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MG TD TF 1500 - boiling sound from radiator

My newly restored TD develops a boiling coolant sound from the radiator. Although the temp meter is not rising above 80 Celsius have checked with a infra-red temp meter at the radiator. The engine is newly overhauled and running perfectly. Ignition timed > OK. Radiator rodded and free of any goop. Carb's are tuned and not running lean ( exhaust gas tester on hand here )
The two holes in the block behind the freeze plugs are open . The water pump is new and is running with a plastic fan. While engine running no bubbles to notice by looking in to the radiator. The thermostat housing has a restrictor plate at the elbow for the bypass ( drilled 1/8 ) the thermostat itself is new and I also drilled a extra whole in the top plate 2/16.
QUESTION : what am I overlooking to cure the problem and am I creating a hot spot some in the head ??

I hope you guy's are able to give me an idea what to look for.

Thank you for your time,

Gerard

Gerard Hengeveld

Pressure test your cooling system and check for bleed down, this will confirm head gasket, head and block are OK.
G Evans

The TD cooling system is not pressurized.
Gerard - you are probably experience a totally normal situation. Once you shut the car down, there is no circulation of the coolant, thus no cooling of and the coolant in the block starts to boil, which you hear in the radiator (the bubbles peculate up through the radiator). This use to be a very common situation years ago (back in the 40 sand 50s). Cheers - Dave
DW DuBois

Dave , thanks for the comment, your explanation sounds plausible , but what I don't understand that my black TD ( just sold ) didn't have that problem.

MR , G Evans , also thank you I'll look in to that tomorrow,

Gerard
Gerard Hengeveld

My car often does that a little after a hard drive on a hot day. I think a fresh engine may be a little tighter and run a bit hot? Do you have 50/50 coolant/water? George
George Butz

Ditto on boiling/bubbling sound...perfectly normal on shutdown.
Gene Gillam

Mine too on a hot day. At higher elevations, water boils at a lower temp than 212F also.
MAndrus

Thank you very much for all your thought's and experience shared . I drive my TD mostly at a elevation around 2000 ft. Yes I have coolant with 50/50 anti freeze. Am I at ease now ? Hm, not exactly , this given the fact my (ex TD now ) never did. even so my 1930 Model A does not.

Thanks again,

Gerard
Gerard Hengeveld

The continuing 'story behind it. As I am not easy pleased specially if I cant find a reason behind a problem.
The search for a answer went on. Yesterday evening the decision was made to take the water pump of the engine (my knuckles are still fine )at first sight nothing wrong but......... after I turned the axle by hand and holding the impeller in the other hand I could turn the impellor with no effort. From my stock I mounted another pump after running it dry for about a minute ..put it on the car and went for a test drive . No more bubbling from the radiator at last.

Now I'll go for some fine tuning the mixture but that's another post to come ,

Thanks all,

Gerard
Gerard Hengeveld

Mighty interesting that your engine temperature was only 80C (176F) with a non-functioning water pump.
Gene Gillam

Gene , you are right but I forgot to mention that I replaced the tem/oil pressure gauge with a new today also. Just to be sure.

Gerard
Gerard Hengeveld

Gerard,
What do you mean when you say "I also drilled a extra whole in the top plate 2/16".

If you are talking about an extra hole in the thermostat - why would you do this ?.

Once the thermostat is fully opened, you are allowing more flow through the radiator than was intended. If the flow rate through the radiator is too quick, heat transfer is less, so the water enters the engine hotter than it should - passes through the engine picking up more heat, and arriving at the thermostat hotter than it's last visit.

This can lead to gradual creep of water temperature when driving at constant speed and load.

I am a big fan of the original bypass type thermostat - they are expensive, but are part of the original cooling system design.

Tony
A L SLATTERY

I also drilled a 2/16" hole in the top plate. I later changed it to 1/8" and found it made zero difference.

.....

