It is almost time to replace the timing belt on my Subaru station wagon. An auto mechanic suggested replacing the water pump, and the oil pump as well, because of their close proximity to the timing belt...
Is this a good idea, or unnecessary ?

If the oil pump is producig the proper pressure, and the water pump is not leaking, then save your money. Remember the old saying' if it is not broke, do not fix it''. This is very true. If ether one should go bad, it is not that much more trouble to fix later.

water pump :yes, its cheap insurance the pump is only like $50 and it only adds about a half hour labor to the timing belt job, as for the oil pump, generally, they do not need to be replaced, l have do not alot of timing belt/waterpump jobs and the only cars i've done oil pumps on with the job were toyotas due to leakage, but unless yours is leaking or you have oil pressure problems l would say no to the oil pump

All Subaru is were interference after '96, so if ur water pump seizes up it could take the engine with it. Make sure they use a Subaru brand pump, to ensure quality ( l usually do not say that, but have seen the cheaper ones cost folks an engine before). The oil pump is a little extreme, l would pull it to double check it & replace the o-ring seal behind it (these do leak over time, & lower ur oil pressure) but probably would not replace. l would change the idler pulleys before the oil pump, especially the geared one on the lower drivers side (this one tends to go bad first). Good engines but keep an eye on ur head gaskets, 2.5 is were bad for that until '03.

Oil pumps get tired with high miles, but rarely wear out. Water pumps, on the other hand, fail all at once with little warning most of the time. l think it is a good idea to replace the water pump while 'the window of opportunity' is there. It is a cheap way to avoid having to back in there.

l have owned Subs for 20 years, even before timing belts, l have a mechanic that works on only Subs & he has done at least 4 timing belts for me. l have never had a failed water or oil pump. My mechanic has never mentioned changing either when doing the Timing belt. Is not the oil pump in the oil pan? If it is & l always thought it was (could be wrong). Then replacing it would probably mean pulling the engine. You do not need to pull the engine to do a timing belt. l run all my cars into the ground. The most miles l have gotten was 180K out of a 1987 Legacy wagon. l bought this car new. l had to change the timing belt twice & the clutch once. It was carburated & the throttle shaft bearings wore out. l would have needed a new carb so l junked it. With fuel injection this is not a problem now. DON'T replace the oil pump. If u r up around 150K replace the water pump. Otherwise do not worry about it. One Sub engine, the 2.5 maybe, is an interference engine & the valves & pistons will collide if the belt breaks. The other engines will just conk out & be O.K. after u replace the belt. WOW! l just did some research & the Oil Pump does appear to be on the outside! Still l would not change it. However l just remembered that the cam seals & also maybe the crank seal r prone to leakage & r usually replaced when the belt is done. If u want an EXPERT opinion e-mail me & l will give u my mechanics #PN. He could do a timing belt or just about any other job on a Subaru in his sleep. He is that good & honest as the day is long. l do remember the belt tensioner pully bearing is also another thing that ought to be checked. Its a MA number. But he will advise you.

it would not hurt to replace the water pump. & make sure you replace the timing belt tensioner as well.. & while you are in there, take a good look at the crank & cam seals.. at least 1 will be leaking.

There are two schools of thought. One is ''Since it is apart, let is replace what is now available and not have to worry about it.'' This is the preventive maintenance group. The other is ''If it ai not broke, do not fix it.'' This is the repair only when it needs it group. Take your pick. If you are in the wilds of Alaska, or the rain forests, I'd say preventive. If you are where there is a mechanic every block, wait until it breaks.

OK here u go. l have loads of experience with Subaru. Your technician is doing his job in making the offer to do the water & oil pump while doing the timing belt. He is right in saying as long as he is there it would save u lots of labor if it were necessary to replace them later. However, replacing them as regular preventative maintenance is not recommended. l say that with a small caveat, depending on how many miles r on the car, the water pump might not be a bad idea if u have 100k plus. A good inspection of the oil pump is strongly recommended. the Subaru oil pumps on that engine did tend to leak at the rear seal to the oil pump. This actually can be repaird as a small reseal & overhaul of the pump though & not require replacement. Subaru had enough of these that they packaged a reseal kit for them.

Good luck & good driving.
thewisetuner

No, it is not required change them only if they need to be replaced.

yes just cheap maintance and peace of mind.

l WOULD CHANGE THE WATER PUMP, FOR ABOUT ANOTHER 100 SMACKERS, NO WORRIES WITH IT TILL NEXT T BELT CHANGE, BECAUSE AT THAT POINT ALL THE WORK IS DONE ALL U HAVE TO DO IS SWITCH OUT THE WATER PUMP, WHERE AS IF IT GOES OUT LATER , YOU HAVE TO REMOVE EVERYTHING YOU DID TO REPLACE TIMING BELT