MTFCA Forum

This has been an issue for some time, If I keep my speed no faster than 35mph the engine runs at normal temp. If I push the engine to 40mph it wants to run warm. The moto meter will be full red. As soon as I back down the speed she cools back down and the moto meter runs in the right range. 10/30 oil, Relatively new Burgs rad, High comp head. No water pump. Air temp low 80's. Timing?

When it's hot, are you also blowing steam out of the overflow tube?

While a Model T will heat up more than normal when not adjusted correctly locating the source of the problem can sometimes be challenging.
I like to use a handheld laser thermometer and check around for clues.
The motometer could also be not calibrated very well.
When using a laser temp probe it does not work well on shiny surfaces so keep that in mind.
A properly operating Model T will run hotter than you might think, but below boiling.

Any extra drag or friction, including using the brakes too much, will make the car run hot.
Bad Timing, lean mixture, and bad running, or running too hard will also make it heat up.
The fan is only a factor when the car is not moving, once it gets up to speed the air will be moving faster than the fan .

See the following links:
https://dauntlessgeezer.com/DG96.html
https://www.mtfca.com/discus/messages/7 ... 1503585360
viewtopic.php?t=23118
https://www.mtfca.com/discus/messages/2 ... 1334508519
viewtopic.php?t=44772

I set my timing to lever all the way up, spark starts when the piston is 1/16" to 1/8" down after TDC.
It runs well and is plenty safe for hand cranking.
When driving set the timing lever to where it is happiest (most power).
Mike

If the car is not boiling over, it is not running too hot. In warm weather a Model T will usually run from 180F to 200F. At speeds over about 27 MPH, full spark advance is needed. It is important the the spark lever linkage be adjusted correctly so that the timer is actually responding to the lever as it should. The same is true of the carburetor adjustment linkage as well as the pedal and lever linkages.

more speed = more fuel = more heat

The T cooling system is adequate for speeds up to around 50 MPH at temperatures over 100F. The engine will run hotter, but the coolant will not boil. A very long climb or a strong tailwind might cause problems. Higher elevations will lower the boiling point of water, and could lead to issues in mountain country. The engine will run best at temperatures of 180F to about 205F.

Timing seems to be #1.
#2 is it running lean? The EASY test is to adjust the choke knob and try slightly richer at high speeds. If improved results, then you know to check fuel flow or blocked "jet".

Your profile shows you own a TT. Are you talking about the TT?
What you are experiencing seems to be normal pushing a TT with stock gearing this fast.
(My last thoughts)

My first thought was - are you dealing with a barn find car that was worn out during the depression? A worn out motor putting out 8HP working too hard after 35mph? That performance would not be unusual.
Then I see you have added a hi compression head. Do we assume this is a fresh rebuilt motor? What is the condition of the motor?(be specific)
Have you checked that all 4 cylinders are working? Short out 1 plug @ a time & see if there is a change.(stationary)
While running @ speed, hold the points open 1 @ a time. Should notice a big performance difference. If not, coil or timer crapping out.
Leaning out? try opening the mixture needle @ the higher speeds. If missing, possible fuel starvation.
A compression test would be useful.
Worn cam? Not enough lift from wear or a bad lifter? Deep valve seats? A new defective ground cam? Timing off?
Could there be a rat nest in the muffler?

TXGOAT2 wrote: ↑

Mon Dec 29, 2025 12:28 pm

The T cooling system is adequate for speeds up to around 50 MPH at temperatures over 100F. The engine will run hotter, but the coolant will not boil. A very long climb or a strong tailwind might cause problems. Higher elevations will lower the boiling point of water, and could lead to issues in mountain country. The engine will run best at temperatures of 180F to about 205F.

I sure thought the Model T was DESIGNED for 35 MPH top speed?

love2T's wrote: ↑

Mon Dec 29, 2025 4:04 pm

TXGOAT2 wrote: ↑

Mon Dec 29, 2025 12:28 pm

The T cooling system is adequate for speeds up to around 50 MPH at temperatures over 100F. The engine will run hotter, but the coolant will not boil. A very long climb or a strong tailwind might cause problems. Higher elevations will lower the boiling point of water, and could lead to issues in mountain country. The engine will run best at temperatures of 180F to about 205F.

I sure thought the Model T was DESIGNED for 35 MPH top speed?

