2007 Ford Fiesta coolant system problem

TUSHARRAJA

MEMBER
2007 FORD FIESTA
1.4L
4 CYL
TURBO
FWD
MANUAL
73,000 MILES

There is a tiny hole in my 2007 model ford fiesta's coolant expansion tank. I closed it with an epoxy and everything is fine. I drive car and there is no decrease in coolant level, the problem started when I switch ON the AC. After few kms drive with AC on, I open the hood and that hole was open and tiny bubbles were coming out of it and aprox 250ml of coolant was lost and engine starts to overheat. I want to ask does the pressure increases with the use of AC? Does replacing the coolant tank will solve the problem? Or with the AC on the car is drinking coolant?

there are no signs of faulty head gaskit.
no wet spot is formed when the car is standing.

1 Reply

ED-WEEZY21

MECHANIC
248 POSTS

I would expect that replacing the coolant expansion tank would solve your problem. Using the AC causes a higher load on the engine which makes the engine work harder thus causing the coolant to heat up faster which is why most cars will have 2 cooling fans. One that runs when the AC is off and the other fan typically only kicks on when the AC is on. On rare occasions, if the first fan doesn't kick on or if the engine is getting too hot, the computer will kick on both fans even when the AC is off. Other cars that don't have 2 fans, use a high or low speed on the 1 fan. Same concept though as the other set up. So ultimately, if you see no leaks anywhere except from the pin hole in the expansion tank, I would replace it. Coolant will become extremely hot and epoxy stands no chance between the pressure inside the expansion tank and the heat.