MTFCA Forum

I drove the 12 over to a friends house and while driving I noticed the dogbone radiator cap with the motometer started spinning. It was un screwing. I put in a new rubber gasket from Lang’s and it was nice and tight but it started unscrewing by itself again while driving. It is a original round tube radiator and old cap that is not all worn out with new rubber gasket, the cap threads are tight as I screw it on the radiator, what am I not seeing. Frank

You could move South of the equator; the Coriolis effect would then cause the cap to tighten.

Try a leather or fiber gasket ?

What you are seeing is how much the motion and vibration is acting on the filler neck with the weight of the dog bone cap and motometer.

Those dog bone radiator caps are not beneficial on brass cars that are driven, they often cause unneeded vibration and stress due to weight imbalance that will cause cracks and leaks in the solder at the base of the radiator neck.

Frank---I had a similar problem on my `24 Touring---replaced the std. rad gasket with a large o-ring--this allowed better tightening and now keeps my dog-bone rad cap firmly in place---good luck! paul

I have experienced caps bottoming out on the threads before contacting the gasket. Remedied by adding one or two more gaskets. I believe it would make a more snug fit.

At any hardware store you can purchase a sink drain gasket, made for a bathroom sink. These will fit into the neck and are soft enough that you can tighten the cap to the desired position. In my experience with the dog bone or wing type cap, they stay in place when driving.
Norm

John Codman wrote: ↑

Wed Jul 14, 2021 9:48 am

You could move South of the equator; the Coriolis effect would then cause the cap to tighten.

sorry, but that is funny

Well, I am not planning on moving to south of the equator, but, I am going to try some pipe dope or pipe thread compound. It seems to work really well sealing dripping oil where I used Teflon tape before. All ideas welcome. Frank

John Codman- thanks for that! I laughed out loud at work!

Maybe the "arms" on the dog bone need to be balanced

By the picture you submitted, you seem to drive at precarious angles.

Sincere question: Do the dog bones and wings cause the separation problem on the riveted 1913 radiator filler necks to the tank?

What you are seeing is how much the motion and vibration is acting on the filler neck with the weight of the dog bone cap and motometer.

No motometer needed.

One fiber gasket at the bottom, then the neoprene, followed by pipe tape worked for me.

On my Fordor I had the motometer NUT come loose and disappear into the rad tank! A club friend had a new nut that fit.

I heard getting the rad tight solves the problem!

A refresher on radiator cap installation is required here I’m afraid.

Confirming, per John Codman's information, that 'down under' we don't have an issue with the cap unscrewing during use.

However we have some difficulty checking the level 'cos the water just falls out when we do take the cap off...

Many of you know Dean Yoder drove from Richmond, IN to Spokane. I am not sure if he lost his cap, but he replaced it with what looks like a Gatorade bottle upside down. He has driven with that replacement for at least a thousand miles. It works

I have a friend with a vintage Rolls Royce and when he goes to an informal car show or cruise-in, he removes the 'flying lady' (Spirit of Ecstasy) mascot and puts this in it's place. I don't have an actual picture of his car and the ornament so I grabbed a stock picture from the World Wide Interweb.
He duct taped a wooden plug to the bottom of it and plunks it in the filler neck.
His theory is if someone wants to steal Snoopy and his biplane, then have at it!

A refresher on radiator cap installation is required here I’m afraid.

I was lucky that it just turned over and didn't fall off before I noticed it had worked loose. I do make sure it's screwed down tight now.

The strangest parts often work themselves loose on a T. If you haven’t lost something while driving a T, you are in the minority I would guess.

The radiator cap becomes loose or spins off because you are using the wrong motor oil!

A couple flat rubber gasgets from the plumbing dept. In the hardware fixed mine. Before that I had to drive in reverse to keep it tight.

Frank, when you tighten down the cap with the rubber gasket, can you feel it "snug" down on the gasket nice and tight? I have used one of those rubber gaskets from Lang's for years with my dogbone cap with MotoMeter on our '25 coupe and on the TT that Dallas now has with absolutely no problems. Granted, that's not the same neck as yours, but I don't see how your cap could loosen that easily if it is contacting the rubber nice and snug. As was said, an extra 'O' Ring might be worth a try. I did have the MotoMeter nut loosen up once, but I caught it before it fell into the radiator. Dave

I've lost two Motometers now so I don't run them anymore. The cap, Motometer and neck all left on their own. Running dirt roads just makes it happen faster. The replacement pictured worked well, no vibration.

Video still showing Dean's current motometer.