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MG TD TF 1500 - How hot is too hot?

The temp gauge shows between 85 and 95c on a warmish day, it hasn't gone past that yet. When it's at 95 and I shut the engine off I can hear the water in the block boiling. A lot.

I don't remember my MGB doing this (back in the 70's. 'Course, I don't remember much from then anyway).

Should I be thinking about getting it to run a bit cooler (thermostat), or is this pretty normal for a TD?
MAndrus

I'm a farenhite kinda guy..so... 85 works out to 180 F
100C is boiling at sea level..220F When you shut it off and you hear the boiling...whats going on with the gauge? Does it climb past 100? If not I'd suggest you use a temp probe..if you use the wife's meat thermometer don't tell anyone....and test the temps against your gauge. 85 would be a desirable running temp. Changing the thermostat will not make it run any cooler in warm weather
MG LaVerne

Straight water shouldn't boil at 95C. With 50/50 antifreeze it shouldn't boil even at about 110C except maybe up on top of Old Rocky Top. My TD cruises all day at about 195F (~95C) in 85-90F ambient. Jud
J K Chapin

MAndrus...(what the heck is your name?)

Once upon a time, a long, long time ago, I installed a head gasket back to front (yes, it fits perfectly both ways) and blocked the rear water passage. There was enough water coming up through the small holes from the block to the head to keep some semblance of water flow but not enough to keep it cool on a HOT day while idling. It's easy enough to check by removing the back plate from the head and looking down...you should see an open passage to the block. If not, swap the gasket around.

Gene
Gene Gillam

The dash gauge hasn't gone past 95c.

I guess what I'm really wondering is: If my thermo isn't opening enough (or the radiator is overdue for cleaning) the block is getting overheated. If the block is getting too hot, perhaps the barbs are getting too hot and I'm boiling fuel causing my 'sputter to a stop, runs again after 5 minutes' problem. Also, it can't be good for the oil and a bunch of parts.

I DID use the wife's digital meat thermo, but the water sitting in the neck isn't being heated anymore and shows 190 - 200F.

The dash gauge pick-up is in the upper tank but not really in the water stream at the point of exit from the block (upper hose) so I'm guessing the block might be getting just a bit hotter than the gauge is showing, right?

My car is pretty much a barn find bought from someone who owned it since 1960 but put only 57K miles on it. The thermo is likely the original as is the radiator.

So, the block is getting past 100c for sure. Zat OK?

Getting the antifreeze balanced just right might keep the coolant from boiling, but won't change the temperature.

I'm at 2,600 ft altitude.
......
MAndrus

Sections of the block only remain below 100C as the water flow is taking away the heat. When you stop the flow, heat soak causes local boiling which does not take the total water volume above boiling . Only worry if it boils when running.
Boiling point at your altitude is 97F.
My TF sizzles to itself for about a minute after a fast run.
Ray TF 2884
Ray Lee

The cooling passages in your engine are pretty likely rusted up, which is normal for these engines with some time and miles on them. Nothing short of dismantling the engine will fix that, although you can remove core plugs and run water through the cooling system to somewhat flush things out. Replace (using brass core plugs, of course).

You can get some idea of radiator condition by removing the radiator cap, and seeing if the tubes visible through the filler neck have little bits of crud blocking them, or look open. I remove the radiator and back-flush it upside down, which seems to help.

I sell (but am out of, right now) stainless thermostat housing, taking modern thermostats, which are a great up-grade. See mgtrepair.net

Tom Lange
MGT Repair
t lange

Tom, let me know when the SS housing is ready. I've got all the hoses and by-pass pipe for a maintenance swap over. I'd like to be able to use currently available thermo if possible.

OK, It's not boiling while running. I guess I'm not over the brink yet.

....
MAndrus

It is common for the plain water at 95°C in the engine to boil when the engine is shut down. Once shut down, there is no circulation of the water through the radiator and no air flow through the radiator and across the engine to carry away the heat. The conventional wisdom is that the engine is not overheating (regardless of the temperature) if the coolant is not boiling while the car is in motion.

The cooling system should have at least a 25% mixture of antifreeze and water, not to keep the coolant from freezing, but to raise the boiling temperature of the coolant so that the coolant doesn't boil, even when the engine is shut down, but more important, that it doesn't boil while the car is being driven (see the attached picture). The anti freeze provides lubricant for the water pump and anti corrosion components to retard rust formation in the coolant passages in the block. Water wetter will also help with the cooling of the engine and you can put water pump lubricant and a separate corrosion inhibitor in the coolant, but to my way of thinking, the anti freeze is easier to deal with for the same protection. Cheers - Dave


D.W. DuBois

Running a supercharged TD 80+mph on hot summer days, our car used to run 230F, but the radiator has been recored since and the temps are down. 50/50 antifreeze boils right about 230F! There were occasions where steam would force us to slow down or take a break.

