A couple of times recently while working up my mostly 1923 Runabout I have been treated to a small geyser from the radiator cap. The cap is an old one found in a box of Model T scrap that was found at a swap. It was beat up and threads into the neck but not tightly. It is NOT a good seal.
The radiator is a little used Brass Works flat tube that had been crudded up by a head gasket leak. I cleaned it myself and after noticing a loose side panel that was sent to a radiator shop for repair I had then clean it again. They said it was clean as a whistle.
I had just filled the radiator before the drive but not that high, only about half way from the top of the core to the bottom of the neck. I had thought that would leave plenty of room for expansion.
The car was running good and warm but it did not feel act or small hot yet a one time burble of coolant escaped the bunged up cap & showered the windshield, hood & fenders with droplets.
I'm far from sure that the motor was overheating but to investigate a little further, a repop Motometer was fitted for the most recent drive. The day was warm, 77° or so and all sorts of driving was done including slow & high speed, stop & go traffic and climbing steep hills (including racing a bus) and going down the other side.
The Motometer was reading just below the line under the circle. I didn't expect another eruption as the Motormeter fitted the threads tightly and the coolant behaved itself.
What is normal for driving on a warm day? Do Ts get steam bumbles? Is that Motormeter reading normal?
Vintage Paul, trying to keep cool . . .
A well-running T with a clean cooling system will barf out extra coolant until it reaches the right level. It should go out the overflow tube, not the top. Make a cork gasket to fit under the cap or the Motometer.
My T seems to like the coolant level just touching the bottom of the v-shaped baffle under the filler neck. Any higher than that and it drips out the overflow during and after a drive.
If you have a stash of plumbing repair stuff, a rubber sink drain washer works great as a filler neck gasket.
You might check the overflow pipe in the neck and make sure it is not clogged. It should bleed off any excess expansion.
Your T coolant will expand with temperature. It will take the easiest way out. If the cap is not sealed it will go out around the cap. If it is sealed it will go out the overflow tube providing the tube is not plugged.
Note, When the engine is hot but not boiling, it will not boil over, but expel coolant to the level of the overflow tube. Then when it settles down and cools off, it will be above the core but below the top of the filler neck. Remember also that there is some resistance to the passage of coolant through the tubes of the radiator and that the fluid rises with temperature increase. It won't go back down until the coolant in the radiator cools and sinks to the bottom. So what you have experienced is normal. It is also normal for the coolant to gurgle a bit right after you turn off a hot engine. That is caused by a momentary overheating because no cool air is blowing through the radiator either by movement of the car or by the fan.
The normal temperature for running with a motometer is just below or around the circle on the motometer. Your post is correct for an accurate motometer.
The last line is, that you need to seal the cap.
Mark has the best idea for gasket. Other plumbing gaskets may also work. I had to add additional thin gaskets to allow my bird to be flying forward.
Only time I have had issues with leakage at the cap is after a hard braking with radiator level a little high. I'm sure the new BrassWorks early brass ones have the best baffle design or maybe I brake a little too hard.
Glad your out driving, Paul
Thanks guys, it sounds like a seal or just installing the new cap that is sitting in the parts box might solve the issue. I like the old beat up cap because I painted it black & it contrasts nicely with the nickel plating on the neck and being old & beat up, the cap is a lot less likely to wander off while the public is enjoying the car.
The best news is that the steam bubble or eruption is normal and not a sign of impending trouble. I have had so much trouble with this car that I am possibly a bit suspicious when something happens that I don't understand.
Gene, I have to say that it sure is sweet to be out driving the car after spending more than a decade pouring heaps of time & wampum into what often seemed like a vast bottomless pit. There were times that I would get frustrated and work on other projects but I always came back and with the help of many friends & fellow T folks the car is at last drivable. I hope to have it on its first Club tour next month.