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MG TD TF 1500 - Running Too Cold

I'm having an issue with my TF1500 that from all accounts is rather opposite of most cooling issues I have read about.

My engine temp will not climb higher than approx 122f when the ambient temp is below 60f +/-. As the ambient rises up to the high 70s and above all is well and the gauge rests at the 85c mark.

Engine is a fresh rebuild with one of Len's roller cams. I have replaced the T-stat twice (with the 1/8" bleed hole) and nothing has changed. The water pump is a Moss furnished six-fin. Running a standard anti freeze coolant (green). Radiator is a stock unit boiled out and painted black.

Running this cold in my experience is not a good thing and will most likely lead to premature wear.

Any ideas/suggestions on how to solve this problem.

Thank you

Dan
TF7946
Dan Nordstroom

Is the gauge accurate? Suggest shooting various parts of water passageways, radiator, etc. with IR thermometer. I just bought a decent one for about $25 in Amazon. With wide open or no thermostat I think it would run at least 160 or so. George PS- Are you sure water is actually circulating and not blocked somewhere? The hottest water shoud be coming out of the front of the head, the coolest out of the bottom of the rad and the side block water passage.
George Butz

Sounds like the water could be bypassing the thermostat?Being more of a TC man than TF, I am not sure of the TF system to block bypass when thermostat opens. (Probably a special thermostat with secondary devcice.)

I assume the temp gauge sensor is in the original spot, not transferred to the header tank?

Bob Schapel
R L Schapel

Did you test the thermostat in a pan on the stove with a thermometer?
Regards, tom
tm peterson

Thanks for your responses. Yes, I did check the temp guage with a candy Thermometer at time of rebuild. Right on!

The block was tanked, rodded and blown out with compressed prior to rebuild.

I will do the IR test tomorrow.

Since all is fine when ambient is above 70ish it would seem the guage is reading accurate. Its real obvious that the engine is too cool as the heater is blowing barely warm air.

I'm thinking about trying a thermostat without the bleeder hole. What's the consensus on this issue?
Dan Nordstroom

When you take out the IR reader remember you will get startlingly different results from different parts of the system.



I am afraid I can't find the link now but if you do an internet search you will find a 'map' showing you roughly what to expect.

Dave
D Moore

IR thermometers give very different readings depending on surface, glossy, math, black or white, even if the temperature of the surface is the same. It usually helps to paint the area with a black ink pen.
YS Strom

Dan,
I don't think your engine is running too cold. Seems quite normal to me. My TD very rarely goes beyond 82°C (180°F) even with the ambient temperature at 35°(95°F)which we get here pretty often-tendency rising!

Regards
Declan
Declan Burns

Maybe an air lock and coolant is not fullest.
M Grogan

Dan
During your engine rebuild and refit could it be possible that somehow the heater hoses might be hooked up in the wrong position causing a flow of coolant back to the radiator that is not going through the thermostat--coolant must be getting back to the radiator without passing through the thermostat somewhere
willy
William Revit

I would doing a revisit on my temperature gauge accuracy, easy enough with submerging the sensor in boiling water.

The cooling system on these vehicles is marginal in performance, just check archived posts containing MgA fans, improved water pumps and 4 core radiators being fitted.
G Evans

Dan
Any chance of a pic of where the heater hoses and bypass hose are plumbed in
willy
William Revit

Delcan,

How do you explain the heater blowing cold if the engine is running at 85c. That can't be. As ambient moves up so goes the heater temperature.

I'm wondering if the six fin water pump is performing too well.


I'll attach a few photos of my piping.

