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MG TD TF 1500 - Cooling system perplexities.

What the heck is the fitting for in the top of the radiator header tank? Every one of them I've seen is capped off. That isn't where the water temperature sensor plugs in, is it? Please tell me it isn't. You could cook the engine and never know it until it is too late. On the other hand, I don't see where they plug the sensor in. Our running TDs have had it adapted into the back of the head, but it looks like they were both jerryrigged. That sure is a smarter location.

What MG engineer out there can tell me why they designed the bypass circuit? I can appreciate it circulates coolant around a cold engine until it warms up, and possibly saves maybe a horsepower as opposed to running a dead headed pump.

Removing the thermostat, or replacing original type thermostat with the bypass sleeve with one lacking the sleeve, means there is a direct short circuit of hot coolant right back into the engine after the thermostat opens. That doesn't help the cooling issues.

At first, I thought it was maybe blanked off from the factory and left available for an optional heater, but I doubt that seriously, because there'd be no circulation to the heater once the thermostat opens. Our first TD had a coolant detour to a pair of heater hoses coming off the bypass. I finally discovered there was no thermostat in the housing, so there was virtually no circulation to the heater, whatsoever. On one of our other TD's, it looks like they tapped off the back of the head for the heater and ran it back to the bypass, but an open bypass would've been counterproductive to pumping hot water into the car.

As a journeyman steamfitter, I think I have it planned out how we'll get some heat into the tub (keeping heat in is another problem). I'm blocking off the bypass completely and tapping off the cover on the back of the head for the heater and also install the temp sensor there. Heater water will return to the suction side of the pump via the tube from the lower radiator hose. The heater circuit will be the new bypass for us, but I'm valving the heater lines to stop circulation in hot weather. I installed a conventional stat and have just 1 small hole in it. I like the idea of purging air out of the engine quickly, having a small flow out of the front of the head past the thermostat so it can sample water temp, and I'll give up a tad of heat

An Australian told me today the bypass was put there because thermostat sticking was so common, it helped prevent sudden catastrophic overheating; just sort of delayed the inevitable a bit with some circulation. He said, down under, they'd take a conventional thermostat and drill 4 small holes in it to let it bleed past the thermostat into the radiator and give it a longer period before meltdown, in case it sticks shut. Unfortunately, that also means it would take a lot longer to warm up, but who worries about that (only those who count on a heater in cold weather).

Any opinions as to what the engineers had in mind???
jrn Northrup

JRN,

The bypass with the blanking sleeve was put there as you said, to provide flow with the thermostat closed. Most are running a modern thermostat in a modified housing with a slight bypass built in. Further, they provide a blanking plate to the bypass hose and install a 3/16 hole in the blanking plate. The system is semi-thermosiphoning. My TD runs very consistantly at about 75 deg C in cool weather (the thermostat opening temp is approx 75) and runs warmer in hotter weather, never more than about 87 deg C. The header tank is quite useful. I never have to add fluid, it does expand into the header, and at that point I can read the temperature. Since it is a non-presurized system, the temperature gauge isn't really necessary. If it is boiling, it is too hot.

Your plans for a heater are sound. I have found that the heater simply heats the one leg that is close to it, and interfers with the enjoyment of the car otherwise. I dress warmer when I need to. Last year in Minnesota, I drove the car in every month except January and February.

Engine temperature can be controlled by careful timing, dwell, valve adjustment and carburetion. Last week, just for fun, I leaned the engine one flat found the temperature to rise an additional 4 deg C. In addition, there is a closed point in the block casting that can be opened up with a drill. You may wish to view that on my website, http://www.dbraun99.com

warmly,
dave
Dave Braun

Dave,
Here in Michigan, the MGs are parked when there's salt on the road. We have a hardtop that helps keep the wind down a touch in cold weather... just a smidge better than riding a motorcycle.

So you're saying the temp gauge is normally tapped into the header tank? If water drained dangerously low, you'll find out when the car is enveloped in steam, or the engine locks up. No sense in getting worried about it ahead of time. Seems like the same engineers must have designed that system that designed the Motometer... it doesn't reach down into the coolant so you don't have to worry about overheating.

My drove to Minneapolis a couple of years ago in our Honda. The thermostat failed on the way- it stuck about a sixteenth of an inch open and we about froze.

I went to check out your TD but the pictures don't open.
jrn Northrup

I couldn't get Dave's link to open either...although it used to...
Seems there are a couple forward slashes instead or as well as back slashes in the address on the main page?

