Is the Radiator Cap a standard 7 psi cap or specialty part"?

[Mike Shumack]

My '05 Patriot with the plastic coolant surge tank has a 7 psi radiator cap. It looks like a standard "Stant" or equivalent automotive radiator cap (there is no name on it), but it doesn't seem to fit well.
It is real hard to get on/off and it looks like it is not seating properly.
It looks like the tabs are not deep enough to fit around the extra thick plastic of the tank (unlike a thin copper radiator neck would be).

I see on the website where the replacement surge tank is sold, that they also sell a cap for it.  https://shop.findmyrvparts.com/surge-tank-radiator-overflow-monaco-rv-01806583-p/190014.htm  They want $25 for the cap. https://shop.findmyrvparts.com/searchresults.asp?Search=190056&Submit=  I'm wondering if this is a special cap for thick flange tanks (or if they are just marking up the price 1000% for a regular automotive radiator cap.

EDIT: I should also ask "is the 7 lb cap the correct size?" On the link above that cap appears to be a 16 lb cap. I can get a 7 or 16 "Motorad" cap at Rockauto for under $2 + shipping.

[Gerald Farris]

Mike,
The radiator cap on your coach is not a specialty part, and the cap that you have now is not the OEM cap. Whoever changed your radiator cap from the original 13 to 16 PSI cap to the 7 PSI cap that you now have apparently used the wrong cap. There are many different regular automotive radiator caps, and many of us have changed the original cap to a 7 lb. cap to lower the chance of the plastic surge tank cracking, especially on the SMC design coaches that use the Ford truck tanks because a 7 lb. cap is all that is needed for an engine that never runs above 205 degrees. You can either try to match your tank with the right cap at the parts store or you can just borrow the cap from an identical coach at your next rally and take it to a parts house to duplicate it in what ever pressure rating you want.

Gerald

[David T. Richelderfer]

Our surge tank radiator cap is also nearly impossible to remove and replace.  Of course, the other problem is it's located up high with barely any room over it making access difficult for removing it and putting in fluids.  Our tank has darkened to the point we cannot see the liquid level in the tank.  So I drilled two holes in the tank, above and below the hot and cold fill level marks, respectively, screwed in small metal elbows, and installed a clear hose on/between the elbows.  Now I can see the tank's fluid level very easily without removing the radiator cap.  I seldom need to remove the radiator cap anymore.

[Mike Shumack]

Thanks again Gerald - you really have a wealth of information on this stuff.

I'm going to stick with the 7 lb cap.
I was able to take a pair of needle-nose pliers and slightly bend the two tabs on the cap so it is a lot easier to get on and off now. It didn't take much.