A lot of the Japanese cars have the water pump buried and driven off the timing belt or chain. Because they are in such an awful place to get to, many folks change them preemptively when replacing the timing belt, or at least every other time.
Actually, if an engine uses a timing belt, it makes sense to drive the water pump off the timing belt. The water pump will then be included with the timing belt kit, and replaced at each timing belt replacement interval. If the water pump, or its gasket starts to leak, this will be an external leak, which should be noticed before major damage occurs.
What does not make sense is when an engine uses timing chain(s), and the water pump is internal and driven by a timing chain. This is a terrible design, because most such engines require major expensive effort to get at the timing chain(s), and while there is no recommended timing chain replacement interval, it is unreasonable to expect a water pump and its O-ring or gasket to last much more than 150,000 miles. When the water pump fails, it often leaks coolant, which on this setup will contaminate the oil and ruin the engine.
If there is any air in the engine the cooling system is not full, the cooling system must be full to operate properly.
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Umm, the water pump on Japanese cars is not âexternal.â You have to get all the V-belts and crankshaft pulley (cleverly blocked by the frame horn) and belt dust covers off to see it and get to its mounting bolts. I have NEVER seen a water pump included with a timing belt kit. Maybe your cars come from a different universe. Timing belt change intervals are often 60K mi. Water pumps typically last 120K mi. It makes sense to change the water pump on every OTHER belt change.
As you note, timing chains last much longer. It would indeed be frustrating to do that teardown just for the water pump.
My opel v6 has a timing belt and dohc design. The WP is driven by the SERP belt. Still not easy to remove WP but it can be done.
No problems from the water pump on my Focus (now recently totaled out because of an accident 
) at the 11 year 215k mile mark. Original Pump, gaskets, etc. It did have metal blades, which I think probably made a difference in longevity based on what Iâve read on various BMW forums. It seems like a common thing for BMW drivers is to replace the OEM version with the racing version at 30k when itâs due and then never worry about it after that (apparently the only difference between the two is the metal blades).
Thatâs odd. Thatâs the only way we buy them. I canât think of a reason to buy a TB kit that doesnât come with a WP. Since we warranty our work for 3 years/36K miles, when we have a timing cover opened up we replace all components. Anything less just doesnât make sense.
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For some reason chain-driven water pumps seem to have fewer failures than the belt-driven ones.
check Rock Auto, our old 05 Odyssey has the entire kit available including the water pump
The timing belt kit I bought from Rock Auto included an Aisin water pump, like the original one on my Honda.
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Possibly because there is considerably less tension on the pump gear with a chain compared to a belt
Well, just for fun I looked up the timing belt at Rock Auto for a 1992 Mitsubishi Expo LRV, a car for which I have changed the timing belt about five times (250 Kmiles). It comes three ways:
âJust the belt
âBelt + tensioner (Tensioner also sold separately)
âBelt + tensioner + water pump
Given that I only changed the water pump on the car once in 250K miles it would have been pretty wasteful to put them on every time.
With all due respect the maintenance history and requirements for a 30 year old car is a statistical outlier and not really relevant to general auto service these days.
Timing belt replacement intervals are 100,000 to 120,000 miles. Itâs reasonable to expect that a water pump may last 120,000 miles. Itâs not reasonable to expect one to last 240,000 miles. The timing cover comes off at, say, 110,000 miles, everything gets replaced, and the service lasts for the remaining life of the car. Because most people donât drive cars for 240,000 miles or 20 years.
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Timing belt interval on that particular vehicle is 60,000 miles. Did you think I was making it up?
That interval isnât uncommon for vehicles of that vintage, IIRC.
Certainly not. I know full well that those cars were supposed to have the T-belt replaced at 60K. I also know that was back in 1992. Cars on the road today that still use a timing belt have a replacement interval of 105-120K.
25 years ago we would replace just the timing belt at 60K and at the 120K service recommend the water pump as well. Made sense back then. Modern cars require far less routine maintenance and go much farther between major services than yours does. Using the maintenance needs of a 30 year old car compared to the cars regularly found on the road today is comparing apples and oranges.