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Timing Chains and Water Pumps


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5 replies to this topic

#1 The Dude

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Posted 15 July 2009 - 08:02 AM

A recent incident with a friend's car (not a Subaru) got me thinking about timing chains. Among the advantages of a timing chain is longer life than a timing belt. A timing chain is usually supposed to be good for the life of the engine, or about 200,000 miles. But what about the water pump? It takes about the same amount of labor to change the water pump as it does to change the timing chain. You're probably looking at around $800 to change the water pump on a motor with a timing chain.

So, is a Subaru water pump going to make 200,000+ miles? A mechanic usually replaces the water pump along with the timing belt on a Subaru. Does the H6 get a "special" extra long life water pump? I don't think so.

Edited by The Dude, 15 July 2009 - 02:10 PM.


#2 Suzam

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Posted 15 July 2009 - 08:54 AM

It's not that a water pump can't go 200k, my sister never replaced the water pump in her Toyota and it has 180k+ on it now.

Changing out a water pump with the T-belt isn't mandatory, just preventive maintenance. More of an insurance thing or piece of mind. I've gone 2 T-belt changes before the water pump, so it had 120k on it. You aren't guaranteed a failure if you don't change it, but the odds do go up.

You don't change out the alternator with every timing belt because it has easy access. Water pumps are more labor intensive to replace on their own so it just makes economic sense to replace while you're in there.

Another factor is the potential of a bad water pump is bearing seizure which can cause the T-belt to jump or break. Not a good thing, so again, it's insurance.

I'm not saying you don't roll the dice if you don't change a water pump, but there isn't any reason to think it couldn't go the distance. Depends on if your a risk taker.

Edited by Suzam, 15 July 2009 - 08:58 AM.


#3 CNY_Dave

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Posted 15 July 2009 - 09:46 AM

A recent incident with a friend's car (not a Subaru) got me thinking about timing chains. Among the advantages of a timing chain is longer life than a timing belt. A timing chain is usually supposed to be good for the life of the engine, or about 200,000 miles. But what about the water pump? It takes about the same amount of labor to change the water pump as it does to change the timing belt. You're probably looking at around $800 to change the water pump on a motor with a timing chain.

So, is a Subaru water pump going to make 200,000+ miles? A mechanic usually replaces the water pump along with the timing belt on a Subaru. Does the H6 get a "special" extra long life water pump? I don't think so.


I am guessing if you looked at a stock H6 water pump it would look like a pretty well designed assembly.

The H6's have been around for a while and there are not complaints about the water-pump longevity, but not many cars hit 200K miles so we need to wait a bit for a good sample size to accrue.

Probably the most fragile thing about the pump is the seal, so changing the coolant at the prescribed intervals is important.

If I had to replace the timing chains and/or guides on my H6 (or if I had the cover off for any reason), if I had some miles on it (say 50K? 75k? def. at 100k) there is exactly zero chance I would not replace the water pump (with a subaru original), just because there's so much effort to get to it.

The H6 has the added negative consequence of a water-pump leak putting coolant in the oil.

Dave

#4 bheinen74

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Posted 15 July 2009 - 10:09 AM

just my 2 cents. on a GM3.8 with timing chain, the sprocket gear the chain goes around is made of plastic, and it wears out over time, causing problems.
Yes-chain wears longer
no-gears to drive it still fail.

#5 grossgary

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Posted 15 July 2009 - 12:56 PM

Yeah this is the one thing I'm not sold on about the H6. But I plan on having it another 100,000 miles so we'll see what happens.

Thing that's annoying to me is the ideal solution in my book has been around for a long time - timing chain with an external and easily replaceable belt driven water pump.

I do not like the idea of the water pump seaping or leaking and not being able to tell as easily.

#6 nipper

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Posted 15 July 2009 - 03:42 PM

I wonder this too. There are some things that MAY make the waterpump last 200K or more. Since it is a chain, there is less side force on the waterpump shaft then with a timing belt. The shaft end is in a happy place (getting sprayed with oil). Subaru uses a new high mileage coolant made for this pump. The new pump is very hardy in contruction, but only time will tell.

It also depends upon what the life of the car is. 200,000 miles is a respectable mileage for ANY car part, period. I think anything past 160,000 is gravy (for non soobys). I did the math and the cost of replacing a sooby timing chain is the same as two timing belts, so thats a wash. The placement of the sooby waterpump is not in a horrible place, but it could have been much better. If you already have the cover off it is right there looking at you.

http://endwrench.com...dfs/Tribeca.pdf

On page 11 its the little gear next to the crank. What joy three timing chains can be :)




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