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MG TD TF 1500 - TD operating temp.

What is the normal operating temp for a TD?
I am running around 85C and a little above.
Would the cooling efficiency be improved if
I removed the thermostat? I don't plan on
running in the winter.
gary dewitt

Gary
Removing the thermostat can cause it to run hotter. Check that the thermostat is opening but don't leave it out.
John Green

I have both water and oil gauges on my 1950 TD. When running normal, flatland, no particular stress, I have 70-75C on both gauges (notice that Southern Switzerland is a hot place). I think this should be the normal range. Only in exceptional conditions - alle the way up-hill at over 4,000 rpm - did I occasionally went over 100C for the oil and around 90C for the water. I never boils though no matter what I do.

I make sure the radiator is clean, has anti-freeze, water flows through the bock and the head. I assure you that, if you have problems, removing the head and cleaning whatever needs to fixes any problem.

Denis
Denis L. Baggi

You must have a 180 degree thermostat installed. 85 C = 185 F. Sounds like it is just where it ought to be.

With as 160 degree you might run at about 75 C

It always seems to run a little hatter than the thermostat setting, or it could be the error on the temp gauge of about +/- 5% (its hard to read it precisely)


My TF in winter reads lower, but the rest of the year
in normal driving runs around 85 C.
Except when driving up the steep grades in the North Georgia mountains.
Don Harmer

Removing the thermostat should make it run colder not hotter. This would not be good at all.
R Coates

My rebuilt TD runs at about 65 to 70 degrees under normal conditions, going up to 80 or 85 working hard on hot days. A week or so ago I was stuck in some severe traffic (traveling one block in about half an hour) in 80 degree F weather, and water temp got up to about 95.

Looking for opinions on how to conserve engine temperature when stopped in traffic. Turning the engine off for the repeated five-minute pauses between creeps would produce less heat, but of course the water wouldn't circulate. Racing the engine would circulate more water but produce more heat. Problem, of course is that no air is circulating through the radiator. I left the engine running at slow idle, and got through the jam before reaching 100, but I wonder what others might have done in similar circumstances.
Andy
52 TD
Andy Moyce

Removing the thermostat, unless the thermostat is not opening, will increase the temp not lower it.
John Green

I know I disagreed with John Green on the temperature change when the thermostat is removed, but I want to know why if I am wrong.

As I understand it, the thermostat stays closed while the water surrounding the engine is heating up. Once the water in the engine block is at the its opening temperature, the thermostat opens to allow cooler water from the radiator to flow around the block and then closes as the block water cools, and so on.

Temperature is maintained at the desireable level by the thermostat limiting the cool water flow from the radiator. If the thermostat is stuck closed, the block water will rise too much. If the thermostat is removed, cool water from the radiator will circulate continuously through the block, and it will not reach operating temperature quickly, or not at all if the ambient temperature is low. Am I wrong on this?
R Coates

R. Coates,
The direction of water flow is from the bolck to the rad. not the other way around. There is a small by pass passage that will let the water flow even when the thermostat is closed. What causes the thermostat to open up is the water temp. in the block warming up the thermostat. The thermostat will start opening and let the hotter water move on to the rad. If you take out the thermostat the water will be free flowing in a complete circle. This sound good at first, but the thermostat keep the water in the block to allow for the heat to transfer. If the heat does not transfer from the block to the water you will burn up your block and your water will remain cool. I hope I explained it ok
Steve
Steve Bourgeois

Mr. Coates
Removing the thermostat allows the water to flow too fast thru the radiator to have time to do the heat transfer required. Thus it runs hotter in hot weather.

If you remove the thermostat, then you must supply an equivalent restriction in the flow to match that of the open thermostat. People who race MG's do this.

A second complication is that the "bypass" is supposed to be shut off by the thermostat when it is open. The bypass circulates the water without going thru the radiator. It is supposed to do this only until the engine has reached operating temp. Most replacement
thermostats do not do this. The racers restriction plate device cuts off the bypass.
Many of us have had to put a restriction in the bypass
if we are using a "modern" thermostat, to reduce the bypass flow to keep from overheating in hot weather.
Don Harmer

R
Your idea of more water flow equals better cooling sounds quite logical.
I thought the same until I discovered, by trial and error, what Steve has explained [above].
I also discovered, in regular Perth 90 to 100 degree summer temperatures, that by fitting a one inch long piece of hose inside the bypass hose the water temperature is slightly lower.
The idea is to slow the water flow but not to totally block the bypass hose.
It works!
I am told that Red Line Water Wetter also helps and will try it this "Downunder" summer. Still quite cool at the moment, about 60 degrees.
Cheers
John Green

Don's message was not on the board when I was typing mine. He explains it better than me.
John Green

Logically, I am still not convinced, but empirically, if the temperature goes up when the thermostat is removed, then there must be some reason apart from those described in the pervious notes (unless the system is operating under Australian Rules!).

