Hi! I just bought an MG TF from 2003 and need some advice

I just found this on YT.  I'm not affiliated in any way but it will give you some insight in to a coolant alarm system.

Coolant Alarm.

There numerous ways to a low coolant warning alarm, this is what I used for a replacement expansion tank, they are better made than the MG one and are fitted with two prongs for sensing the coolant level, some vendors include the plug and a length of wire as this one does.
VW Volkswagen Polo 6R Coolant Reservoir Expansion Tank Fluid Bottle 6Q0121407B Completed
I used the LOW water level version of this HIGH level alarm; High Water Level Silent Alarm With Random Colour Flashing LED 12V Buy It Now
The seller will list one if you ask, because I have lost all of my high frequency hearing a buzzer is of no use to me but they  do make one with a buzzer. Installation is simple, after mounting the tank with a short strip of metal for a bracket, you then connect the two white wire (they need to be extended to reach) to the expansion tank plug, then a source of power (I got mine from the USB charger that replaced the cigarette lighter)  and fit the warning light. I placed the light in one of the switch blanks in front of the gearlever, when the LED flashes in alternating colours you will certainly see it. I got the idea from someone on the MGF Register

TA22GT wrote:

I just found this on YT.  I'm not affiliated in any way but it will give you some insight in to a coolant alarm system.

Coolant Alarm.
 

That is the Browns & Gammon unit, which I have, it is excellent, very easy to fit and  over 10+ yrs has not given me any trouble or false alarms.

I’ve used the VW tank for more years than I care to remember & apart from the blue screw top interfering with the cat flap when topping up, it’s fit & forget.
Fit & forget, that is until someone points out that the blowoff value of the cap is greater than the designed pressure of the original.
I then have a week of worrying until the thought fades again.
As our friend says a simple angled bracket & a little rearranging of the plumbing & it’s fine.
How the alarm is instituted by others is unknown to me as I built my own until I bought a monumentally good Australian unit at a monumentally cheep price off eBay.
The days of carrying a spare cap are now long gone.
M

Bruce Cotsell's low coolant alarms are reccomended. I've fitted 2 of them to TFs. Inexpensive and straightforward

I recently fitted one of Bruce's alarms and I agree with Notanumber.
They are easy to fit, it comes with comprehensive instructions and for the price I should have fitted one years ago.

With our car I should probably get a high water alarm 

Coolant-wise, go for the oat stuff like others said. Maybe grab a spare cap too, they can be finicky sometimes.