The radiator on my 1987 accord was replaced a while back and the new radiator cap didn't seal and coolant was lost so I got another brand of cap that seemed to seak better and the problem was solved.

Fast forward, I recently got another new cap and again the coolant went into the reservoir and wasn't sucked back after cooling. I pulled off the tube to the recovery tank and squeezed the top radiator hose and could feel and hear air moving freely past the cap. I'm pretty sure the filler neck of the replacement radiator is too deep compared to the OEM and the cap seal doesn't reach the bottom.

I'm considering machining a ring spacer (.100" or so) to go in the bottom of the filler neck so that the cap will seal. Any thoughts about doing that? I don't want it to over pressurize. I wish I knew the depth of the filler neck an OEM radiator.

 

A) Try to contact the radiator seller / manufactureer for support.
B) Rather than machine a steel ring, I'd get 1/16" and 1/8" firm rubber sheets and cut with tin snips (?) - that rubber material will be kinda forgiving and likely easier to seal.
C) So you got another cap; from where? My go to auto parts firm is now NAPA because their stuff has worked for me - where as AutoZone, Oreilly's works only 1/2 the time. Yeah, likely this is too easy a solution. YMMV

Luck

 

Thanks for responding.

I like the idea of a rubber gasket but I don't want it to fall into the system. I was thinking of an aluminum ring held in place and sealed with a thin coating of 380 deg hot melt glue (Just thinking out loud on that). The geometry is more complected than it first seemed.

3 caps leaked, OEM, Stant and Gates (newest), the one that didn't leak was unbranded from O Reilly which I hate and measures .050" taller than the others.

I usually do my own repairs but this time I had a reputable repair shop replace the radiator and I told them about the problem and they pooh poohed my contention that it was incorrectly manufactured but since I posted this I found the filler neck depth should be 19mm .748" but it's actually .783" deep so I think my suspicion might be correct.

The O Reilly cap works but eventually I'll have to do something about the problem.

 

Think on the rubber gasket concept - the pressure cap is going to hold it in place solidly, so it's not going to walk away. If it did, the rubber ring would only go into the top of the radiator where it's going to sit in coolant for the rest of its life - does no harm.

OMG, I'm going to have a heart attack before I can even open a brew; hot glue to fix a radiator issue! Oh, gotcha, j/k. I recall my kids using hot glue for everything -