Classic/Antique Car Repair: 1966 Mustang Overheating, mile test drive, upper radiator hose

Question
Dick,

We have a 1966 Mustang, 289 V-8, with almost the same issue as item 3 in your answer on 6/22/2007, which is percolating in the upper radiator hose after the engine warm.  So far, we've installed a brand new radiator (from Performance Radiator in Seattle), new hoses (upper and lower), a new radiator cap (13 psi), and today I installed a new 195 degree high performance thermostat.  The car heater works great, and it runs well.  The temperature gauge shows needle is to the right of the "M" on "TEMP", and is steady there, too.  When we shut down the engine today after a two-mile test drive, the top radiator hose sounded like a washing machine off-kilter, and I could feel like a boiling of fluid inside the hose.  It felt like it was ready to blow!  The only other thing we haven't done is to replace the water pump.  Please help.  Sign me - Stumped in Seattle.

Expert: Dick Benjamin
Date: 6/22/2007
Subject: radiator and thermostat


Answer
I don't remember the previous question (I've done almost 4000 of these Q&As since I volunteered on this site), but your symptoms sound like the block needs to be cleaned out.  This requires removal of the "core" plugs (AKA freeze-out plugs), and then a careful digging out of the crud and mud that has accumulated over the last 42 years in there.  If you are not familiar with this process, I'd recommend you have a mechanic do it for you. It is a very dirty job, and may require removing the starter and possibly even the motor mounts to get at all the core plugs.

If you want to check yourself to see how much crud is in the block, open the two block drains (one on each side of the block, just above the oil pan flange).  I'm betting you can remove the brass plugs and nothing will come out!  Stick a screwdriver in there, wiggle it around and then jump back - you'll get a lump of mud and then a stream of really dirty, rusty water. If you get that, you know it is time to clean it out!

One thing you did not tell me - so I have to ask - you do have at least a 30% solution of anti-freeze in there, right?  If not, do that first.  If you have only plain water in the cooling system that is part of your problem.

Dick