Coolant bypass hole

[weezzell_5400]

I got a boat that needed a new motor ....I got said motor as a long block from a dealer ...old motor was a 5.0 mercruiser ..new motor is a 5.7 mercruiser ....now ...the old motor has the coolant bypass hole for the water pump ...so there are 3 holes that water flows through ....the new block does not have said hole for the bypass ....is this a problem ....or can I just put some rtv on the gasket surfaces and bolt it up like normal ...or do I need a differant water pump all together

 

[Scott Danforth]

are you mixing vintages? if so, get the correct marine water pump for the block.

 

[alldodge]

Don't use RTV, not good

Also going to newer year, some of your other items may have issues including the carb (5.0 to 5.7)

 

[weezzell_5400]

I'm not sure about mixing ...but dosent the newer pump have a small pipe coming out of it for a water bypass... If so where would that hose run to on my thermostat housing... It only has four hoses on it

 

[Scott Danforth]

post a serial number of your broken motor

we can then tell you the how that was originally plumbed.

then post a picture of your new motor. most likely your mixing vintages.

 

[Bt Doctur]

the only time there is a extra hose fitting on a pump is for the hot water heater. most water circ pump have a plug in there

 

[alldodge]

I'm not sure about mixing ...but dosent the newer pump have a small pipe coming out of it for a water bypass... If so where would that hose run to on my thermostat housing... It only has four hoses on it

OK, my bad again, thought you were talking about the circulating water pump which has additional holes where in bolts to the block, you mean the top hole that normally goes to the intake manifold.

What year is the original motor?

 

[weezzell_5400]

Thanks for the reply

 

[Bt Doctur]

standard cooling or fresh water cooled(closed cooling)
serial number shows a hose from the circ pump to the intake manifold

 

[Bt Doctur]

 

[weezzell_5400]

Its a fresh water cooling ...not closed

 

[alldodge]

Your serial number shows 1998 to 2001 and does use a bypass hose but as BT mentioned the tube would be used for closed cooling (which you don't have) and may have been done by a prior owner swapping motors

Both types
http://www.mercruiserparts.com/bam/subassembly/31837/2697/180

open cooling
http://www.mercruiserparts.com/bam/subassembly/31837/2697/110

 

[Fun Times]

mr300z87 had gone through a similar type dilemma which may be helpful in your case here too.

https://forums.iboats.com/forum/eng...rives/9928380-5-7l-circulating-pump-questions

 

[mr300z87]

If we are talking about the circulating pump flange having and extra small hole below the water jacket on I think the starboard side vs the newer block not having the extra hole? I would recommended getting a newer water pump as would guess the is water in the small hole on the pump. Seem GM made this change on sometime post Vortec on 5.7L 5.0L and 4.3L. I was going in the opposite direction and my block was weeping form the small hole in the block. I still have the in newer water pump PM me if interested.