I have a 2007 f-150 4.6l with 137,000 miles and I recently replaced the intake and have come across a new annoying problem. The coolant bypass cap keeps getting blown off causing all my coolant to spray out. This seems like a useless part. What could be causing this a d how can I fix it????

 

Hi Robert,
If this is what I believe it to be, a couple of things might come into the picture.
What is holding the cap in place?
If pressure is building in the cooling system, how much and why?

A defective or incorrect radiator cap not releasing expansion into the recovery system.
You don't mention why you replaced the intake manifold, could there be an underlying reason which you did not mention?
Excessive pressure build up possibly due to compression getting into the cooling system?
What is the engine operating temp at the time the cap takes off?

This seems to be one of those times when an answer brings more questions than it answers. Can you provide some addl info? Thanks.

 

I was told by a mechanic that my intake was warped causing coolant loss and plug 8 to fault quite often. So I let him do that now I have this problem. The radiator cap is the same as before and I don't believe this is temperature related if I drive like a normal person it seems ok but when I hammer it to pass it blows off. This last time it took the hose clamp with it too and sounded like a gun shot as it hit under the hood. I was able to get air all the way through the system when I drained it last time. I really need to narrow this down or shove the truck in my mechanic's shop.

 

From what you describe, it seems like under load compression is getting into the cooling system. That is easily confirmed with only a cooling system pressure tester. When the engine is under load a questionable head gasket could allow compression into the cooling system.
Did the engine ever overheat ?