Water Pressure

[Mike Hayes]

Anyboby out there know what pressure the cooling system runs at, the engine is a Ford 351 windsor, having great problems with the pressure cap letting by when the car is warm, water temperture is about 160.
For the CAV owners what length is the spring on the pressure cap fitted to the expansion tank??
Thanks

 

[Bill Musarra]

Mike,
I have a 351 Windsor and run a 25# Stant cap. It has held up fine and works well. I accidently left the electric water pump off too long one cold day and the temps went very high for a few minutes. When turned on it immediately came back down to normal temps. Didn't lose a drop. If any got by it was then sucked back into the system. Checked the fill tank after cooling down and the level had not dropped. You do realize you need an overflow tank just like all the modern cars do. It allows for expansion of the water and any air bubbles in the system. Then when it cools down it will suck the water back into the system eventually purging the air.

Bill

 

[Dave P]

Most racing caps are 21 to 25lbs I used Stant like Bill also

 

[Pat]

Mike, you may want to be sure you don't have a bubble in your system and the thermostat is good. If there is air trapped by your sender, you may not be getting good temp readings. My CAV has a 18lb Stant and I never get boilouts since I replaced the thermostat. But I have a 302 not a 351.

 

[Randy V]

Quite honestly, while running a 50/50 mix of antifreeze and water, I have not ever seen the need for more than 15# radiator caps. Typically run a 13# Stant Lever-Vent..

 

[mark b.]

on the pressure side, the water pump can make close to 16# of pressure, probably seen when the thermostat opens. so you have to cover this, plus the pressure increase through temperature, hence the 20-25# caps you are seeing.

 

[Rick Muck- Mark IV]

Have the cap pressure tested. I have personally checked a batch of ten 13# caps new in the box and only 3 held the rated pressure.

 

[Mike Hayes]

Thanks for all your help the pressure cap was rated at12lbs when I bought the car, but one the hoses had a slight leak, fixed that problem, I have changed the pressure cap to 21lbs but still venting water. Checked the water temp on the hoses and rad all about the same 160, so the water flowing OK

 

[Cliff Beer]

Pressures have gone up over the years....in the old days (70's/80's) it was common to run 12-14lbs of pressure in sports cars. Now it's more common to run 14-18lbs. Of course, higher pressures put a bigger strain on the hoses and clamps and such, while at the same time raising boil over temps. It's a trade off.

My cars all have caps in the range of 12-16lbs (.9-1.2 bar). Seems to work pretty well for me.