;)
MAndrus

I think you would have been better of using a 4/32 drill,, HUGE difference!!

STEVE
Steve Wincze

Fractions - you can read them in many ways !!!....
A L SLATTERY

Fractions can be so confusing therefore to simplify things ( no pun intended) I'd recommend a 0.125" bit. That way you just can't mess up. :-) Cheers
Peter TD 5801
P Hehir

To : Tony Slattery, Thanks for your comments what you stated is absolutely correct. I have a two row radiator ( absolutely clean )my grill slats after market type, open about 3/4 inch between the slats this was done in conformity with my other TD. The heat loss measured with infra-red temp, meter:
just after shutting down from a trip .Top tank temp,reads about 85 degrees Celsius bottom tank about 55 degrees Celsius . But still the dam....d boiling sound to notice. Ambient temperature 40 degrees Centigrade, Alt 2000 ft.
New engine 60 miles driven.

Thanks Gerard
Gerard Hengeveld

Gerard, I had exactly the same symptoms in another XPAG engine - all seemed ok, but when switched off you could hear that boiling in the engine.

The engine did around 2000 miles before it blew the head gasket and the cause was revealed.

The cause was the engine builder fitted the head gasket back to front - yes it fits, but it blocks the main water passage at the back of the head - hot water got trapped under the gasket in the block and could not escape up.

You need to remove the plate on the back of the head and make sure you can poke a wire down into the block - if you can't - it's off with the head.

Tony
A L SLATTERY

Tony , I never thought of that but going to check that this weekend and let you and the others know.

My rebuild engine came with the to be "restored" car I bought 2 years a go. The company who performed the rebuild has a good reputation but s you wrote ".. a back to front installation could be the case.

Many thanks,

Gerard
Gerard Hengeveld

1) Gentleman could someone please explain to me what the effect will be when I Block the bypass completely ?.
2) If I have to remove the head in case Tony Slatterly
is spot on with his remark that the head gasket could be wrongly mounted ? And to find that I have a round hole block fitted with a banana head ?( I have a banana for sure )
What type of head gasket you advise.

Thanks,

Gerard
Gerard Hengeveld

My research suggests that without the small hole, about 1/16", it is possible that you may get an air lock, which can interfere with the flow through the system. If you have a mismatched head & block then the banana is the gasket to use. Gaining access to the slot head machine screws securing the plate at the rear of the head in situ may not be easy. A screw driver with a right angled bend may be needed. These can be replaced with correctly threaded bolts on assembly if you're not into total originality. Cheers
Peter TD 5801
P Hehir

Thanks Peter, I have angled screw drivers , airlock ? never to old to learn ( ME )

Gerard
Gerard Hengeveld

Gerard, have you tried using a stethoscope to locate the actual location of the boiling? Bud
Bud Krueger

I thought the problem was fixed with the new water pump?

Also, Tony was dead on about the head gasket possibly being turned back to front. Been there, done that!
Gene Gillam

BUD . I have use a stethoscope but could not find a hot spot .

Gene , I thought also the problem was solved but after another longer drive it happened again.

Have to do the honey - do list today first before I proceed with the head .

Gerard
Gerard Hengeveld

It can be seen from the diagram that many parts are running at over boiling point, when the engine is running then the heat is removed by water/oil circulation. When the engine is stopped this residual heat has to be dissipated, hot spots can cause local boiling until the temp drops. My TF has done this for a couple of minutes for the 40 odd years I have had it, a couple of rebuilds and many thousands of miles with no ill effects. A high efficiency water pump will only make a difference if it is running.
I was a Marine engineer and it was the done thing to continue the cooling circulation after engines were stopped for this very reason.
Ray TF 2884

Ray Lee

Ray , thanks for diagram I had that but yours is more easy to read. I usually let my engine run for a short time after coming home to a complete stop.

TONY, I removed the cover plate and could stick a lead rod straight down in both holes almost 5 inch down.
So I assume the engine rebuilder ( ABACUS RACING Virginia Beach ) did that job properly.

