Heat exchanger - can coolant mix with raw water?

[SimonA]

In a bowman type heat exchanger like the one in the image can coolant escape into the raw water? What keeps the two separate and is it something to do with the rubber end caps? When I fill mine via the filler on top the coolant level drops quickly with a flow to the exhaust end, trying to work out where the coolant is going.

 

[volvopaul]

In a bowman type heat exchanger like the one in the image can coolant escape into the raw water? What keeps the two separate and is it something to do with the rubber end caps? When I fill mine via the filler on top the coolant level drops quickly with a flow to the exhaust end, trying to work out where the coolant is going.

View attachment 58176

The two rubber end caps keep it all separate so make sure the clips are tight and the tube stack is central I E equal amount of stack protruding the main housing.
Or you have a tube leaking.

 

[omega2]

Take it off and clean the surfaces, thats if there are any left! the final clip exhaust end looks a bit off line.

 

[SimonA]

Just for future reference in case anyone searches for this problem, it was indeed the rubber end cap causing coolant to leak into the exhaust when the engine wasn't running. When the engine was running back pressure from the exhaust found its way into the coolant giving all the classic signs of a blown head gasket, lots of pressure and coolant overflowing from the pressure cap. The issue was the second clip wasn't sat on the heat exchanger stack tube. Raw water was also able to mix with the coolant.