Actually 45mph @ 1800 rpms.

But a tip top rebuilt motor, with stock gearing, will do 55 easy & Cruse very comfortably @ 45 all day.
Remember, the Montana 500 boys AVERAGE 55+ over 500 miles with stock motors. That includes driving town speed limits 25 & 35 during the race.
A little "blueprinting" without rule constraints will get you well over 55.

Ts had no designed top speed. Ford literature claimed the T had "All the power you will ever need", and "Speed to 45 MPH, if you want it." Road conditions and common sense limited speeds to 35 MPH or less, often far less, during the balance of the T era.

Will wrote: ↑

Mon Dec 29, 2025 7:13 am

This has been an issue for some time, If I keep my speed no faster than 35mph the engine runs at normal temp. If I push the engine to 40mph it wants to run warm. The moto meter will be full red. As soon as I back down the speed she cools back down and the moto meter runs in the right range. 10/30 oil, Relatively new Burgs rad, High comp head. No water pump. Air temp low 80's. Timing?

Motometers are not precision instruments. How old is yours & have you ever calibrated/compared its readings to a infrared digital thermometer?
"Normal" engine operating temperature is 180 °F. What coolant are you running with, just water, 50/50 antifreeze? Remember to that Motometers were design to measure coolant vapor. What I'm getting at, the first thing to do is to validate the reading from the Motometer. Without that verification you'll be chasing a ghost.

I have seen High compression heads installed to revive a worn out engine.
Including on my Centerdoor estate purchase.
I trust nothing unless it is proven to be good, almost all the time.
Measure what it really does and when it does it.
Even measuring cylinder and spark plug temperatures can tell a lot about what is going on.
I love my handheld unit, it's useful for lots of things.
And they are not expensive anymore.

Will wrote: ↑

Mon Dec 29, 2025 7:13 am

been an issue for some time, If I keep my speed no faster than 35mph the engine runs at normal temp. If I push the engine to 40mph it wants to run warm. The moto meter will be full red. As soon as I back down the speed she cools back down and the moto meter runs in the right range.

Have experienced the same, a good running T with same equipment, runs cool, but the motometer will show the added engine heat when running wide open on a busy road!


Installed a fairly accurate temp gage, sender in the water outlet, running normal speeds, right at 180 degrees.




Now on the open highway, speeds to 40-45, the temp will rise.



Speed equals Heat! Slowing back down brings the temp down too.

Will,

My reason for asking if you're making steam is that the motometer, while giving interesting feedback of relative temperatures, is not a precise instrument. As others have mentioned, take the coolant temperature using a more accurate method, or simply notice if it's actually boiling.

Hoping for your feedback...

My experience is similar to Dan's, with the engine running about 180F in mild weather and at lower speeds, and around 200F in very hot weather or at higher speeds, such as 40 MPH+, or on a sustained climb, or with a steady tailwind. If you are using 50/50 green antifreeze, the system may run a little hotter than with plain water, but the boiling point of the coolant will be a little higher also. The engine is perfectly happy with the water outlet temperature at 200F to 205F, or a little more. Boiling is to be avoided. You don't want steam bubbles in the engine. You want liquid coolant in contact with the interior water jacket surfaces. /// The thermosyphon system will not circulate the coolant until the engine is fairly hot. Once circulation begins, when most of the coolant in the engine is at around 180F, it will circulate faster as the coolant gets hotter, so long as the radiator and coolant passages are clean. If the system reaches the boiling point, it's time to back off or stop. Coolant boiling in the block will impede the circulation and can prevent coolant from being in full contact with the interior surfaces of the water jacket, especially at the hottest locations around the exhaust valve seats, and you don't want that.

After reading the posts here I’m of the opinion that the spark lever is being improperly used. Any one that’s familiar with a distributor with weight and vacuum advance units knows that timing isn’t static at all but varies with speed and load. Some T drivers set it and forget it and that seems to work for them. I have in fact seen Steve Jelf do this exact thing. Started the car and pulled the spark lever way way down. Actually I was surprised at this. Again what ever works for you. Until a problem develops. Sometimes under unusual circumstances. He doesn’t over heat at lower speeds but cooks at high speed. Really sounds like timing. I’m reposting the spark lever chart which can be very helpful in setting the T’s spark lever correctly. Try this before spending any $. It might be all you need to do.