Coolant Expansion Tank Aftermarket Caps

I think I've replaced the coolant expansion tank cap three or four times in the last six years.

Reproduction caps are not expensive at around $7 plus shipping charges each. However, when you multiply that amount by three or four, the real cost becomes clear.

I am not questioning the design per se, since they look almost identical to the originals, but I do question the quality of the materials used.

For the record, I also have an aftermarket coolant expansion tank which has performed great since I replaced it several years ago. However, the caps always fail in the same general area. I've tried repairing them with mixed results.

I've used instant glue and a plastic wire tie around the perimeter, which I also glued in place but that has not stopped them from failing again.

I tried epoxy both on the outside and inside after gluing all the cracks, but there's only so much epoxy you can apply to the inside of the cap and the repairs usually look awful.

The overflow tank cap, because of its design, is constantly under stress by the hoses attached to it, and I admit that using a heavy hose for overflow evacuation probably is not the best idea. One of these days I will find a lighter hose and replace the fuel hose I've been using.

However, the overflow hose needs to be stronger and reinforced since it is directly connected to the radiator, but at least that one is of a smaller diameter.

Fortunately, I saved the original cap which, after decades of service was pretty discolored. But, aesthetics aside, it is in excellent condition.

As you can see, the clear plastic has yellowed over the years, and even though I soaked it in a water and bleach mixture a while ago, there's only so much you can do as far as cleaning is concerned.

Besides that, the cap snaps tightly in place and it feels stronger than the aftermarket cap that cracked and failed after approximately two years.

As the pictures show, I used metal hose clamps to secure the hoses, and the photo below also shows how the hoses apply downward pressure to the cap's inlet and outlet tubes.

When I replaced the original cap and both hoses, I simply mimicked how the old hoses were routed which, according to the Corvette factory assembly manual, were routed correctly, but I may have to revisit that to see if there's a way to route and connect them without downward pressure.

Above: The assembly instruction manual shows the routing of the coolant tank hoses.
I added the yellow highlights.

I also published a video about cleaning an original GM coolant tank cap I purchased at a swap meet. To watch the video visit my YouTube channel or click the image below.

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