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MG TD TF 1500 - Accurately Draining and Refilling Coolant

Len Fanelli convinced me that I need to totally purge and refill my coolant to avoid vapor lock issues. After a bunch of years of doing such things I would think that I'd have it down to a science. But, now I'm not so sure about installing the 14.4 U.S. pints called for in the Workshop Manual, Page 7. Nor, draining all of them out of the car. (Forget about the heater.) Does anyone have a cut and dry technique for doing this?
Is it best to mix your anti-freeze and distilled water together before installing them into the radiator?
How do you know if your thermostat is allowing the fluids to go where and when they should go?
Anxious to hear what you folks are doing? Bud
Bud Krueger

Bud, you're the expert -- not me! Here's how I do it:

I open both drain taps - radiator and block. If you are changing hoses, then remove the hoses too.

The drain tap on the block is supposedly at the lowest point, so it is probably the best way to empty the block.

Poke a wire into the open drain tap on the block to clear muck that may be blocking it. May have to do it a few times. A blast from an air hose will also clear it sometimes. Run water from a hose to flush the block and radiator.

Thermostat isn't hard to remove if you think that it may be blocking the new water-antifreeze. (You will probably need to replace the new upper hose if you do so.) Otherwise, run the engine to operating temperature and squeeze the upper hose to purge trapped air. Difficult, because the hose isn't very flexible.

I pour the required amount of straight antifreeze into the radiator. Then add distilled water to the proper level. Add more water after running the engine if needed.

I do this because there will probably be trapped water in the block after you flush it. Pre-mixed water/antifreeze will be diluted by the trapped water.

Example: unknown amount of trapped water + 7.2 U.S. pints of straight antifreeze + distilled water to proper level = 14.4 U.S. pints of 50/50 antifreeze.

Lonnie
TF681
TF7211
LM Cook


+Bud,
After I installed the water catch tank system under the bonnet I don't worry about how much antifreeze I fill, as I fill it to the very top of the rad and mount the rad cap to seal it there. I do as Lonnie says about draining the coolant first, so that is spot on.
Now as water evaporated or, God forbid, boils out through the tank overflow. I just top up the coolant catch tank with 50/50 and after any air is expelled on the next startup, it is sucked back into the rad to maintain the lever at Full. So far absolutely no issues. I now trust the temp gauge, as I know the bulb is totally submerged.
For what it's worth.
Rod





Rod Jones

Hi Lonnie,Thanks for your responses. Must admit that the one about poking the wire into the spigot on the block is significant. At least an additional quart showed up after the poke. I think I'm at my fifth fill, run, drain. Another one set for tomorrow morning. Haven't seen the temperature gauge over 80°C since the initial flush with the cleaner. Bud
Bud Krueger

I'm not sure what engine coolant has to do with vapor lock. If the engine isn't running hot then the coolant is doing its job and I see no reason to mess with it. The exhaust temperature has an effect on vapor lock since the manifold is directly under the carbs, so maybe look at that instead. If you suspect engine temperature is encouraging vapor lock then maybe try running a cooler thermostat and see if things improve.

If the engine is running hot then sure maybe improving the efficiency of the coolant will help a little. But unless something is really wacky, there are other things that will make far more of a difference, like mixture and timing, and of course blockage (especially radiator tubes).

I've found that in an open cooling system, air pockets work their way out pretty quickly on their own. I just top it up after the first couple runs. I don't bother to pre-mix since it will mix on its own as the fluids circulate. Recovery bottles are fine too, but they don't really increase cooling, they just keep the level in the radiator higher. In a sealed system they can make more of a difference because as I understand it they help prevent air from being pulled into the system during cool-down.

