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how to backflush a 496 ho

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Old 08-02-2012, 09:58 PM
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Default how to backflush a 496 ho

Hi, i have never owned a closed looped 496ho before. It runs a little hot after a few wide open runs. I am going to check the sea pump but how and what do i flush. I have been told to flush the heat exchanger and hoses. Is it posible to screw anything up if i do it wrong? how and were would i install a gauge to check water pressure? any help would be great. Pics would be awesome. sorry to be an ignoramus. Oh, if it matters it has a whipple kit. Dustin whipple has been a big help on what to check and flush, i just dont know how. Thanks!
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Old 08-03-2012, 01:02 AM
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I had trouble with overheating a couple of years ago. I checked the heat exchanger by pulling the end caps off & looking through. That wasnt the problem, the oil cooler & p/s cooler are before that in the cooling system. I took the inlet hose off the heat exchanger & put a spray nozzle in the hose to backflush. Worked fine for me. The waterpump housing is a problem as the ends get grooved & reduces water pressure. Hardin marine makes a stainless housing replacement for about 350.00 as compared to 600.00 for merc. Hope that helps, Randy
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Old 08-03-2012, 02:55 AM
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Order a scan tool. It's a smart investment for anyone with that engine. It will allow you read the seawater pump pressure and the the various temperature sensors so you're not shooting in the dark.

http://www.rinda.com/marine/marine.htm#merctool
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Old 08-03-2012, 03:00 AM
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Originally Posted by boatnutt View Post
Hi, i have never owned a closed looped 496ho before. It runs a little hot after a few wide open runs. I am going to check the sea pump but how and what do i flush. I have been told to flush the heat exchanger and hoses. Is it posible to screw anything up if i do it wrong? how and were would i install a gauge to check water pressure? any help would be great. Pics would be awesome. sorry to be an ignoramus. Oh, if it matters it has a whipple kit. Dustin whipple has been a big help on what to check and flush, i just dont know how. Thanks!
Disconnect the downstream hose from each of your coolers (oil on the front, power steering on the back of the motor) by loosening the hose clamps and sliding the hose off. Sometimes they are had to get off, I used a very small flathead screwdriver working parallel to the hose to loosen it. Don't pry up or you will tear the hose. Then take the big hose loose on the front of the motor. Blow water backwards thru the cooler and engine. Most likely you have some passages of the oil cooler blocked, causes engine to run hot and oil pressure to be lower.
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Old 08-03-2012, 03:08 AM
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That info was sent to me when I asked the same question by another oso member (knockld ) I did exactly what he wrote ( what I forwarded to you ) and it fixed my problem. The guys here are awesome and always willing to help!

Rick
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Old 08-03-2012, 06:09 PM
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You guys are awesome! thank you!!!! will let you know if it helps.
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Old 08-03-2012, 07:04 PM
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Originally Posted by NightHawk View Post
Order a scan tool. It's a smart investment for anyone with that engine. It will allow you read the seawater pump pressure and the the various temperature sensors so you're not shooting in the dark.

http://www.rinda.com/marine/marine.htm#merctool
+1

You should have 3-4 lbs at idle.

When was the last time you changed your impellor?
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Old 08-03-2012, 08:27 PM
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You should have 3-4 lbs at idle.

When was the last time you changed your impellor?
just bought the boat. previous owner didnt know much about boats. So i dont thing impeller was ever checked. Boat is on its way to me now. How do i check water pressure at idle and at speed?
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Old 08-03-2012, 08:31 PM
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duh, i didnt read the post in front of your. i will order the tool.
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Old 08-03-2012, 08:44 PM
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You said your Temps are getting up there, do you know if there is a separate water pick up for your inner cooler, or is it one pick up teed off?

Last edited by Rwbrew3; 08-03-2012 at 08:46 PM.
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