Now, I run out of options . Any more helpful hints please .

Gerard
Gerard Hengeveld

How much boiling? A few bubbly sounds for a minute or two, or like a pan on the stove on high? Again, a little boiling/bubbling sounds at shutdown are normal with the unpressurised cooling system. Do you have an IR thermometer? They are inexpensive. You could shoot the temp. of various places of the cooling system, water jacket/head/hoses etc. and get a true reading. George
George Butz

Hi George, As I explained a few posts above temperatures have been taken at the top tank, halfway the rad and the bottom tank with a infra-red temp meter. Those readings taken did not alarm me.
85 / 60 / 50 Celsius.

BUT I DON'T understand why !!! the boiling sound is there. My other TD ( just sold ) did not. Maybe I am over though full or as some of my friends call me :.. pain full precise.

Thanks,

Gerard
Gerard Hengeveld

OK, It's a thermosiphon system with pump assist.

If the water in the head starts to boil on switch off, it should move from the head to the top tank of the radiator and force the cold water in the base of the radiator into the engine passing the stationary water pump impeller, along the side of the block & up into the head - this probably takes 30 seconds.

So if the boiling sound occurs from 30 seconds to 2 minutes after switch off, it's probably ok.

I would check the temperature of the outlet elbow, before switch off and then every 10 seconds after to see what happens. It may be that the thermostat is not opening fully ?.

Can enough colder water pass the water pump when it's not running ?.

While I can understand localised hot spots, the water mass should absorb that easily & stay under boiling point - unless the near boiling water cannot rise for some reason.

It would be interesting to fit a flow meter in the bottom radiator hose to know just how much water continues to circulate in a thermosiphon system after switch off.

Your top tank temp is 85 degrees, which is what you would expect with a 82 degree thermostat, and the bottom tank at 50 degrees is in agreement with that cooling system diagram, so the radiator is doing it's job.

As you say Gerard, the old TD did not have the issue, so what is different in this engine ?.

I have a YT & YA that are both driven pretty hard at times on highways & in urban areas - they don't boil on switch off and we are in a sub-tropical zone.

Keep searching & thinking,

Tony
A L SLATTERY

Hi Tony, well I'll keep scratching my head and almost get bold from that, LOL. Also today I removed the thermostat. Now I have to get back to the neglected ( for a long time ) honey do list. Will drive it tomorrow. I'll keep you posted . Un-fortunately I don't have a flow meter could be interesting to have those figures

Thanks Gerard
Gerard Hengeveld

Good data on the rad. temp. Take temp of the block and head at various places- core plugs, right side water passageway, rear head cover plate, etc. That may give idea if any blockages, etc.
George Butz

Gerard - try some Water Wetter - not snake oil and may well get rid of your boiling noises.
Gene Gillam

George I did take various readings at the block but none of them stood out as outrageous. I took the thermostat out yesterday . This morning I let the engine warm up at about 40 Celsius in the garage before going on the road .Checked temperatures again with infra red at various places on the engine. The temperatures again all normal no hot spots to found.
After shutting down the boiling sound was there but not so alarming as before and stopped after 1.1/2 minute. Oil pressure did not drop a bit during the drive. After looking again at the picture Ray Lee posted the only explanation I now have the internal friction is the culprit After all it is a brand new engine . OR , ? the pinch bolts are facing the wrong way for cooling the cylinder linings.

Maybe I have just to live with it .

Thanks to all your guy's who where so helpful.


Gerard
Gerard Hengeveld

If you give your modern car a fast run, stop the engine then switch on the ignition. I can virtually guarantee that after a while the cooling fan will trip in as the residual heat transfers from the block to the coolant. I have been living with a gurgle as long as I have had the TF, no problems in 40+ years, don't worry about it.
Ray Tf 2884
Ray Lee

This thread was discussed between 05/07/2015 and 14/07/2015

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