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Old 06-28-2016, 11:14 PM   #11
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I will check the risers but in freshwater.
We did not change the water inlet hose on the transom assembly. seems just about impossible to get to inside the boat and it looked good.
I'm considering changing it to a through hull fitting rather then picking up water from the bottom of the outdrive.
Then you'll still to get to the inner connection to install a block off plate.
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Old 06-29-2016, 02:45 AM   #12
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Default Back flush

Does anyone have the backflush procedure?
Can't find it anywhere on the web.
Thanks. BB
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Old 06-29-2016, 12:08 PM   #13
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Can't see how such a procedure would exist or be possible. Everything in these engines is designed to flow only one way. You have two pumps forcing water through the engine and even if you hooked water up at the elbows, it's just going to go out the exhaust, not back into the engine.
Maybe instead you make a flush adapter and try something like salt away.
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Old 06-29-2016, 12:31 PM   #14
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Does anyone have the backflush procedure?
Can't find it anywhere on the web.
Thanks. BB
IMO this is a waste of time for a boat raw water cooled engine. You can remove the hoses from the manifolds and flush water into them but you will need to bypass the raw water pump. this is done with the engine off.

This type of flushing is not going to remove marine growth nor rust scale.
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Old 07-01-2016, 01:19 PM   #15
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thanks for all the great info here. I'm going to return the circ pump and try another one. This started literally right after I replaced it. My thoughts where that a circ pump either works or leaks when failing.
I will posted the results along with IR exhaust temps.
thanks, BB
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Old 07-02-2016, 12:36 AM   #16
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Default IR temp readings

I install another recirculating pump to rule it out.
Here's the temps I got ideling down the river. Lake Erie way too rough to get out and run it.

Gauge back where it's been the last two seasons 177ish.

IR temp readings
Thermostat housing 174

Starboard riser. 125
Port riser 144

At dock idling the port riser came down to 126.
I took these riser readings on the large metal tubes between the rubber boots of the exhaust.
Possible obstruction or rust etc on that riser?
Should I take the entire exhaust manifold off and try to clean it out?
Amy tips how to do this greatly appreciated.
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Old 07-02-2016, 01:43 AM   #17
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Not the end of the world and should get you through this season without any issues.

How old is the exhaust? May just be time to replace it however I guess Lake Erie is not salty but you do have them damn zebra mussels.
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Old 07-02-2016, 02:31 AM   #18
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Default Exhaust

Yes. Fresh water. Zebra mussels a bit of a pain but not horrible.
I'm sure the exhaust is original so 1998.
Are they usually changed as the pair?
I'm assuming your referring to the exhaust manifold coming off the block and not the riser part right?
Thanks again for all your info. I really appreciate it.



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Not the end of the world and should get you through this season without any issues.

How old is the exhaust? May just be time to replace it however I guess Lake Erie is not salty but you do have them damn zebra mussels.
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Old 07-02-2016, 02:51 AM   #19
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I am refering to both the riser and manifold.

Yes they typically are replaced as pairs.
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Old 07-02-2016, 08:50 PM   #20
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Default I think it's resolved

Thought I would post my results today as I think the temp problem is solved.
Our boat is a 1998 scr with a 7.4 mercruiser
Apparently our engine is a 1997.
1997 was the last year for carb for the 7.4.
I then found out that a carbed 7.4 requires a 143 degree thermostat and a mpi engine takes a 160 stat
I changed to a 143 stat and the temp never got over 170. Riser temps down also to around 120. This with 7 people on board. I think we are all good.
Thanks for everyone especially mmmjr for all the great info as always.
Have a great 4th of July!
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