MG Car Repair: MGB foamy rad

Question

MGB 74 rad 06 15   hi Barry, I noticed that after cooling down from a 100 mile drive, the rad fluid had a thin layer of white foam on top which dissipated later. No overheating or rough running, smoking etc..was evident, but I do seem to have an exhaust manifold leak which is vexing me as well. Note in the picture the fluid has a muddy river green colour. Is there a way to find out if the head gasket is blown and I am seeing intake into the coolant?
   
regards
Paul

Answer
Hi Paul

I am afraid it doesn't look too good.  It could be a blown gasket allowing compression gasses to get into the cooling system.  I would start with a pressure test (both ways):

1) Use a compression tester to check the cranking pressure in all 4 cylinders.  The actual reading is not that important, but they should all be roughly the same, plus or minus 5 psi.  

2) Use a cooling system pressurisation kit clipped on to the radiator where the radiator cap normally sits.  When pumped up to 15psi or more the system should hold pressure.  If it leaks you may be able to tell which bore it is by using a length of rubber tube to listen to each spark plug hole.   

Let me know what you find.