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MG TD TF 1500 - TD Coolant Recovery System

Not trying to re-open the debate as to the need, or lack thereof, for a coolant recovery system, but I never really sure if it worked or not. It was too hard to tell with the metal tank.

In a previous thread, Bud Kruger said, "The workings of this coolant recovery system is akin to a bumblebee. Theoretically, they can't fly - but they do." So here here's some evidence that it does indeed work in an unpressurized system. I'm not even sure anyone really doubted, but what the heck :-)

I recently aquired a plastic transparent coolant recovery bottle (expansion tank) made for the MGB. Same size, shape etc. EXCEPT, I like this one better due to the placement of the input fitting at the bottom, instead of way up near the top like the metal tank, it allows for much more expansion. I installed it last night, and tested it while commuting to our monthly Natter today.

In the LEFT picture below, you can see the level of the coolant, shown by the arrow, BEFORE and AFTER cooldown for a 24 mile run, on a fairly hot summer day (95+F), at 60-65 MPH (freeway), and a few side streets. Highest gauge reading was 95C -97C. On the RIGHT is the coolant level immediately after the run. You can see the coolant has risen about 1 1/4" in the tank.

By comparing the pictures, it is evident that the coolant in the rad did expand into the recovery tank, and after 10 minutes of cooldown, returned to the radiator.

Now if I can just move that input fitting down to the bottom of the metal (Brass) tank, and polish that puppy to a high sheen, wouldn't that look nice under the bonnet (not for the purist, of course :-)

Once again, not debating the necessity of a recovery system in a TD.

Cheers

Larry


Larry Karpman

Larry I have a brass expansion tank from a MGB and although the fitting is near the top, the tube on the inside goes down to within 1/2 inch of the bottom of the tank.

Dallas
D C Congleton

Hm, thought I'd answered, but I don't see it. So, I'll answer again - DUH! Guess I'll get to plouish up my brass one :-)

Larry
Larry Karpman

Larry, it seems to be working fine, as mine does. I would leave the white plastic tank where it is, and you really wish, paint it.

Denis
Denis L Baggi

Larry,

Unless I have misunderstood, it looks as if you have converted your cooling system to a pressurized system, was this intentional? If so what pressure are you using?
Also have you pressure tested the radiator? this last point is important as it was not designed to withstand a pressurized system. I would not be confortable not knownig the pressure the radiator could support.

John
John Scragg

John/Denis: No, the system is not presurized, as the cap is just a plain cap (no spring, etc.) with a hole drilled in the center.

No need to paint it Denis, as I have the brass MGb/midget metal tank that I plan to polish up, clearcoat, and reinstall.

Cheers

Larry
Larry Karpman

Sure Larry. John, having an expansion tank does not imply that the system is pressurized! I have tried to stress that in another thread noticing that many people do not understand that. For instance, my tank from a Ford is in two compartments, when the one that gets the water by expansion is full it spills in the next one which has an outlet at the bottom. So the system initially releases excess water, then in normal condition the tank is empty when cold, receives some water when hot, and as it cools the water returns to the radiator. All at atmospheric pressure.

This system is NOT to pressurize the radiator, block etc., it is just to not have to add, every time you start from cold, the water which was lost when hot. In other words, it keeps the amount of water.

Denis
1950 TD
Denis L Baggi

Why would you have to add water every time it cools down? If you don't do that, the water will stabilise what just enough headspace to allow expansion. IOW, it will be down a little when cold, and completely full when hot. The water which was lost when hot is the amount by which the system was OVERfilled with cold....

HTH!
Rob Edwards

"with cold...." --> "when cold..."

Ooops!
Rob Edwards

As much as I don't want to get back into this again, I'll try another approach. One of the things that led me to install the recovery tank was the realization that my MotoMeter wasn't giving me truthful indications. (I had not yet installed a water temperature gauge.) The bulb end of the MotoMeter must be surrounded by the coolant whose temperature it is purporting to measure. The amount of coolant expelled by the TD's cooling system is such as to bring the level below the bulb of a MotoMeter. That's another reason for using the tank, along with avoiding the mess on the bonnet and fenders.
Bud Krueger

Totally agree with Bob. Now to Rob:

"Why would you have to add water every time it cools down?"

