back flushing closed cooling on 496HO ???
 

ran over a mud/weed bar in RI over the weekend at idle in a long no wake zone, seems I sucked a bunch of junk into my HO. shortly thereafter the high temp alarm went off, right before the end of the no wake, she was at 180 degrees. let her cool off a bit and tried running again. water pressure seemed low at idle, but fine at speed, water temp seemed to act a bit flakey, running 160 and 175 but never setting off the alarm again for the rest of the day. Trailered her home and flushed on the hose, suction at idle on the hose does not seems as good as it once was and the water exiting the tail pipes seems a bit warmer than normal... Long story short, she seems to be running a bit hotter than normal but no alarms are going off, before I pull the impeller to see if I scored it, is there any way to back-flush the close cooling system ?? any other suggestions ??? Thanks Chris...

Re: back flushing closed cooling on 496HO ???
 

Anyone ????????? Do the end caps come off the exchanger to flush it out ???

Re: back flushing closed cooling on 496HO ???
 

Chris,

Here is a quote from a post back on 8/4 on how to back flush a 496. Hope it helps.
Harper,
Something you may try, facing the front of the engine the lower hose, on the right hand side of the heat exchanger ( about 1- 1.5" diameter) can be removed, then remove the 2 blue drain plugs from the sea water pump. Hook up a water hose to the hose you have removed and back flush the engine. This is a quick, and easy way to flush any blockage from the oil coolers. Especially if you have twins, and access is difficult. I found a common fitting at the hardware store, that would allow me to clamp to this hose and get good pressure back through the system. The amount of debris that came out was alarming. You are definitely having a water flow problem if the exhaust is getting this hot, on the one side.

The back flushing may resolve this, but if this does not work, do not rule out, your pump housing may be worn out. As I said in an earlier post, I had to replace both of mine after 60 hours. The brass housings will erode in time in a river environment, and new impellers will not help, if they are worn out.

One other possibility, the 496's had an issue with the fittings on the lower side of the exhaust manifolds corroding and breaking. A recall was issued to replace these a couple years ago, to replace the original brass fittings, with aluminum ones. Even if this is not your problem, I would make sure this has been changed, before it is a problem.

Good luck, let us know what you find.

Re: back flushing closed cooling on 496HO ???
 

What temps do you guys see normaly on your 496? I usually am around high 160's maybe low 170's when up on plane and running regardless of speed. When I come off of plane and I go up to about 175 maybe 180. As soon as I get on plane it goes right back down. No alarms or guardian mode ever. What temp does guardian mode happen at?

Re: back flushing closed cooling on 496HO ???
 

Thanks much appreciated.... My temp never budged from 160 ever.... now it fluctuates between 160 running and 170-175 at idle... guardian mode came on for a split second at 180...

Re: back flushing closed cooling on 496HO ???
 

If you have sea strainers you need to pull out all the screens, I did the same thing last summer and I picked up more silt than anything else.

Re: back flushing closed cooling on 496HO ???
 

155 degrees I run no matter on plane or not 160 tops

twin's

Re: back flushing closed cooling on 496HO ???
 

yeah but it looks like ou have hp 500's . Not closed cooling like a 496

Re: back flushing closed cooling on 496HO ???
 

Chris,
Mine seems to be acting exactly like yours. Let me know what you come up wtih as your culprit. I'm going to back flush and go ahead and change my impeller. I'll let you know what I come up with.

Re: back flushing closed cooling on 496HO ???
 

Took the pump out and when disasembled I saw the large scoring marks on both the body and end plate. Just ordered a complete pump assembly (PN 46-862914A2) from BAM. My question is does this include the shaft and pulley along with the impeler and o ring gasket? Probly not the mounting bracket or pressure sensor though. I think a saw previous thread on this a while back and they said it did include the shaft and pulley. Does any one know for certain.

Re: back flushing closed cooling on 496HO ???
 

