On the 65 SHP engine there's a bypass hose under the thermo housing that goes to the top of the water pump. Does anyone know the reason for the bypass and where to get the hose? Also, could it be eliminated- I remmember how hard it was to replace the last time I renewed the hoses. Thanks all!
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Re: Hosed again!
It'd look pretty 'ugly' with top of water pump and intake plugged off.... Paragon lists the hose as well as most other catalog houses, plus I'll bet functional replacements are easy to come by at NAPA, Etc. Purpose is to coolant an alternate path during the period when engine has just started and thermostat hasn't opened yet. -
Re: Bypass Hose
Tom:
This hose is called an "external bypass", and allows the water pump to circulate the water within the block, prior to thermostat opening. This results in more even heating/thermal expansion during engine warmup, and is in addition to the smaller "internal bypass" that exists within all water pumps. In order to utilize this, you need to purchase the special 87 degree fitting for the top of the pump, the nipple for the front of the intake, and the 90 degree bypass hose. All these are available from most of the Corvette specialty parts houses.
JoeComment
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Re: Bypass Hose
Joe- Thanks for the information. I'm currently rebuilding the engine and have the fittings but need new hose. I just remember how hard it was to get the hose back on in the small work space between the manifold and water pump and thought I could eliminate it. Looks like it's needed!Comment
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Re: Bypass Hose
Tom-----
External bypass was used on most pre-1970 Chevrolet small blocks with aluminum intake manifolds. However, it was NOT used on ANY Chevrolet small block used in a passenger car with cast iron intake manifold. Cast iron intake manifold-equipped small blocks relied on the internal bypass provided by the 3/8" hole between the right side water pump leg and the block. This circumstance strongly implies that the external bypass could be eliminated from small blocks so-equipped as long as the internal bypass is present and functional.
Having said that, would I remove the external bypass from a small block and rely solely on the internal bypass? ABSOLUTELY NOT. The bypass serves 2 functions. One is the function described by others. The second function is to provide a coolant path if the thermostat fails in the closed position. In this circumstance and without an effective by-pass, the engine will overheat rapidly and, likely, catastrophically. The external bypass provides a much better and higher flow bypass capability under this circumstance.
By the way, for whatever reason, possibly cost and serviceability, the external bypass was eliminated from virtually all small blocks installed in passenger cars beginning in 1970, whether they had cast iron or aluminum intake manifolds. Big blocks used external bypass from 1965 to this very day.In Appreciation of John HinckleyComment
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Re: Hosed again!
Tom, regarding the difficulty of replacing this hose and its clamps, I came to the conclusion after the last time I tried it (and having ill thoughts against the responsible engineer) that the intent is to remove the water pump to replace the bypass hose. I guess they figured the pump wouldn't last any longer than the hose!Comment
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Re: Hosed again!
Scott----
The by-pass hose should be replaced every time that the water pump is replaced. Unless it suffers from damage, the hose should not require replacement during the period between pump replacements. This is particularly true for pre-1971 Corvette small blocks (the only ones that had by-pass hoses, anyway) since the 5/8" shaft water pumps rarely have a service life exceeding 50,000 miles.In Appreciation of John HinckleyComment
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Re: Hosed again!
Which brings up a question.My bypass hose on my 65 roadster seems to have a small fullness or swelling beyond the clamp towards the block. I do not really
want to change it. Does the nipple have a diameter such that even a new hose has
this appearance? I really don't know the age of the hose, but it looks fine otherwise. Any thoughts?Comment
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Re: Hosed again!
John-----
The raised edge on the end of the nipple, designed to improve hose sealing and retention, will cause the effect that you describe.In Appreciation of John HinckleyComment
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What's the problem?
I have a 1966 L-79 engine with an original functioning hose on it. I've had the intake off several times and the water pump (still original) twice and I'm still using the same hose and clamps. Maybe I have a problem and just don't know it. Before this engine, I had one of these set-ups and the hose blew out when it was brand new. I didn't have a job and no money for a new hose so I got a pine branch out of the yard, cut off two plugs and drove them into the fittings. Drove it for 6 months this way.
Was I endangering my engine?Comment
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Re: What's the problem?
The heater circuit also functions as a bypass, and I suspect Chevrolet Engineering came to the conclusion that the external bypass was redundant, however, it would be a good idea to keep it if you installed a shut off valve in the heater circuit.
DukeComment
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Re: Bypass Hose
Joe- Thanks for your detailed responseComment
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Re: Bypass Hose
A couple years ago I needed to replace the bypass hose on my '66 and struggled with it until I figured out a very simple solution. Get a cup or other container and put in some very hot water right out of your tap and drop the hose in for several minutes. The hot water will soften the rubber and make it very easy to install the hose.Comment
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Re: Bypass Hose
Thank youComment
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