Dan Nordstroom

and another

Dan Nordstroom

Try this again

Dan Nordstroom

Is it possible that the head gasket is the wrong way round (they will fit that way).
The pump draws from the radiator most travels down the transfer way to the rear of the block then back through the head to the stat and back to the rad.
If the gasket is upside down the ports at the rear will be blocked and the water will short circuit immediately behind the pump which will overcool that area. There would also be no or little flow through the heater
It may be muddled thinking but that is the way it looks to me.
Ray TF 2884
Ray Lee

Thanks Ray,

You may have hit on the problem. This problem started right after I installed Len's roller cam. We may very well have reversed the head gasket.
If you are correct will there also be hot-spots that could be doing damage to the engine?
I'd like to wait for winter to take things apart....again.

Thanks, Dan
Dan Nordstroom

Suggest not driving at all until fixed, as you could overheat and damage the head/valve seat area. Pull the rear head cover plate off, and you should be able to look or probe straight down into the block. If you are looking at a copper gasket, that is the problem. George
George Butz

Thanks George

I will pursue your suggestion.

Thank you all.

Dan
Dan Nordstroom

Pulled the plate and the gasket is in as it should be. Passage ports are open and clear.

Very puzzling.
Dan Nordstroom

Archive Dead on the highway mystery for a thread about a reversed head gasket.

See http://www.ttalk.info/XPAG_Cooling_System.htm
for Gene Gillam's coolant flow .

Not sure where the IR trace is. Bud
Bud Krueger

Bud,

Did not want to run the motor until I confirmed the gasket orientation. I will have to wait until tomorrow for those readings. Gasket sealer needs to set.

Can you confirm thermostat orientation please.
Dan Nordstroom

Archive Heater or no heater for gordon lawson's temperature traces.

Bud

Bud Krueger

Dan, it looks to me as if you are drawing your heater water from the coolest spot in the system, the bottom, exit, of the radiator. I'll always admit to not knowing beans about TFs, but I think that your heater return is just below the thermostat.

If your thermostat is not functioning below 60F, I suspect that something is wrong in your plumbing. Bud
Bud Krueger

I'll second Bud's observation. The heater plumbing is essentially a cold water by-pass. Cold water is taken from the bottom of the radiator and dumped into the thermostat and the top of the radiator where the gauge sensor is. So your engine temperature is probably significantly hotter than your gauge reading.

Jim
J Barry

This is very puzzling. I appreciate you guys sticking with me. I need to figure this out.

Paul (PJ), if you pick-up on this thread I'd like to ask if you've ever had this problem. Our cars are plumbed exactly the same. As I understand it this is the way the factory had intended for it to be. Hence the factory branch pipe.

Does anyone have a flow diagram for the XPEG?

Dan
Dan Nordstroom

Dan, there is an article on the xpag cooling system in the latest edition of Totally T Type that might help throw some light on your problem. I have no knowledge of the differences between the two engines but it is very readable and includes some flow diagrams.
Chris
C I Twidle

Thanks Chris.

The article is helpful.

If I use the flow diagram shown in this article (although it's of a TD) it suggests the heater feed on my XPEG is coming from the tap right alongside the temperature sensor bulb located in the thermostat housing. If I am correct this should be the hottest location available on the motor.

Is this correct?

Thanks, Dan

Dan Nordstroom

I'm going to back track a bit and say it's a cold water by pass if it flows in that direction (radiator bottom to thermostat). The question is which way does it flow? Which is the high pressure side? That's a tough one to answer.

From an elevation stand point, the top of the water level in the radiator would be driving the flow from radiator to thermostat.

Jim
J Barry

Aha! I was wrong again, as usual when it comes to TFs. The heater flow is from the port on the left side of the engine, at the water pump. The return is from the pipe from the bottom of the radiator. Coincidentally, as shown in Dan's image (14:19:42), the water temperature gauge sensor is virtually adjacent to the heater line source.