Because, if you fill the radiator, water expands as the engine gets warm and leaves from the pipe at the r.h.s. of the radiator. Then, next time you want to go out, you have to add water.

In my case, instead, I have a plastic pipe at the end of the radiator pipe, so excess water moves up the pipe to the tank instead of getting lost on the street, and then when it cools down returns to the radiator by siphon effect - not by extra pressure! So I don't have to add water.

Denis
1950 TD with an expansion tank
Denis L Baggi

>water expands as the engine gets warm and leaves from the pipe at the r.h.s. of the radiator. Then, next time you want to go out, you have to add water.

In other words, the water expands and when hot and water in excess of what the system will hold will be expelled. When hot, the system will eject the amount of water by which it was overfilled when cold. It will be full when hot. When it cools down, it will appear less than full -- BUT, when it heats up again, it will be full again!

If you fill a plastic bottle all the way to the top, then squeeze it, water will come out, but the water level will still be at the top of the bottle. When you release it, the water level will drop. But when you squeeze it again by the same amount, the water will come back up to the top again, yes? Same idea....

I'm not saying that there aren't good reasons for having a recovery system, but if you're filling the system every time it's cold, then you're overfilling the system every time.

HTH!
Rob Edwards

rob hits it right on the head. that is why motometers design hasn't changed for 80 years. regards, tom
tm peterson

Rob, you are right but by "filling" I only meant to make an example. Let's say you overfill: my expansion talk is built in such a way that excess water spills over to a second compartment, and leaves through a bottom pipe of that compartment, going to the street.

Which means that, even if I overfill, eventually the system will have the correct amount of water, which will remain constant. Not so if you rely only on the pipe at the side of the radiator: then you have to refill every time you want to drive because water has been lost for good.

So your analogy with the bottle is not correct. Correct is, once the system has the right amount of water, no more no less, as it expands it finds its way up the tank, and when it cools it returns to the radiator. So it is simply a temporary storage, like an extra room you put furniture in when you want to move things around, then you put everything back.

I hope that's clear, but I welcome any questions: as you see, this is not theory, I have done it.

Denis
Denis L Baggi

Denis if you get rid of the extra furniture you will not have to keep moving it back and forth. That's all that's happening in the "recovery bottle". The space above the perceived low level when the radiator is correctly filled just above the tubes serves the same purpose for expansion. The motometer tube, and the bulb from the temperature gauge will be wetted and work when the system comes up to temperature and the fluid has expanded.

Having said all that, the advantage of a recovery system when first installed by the factory, was for large block engines that had a lot of residual heat and continued to heat the fluid after the engine was stopped. The cooling fan and circulating water pump also stopped and the water absorbed all the latent heat in the block, and would then boil over. Consequent designs not only included expansion tanks, but temperature controlled fans that come on after the engine is stopped.

If the system is properly filled, and the radiator tubes and block are not scaled the TD will work fine, but having a recovery system doesn't harm anything and gives the owner something else to play with :>)

Dallas
D C Congleton

Hi Denis,
I've done it too. The water that gets pushed out when the engine is at operating temperature is the water that won't fit, correct? So that's water that is in excess of what it takes to fill the system (when hot), yes? So then that's water that is the amount by which it's OVER full.

When the system cools down, yes, there will be some air space in the top tank, but who cares? It doesn't matter -- the engine is off and cold. When the engine is next brought back to operating temp, the system will return to the full state, and no more water will be forced out.

The problem then is not that the system cannot be kept full, but rather what the perception of "full" is.... Rather than fighting to keep the system over full, it's a matter of calibrating the eye to how far down full is.

There will be a need for (infrequent) topping up, but only to replace that coolant lost through evaporation or what little sloshes out the overflow turn whilst cornering, etc.

