Going to replace timing belt and I figured I'd go ahead and do water pump and was wondering what type of coolant is recommended? Is it just the red dex cool stuff? Or would the yellow prestone 5 year stuff be fine?
Neither. Never. Neither will give you the protection from corrosion that the correct coolant will. And neither will last as long. Here are the options in my order of recommendation:
1) Subaru Long Life Super Coolant. It is prediluted and is rated for -34°/265°F, and good for 6 yrs/75k miles. Note that Subaru the factory fill for 137.5k miles, but recommends only 75k after drain and fill. It is my understanding that this is based upon Subaru suspecting that most will not get a complete flush of the old coolant, and that the fresh coolant will be contaminated with old coolant, effectively reducing it's life expectancy.
4) Beck Arnley Extended Life Blue. Also prediluted, rated for -34°/265°F, but no claim is made for longevity. I would be confident using a hybrid life expectancy of Subaru and Zerex, going 5 yr/75k miles. FYI. Beck Arnley is to auto Parts what Kenmore is to appliances. They don't make any of their own products, instead having product made by other companies, and labeling it with their brand. http://beckfluids.com/wp-content/uploads/2015/11/Extended-Life-Blue-LR.pdf
I really don't think you would go wrong with any of the four. The Subaru Super Coolant is probably going to be the most expensive, and the most difficult to come by, as you will probably get it from the dealership. But it is also what Subaru put in your car when it left the assembly line in Indiana. Zerex is available at NAPA, Autozone, Advanced, O'Reilly. I recently saw Pentofrost at my local Autozone, and I know Advanced carries it also. Not sure where you would find Beck Arnley.