This got me there....

http://www.dbraun99.com/mgtd15470/

(He does this so I get sucked into spending another 5 hours looking at all his great shots....)
gblawson(gordon)

JRN The hottest water is at the front of the engine where the thermostat is/was. If the original 'stat has been replaced with a modern one then as Dave said above put a blocking plate with a 3/16" hole in the bypass path. Then silver solder a fitting where the 'stat used to be and put the temp. bulb in it. That will permit you to have a reasonably good temp indication and the hottest water to the heater. The water at the back of the head is the cool water from the bottom of the radiator. I know a lot of heads were modified to tap the water at the back of the head but that is almost as bad a choice as the fitting in the radiator tank was.

The factory finally, in effect, admitted it when they brought out the TF. The temp gauge fitting was in the elbow from the front of the head and right beside it was another hole tapped for the hot water outlet to the heater.( maybe only in TF1500's).

The cool water from the heater should go up to the pipe that is between the radiator and the water pump.

If I were more computer literate I would put up some pictures.

Cheers,

Bob
R. K. Jeffers

Remeber that TCs and TDs did not even have a water temp gauge until car #14000-something. You have to remember this engine/cooling system is pretty much a pre-WW II design. When my TD overheated, you know it because it starts boiling- not hard to miss! Bob J is right about the take-off for a heater- the water at the back of the block/head has just gone through the radiator, up the bypass casting in the block and straight up, so it is not very hot. You want the hot stuff after it passes through the head. George
George Butz

I dunno... the link worked for me!
Dave Braun

The link on your main page to the photos came up as: www.dbraun99.com/(back slash)mgtd15470(back slash)
(Have tried putting the actual back slash in this message but it doesn't seem to want to show)

Funny, it brought up a page with all your text but no thumbnails...and the links took me to a 404 Page not found page?
gblawson(gordon)

Cooler water enters the front of the block. This water moves predominantly towards the back of block, and is shunted fairly evenly through the smaller passages up to the head. Sometimes, head gaskets have holes much smaller than the passages to even out the distribution. The path of least resistance is to move through the head at the front, while the coolant in back is much more slower to motivate forward to the gooseneck.
The rear cylinder and back of the head are a touch hotter than the front. Tapping water off the back of the head not only gets the hottest water, (and the shortest path), it more improves circulation to the rear.
I like the idea of a small hole in the thermostat so it vents air out quickly when filling, moves water past the thermostat while it is closed and also generates a bit more circulation at the front of the head. It'll also provide the the only bypass circulation with the heater valved shut.
jrn Northrup

JRN,

You're correct about the water entering the front of the block BUT it immediately runs along the outside of the block in the squarish passage under the intake/exhaust manifolds where it then goes into the covered chamber in the rear rear of the head. It's here that the water actually begins the engine cooling process. While there may have been some heating of the water along the way under the manifold the water is much colder here than at the front where the thermostat is located.

By the way, that valve is on it's way...postage was cheap so don't worry about it...maybe you can *pay it forward* to someone else in the future.

Gene
Gene Gillam

JRN, you are right for many engines, but Gene is correct as far as the XPAG engine circulation. The sqaurish raised passageway from front to rear carries 100% of the water from the lower (cooler) radiator via the water pump to the back of the block. There is no communication from this square tube with the internal block water jacket at all on the XPAG block. The passageway goes up into the back of the head, and is pumped and flows rear to front through the head. There is minimal to no active circulation through the block water jacket around the cylinders- it is just thermosyphon (ie hot water rises). If your engine is hotter at the back, something is restricting the circulation. George
George Butz

Live & learn! I'm going to have to check out the block in the garage later tonight.
Remember the Vega? Any shortage of coolant would result in scoring of the back aluminum cylinder. Reynolds engineers said GM took their technology then shrunk the external block dimension and choked circulation down to a minimum. Numbskull peanut counters took an exquisite aluminum engine block and slapped a cast iron head on it to save pennies. Head gaskets were a real issue.
Reynolds also built an aluminum prototype Vette. GM had the aluminum 427 engine back then but stuck a cast iron 396 in that show car. My MG engineers WERE a cut above their GM counterparts.

