QuestionI have a 73 buick with a 401 that over heats.
I had the radiator flow tested and it tested 95%
Checked compression and they are 125 lbs + or - 10 lbs
new cap at 14 lbs
time 4 degrees before top dead center
flushed the motor both ways
filled the water up to the neck on the intake manifold with fan belt off, there were no bubbles
took the water pump off and it seems good, no play
changed the themostat,nothing changes
it over heats in as little as five minutes after starting
thank for any idea..........mike
AnswerYou've done all the right things, except one or two: When you had the water pump off, did you verify that the impeller was securely fastened to the drive shaft and pulley assembly? These are pressed on, and if the last rebuilder took a short cut, it might not be turning with the fan. If that is the case, you will not see water circulating when you look into the radiator after the thermostat opens. If you can't see far enough to tell, feel the upper hose - it should get hot rapidly as soon as the thermostat opens.
Second, if it has never been done, you need to remove all the "core" plugs (AKA Freeze-out plugs) from the sides of the block and dig out all the accumualted mud from the last 34 years. Flushing doesn't get those deposits out - it has to be done mechanically, with hacksaw blades, ice-picks and whatever else you can use to get into the crevices and lower regions of the block casting. Use a garden hose with a good pressure nozzle to flush out the crud. You'll get very dirty, and so will your driveway - that's part of the fun of old cars. Wear glasses! If yo want to prove to yourself that this is neccesary, open the block drains and see what comes out. Nothing? Try poking in the hole with a toothpick - when it starts to dribble out, stand back and poke some more. You'll be shocked!
The rear sides of the block are always the worst, so you'll have to remove the starter to get at one side. It is also probable that there are accumulations in the heads, but do the block first- it's easier and cheaper, and that may cure your problem. Before you start the engine after this operation, install a coolant filter in the upper radiator hose, because you will inevitably dislodge some crud that you can't get out - you want to catch it in the filter before it plugs your radiator! I like the "GANO" brand filter, because you can see what it catches and clean it out periodically until no more comes through.
It is remotely possible that you have an exhaust blockage - but if the car drives OK with normal power, forget that one.
Dick