Could it have anything to do with the fact that these coolant lines are below the thermostat? Bud
Bud Krueger

Try taking heater out of the loop and see what happens. All you need to do is cut off flow of coolent through the heater core and run engine. May come to nothing but will tell you if you can cross heater pluming off the list as you did when you checked head gasket. Forrest TD/C 22679
Forrest Rubenstein

Thanks for the plumbing pics--
Your hoses look correct to me--
By the way the cooling system works like this-------
Bottom hose is cold -water goes to the pump and is circulated through the block, up through the rear of the head and along the head to the thermostat
While the thermostat is shut(not up to temp) the water will then flow down through the bypass hose to the pump inlet again and will keep going around and around like this till it is warm enough to open the thermostat, at which time hot water ,controlled at a set temp by the thermostat will flow via the top hose back to the radiator and allow a bit of cold to flow to the pump via the bottom hose
If the heater is connected properly, which yours is the hot water is pumped out just below the thermostat(like yours is) and travels to the heater and back to the suction side of the pump (bottom hose)
While the thermostat is shut the heater water circulates through the engine exactly as the bypass hose does
When the thermostat opens the hot water still circulates exactly the same but on return to the bottom hose it blends in with the incoming cool water from the bottom tank

The thermostat controls the temperature

The only thing that can be stopping it getting up to temp is water bypassing the thermostat--With your hoses hooked up correctly as they are it won't be that so it only leaves one thing----------thermostat
You say you have replaced it, but there must be something wrong there- Is it sealing in the housing Ok---why have you got an extra hole in it-did it have this hole before--have you tried it without the hole
I'm thinking the hole is allowing too much ware to circulate past the stat
Maybe worth blocking the hole for a try
willy
William Revit

Willy,

Excellent description!


I read somewhere here on the BBS that it was a good idea to have this hole so not to trap air. I have once again installed a different stat (with the hole) and tomorrow I will test it to see if I have the same problem. If so, it will be replaced with a no-hole stat.

Process of elimination.

Thank you, Dan
Dan Nordstroom

The stats with a hole normally have a jiggle ball. This is lifted into the hole to block it when the pump starts preventing flow.
Dan,
you asked about thermostat orientation. On bellows type, bellow into head and waxstat the bulb into head, should be just flat when looked down on ( see WSM page A34 ). Bellows type opens upward and waxstat down. Wrong orientation would cause overheat I think.
Ray TF 2884
Ray Lee

TF XPEG heater hot supply.


PJ Jennings

TF XPEG heater return. 1250s are hooked up differently.


PJ Jennings

Here's a better pix.


PJ Jennings

The thermostat housing with the additional threaded hole used on the xpeg, will also fit an xpag, if you can find one.
Dave H
Dave Hill

It is also on the XPAW engine,
Don't mix up the fittings, the rear one is NPT (thermometer) and the front BSP (heater).
The early XPAG heater supply came from a cast ally plate at the rear of the head.
Ray
Ray Lee

Gentlemen,

I think the problem is solved.

This morning I replaced the thermostat (again) with a new 190 degree unit (without the bleed hole) and all seems normal. I will always remain puzzled though. How can a hole the size of a toothpick have such an impact. Lesson learned...again.

I took some temp readings from around the motor for informational purposes.

They are as follows:

Rear head plate cover - 130f

T-stat housing right at the temp sensor nut - 160f

Elbow just above the T-stat - 160f

Radiator tank bottom - 70f

Front soft plug - 190f

Rear soft plug - 150f


These numbers seem about right on to me.

Comments are welcome.

And thank you all for sticking with with me on this. It needed to be corrected as soon as possible.


Dan
Dan Nordstroom

Good result Dan. Can you please post a pic showing the hole in the thermostat? I've used a Waxstat & drilled a couple of small holes as was recommended. I've also blocked off the bypass hose & also drilled a small hole in the plate that I used to block it off. This was again recommended to prevent the possibility of an air lock. Your experience suggests that I should replace the thermostat with one without a hole (or holes) drilled. Easy to do at my stage of reassembly. The pic below is of my thermostat fitted to the internally modified original housing. There is a thin brass plate just visible between the two gaskets at the bypass.