Gene,
Got the oiler today. It is magnificent. Some of us engineers are easily entertained with trinkets!! Any moving parts have a hypnotic effect! Can't wait to see it drip and tweak the needle valve!!! Thank you so much!!!
We're heading out for vacation soon so it may be a few weeks but I'll post a picture of the installation.
jrn Northrup

While correct that the early TD's did not come with a temp gauge, there were Jager gauges that were add on. I have one in my 1950 TD and saw another at GOF Central on another early TD. My radiator did have the plug for where the temp guage goes. I have no issues in getting accurate temperatures.
Bruce-C

The XPAG block looks like they gave water circulation a lot of attention. Just behind the pump, the block guides most of the flow into the channel on the side, but some goes to the oppposite side back around the front cylinder. Poking a long screwdriver down the block water passages reveals openings up from the channel at each cylinder up to the head. Without popping out freeze plugs, it appears water would flow across the cylinders from the channel side to the other (can't say driver's side or passenger's side for a T model). I must say they tried to insure adequate flow to the back of the block.
Now should I go with the plate I brazed up today for the back of the head or revamp my thermostat and tap coolant at the bypass?
Hmmmmmmmmmmm!!!!!!!! More fun and games!
jrn Northrup

JRN,

Take a look at http://www.mg-tabc.org/techn-up/The%20Hidden%20Water%20Passage.htm

There are only two small holes leading down into the block from the square water passage on the side of the engine. One, the rear, is on all engines, the second, up forward was on the later engines unless someone has opened it up later in it's life.

Other than these small holes there is no other way for the water to get to the block from the front to rear channel.

If you want hot water take it from the front of the block, if you want warm water take it from the rear.

Gene
Gene Gillam

I tapped the back plate as well...and although I can keep my right knee warm, I think I should be able to get more heat...am going to switch to the thermostat housing this fall...! Just hate so much 'plumbing' happening!

gblawson(gordon)

Gene,
I'll bet those holes are for just the opposite- not prevent overheating but prevent freezing and bursting the block. Without them, that channel probably can't drain.
I just inspected a block with no head. About every other water passage at the top of the block runs right up from that square passage. It does make a nifty way to insure circulation to the back of the engine.
As I text this, the paint is drying on the head rear plate I brazed up today. I might blank off the heater port but still tap the temp sensor there. Our TD that's on the road now has the temp sensor in that plate and it works good and correlates with the Motometer thermometer.
I really liked that brass bypass elbow, polished to a golden shine and clamped on what looks like vintage 7/8" cotton covered hose. I hated leaving them off, so what I'll probably do is turn the thermostat housing 180 and run the bypass elbow over to the distributor side and the hose back to the firewall on that side. The trick will be installing the thermostat above the bypass instead of below. I checked one thermostat housing and found someone had tried tack welding the steel thermostat to the cast iron housing, unsuccessfully.
jrn Northrup

"The cylinder head carried the major water flow for cooling, being fed into the rear of the head, via a waterway along the offside under the manifolds. A water pump assisted the water from the radiator to the rear of the head. The cylinder block relied on internal thermo-syphon for its cooling. The engine had a very complex thermostat in its own housing."
Quote from MG engine guru Neil Cairns' book on the XPAG engine. Interesting, this is how always thought it was. JRN, have you actually shined a light through, or fed a piece of wire from the top of the block into the square tube with the freeze plugs out to make sure they actually connect? Just curious. Could be Neil (and the rest of us) are wrong. Or maybe your block had some mods done to it? I remember years ago when Ford started back in NASCAR and the Elliotts had used up all of the 351C blocks, they tried to use 351W's, which had hot spots that boiled. They found the older gentleman that had been involved in designing the original casting and he suggested spots to drill extra holes for coolant flow. I bet you are right about the tiny holes into the lover jacket, otherwise no way to drain. George
George Butz

JRN,

Here's a series of photos I took this morning on a spare block without freeze plugs.

I've used a piece of white wire to show what connects where on the block.

This first photo shows the square passage connection to the top of the block. It is also connected to the bottom of the block but not directly to the rear opening.

Gene Gillam

This next photo shows the rear of the block connecting to the side of the block. Water also comes up from the bottom of the block at this rear opening.

Gene Gillam

This next one shows the connection from the block to the openings that lead to the head.

Gene Gillam

This one shows the connection the top of the block to the bottom of the block.

Gene Gillam

And finally in this one I tried to show there was no connection to the square water passage from the top.

Gene Gillam

As for the small holes (one easily seen in the above photo) being there to prevent the block from cracking...I don't think so. Neil Cairns said they were there to evacuate the sand in the casting process...he also said that he didn't think they were there to aid in the cooling process but I, like many others, found that opening them reduced the engine temperature significantly and I recommend doing so.
Gene Gillam

Most excellant series of photos....well done!!!
gblawson(gordon)

Wow Gene, that sure tells the tale. So there is indeed some active coolant flow through at least the upper part of the block? Great job on the photos. George
George Butz

When you drill out the little holes, what does the square passage then connect to...
gblawson(gordon)

Gene, please write this up, with the photos for T-Talk or to post on my website... or both. I think your work is excellent!

George, as always your observations and grasp of the thechnical details are a pleasure to read. Thanks!

