29 radiator cap stuck/broke What now?

[P.S.]

A barn find all original 29 pickup rolled into my shop (under its own power) with an original radiator that I don't want to break. The owner wants to keep it all original. Owner tried to remove the radiator cap using tools and the cap came apart, the outer half appearing to spin on the inner which has kinda adhered itself to the rad neck threads. I think the cap might be a really old repro, but not real sure. I don't want to damage the neck or cause the radiator to be damaged, and I need to get this cap off, so the rad can be filled etc. The only thing holding it all together is a really old motometer they drilled the cap to install.

How might you suggest removing the two parts of this radiator cap with the inside part stuck to the threads and the outside part now separated from the inner?

Owner is trying to surprise his dad with it since it was his as a young man, I'm just trying to help make that happen. Thank you in advance!

[Richard Knight]

Paul, I am afraid the cap may have to be sacrificed to save the original radiator. Particularly if is possibly a replacement cap. You could try cutting a slot on one side vertically with a Dremel tool cutting down deep enough to see the radiator neck threads and then with some penetrant added try to un screw it.

[Big hammer]

Use a worm screw hose clamp around the outer part and squeeze it on the inner part and try turning both off ? IDK ? Surgically start cutting the outer off of the inner until you have just the inner part and then use a strap wrench and try turning it off or if that doesn’t work continue surgery removing the inner ? Good luck !

[Ernie Vitucci]

Paul...Just an odd thought. If the outside top is spinning and the inner is not moving...how about drilling one small hole and putting a grade 8 sheet metal screw or a bolt in the hole and then putting a strap wrench around the cap and see if it might move. A little sodder in the hole later might make it still look pretty good. Ernie in Arizona

[Marshall V. Daut]

I had the same thing happen to me last year: the chrome top part came loose from the inner screw-on base. The base could not be removed by hand. I took a large plumber's wrench with good teeth and rocked the remaining bottom half of the cap back and forth a little bit at a time until it could be spun off. I was careful not to twist the neck off the radiator's top tank. My guess is that the radiator and head gasket sealant I had run through the cooling system got in between the radiator cap and the threads on the filler neck, effectively gluing the two pieces together.
Before attempting this, run the engine until the radiator gets hot. This will help expand the broken inner bottom piece and perhaps begin separating the death hold between the cap and the filler neck.
Marshall

[Y-Blockhead]

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Originally Posted by Ernie Vitucci

Paul...Just an odd thought. If the outside top is spinning and the inner is not moving...how about drilling one small hole and putting a grade 8 sheet metal screw or a bolt in the hole and then putting a strap wrench around the cap and see if it might move. A little sodder in the hole later might make it still look pretty good. Ernie in Arizona

I like Ernie's suggestion. Lock the inner and outer together with a screw. I think the issue is when they installed the Moto Meter they probably drill thru the fastener that was holding the inner and outer parts together.

[alexiskai]

I agree, I would attempt to lock the two halves together and then twist off. If you have an induction heater with a large loop, you could use it to heat the halves of the cap after locking them together; this would help dislodge any corrosion fusing the bottom half to the radiator.

[P.S.]

Excellent suggestions! Thank you. If it was my car, I'd be more gorilla-like with it. Since I don't know the history on it (like maybe someone used a sealer as mentioned above), I need to approach this with kid gloves. Not worried about ruining the cap, just the radiator, so cutting a slot might be the way to go, then the screw idea to lock the two parts and unthread. Thanks!!

[Richard Knight]

Cutting the slot will relax the grip of the cap on the radiator neck. All the other methods mentioned will put unnecessary stress on the radiator neck. Just saying!

[LoudPedal74]

I spun the stainless cover right off my gas cap one day. Covered the remaining bit with a red rag and removed it with a vise grip chain wrench. worked like a champ and did no damage.