Stant 11233 Radiator Cap Problem

[prbarr]

First off, I want to give a big thanks to all the contributors here, especially Stretch and Mustang!  I've spent the last few months reading through the various how to's on the site and purchasing all the necessary tools. Last weekend I did my 24,000 mile maintenance.  I saved a few hundred dollars and learned a lot.  

Now on to the subject of the post:

After replacing my coolant on my '05 I noticed a small coolant leak from my stock radiator cap.  I went to the store and purchased the Stant 11233 16 psi (1.1 bar) replacement cap.  I took the tank back off and replaced the stock cap with the Stant.

When my coolant heated up with the Stant cap fitted, the coolant would start quickly filling the overflow.  It would puke some coolant until the fan kicked on, then the coolant would slowly drop below the min level.  This kept repeating as the coolant heated and cooled.

It turns out that the Stant 11233 cap is a few mm shorter than my stock Triumph cap.  The attached picture shows the Stant 11233 on the left and the stock cap on the right.  Because it was shorter it did not seal correctly in the thermostat housing, allowing the coolant to freely flow into the overflow reservoir.

I cleaned up the stock cap, checked that the rubber seals were ok, and re-fitted it.  I haven't had any problems since.

Anyone else run into this problem with the Stant caps?