JRN, I think you've just changed my mind about the extra 'cooling' hole in my block I drilled during the rebuild. I have to admit that Gene's explanation is compelling, but I don't think I would want to evacuate sand through a 3/16 hole. Although my rebuild puts out more power, but runs cooler, there is a myriad of reasons why that is possible aside from the extra hole being discussed, but like Gene, I'm reluctant to dismiss the hole entirely.

Gordon, the little hole ends up connecting the square transverse passage to the lower block. Generally you are adding the front hole, the rear hole exists unless clogged by debris. See photo.

warmly,
dave

Dave Braun

Gene, I'd be delighted to put a page together from your images and description. Lots of room on the site, so any additional images, or words of wisdom would be included. Thanks.

Bud
Bud Krueger

Thanks for the kind words guys.

Bud, I'll get some more photos together and send them to you with a write-up by the weekend. Thanks for offering to host them.

Gene

Gene Gillam

Gene,
I bent a welding rod and probed down the water passages, and you're right, no openings from the channel to the block (other than those 1 or 2 little drilled holes)- virtually all the water flows to the back of the head.
There is a sliver of an opening from the front cylinder to the cavity where the pump plugs in. Looks to be another "bypass." Interesting.
You talked me into taking heater water off the front. I installed my conventional thermostat up in the housing above the bypass and installed it with the bypass on the distributor side of the block. My 7/8" cotton covered hose is overkill but fits onto the polished brass bypass elbow and has this sort of "period" appearance to it; another conversation piece.
jrn Northrup

Reactivating this thread
jrn Northrup

Hey fellas, I am trying to make a decision about drilling a new hole in the front of the square water jacket under the core plug. I have read repeatedly in the archives what Gene G. and Bud K. have written and I am still mystified. They use phrases like "open up the holes". Does that mean drill a new one up front or enlarge existing ones? I have an early EXPAG for my TD. It has but one hole now in the rear only. My engine is still at the machine shop. Now is the time to drill and or enlarge these holes. Is it advisable to make this alteration. As always, thanks for any help you can give. Sandy
smb brainsky

sandy, the answer to your question is early blocks don't have the front hole..you drill one..the later blocks had a small hole towards the front so posters here advocate enlarging the existing hole. i think one of the MG restoration books had a picture of this hole..(the picture taken with a drill bit in that hole if i remember correctly). not sure what an EXPAG is..i've heard of XPAG's and XPEG's. more info on that engine would be helpful. regards, tom
tom peterson

See http://www.ttalk.info/XPAG_Cooling_System.htm for Gene's images. The discussion is about 1) opening up the existing rear hole and 2) opening up the front hole (if it exists) or creating it if it's not there yet. I think school is still out on this topic. Bud
Bud Krueger

Hi all. When the engine is not running, the
hole sysrem is filled with water up to the level in the tank. when the engine is started
the pump pushes the water through the square passage to the back of the block, up to the head and thru the head to the front of the engine and up to the tank, being cooled on its nway down through the radiator and rond again. the "cold" watwater in the lower part of the block is siphoned up against the head through the openings in the head gasket lower part of the block is geting "cold" waterfrom the square passage through the small holes
drilled behind the frost plugs. The hottest water is in the front of the head. The " coldest is at the bottom of the radiator.
There is no pressure in the system thanks to the overflow tube jn the radiator.
IMHO.
Thoralf. Norway TD4490
Thoralf Sorensen (TD4490)

Sorry about the long delay in thanking you guys. You have cleared up my hole drilling dilema. I have to get out to my machinest guy to discuss this now. A couple of drill sizes larger on the back and a new one entirely on the front. And Tom, I think my engine is an EXPAG. It has been separated from it's chassis for so long, it probably thinks it's divorced. Ha. I hope some day I will be able to answer somebody elses questions. But until then, I am awfully glad you guys are around to help out us newbees. Till next time, thanks again. Sandman
smb brainsky

Getting back to the heater....
I just followed the method used by Arnolt on the after-market heaters....While it may not be the hottest water, it is quite hot, and I get plenty of heat....Of course, there's no way to keep it in the car, if the top and side-curtains are not on....
I really can't imagine that more BTU's are needed, the problem is more about the cabin design than the hot-water location.
Edward

E.B. Wesson

Reactivated for Geoffery

Check out the holes in the pictures and in particular go to the link on Bud's site with Gene's pictures and cooling discussion.
MG LaVerne