You have a long ways to go before there's anything to really worry about.
JRN JIM

One thing I would look at is the type of thermostat installed, especially if you don’t know the history of the car or the previous owner. Too often, the original thermostat, with the sliding sleeve, is replaced with a modern type. The sleeve was intended to close off the smaller bypass port when the water was at operating temperature. Without the sleeve, the cooling water is all too happy to return to the radiator, skipping the trip through the engine to pick up heat altogether. Using a modern thermostat requires flow restriction in the bypass port. You can see this in Tom’s picture of the stainless steel housing on his web site.

Frank Bruns
F. J. Bruns

Neil Cairn's article "Short Stroke Morris Ten Cooling" describes the water flow as follows. If the sleeve is not fitted the water from the block takes the path of least resistance & uses the pypass to return to the block so it doesn't get the cooling effect of the radiator, thus raising the temperature in the block. I'm curious as to which way the water flows in the bypass. Frank's description of the direction of flow seems to suggest the water is flowing in the opposite direction, though of course the net result is the same, the radiator is not cooling the water in the block. Does the water flow both ways up & down the bypass? Just curious is all. Gene I think someone addressed MA as Mitchell on another thread. Cheers
Peter TD 5801
P Hehir

It has been awhile since I looked at the coolant plumbing so perhaps my aging brain is playing with me..
Isn't the water drawn through the block by the pump and just dumped into the tank at the top of the radiator? Least resistance out of the pump is the big hose to the tank. Thermo siphon, fluid seeking it's own level etc. in addition to pump draw contribute to circulation.
But perhaps I am wrong.
All that being said, your engine cooling is fine as you describe it.
Regards, tom
tm peterson

Frank, thanks.

It's Mitchell.

....
MAndrus

Been down this track with a rebuilt XPAG that was not subjected to a block descaling and cleaning process.

I have no commercial interest with this company however I keep communicating on this forum that this product works; Google "Liquid Intelligence".

After using their product my running temperature decreased by 10 degrees and I no longer had boil over when I closed the engine down which resulted in displacement of coolant from the radiator.
G Evans

The thermostat housing is discharging under the increased pressure from the pump, but the return hose to the water pump is at a lower presssure. Some of the hot water leaving the engine will take the path of least resistance and head back into the return hose to recirculate in the engine.

For years, the concensus of opinions is to fabricate a gasket at the bypass elbow with a small hole (1/8", 3/16", whatever) to offer a tiny bit of circulation with the thermostat shut, and keep it just a trickle after the engine heats up.
JRN JIM

Ok, a bit on the colored stuff you put in your radiator. (Some call it antifreeze, some call it coolant).

If your car is parked in an area of the world where it gets below 32f or 0c, you need to use at least a 50/50 mix of antifreeze (follow the manufactures directions depending on how cold it gets.)

If you are trying to cool your engine, use a 25% or less coolant to water. Water is actually one of the best heat transfer fluids, so straight water will do a better job of heat transfer than a mixture.

Coolant/antifreeze also contains antirust agents, lubricants and other things that are good for the engine.


I flush my engine with a engine flush compound (follow the directions correctly) and back flush the motor. In the winter, I use antifreeze to below -30f (it gets that cold in Wisconsin). Since the car is in a unheated, but insulated garage, I feel ok down to that level.

In the summer, I drain the fluid and save it (antifreeze does not go bad, it just gets contaminated with rust. Filter it through a paint strainer or cheese cloth and it is good to go again). I add a pint of water wetter about 10% coolant (primarily for the antirust agents) and water. Some use distilled water, but I have not had any issues with regular water. If your water has a lot of minerals, distilled might be a good idea.

My TD runs around 85c to 90c normally. My MGB runs 185 to 190 all the time.

To give an example of what cleaning your motor every year or two does, this is the water pump out of my 67 B GT. The pump was replaced by the PO, but has at least 40,000 miles on it since I got it. No rust.


Bruce TD4139 Cunha

Dave's information on boiling is correct, but the other factor is heat transfer. Coolants are only 65% as effective as water in transferring heat out of a motor.

Also, remember the TD has an open cooling system. No pressure cap, so the first column (o psi) is the correct column for the TD. So with 60% coolant, you gain 19 degrees above boiling, but you loose a significant amount of heat transfer.
Bruce TD4139 Cunha

Also the cooling system needs the restriction of a thermostat to work properly. A pressurized cooling system will raise the boiling point as well. This can be easily done by installing a radiator cap neck & cap to the overflow pipe.
Len Fanelli

This thread was discussed between 12/05/2015 and 14/05/2015

MG TD TF 1500 index

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