The original thermostat was a beautiful piece of design, permitting no flow on startup through the thermostat when it was closed, with all coolant returning to the block via the bypass when the sleeve covering it was open. The reverse occurred when the engine attained operating temperature & the bypass sleeve closed. It also permitted an almost infinite number of varied positions in between, thus constantly regulating coolant flow & ensuring a perfect engine operating temperature. Cheers
Peter TD 5801


P Hehir

Dan - good result
Dan-Peter
If you are going to have a hole in the thermostat it should only be a tiny little one like 1mm (40thou)- just enough to let it self bleed or let little stray air bubbles escape
Anything bigger than this is like fitting an equivelant size cold water supply to the engine----If you have that 1/8" hole in the thermostat there will always be an 1/8" stream of hot water escaping back to the radiator with an equal amount of cold coming in the bottom
At idle and just driving around an engine doesn't generate all that much heat really and having a constant flow of cold water through the larger hole was ,it appears enough to stop it getting up to temp
Most thermostats you get now appear not to have a bleed hole at all but if you have a real close look at them, on the edge of the opening door there is usually a very small flat or a nich to allow a minor bleed
It is more common on engines with a headgasket problem or on racers to see a larger bleed hole, but for most users it is a no no, all it does is slow up the warm up process
Peter--Blocking off the bypass isn't all that good of an idea--smaller is ok but not blocked off-----Reason being that with it blocked off, every time the thermostat opens
you get a charge of cold water in from the bottom of the radiator so the poor old engine will be going through a hot-cold-hot cycle all the time which isn't the healthiest situation for headgasket life etc
(MGF owners know the result of this)
There needs to be at least some circulation through the bypass to supply a bit of returning hot water into the cold input side just to take the temperature shock out of the cold water----Also the bypass is there for a reason,so that water from the water pump has got somewhere to go when the thermostat is shut otherwise the poor old water pump will simply cavitate itself to death

willy
William Revit

The attached photo is of the last one I had in the car. The other one went to the trash bin. They were both the same anyway.

I went through a few of my old stats from years back and there is one with a pin hole about the size of a hair. I suspect I just over did a bit so now I know. Hopefully learning the hard way will help me to remember next time the situation arises.

Memory is slowly fading away.


Thanks again to you all. I really appreciate the help.

Dan

btw, In just drove the car for a couple of hours and the stat remained steady at 80c. Ambient was around 86f.


Dan Nordstroom

Willy there is a hole in my blanking plate of about 1/16". No argument about the purpose & function of the bypass. As I said the original thermostat design was the best. Dan I'll be silver soldering up the two holes shown in my pic above & may re-drill one at about the pinhole size you suggest. I'll also contact Waxstat & attempt to discover if there is a 'minor bleed' built in. If so I'll just fill the holes. Cheers
Peter TD 5801
P Hehir

Peter,

I considered welding up the hole as well, but since a new one was only $8.00 I chose new. I was also concerned the heat may distort the metal which could effect function. Considered a small sheet metal screw to. But if it came loose who knows what it might do.

And I really don't want take it apart again. I'm wearing out the bolt heads. :)
Dan Nordstroom

Peter

You would get away with soft soldering the holes.
G Evans

Great thread Dan! Thanks to all. Cheers
Peter TD 5801
P Hehir

all my waxstats have had a non flow valve in the vent hole.
See pics

Ray Lee

pic 2

Ray Lee

Ray,

Do you know if these are still available? Do you have the manufactures name and part number?
Are you using this in a TD or TF? I suspect they would be different looking at the way the TD installs. But I've never touched a TD, so I really don't know.

Dan
Dan Nordstroom

I am away from home at the moment and will reply when I get back.
Ray TF 2884
Ray Lee

Rang home.

WAHLER marked 7/6 on one side and 82 deg C on the other.
They are still in business, checked their site and they make them vented and un-vented. Take a bit of detective work to find a suitable one.
Ray TF 2884
Ray Lee

Thanks Ray,

I'm going on the hunt.

Dan
Dan Nordstroom

This thread was discussed between 27/07/2017 and 31/07/2017

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