Hope this helps clarify!
Rob Edwards

Rob: If you are saying that a properly filled radiator as you have described(not a topped off one) will never loose coolant even in the most extreme ambient temperature and driving conditions, then I would concede the lack of benefit of an expansion tank. If not, then they do serve a useful purpose, on occassion, depending on your climate and driving conditions. Oh yes, as Dallas said, playing with putting one in is fun too :-))

Cheers

Larry
Larry Karpman

No, I'm not saying that -- completely. I'm saying that _under normal conditions_ it should be unnecessary to frequently top off the system. If the engine gets hotter than normal, more coolant than normal would be expelled. You'd probably want to replenish that. An there will be "sloshage." But trying to maintain a system over-full is not a valid reason to install the recovery tank IMO. Rather the owner just needs to be comfortable that the system won't be full-to-the-top when the engine is cold.

As I said above, there are some valid reasons. I'd list among these: it'll keep the car cleaner since you don't have the occasion coolant release onto the car, it keeps the expelled coolant out of the environment (that would be the biggest reason as far as I'm concerned), and it would reduce the top-ups from _occasion_ to _almost never_. But that could count in the minus column as well, because if you never need to check it, you could get complacent....

Cheers!
Rob Edwards

Rob, I agree completely, however I guess it's the definition of "normal conditions." I know you are not in exactly the coolest part of the USA yourself, but around these parts it is "normally" blazing hot all summer. A few summers ago we had 40-45 days over 100F. I'd say my normal, might be your abnormal :-))

Cheers

Larry

Larry Karpman

We had something like ten consecutive 100F-plus days this summer, and normal summer temps for us is high 90s. I don't think you're that much warmer than we are. But regardless, when hot, the radiator can only be so full - any more gets expelled. So even when it's very hot, why try to maintain the system more-than-full? :-)

Cheers!
Rob Edwards

Rob: I don't think the point is whether or not one should or should not maintain a system overfull. I think the point is that all TDs, at some point, will expell coolant and need to be topped up. If a TD, with the level of fluid you maintain, gets very hot, or sloshes, etc., it will expell coolant and there will be a need to top up. Plus, as you said, it would be expelling coolant into the environment. With an expnsion tank and the same fluid level as you maintain, there's no need to top up and no fluid is expelled into the environment :-))

Cheers

Larry
Larry Karpman

Bud indicated that a motivation for installing a coolant recovery system was so that the headspace in the radiator would stay filled, allowing him to get more consistent readings from his MotoMeter. The MotoMeter has a short bulb which only contacts the coolant when the headspace is largely filled with coolant.

To maintain a more original appearance and because the cooling system in my TD does not tend to run hot, I solved the MotoMeter problem a different way. A machinist friend made a brass cylinder that, when installed, extends just above the radiator fins. The cylinder is threaded, so that it screws onto the existing threads of the MotoMeter (see attached picture), in other words there was not irreversible modification to the MotoMeter. I also made a thick rubber washer that isolates the brass cylinder from the radiator cap, to minimize heat loss to the cap.

With this modification, the MotoMeter reads the temperature right from the start.

Larry


Larry Shoer

Hi Larry,
I think we're talking a little past each other. My point was not that a system without a recovery tank would never need to be topped up. My point is that _it is not necessary to fill the system after every heating/cooling cycle_. I was fighting the misunderstanding that "functionally full" means "full to the top, all the time." I think we agree that "functionally full" allows for headspace when the system is cold, yes?

Cheers!
Rob Edwards

Rob: Agreed. Of course you don't need to fill it to the top. I didn't think anyone was disputing that - at least not me. I installed the expansion tank to avoid the overboard expulsion, the occassional replenishment, and to have another project. I removed the temporary plastic one and now I have a shiny brass tank in my engine bay :-)

Cheers

Larry
Larry Karpman

My point was that if the radiator contains the "right" amount of water, not filled to the rim, with an expansion tank you hardly have the need to top it. Without it, you always loose water through the narrow pipe that runs at the right of the radiator. Even if you don't overheat. At least that's my experience.

And I would like to repeat again that such a system is not pressurized. If works the way Dallas explained above, it has happened to me that the water starts boiling after I have turned the engine off, and I don't want to keep buying coolant or wetting the garage floor!

Denis
Denis L Baggi

This thread was discussed between 08/09/2007 and 17/09/2007

MG TD TF 1500 index

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