Dangerous to run with radioator cap backed off a half turn?

[N Heat]

I did my waterpump a few months back, and it started to leak. I figured that it was the gasket cuz I didn't clean the block surface that well due to time contraints. I pulled it down this past weekend, and now it's leaking again. I have heard that backing your cap off a half turn will slow the leak. Any problems with this? It will have to due for a week or two. I drive about 100 miles a week.

 

[michaelc80]

Running it with the radiator cap half a turn off? On all of mine that is not fully sealed and could make it interesting when the system is pressurized. If it's a slow leak you're better off letting it leak a little then leaving the cap loose.

 

[brianl703]

It will probably be fine..for the longest time my 1988 Mustang GT wasn't pressurizing due to the use of a "drop center" cap (but I think it probably puked a bit of coolant out of the overflow due to that, too).

I replaced it with a spring-loaded center cap when I found out that it wasn't pressurizing.

As far as I can tell, the Motorcraft cap is a spring-loaded center cap, but the cap Stant specifies for it is a drop-center cap..

 

[jamesn]

as long as you are running a 50/50 antifreeze and water mix in your car, you should be OK. you see, pressurising water raises the boiling point about 3 degrees farenheit for each pound above ambient (sea level) air pressure. so if you ran straight water and no antifreeze you would not boil until 265 degrees or so. with the cap and 212 without it. if you run 50/50 you should be able to get to 230ish before boiling without the cap. do not remove the cap completely, it will steam all over the place.

 

[Kestas]

I've done it in the wintertime with no loss of coolant.

Like jamesn said, as long as the coolant strength is up there (50/50) you should be okay until you can revisit the water pump.

 

[jimfulco]

Taking the pressure off the system lowers the boiling point of the coolant. Some cars' cooling systems are over-engineered enough that you might not have a problem, but others are not.

 

[CBR.worm]

I have done that when I had a radiator hose burst. tape up, refill with water, and drive carefully home with cap loose.

 

[pmwalter]

My company drove a Ford E350 with a 460 engine without a radiator cap for over a week. The radiator had a leak and was able to drive without the cap on. However, once the cap was on, it pressurized and started to leak further. I remember looking into the radiator fill neck and watching the green fluid circulate.

 

[mechtech]

Running your car with the rad cap loose stops the pressure from building, and reduces many leaks.
Your boiling point is less, however - watch out.
Run your radiator low on fluid - a few inches down when cold.
This is a temporary fix that does indeed work, but monitor your temps when driving.