EMERGENCY!

I wish I had your problem. It's snowing here today, and my car is in the garage till spring.

Gumby '04GT

it goes anywhere it might fit in the hose that comes FROM the thermostat area, This is to prevent pressure from the water pump from overpowering the heater, while the thermostat is closed

Backyard Mechanic

Well.. that last doesnt make sense when you think about it.. as the system pressure probably wouldnt have built up yet.

it would be in a fully loaded (minimal air for buffering) system as the thermostat begins to open that the greatest pressure at the heater would be felt. That would be the pressure rating of the cap PLUS the pressure added by the water pump -maybe about 5 lbs- for a total of 20 lbs.

note: I replaced a core in the late 80's and a slip in the box said to "pressure test before installing"... nothing else.

So I hooked up a short length of tubing to each end and applied a garden hose.

didnt see any leaks but then i made the mistake of putting my thumb over the end of the exit tubing to partially block the flow...and the core blew up like a balloon.

The guy at the parts counter didnt want to take it back, of course, then i put the instruction slip on the counter. He just laughed and said it served them right.

Read what he said again. It's the water pump pressure that builds up at high RPM. The restriction is there to slow the water down so it won't "balloon" the heater core. Replacing this hose with a regular hose is one of the reasons Mustangs loose heater cores.

Some more expensive cars like BMW's actually have a regulated bypass to accomplish this. That way they can get full flow at low RPM (lots of heat) and still not kill the core at high RPM.

Al