Jonathan Davis

I have a mustang 2005 v6
My old serpentine belt was starting to slip so I decided to replace it.
Replacement went well, and everything seems to be turning fine, I've made sure it's routed exactly as it was before (took pictures). No slipping as far as I can tell. However now the heater isn't working as well, and I've noticed coolant starting to boil, which obviously is the most worrying. I made sure the coolant pump pulley is being turned, which it is. I've noticed the heater will start to work with higher engine revs, either at high speeds or starting from a stop. This problem started the next drive after I changed the serpentine belt, so I really think it has something to do with that, and not the heater core.
Any ideas would be super appreciated.

Goldenpony

Are you sure the water pump pulley is turning in the right direction. Sounds like it could be rotating backward.

ucinn

Definitely sounds like a water pump issue.

Jonathan Davis

I will double check to make sure it is turning in the correct direction. Could it be that this new belt is not turning as fast as the old one?

ucinn

No, the belt, if fitted properly will turn at the same rate as any other belt.

Jonathan Davis

Just thought of this, could it be the the tensioner pully? When I was pushing it down, it felt like the bolt I was connected to may have moved a bit. I'm really hoping I don't have to replace the water pump, as that's huge pain.

Goldenpony

You should have a sticker under the hood with a diagram of the belt routing. It almost HAS to be a problem here. It's easy to get mixed up with a serpentine belt.
I doubt very much if you have to replace the water pump, if it was working OK before the belt change it is OK now.

Derf00

a bad water pump will leak more so than just stop cooling...unless the impeller is just spinning n the shaft which is highly unlikely. Check the routing of the belt. everything should be spinning clockwise. A bad tensions would also give some signs like belt slipping (Which would be heard) or belt skipping which would be seen. (Bouncing a lot while spinning)

Goldenpony

How's your problem doing? Did you figure it out?

Jonathan Davis

I found the problem. It was my radiator cap, it had lost it's ability to hold pressure and was allowing coolant to boil out. I have no idea why I never noticed this problem until I replaced my serpentine belt. It seems to have fixed the problem so far though. Luckily this was just a fluke and I don't have bigger problems to worry about. Thanks for the help.