://www.youtube.com/watch?v=Bt9zSfinwFA

took the vid from my iphone 4s. 

o darn, i went to swap meet this morning and saw a timing gun and a dwell meter (analog) the guy wants 10 bucks for both,,,ffff i should've bought it... 

btw what's the dwell for??  what is its significance?

but you are right jeg, that white dot is dancing up and down, especially when i rev it,

when i rev it the white dot goes down to 8 or even higher. 

question: how fast can MM deliver parts if i order them today?  and do they charge one shipping cost for  everything? 

I'm not Dan, so maybe I shouldn't say anything, but that marker should be nearly rock stable and not dancing all over the place.  Looks like yours is dancing from 2° ATDC to 5° BTDC. 

I'll once again advise you to invest in a proper set of (identical) plug leads of the proper type for a small British A-series engine and to take the previously given advice as to setting your dwell angle/contact breaker points gap.

(Regarding the ignition timing figures - Hint: You'll find the specifications for your engine in the articles pages or your trusty Haynes repair manual.)

And, what's with the narrow frame film footage?  Really annoying.

dan, are you happy with your 123 distributor?   thinking of getting one, need advice.   thanks

am i doing it right  ?   should the TDC  be on 0(zero)  

//youtu.be/QeuGVoYLJd8

the points can't be closed all the time or they would burn up, and weld themselves closed. If they're not welded shut, they've been opening, but you can check this by. on a flat level road, driveway,  removing all spark plugs to relieve engine compression, putting the car in 4th gear, with the cap off, and pulling the car forward, or rolling it backwards. You'll see the points open and close as the wiper rides on the dizzy shaft cam.  Check them with a feeler gauge when open, and reset them.

DONT FORGET TO LABEL YOUR WIRES BEFORE YOU REMOVE THEM FROM THE PLUGS.

If you put your location in your profile, someone local may reach out and set you straight.

With minis, it's start with the simple stuff.  Anyway, why would you think you need a dizzy after you banged on the gas pedal?

Get a full tune up kit as others said. Wires, plugs, rotor, condensor, and cap.

Do an oil change if the oil isn't clear. Use the factory specifications and not what you think might work well.

The car was designed over 50 years ago and has given service to hundreds of thousands of folks. There's a wealth of information on this site, aside from daily users who have been through it all before. 

Learn from our experience.  Start simple. Most issues are bad grounds, poor fuel delivery, or a basic ignition foible, all of which might "just happen".

A distributor just doesn't go bad. It degrades slowly.

Good luck.

Possibly a chevy or honda is more of what you need.

Faith somewhat restored.

That plastic part "the heel" needs lubrication usually a little grease will work well unless it has the felt pad attached then let it soak up some motor oil.

Now don't you feel better for not spending $500 on a new dizzy when all it needed was a points adjustment ?

hahaha!!!.... you beat me to it jeg!!!

SO FINALLY! I GOT IT FIXED, someone here said that it might be an easy fix(?) , yes it is!!!

sequence of events:

1) it was starting and running fine when i bought it

2) the problem started when i abruptly hit the throttle and released the clutch, the car jerked, car ran for about 20 feet then hesitate ,and died.

3) then i referred the problem to the board/ a lot were said, dizzy cap? dizzy cable? carb jet(?? double question mark), spark plug? gas cap?(vacuum lock, he meant), then my mini was even demoted to 998cc???, and a small bore 1100cc?? gosh! im so hurt.. etc, etc.  aaaanyway!  ,,,,first of , all your verdicts are very much appreciated.,the mere fact that you replied to my problem is a big honor for me... i thank ya'll

4) ok here comes the solution...

when i accidentally jerked the Mini, the points assembly move away from the center shaft, now i asked you once or twice why the coil is overheating, one guy said that when the points are close, the coil is working,,,now i connect the logic, my coil is overheating??? it means that the points are connected all the time.,, true enough! the points went too far away from the center shaft thats why the points were together then coil heats up badly.

btw, i pulled the dizzy out from the engine thats why i discovered it when i rotate the shaft....

plus, that 59D point(blue) the plastic part that touches the shaft is so poor quality, it wears really quick

now the car is working perfect.

The library:

//www.youtube.com/channel/UCUom1IAMoPuXd_GDMs7fEPg

The event:

//www.youtube.com/watch?v=NcKAO-3uFb4

So, I wonder what the solution was?

I've been waiting to see if this is just a troll. If it is... well played. If it isn't... God help us all.