MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG TD TF 1500 - Cooling system questions

Cooling System drain, flush and re-fill

I am just about to tackle this task, finally. The PO did a full refurbish of this cooling system every 8-10 years and it still cools well and has no leaks. He always did a radiator re-core, block flush and replaced all hoses, thermostat and water pump). However, the coolant in there is still a (Green/Glycol) OAT (Organic Acid) variant.

I collaborated with a colleague on a detailed examination of companies supplying coolants in Australia about their IAT/OAT/HOAT/ etc., formulations. Bottom line, for me, was that NO pure IATs (Inorganic Acid v's Organic Acid and Hybrid types) were available in Australia and that the Penrite Classic Car Concentrate seemed the safest available for these old iron block motors and the brass and soldered components of the radiator. They recommend 0.7litre of the Concentrate to 5 litres of demin water. Antifreeze is not necessary where we are.

A few questions if I may -

1. The brass drain plug: I can see one on the front RHS of the engine block - that has a broken handle/ lever. I suspect because it was stuck in the block previously and just left there (image attached).

2. Is it necessary to open this up or should I leave it alone? I have a spare brass tap. I tend towards leaving it alone. If it breaks off, I would have to remove it, re-thread or even Helicoil (1/4" BSP). Even though I have a hoist at home - a difficult task with the RHD steering column and exhaust pipe in the way!

Can I adequately flush the block without removing this tap? I know from when I replaced some core/welch plugs last year that the block was very clean inside from its last flush 5 years ago by the PO.

I hope I have this all correct!?

Thanks

Merv



M Hyde

Hey Merv,

No need to pay fancy prices for a new ½" drain cock. I bought mine 4 years ago from AliExpress for paltry $12. Link at the bottom. As for a coolant, there's nothing that can beat Redline 'Water Wetter' - Google it. Super for hot climes like OZ. But I can't run it for the Winter (-35ºC) and have to change it out for 50% Prestone.

Gord Clark
Rockburn, Qué.

https://www.aliexpress.com/item/1005001603316568.html?spm=a2g0o.productlist.main.55.26c51fedPVh68B&algo_pvid=5324d3a7-62e2-40db-a659-2f03edc86ec1
Gord Clark

Gord: That is a nice fine but be aware that the original tap is supposed to be 1/8 BSP. So make sure that is the option you select.
Christopher Couper

Since the tap is made of brass, it should come out in one piece with a bit of persuasion. If you're truly worried about it, I think you should be able to do a good flush with it in place.
Steve Simmons

Hi Merv.
Living also in hot climate in France, I use water wetter wich is good for electrocorrosion and a bit more favourable than antifreeze.

I remember that if you only flush by the radiator plug a certain quantity of liquid remains in the block. It's really better to take out the tap.

Laurent.
LC Laurent31

Many thanks for the replies. This forum is most helpful. Thanks Gord. My spare tap is a clean original that works (tested it). If I can remove the existing one (1/4" BS P or 1/8" as Chris notes?) and if there is no blockage behind it I will replace it this morning.

Noting Steve's caution I will not be worried about doing a flush with it in place however.

I did a test of the coolant yesterday and had an approximate reading of 270mv- 0.3 volts between the coolant and an earth, so is still ok as far as acidity test goes.

Thanks also Laurent - point noted and also your the water wetter use. I am planning on the Penrite Classic Car Coolant Concentrate - which is a corrosion inhibitor. Antifreeze is not an issue here also!

Merv
M Hyde

I agree taking it out is best, just saying if the block is basically clean already and it's just a maintenance flush then it's no big deal.

I've A/B tested Water Wetter in a TC and found it made about a 2-3C difference over plain water. Not dramatic but it did do something.
Steve Simmons

My block was clean inside the motor passages and the radiator core was also replaced about 4 years ago by the very diligent PO. It now is well flushed and filled with a very iron, brass and solder compatible coolant. I made sure that the heater also was involved.

It was a slow process and took some hours with several flushes and rinsing.

As Steve agrees, the best news was that the old damaged drain tap on the front of the block came off easily and my new spare tap fitted perfectly with no leaks. I was dreading removing the bottom radiator hose as it is so hard to get at on the RHD TF. Interesting about the Water Wetter. Looks interesting but I can see that there is some debate amongst the vintage car community about its possible reactivity with certain metals?

Thanks to everyone for their helpful advice.

Merv
M Hyde

Chris,

All I can tell you is that mine fits like a glove ... and that ws 4 years ago; and continues to work well.

Gord Clark
Rockburn, Que.
Gord Clark

A helpful summary of the challenges and possible solutions for our old cars.

Merv
M Hyde

Hello all.
I'm surprised about the voltage test done by Merv.
In my opinion, if you measure the voltage between coolant and ground you actually measure the voltage between the electrode of your voltmeter and the ground. What you get is the galvanic cell voltage due to metal difference. It highly depends on the metal of the voltmeter touch points. Nothing to do with coolant as soon as it contains ions.
A good measurement is PH. If PH is greater than 8 the coolant can be considered alkaline enough to not corrode metals. If it becomes 7 then it will soon turn acid and corrode metals. To be flushed.
Laurent.
LC Laurent31

Thanks Laurent. The volt meter check is commonly used here and elsewhere as a check.. https://www.hemmings.com/stories/cold-and-shocking-have-you-checked-the-voltage-of-your-coolant/

I agree that ph strips, if you have them, would be a more accurate check of the acidity level of a coolant.
M Hyde

Remove the block tap and replace it. I have bought the Moss replacements and removed the plug they put in the back of them and not had them leak either a little manipulation. The replacements for the radiator are not like the originals. The spigot directs flow downward rather than straight and do not accept the original outflow tube. So long as you have replaced your coolant say every two years your system should be fine with a simple flush kit. Repeat the process several times until rusty water is no longer present in the drainage.

Note that there are two passageways that are commonly overlooked. One on each end under the manifolds behind the core plugs. They are drilled holes that connect the inner and outer block cores and easily become blocked with crud over time. They can be drilled clean and opened up a bit to improve flow. These holes allow proper flow through the inner and outer cores and do reduce helo to reduce temps overall. They can be serviced in situ and new brass plugs reinstalled once you have thoroughly cleaned the mating surfaces with a wire wheel. Red Loctite on the casting and plug edges on installation to insure that the seal and stay out.
W A Chasser

Thanks Bill. The cooling system on this car has been well cared for. The PO had the original radiator cleaned and re-cored EVERY 10 years and the block and head pressure washed and flushed. The block was great (used my boroscope) when I replaced the Welch/Core plugs a year ago. It never over heats.

I thought about replacing the block drain tap with short bolt fitting when I fitted the new tap (which I had already as a well functioning, NOS spare). Next time a block plug will go in.

Merv
M Hyde

This thread was discussed between 12/06/2026 and 28/06/2026

MG TD TF 1500 index

This thread is from the archive. The Live MG TD TF 1500 BBS is active now.