Can a leaky water pump draw air into coolant? - Subaru Forester Owners Forum
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post #1 of 11 (permalink) Old 06-03-2009, 12:51 PM Thread Starter
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Can a leaky water pump draw air into coolant?

My '98 Forester (130k) recently sprang a leak at the water pump gasket, and I need to replace it. But one thing I noticed is that a stream of bubbles is present in my overflow container. I realize this is a common HG symptom, and I will have the coolant tested for hydrocarbons.

I'm wondering if it is possible that a leaky water pump could draw air into the cooling system, and also produce bubbles? I don't want to go thru the trouble of replacing the pump and not do the head gaskets too, if they are needed. But if it's just the water pump, then I can save some time.

Thanks for any advice!
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post #2 of 11 (permalink) Old 06-05-2009, 10:57 AM Thread Starter
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Oh - I forgot to mention that the compression checks out ok, and there is no water in the oil.

Just wondering if anyone has ever heard of a bad pump introducing air into coolant?
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post #3 of 11 (permalink) Old 06-05-2009, 05:04 PM
Rob
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I don't personally have one but I have read many times that the first noticeable sign of headgasket failure on a DOHC EJ25 is bubbles in the overflow tank.
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post #4 of 11 (permalink) Old 06-05-2009, 09:29 PM Thread Starter
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I'm not sure I have blown gaskets, the air might be coming from something called a weep hole?
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post #5 of 11 (permalink) Old 06-06-2009, 04:48 AM
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Coolant is under pressure - 10-12 psi, I believe. Whatever the value, any leak means coolant comes out, not air gets in. I think Rob likely has it right.

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post #6 of 11 (permalink) Old 06-06-2009, 06:42 AM
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Try starting engine cold w/ radiator cap open. Look for bubbles coming out of coolant. Any significant bubbles and a gasoline smell is almost certainly a head gasket leak. I would have coolant chemical test to confirm, given level of diy effort or repair cost.

good luck

See you down the ROW!
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post #7 of 11 (permalink) Old 06-06-2009, 12:02 PM Thread Starter
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Thanks for the info. I'll see about getting the car tested for the exhaust gases in the coolant to make sure where the air bubbles are coming from.

A mechanic mentioned that air could be entering from a leaky water pump, and to try a tube of Bars Golden Powder seal (a ginger root additive). Supposedly this is added to certain aluminum engines like northstars in order to seal up the head gaskets and any other leaks. Anyone have experience with this additive? Apparently it's safer than metallic or chemical additives, in terms of not clogging the rad/heater core.
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post #8 of 11 (permalink) Old 06-07-2009, 06:18 AM
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Bars stop leak or other will not hurt anything, IMO, but certainly won't cure a leaky water pump. Water pump has a dynamic rotating shaft seal that is leaking in your case. Stop leak works by plugging a static hole, and a loose rotating seal will not seal w/ this type of product.

A small amount of weepage from the water pump drain is OK, but a steady drip and puddle after stopping is not.

One good thing about a leaking water pump is they will run for some time, and will get progressively noiser (bearing lube being washed away) before failure. You don't have to immediately repair, but don't put off for too long, perhaps 1-2 months. If the water pump freezes, the timing belt could break and timing between crankshaft and valves would be lost, w/ damage to valves and potentially pistons which will hit the valves.

good luck

See you down the ROW!
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post #9 of 11 (permalink) Old 06-07-2009, 11:29 AM Thread Starter
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Texas Forester,

Thank you much for the info. From what I could see, the leak was actually coming from the water-pump-to-block gasket, not the shaft bearing area. I believe it would still be cause to replace it, eventually, but I did use the Bars gold stop leak yesterday and I didn't find any further leakage after a good test run.

What I would like to ask you is this: is it possible that that water pump leak might draw air into the coolant to produce the air bubbles in the overflow container?
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post #10 of 11 (permalink) Old 06-07-2009, 05:19 PM
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Unlikely for reasons stated by others. Try cold engine check I suggested in my first post. If you see bubbles, HG is likely.

good luck

See you down the ROW!
1999 Subaru Forester
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post #11 of 11 (permalink) Old 06-07-2009, 06:27 PM Thread Starter
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Sorry - I forgot you gave me that already.

I'll maybe take apart this som***** myself. I've got more time than $ right now anyway!

Thanks for the advice, y'all!
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