In the TD cooling system, the actual level doesn't really matter so long as it's filled as high as it wants to be, so just fill it near the top and let it spit out whatever it doesn't need. The first time you shut the car down, it will purge any excess on its own and the level should stay there indefinitely, other than very slow evaporation of water through the overflow tube. There should be no significant loss from boiling because the water in the radiator should never get that hot. If memory serves, my cylinder head temps don't typically get much over 200F and my coolant boiling temp is around 220F (70/30 mix). I rarely have to top up my radiator, maybe once per year of normal driving.
Steve Simmons

Rod, I've had an overflow-recovery tank since 2004. I use an MGB tank with a 4# cap that I can close if I want a higher boiling point. http://www.ttalk.info/Tech/Overflow_tank.htm. The problem is that if the car is running that hot the fuel system is not happy. I had been running 50/50 (Prestone/H2O) for years. I'm switching to 25/75 for the sake of cooling efficiency.
Being in Georgia vs. Massachusetts I'm not as concerned about freezing temperatures. Steve, I'm with you in terms of virtually never having to top up the radiator. The recovery tank handles that quite well. Lonnie caught me on the clogged spigot on the block drain.
I'll be filling it back up today with 2 quarts of straight Prestone + distilled H2O. Bud
Bud Krueger

With or without a recovery tank, the radiator should rarely need filling. It will of course need it less with a pressure cap in place.

The stock cooling system is not sealed or pressurized, but doesn't seem to lose coolant very fast. But it will of course lose less with a pressure cap fitted. I have a brass overflow tank on my MGB and I can't remember the last time I found the coolant to be even slightly low. It's isn't a necessity, but still a nice accessory on a daily driver.
Steve Simmons

Steve, my first long run in 2004 makes me differ with you about the stock TD need for refills. When I got to Walpole, NH from Plymouth, MA I was embarrassed by the coolant mess on my left fender. That was the result of coolant being forced out of the overflow pipe, into the air stream. Is that top pint, or so, necessary? As yourself, it's exceptionally rare for me to have to top up the radiator. I never close the pressure cap. My Butch Taras water pump can handle it if I do so.
My pain right now is from carboning up the new 4085 plugs from an hour of idling to flush the system. Yecchh! Bud
Bud Krueger

Steve, are you sure the vapor lock issue they are referring to is not in the coolant system vs the fuel system as you seem to infer? Having said that, a poorly functioning cooling system will result in higher under bonnet temps which would contribute to fuel vapor lock as well.

Regards, Tom
tm peterson

If the radiator is filled to the top, it will definitely spill some out while you drive. Then when you shut the engine down, it will spill a bunch more out the overflow. After that it shouldn't lose any except to very slow evaporation. That's my experience anyway.

The term vapor lock is generally used to describe fuel boiling before (or when) it reaches the jet. The cause is of course heat. The hotter the fuel is before it gets to the jet, the more easily it will boil once it gets there. It can occur in fuel lines, pumps, etc as well. In our cars it usually happens at the bridge between the fuel bowl and carb body, right over the hot exhaust manifold. If the cooling system isn't working well and that makes the engine run hotter, then it will definitely contribute to vapor lock. Engine bay temps as well as exhaust temps will rise, making the problem worse. If it starts to make the mixture go lean then the engine will run even hotter, which again makes the issue worse. Ethanol hasn't helped the issue at all
Steve Simmons

Okay, I solved one part, see Image 1. After draining, purging and refilling the system I drained it all out to check the thermostat. The pan that I drain into has a capacity of seven quarts. The radiator produced just about that. I poured that into a gallon jug with the rest into a half-gallon milk bottle. Then I drained the block, including the Arnolt heater, through the spigot. This gave me enough in the drain pan to top up the milk bottle plus a quart measuring cup plus a pint measuring cup. Image 1 above shows the filled containers.:
4 U.S. Quarts in gallon bottle
2 U.S. Quarts in 1/2 gallon Milk bottle
1 U.S. Quart in quart measuring cup
.5 U.S. Quart in pint measuring cup.
Total=7.5 U.S. Quarts (includes heater)

Workshop Manual says 7.4 U.S. Quarts (w/o heater).

Now I know. Bud




Bud Krueger

This thread was discussed between 09/10/2023 and 15/10/2023

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