Not Model A: Mustang Q
 

My son recently installed his commercially rebuilt 260 engine. After about 20 minutes of run time on the road, she burped a mass of water from the cap. Radiator does not leak. Thermostat replaced twice, cap replaced, radiator clean.

Sounds to me like the wrong gasket or an upside down gasket traps water someplace??
Assistance please.

Re: Not Model A: Mustang Q
 

I think with the advent of the serpentine belt that some waterpumps turn the other direction---perhaps the wrong waterpump was used, without a thermostat perhaps you can look for flow and direction with the cap off

Re: Not Model A: Mustang Q
 

Clem: Make sure the thermostat is installed CORRECTLY - if it is backward, exactly that problem will occur - ask me how I know!

By the way - VOTED today: you and I have too much combat time to ever allow this day to pass without recognition. Welcome home, Brother.

Re: Not Model A: Mustang Q
 

thanks. No serpentine belt as tis is a early 64 car. Thanks Marcus. Welcome home to you as well.

Re: Not Model A: Mustang Q
 

it still could be a water pump for serpentine car--made to pump spinning counterclockwise-----I have seen it before with a problem similar to yours----

i have also seen a backwards thermostat (I did it) work for several years then cause problem

take the thermostat out and you should be able to see the flow with the cap off

Re: Not Model A: Mustang Q
 

Head gasket installed backwards.

Re: Not Model A: Mustang Q
 

Probably not the wrong water pump as the 260 timing cover/water pump mount is very different that the reverse rotation pump bolt pattern.
Did you run the motor until the the thermostat opened up and burped and had to add more water or was it just filled and driven?

Re: Not Model A: Mustang Q
 

It has occurred several times

Re: Not Model A: Mustang Q
 

Be sure the heater water valve is ON. That helps prevent AIR locks.
"Maybe" it has a combustion leak????
Bill W.

Re: Not Model A: Mustang Q
 

late timing?

Re: Not Model A: Mustang Q
 

Hi, also be sure thermostat has a small hole in it to release air. Mustangs do tend to release water when hot.

Re: Not Model A: Mustang Q
 

Do you have the right radiator. I think a 144 or 200 CI was a standard for engine for a 641/2
just my W.A.G
JB