I agree the hot water comes through the thermostat to the radiator. You want the hot water at the top in the radiator since, as it cools the density increases, and it moves down the radiator and cooler water is taken off the bottom. However, the direction of flow is not important to the discussion.

I think the bypass is there so that there is always some flow, and if the thermostat is stuck closed, the sytem will not explode as quickly when the water temperature exceeds that desired! Also, the water pump is not pumping against a dead head.

The block is always full, and the thermostat is not there to keep the water in the block.

Concerning the effect of water flow rate: Heat transfer is dependent on area, heat transfer coefficient and temperature difference. The area is constant (the cylinder walls), the coefficient actually increases as the flow increases, and the temperature difference is the main driving force to lower the block temperature. If more cold coolant comes from the radiator in a constant flow with the thermostat removed, then the temperature difference between coolant and cylinders is higher, and the cooling should be greater.

We are still left with John's observation. Anyone else offer an explanation? Ron
RCoates

Mr. Coates
The heat transfer is also time dependant. If the coolant moves thru the radiator too fast not enough heat is removed per pass, and the system will run hotter. This is the problem!!

You can't beat the experience of those who have removed the thermostat and foun it necessary to restrict the coolant flow.

By the way, " Water Wetter" really works! I use pure water + "Water Wetter" in my TF and MGB-GT in summer.
Thus I can deal with the "traffic jams" in our hot weather. My GT has air conditioning, which provides an additional heat load to the radiator. I can run at "N"
or 85 even in heavy traffic at 95 to 100 F ambient.
Don Harmer

Something else is going on. We all know what windchill is. The faster the airflow is, the colder it feels because it is removing heat faster. The same is true for water.
Could it be that removing the thermostat interferes with the flow by uncovering the bypass and stopping circulation from the radiator somehow? Or it changes the shape of the passageways and offers more resistance to flow? These sound farfetched, but something must be going on to reduce flow from the radiator if the temperature goes up.
By the way, in answer to the original question, my TF runs just below 85C when the ambient temperature is around 70 (like yesterday) and got close to 90 in the summer when it was 90+F and I was driving fast on the highway.
RCoates

Mr. Coates,

You don't seem to be listening to Don Harmer as he is quite correct. A thermometer is not changed in the least by wind chill, therefor your wind chill argument is specious. It isn't just MG's that over heat due to the removal of themostats. Many cars need larger pulleys on the water pumps to slow the waterflow through the radiator as well as flow restrictors in place of the themostats when the enginges are operated at sustained high RPM's.

George B.
George B.


Look up : http://covis.atmos.uiuc.edu/geosciences/resources/data/weather/help/surface.obs/obs_wind_chill.html
Not sure which side of the coin this represents, also, does fluid behave like air as far as heat transfer? I just typed in wind chill into a search engine and found this. Interesting.
George Butz

Gentelmen,
David DuBois

I'm not sure I like this system that sends my entries to the BBS before I can finish them! I was going to say, before I was so rudely interupted, that before we get too far afield with the wind chill factor, as stated in the definition in the web site - wind chill ONLY applies to the human (and animal) body - it has no affect on inanimate bodies. Going back to the original question, 85°C is not a tempreature to be concerned about - it equates to 185°F and is about what all of my cars (TD, Magnette and MGB) run at regardless of ambient temperature. Keep in mind that the thermostat temperature is only the tempreature that it operates at, not the temperature that it keeps the engine (or in the case of the TD - the coolant) at. operating without a thermostat, in addition to allowing the car to run hotter, will also delay the warm up of the engine, wich is another undesirable effect. Keep the thermostat in place and if the engine is overheating, fix the problem! Check that the radiator is clear of obstructions (both external and internal), the water pump is operating properly and that the engine block is cleaned of rust and scale. I realize that the last will require the removal and dissasembly of the engine, but it is one of the costs of running a 40 year old car and sometines it has to be done if one wants the engine to operate properly!
David DuBois