Great thread. The initial question "Why they designed the bypass circuit"? was pretty well answered except to say that cold engines wear much more rapidly than hot ones. My research shows that cars run without thermostats show significantly more wear in #1 cylinder which is where the cool water enters the block. The idea of the thermostat (& bypass circuit) is twofold. Primarily to get the engine up to operating temperature as quickly as possible (to minimize wear) & to maintain operating temperature in freezing driving conditions, by partially or completely closing as required. The Neil Cairns article "The Short Stroke Morris Ten Engine's Cooling" is the best I've read on the subject. I've fitted a Holden Waxstat thermostat inside my original housing, blanked off the bypass pipe & drilled a 3'16" hole to prevent an airlock & also drilled two small holes in the thermostat thus allowing some water to return to the radiator when the thermostat is closed. I get the best of both worlds, the function of a modern thermostat & the form of an original housing. And it only cost $16! Cheers
Peter TD 5801
P Hehir

Peter,
Just a heads up- Now that you have 2 tiny holes in the thermostat, the next time you fire up your cold engine, hold your hand on the radiator tank and see how quickly it heats up.

I tried a hole in the stat and then went back in and plugged it. On cold days, when I counted on the heater, there was no heat.
JRN JIM

Thanks Jim. I'll certainly follow your suggestion. I have another $16 thermostat so I can do a "with holes" & "without holes" test & note the resultant time/temperature variation. I've never had a heater or a top & during the 18 months I drove it back in 1969/70 even during winter it was pretty snug inside. But I guess the point you're making is that the holes in the thermostat rob the engine of heat which will allow more wear on start up. Cheers
Peter TD 5801
P Hehir

try a stat with a jiggle pin as well, lots of unholed cheap stats have small cuts in them to bleed air.
mog

That jiggle pin to pass air reminds me of the cotterpin in the bottom of the bellhosing to pass oil drippings!
I removed the jiggle pin thinking a teeny stream of coolant wouldn't significantly effect the thermostat function. Amazing how fast the raiator tank heated up, but not the heater.
JRN JIM

My son, who has been in the automotive cooling system business for over 40 years always drills a 3/16 hole in every new thermostat if one is not present, mainly to prevent hot shock to the newer radiators plastic upper tanks on later cars, which causes them to crack prematurely. He says it helps the radiator warm up a bit taking the chill out as the engine warms up also preventing cold water shock to the rest of the system. My thermostat is drilled. Just sayin. PJ
Paul S Jennings

PJ the small hole obviously doesn't apply to our old girls as they don't have a plastic tank & don't take that much to warm up! :-) Cheers
Peter TD 5801
P Hehir

Hello,

My TD runs with an elbow pipe from a TF between head and radiator. And I use an old thermostat from another car. But I modified this thermostat to open the bypass when cold and to close it when hot. As it was for the original one. But what I wanted to explain now is about heater connections.
Whan I bought the car, the heater was taking water from the back of the head and returning it to the input of the pump. As the water at the output of the pump mainly goes to the back of the head first, the heater is bypassing the head circuit. Not good. Furthermore, cool water is getting in it. So I decided to plug it at the output of the pump and returning to the input of the pump. That way heater and radiator are working in parallel. Unfortunatly, this does not work. The heater is not heating. I guess because, the water at the output of the pump goes the easiest way, toward the big pipe and the radiator. So no water was flowing into the heater.
Therefore, I returned to the former connection. Actually, I use the heater when the weather is cold outside . And when the weather is cold outside, the by pass of the head by the heater does not matter bacause the radiator is large enough to cool the engine. the head bypass might also be negligible. Probably a few hundred watts lost into the heater while the head is probably generating tens of kilowatts.

Laurent.
LC Laurent31

Laurent,
Tapping the outlet of the pump somewhere just before the thermostat and returning it to the suction side of the pump is the best way to plumb the heater. The heater will get the majority of hot water before the stat opens and then share plenty of circulation with the radiator when the stat is opens.

I understand you said heater did not heat up when you tried it. I'll bet your heater has the tubes down at the bottom of the heater core. There are no bleeders to these contraptions. The pump has very little pressure and when the heater is air bound, it sometimes takes quite a while before the air is purged. That's the nature of these beasts and my experience.
JRN JIM

JRN,
The heater was bled. I thought of it. So i put it on the floor. And no heating. Plugged it at the back of the head and it heated immediately albeit under the scuttle.

Laurent.
LC Laurent31

I stopped down to the machine shop and checked the block today. The rear hole is there and looks nice and clean. The front one may or may not already have been drilled - it looks like it might be there under some crud - and my guy is going to dig for it, and if it isn't there he will drill a hole for me.
Thanks for everyone's help in explaining this issue! Always nice to make sure I am returning the engine to tip-top (or even better than original) condition...
Geoffrey M Baker

This thread was discussed between 22/09/2009 and 13/04/2015

MG TD TF 1500 index

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