Question, is it bad to run and drive the engine without radiator cap on?
No, it is a non pressurized system. You may have some coolant flowing over the neck rather than going down the overflow tube if you over filled the radiator.
It wonít harm the engine, if thatís what youíre asking. My T rattles and bounces enough that Iíd probably get near boiling water splashing out as I drive which would be bad for the paint on my rad shell and hood (if I had a hood!).
I once drove about 300 miles with a rag stuffed in the top of my new radiator after the neck fell off. No problems.
allow me to ask... if I have a non pressurized system (as I have always thought I did) Why does my coolant boil out around my radiator cap??
And yes, this has had me baffled for years.
Or too hot.
In a properly working system, the flow is produced by a difference in density of the cool vs. warm water. It is actually a gravity system. As the radiator cools the water, it becomes more dense, heavier if you will, and falls to the bottom of the radiator due to gravity. As it does, it pushes the lighter warmer water in the engine upward and into the top of the radiator where the cycle repeats itself. This cycle is relatively smooth and continuous. It is not the rhythmic sudden surges that you sometimes hear people referring to as thermobarf.
In a system that is not cooling properly, steam can form in the block and build enough pressure to 'blow' the water above it, somewhat violently, into the top of the radiator. When this happens, it is sudden and the water will look for a way out if it can't flow through the radiator or out the overflow tube quick enough.
Thanks Hal, It sounds like it is time for a flush.
In my mis-spent youth, I think we drove them as much without a cap as with, made it easier to pour more water in from the bar ditches and pot holes.
Hal has the principal correct. The technical term for this process is called thermosiphoning. Henry was way ahead of his time when he utilized this form of cooling 100 years ago. This type of cooling is taken credit for as an emergency cooling system in the design of many commercial nuclear reactors in production around the world today.
Check your overflow tube to be sure it is clear.
My Dad, he was born in 1905,told me that a local
had his radiator go bad one winter and with no money had to drive his T all winter with out it. He told me it was an unusually cold winter. This was in N.J. in the late twenties. He said apparently did little damage to the engine. Wouldn't recommend trying it though.
The cap is for one purpose, to avoid boiling hot water in the face of the driver if the windshield is open. In the event of a boil over the cap redirects the hot water down the over flow pipe. These engines had very skimpy cooling and some used kerosene as coolant in the winter.