This is a wonderful discussion, and I don't want to annoy anyone. I am listening, and will finish with a few observations from the previous notes:

1. Wind chill is terminology for people or animals because it describes feeling. It is correct that inanimate objects cannot feel equivalent temperatures, but high wind does remove heat faster than low wind. The temperature of an inanimate object is very quickly the same as the air temperature no matter what the wind speed is, and the wind speed will only change the rate of temperature drop of an inanimate object, not its final temperature. However, for live animals, their temperature is always above the air temperature, so heat is always being removed, and with high winds, it is removed at greater rates. See the excerpt from the web site mentioned in George Butz's note below:

"According to the chart below, if the air temperature was 10 degrees Fahrenheit, with a wind speed of 20 m.p.h., exposed skin would loose the same amount of heat at these conditions as if the winds were calm and the air temperature was -24 degrees Fahrenheit (the value given in the little red box). Therefore, the stronger the wind in cold weather, the colder the air actually feels to the human skin. Sometimes, high winds in below-freezing air can remove heat so fast from the skin, that the skin begins to freeze and discolor. When the skin freezes, this is known as Frostbite."

2. Yes, water and air are fluids and this behaviour applies to both

3. Two comments in previous notes were similar, and I missread the second one:

Steve Bourgeouis said '... keep the water in the BLOCK to allow for heat transfer' and Don Harmer said '... allows the water to flow too fast thru the RADIATOR'

I assumed Don meant block not radiator, and at first thought I had finally understood why I could not convince myself based on all the comments that the higher rate of flow would raise the temperature of the water in the block. However, after more thinking, I am still not convinced (!!!!), but please read on before casting me aside. If the flow were infinite, the temperature of the water would be essentially constant, and the rate of transfer of heat would be constant from the block to the water and from the radiator to the air. The block would only cool if the capacity of the radiator to remove heat were higher than the rate of heat transfer from the block to the water through the cylinder walls. I am pretty sure that radiators must be designed this way and high flow rate through the radiator would still be OK.

4. I do propose a scenario that will handle all the observations and which I believe describes what really happens though I am not really sure:

When the engine is started, the thermostat is closed and water circulates through the bypass from the thermostat housing to the return pipe at the bottom of the block. This is necessary because still water in the block would give hotspots and boil at some points, so the water circulates around the cylinders, warming up all the time and not going through the radiator. When the temperature reaches the opening point of the thermostat, it opens while at the same time closing the bypass (Don Harmer) proportionately. At high block temperatures the thermostat will be fully open, the bypass as closed as it can be, and maximum flow will be going through the radiator, giving maximum cooling. (Don Green's point of putting a piece of hose into the bypass results in lower temperatures because it increases the ratio of water to the radiator versus bypass). Now, if the thermostat is removed, maximum flow through the bypass is maintained at all times. The bypass is almost the diameter of the return line, and very short, so it offers little resistance to flow compared with the loop through the radiator. If the bypass is always open, such as when the thermostat is removed, then the ratio of water going to the radiator for cooling versus bypassing, is much lower than with the thermostat in place, hence the temperature will be higher with the thermostat removed.!!!!!

If you have stuck with me to this point, I thank you. I am not a mechanic and don't have much experience with cars as I know a lot of you do, but am very interested in them, and read the bulletin board every day. Nothing can take the place of experience, and that is why I never doubted that the temperature goes up when the thermostat is removed -- only why.
I have recently retired, and love my TF, and really appreciate all of the comments I read on the board and especially the ones on this thread. I probably have too much time on my hands, but I have really enjoyed the thought process and hope I have not hurt or annoyed anyone too much. There are a lot of smart people making contributions with lots of experience, and I know I will be asking pretty dumb questions in the future. Please have patience. I also realize that I might be wrong with the above arguments. I promise to say no more on the topic. Ron

R Coates

So long as she's not boiling, I'm not worried. On a hot summer day the radiator cap is usually too hot to touch with the flat of my hand. In the evening or during fall and spring it's just pleasantly warm.

I have gotten concerned are when the engine oil dipstick has been too hot to touch. On those same hot days, it's not exactly comfortable but I can grab hold. (This hint was presented in the _Compleat Idiot_ VW manual as a warning that your Beetle was burning.)
Jack Williamson

I still don't know if I should turn off the engine or stay at idle when stuck in traffic! :)
Andy
Andy Moyce

This thread was discussed between 13/10/1999 and 19/10/1999

MG TD TF 1500 index

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