1925 DB Radiator Cap question

[Eclector]

I have a 1924 DB roadster. Should the radiator cap seal tightly using a gasket, O ring or the like? I find that sealing the cap tight, pressurizes the system which is good for a system designed for that but I understand these cars did not use a pressurized system. So seal the cap tight or not?

[Spinneyhill]

On my 1930 DC, the cap seals on a gasket and any pressure that develops is relieved by ejecting coolant through the overflow pipe.

[Minibago]

Both my cars, 17 Roadster and 19 Touring seal tight on the cap and have an overflow pipe so will never pressurise.

Your car should too.

[nearchoclatetown]

No gasket, no seal, no pressure, finger tight.

[RichBad]

No gasket on mine and ended up on the windscreen when it overflowed.  Added gasket now all the overflow goes out the overflow pipe:)

[MikeC5]

I bought a new 'dog bone' radiator cap with motometer and it came with a rubber gasket.  It works fine and as mention above, any overflow goes out the overflow pipe .  It wouldn't hurt to make sure the pipe isn't plugged.

[franklinman]

I’ve always run a gasket, especially with a motometer as it gives that little bit of movement for proper alignment.

[Power Wagon Dude]

"Friends" of Early Dodge Radiator Caps,

 

 For those of you who might be looking for an Early 4-Cylinder Dodge Brothers Radiator cap and have availability to a FORD Model-T Radiator Cap (one with little 'ears' on top).

 

The OUTSIDE diameter & threading on the FORD Model-T Cap is the same as the INSIDE diameter & threading for the Early Dodge Brothers Radiator Caps.

 

 Good luck with your search, 

 

"Power Wagon Dude"

 

[RAH]

On ‎8‎/‎8‎/‎2019 at 1:02 PM, Eclector said:

I have a 1924 DB roadster. Should the radiator cap seal tightly using a gasket, O ring or the like? I find that sealing the cap tight, pressurizes the system which is good for a system designed for that but I understand these cars did not use a pressurized system. So seal the cap tight or not?

O.K. Guys. Here is the answer. The gasket in the radiator cap on DBs was introduced in Serp.'19 at car # 385772.  The Dodge brothers 4 cyl engines were NOT a pressurized cooling system. As such If your car is trying to express water from the rad cap there is another problem, likely a plugged 'Overflow Tube' . Check for wasp nest or crushed pipe. Good Luck and Keep 'em Dodgin'

[RAH]

7 minutes ago, RAH said:

O.K. Guys. Here is the answer. The gasket in the radiator cap on DBs was introduced in Serp.'19 at car # 385772.  The Dodge brothers 4 cyl engines were NOT a pressurized cooling system. As such If your car is trying to express water from the rad cap there is another problem, likely a plugged 'Overflow Tube' . Check for wasp nest or crushed pipe. Good Luck and Keep 'em Dodgin'

 There is a possibly more likely scenario that was not mentioned. That could be a partially plugged up radiator core restricting the proper flow of coolant. That could build up pressure more than would be relieved by that 'Overflow Tube' Have your radiator flow tested.

[Spinneyhill]

6 hours ago, RAH said:

Have your radiator flow tested.

Good plan. But how much should it be? I have not come across any figures.

[RAH]

16 hours ago, Spinneyhill said:

Good plan. But how much should it be? I have not come across any figures.

Spinneyhill,  Sorry I have no specific data only repeating statements from friends that have had that procedure done in a 'radiator shop' Apparently there are different 'Flow' data for different radiators. And I am not a radiator technician.

[trini]

I have an inline thermostat in my 28 DB 6. Before I installed the thermostat I filled the ad right up. The fluid was boiling over the top. After installing the thermostat without the rad cap I could look into the rad and see the liquid circulating. I installed a dogbone and thermometer and ran the engine for half an hour. There was a good size puddle on the floor. I was looking for leaking hose and bleed cock when it suddenly dawned on me the liquid flowed through the overflow pipe.  I forgot the old geysers carries internal overflow pipes. . Most modern rads have overflow on top which empties in a bottle and sucks it back when the engine cools. The system  corrected its level itself. 

[Spinneyhill]

Yes. Many would add water now, which it will just eject again. It is enough to have the water just above the top of the core when cold.

[nearchoclatetown]

On 9/17/2019 at 6:05 AM, Spinneyhill said:

Good plan. But how much should it be? I have not come across any figures.

I don't know that there are actual calculations for that. A friend that owned a radiator shop for 40 years used to eyeball the flow. He would hold the bottom pipe closed and fill with a garden hose. When full he would let it empty while still filling with the hose. If the level went down in the radiator it was good enough. Not very scientific but he worked on everything from modern to antique to tractor trailers and farm equipment and it worked for him.

[Spinneyhill]

23 hours ago, nearchoclatetown said:

I don't know that there are actual calculations for that.

I have found some! Yay!  http://www.starship.org/Bugsby/Adventures/2009/Radiator-Flow2/Radiator-Flow2.php

 

One theory is that if the radiator is clear enough, the flow will be controlled by the size of the outlet at the bottom, in a non-pressurised system where the water flows through the radiator under gravity. Using Bernoulli's equation from the mid 18th century, one can derive an equation for the effective area (and thus diameter) of the outlet:

where V is the volume of water and Ƭ is the time to empty the radiator. g is the acceleration of gravity and h is the water depth from centre of outlet to water surface.

 

So, stand up the radiator and block the outlet. Measure the water to fill the radiator. Measure the depth from water surface to centre of outlet at bottom. Then remove the outlet plug and time (in seconds) how long it takes to empty. This is really easy if you work in SI units; whatever you do, you need to work in a consistent set of units - and US gallons is not one of them. Lets do an example. The radiator takes 8.9 litres to fill = 0.0089 m³. The depth of water is 660 mm = 0.660 m. g = 9.81 m/s². It takes 10.4 seconds to empty (an average of say 5 trials). The effective diameter of the outlet is the square root of a/π = 24.6 mm, just under one inch. So if the measured diameter is 1", this is pretty close and the radiator might be OK. One should still check for partial blockage though.

 

[trini]

Spinneyhill, you are one of my favourite bloggesr, I always learn something from you. There are other guys like MAAt,  Carhartly  and a few others. That is what makes this forum interesting.

Sometimes a little home made remedy helps for example radiator guys boil radiator in a special hot water tank. It works . My view is "how effective"  The regular radiator guy is obsessed with maximum production for the day and so speed is important, not quality, to a great extent. I witnessed that first hand . Since this is a hobby we should enjoy doing things for ourselves as far as possible. There are bloggers on this forum who will jump in and give you oodles of advice. I would make up a steam pot  and direct the steam into the rad or gas tank. It may take a while but you will have the satisfaction of doing a first class job and have fun doing it at the same time.