Took the boat out this weekend, i'm having fluctuating water temps at idle, from 160 - 175, water pressure at idle seems low, around 3-4 psi, but is o.k. under-way around 35 psi, temps under-way appear to be ok too.. I tried back-flushing from the hose on the right side under the heat exchanger looking at the front of the motor, with the blue drain plugs removed, didn't appear anything came out. I was going to pull the end caps off the exchanger and see what it looks like before tearing apart sea-water pump.....

Re: back flushing closed cooling on 496HO ???
 

Chris,

It seems like I'm one step ahead of you. I back fkushed and took the end caps off my heat exchanger. Both were perfectly clean. Then I took the pump off and out (alot of fun) and opend it up and discovered the deep scoring marks on both the end plate and base of the pump. My impeller was perfect though. Searching back through old threads I ran into one by GOOD T who seems to know what he's tallking about on 496 and said if the housing is scored to not change the impeller unless it is bad because it will likely fail and cavitate because the new impeller will not fit well into the scored cavity. I decided to change it anyways though and guess what he was right! It pumped for a minute and then quit. Upon dissassembly again (not so bad the second time) it had flipped a blade on the impeller in the wrong direction which caused it to quit pumping. So I put the original impeller back in and everything was back to normal (170-175) all weekend.
The only fix is a new pump housing $269 from BAM complete assembly for an 03'. I think the newer model is a bit more.
If I were you I wouldn't even mess with taking it out till you have the new pump. I believe it is Arizona speed and Marine has a machine shop out there that will weld in the groves and machine them flat for like a $100, but I don't have time for all that.
Hope this helps and saves you some time, but I would bet anything that you've got the same thing going on that I do.
My new pump should be in Thursday. I'll try to take some pictures of mine apart so you can see were the bolts are that need to come out.

How were you getting your water pressure readings. Do you have a guage in the boat or are you using the scan tool?

Re: back flushing closed cooling on 496HO ???
 

There is a company called R&R in Lake Havasu City, AZ. that makes a kit that has stainless plates that go on each end of the 496 water pump housing, additional plates and gaskets to make it all work, a new impeller, and a new o ring. The kit makes your water pump better then new, and the cost for everything is less then $200.
I would post a link, but I think that is in violation of the boards rules, since they don't advertise on here, but I have been running the kit all year, and it works great. It's a lot cheaper then buying a new water pump that is going to score again anyway.
Also, when you take your pump off, it's easier to remove the pump by unbolting the mounting bracket then it is to remove it from the bracket while in the boat.

Re: back flushing closed cooling on 496HO ???
 

Phebus,

R&R was what I was thinking of. I asked them about those stainless inserts and they knew nothing about it. Just told me about the machine shop. PM me with that info please. I'm going to get my old one done so I have a spare.

Re: back flushing closed cooling on 496HO ???
 

I just mainly lurk here, and I'm not a member, so I can't send a PM. Do you know if I can post the info here, without violating the posting policy? I am in no way connectede to the company, I just found what I thought was a great, overdue product, and wanted to pass on the info.

Re: back flushing closed cooling on 496HO ???
 

Turnerrd,,, thanks for all the great info, much appreciated.... So you were experiencing the same exact symptoms as me ?????

My guardian mode only kicked in once for a split second while still in the no wake zone, have put about 4 hours on since and hasn't gone off again, just experiencing fluctuation on the water temps at idle, seems to be o.k. under way. I am reading water pressure off gauge on dash, idle is 3-5 and under-way I am over 35.

I'm still thinking some mud or sand is stuck somewhere because sometimes its fine, right at 160 and others it spikes to 175 and then back down, which it never did before I ran over the mud/weed bar, it was always exactly 160 or very close...

Please let me know if the scored housing ends up being / fixing your problem.. I am a machinist and could probably machine light scores out of the housing myself, wondering if that would mess up clearances, sounds like the SS plate kit may be the way to go, either that or a whole new ( expensive ) housing...

P.S. I dont see how posting a link is a problem, unless things have changed,, people post links all the time to products we use around here. Either that or please e-mail me at [email protected] Thanks again...

Re: back flushing closed cooling on 496HO ???
 

The new pump housing and impeller didn't seem to do much. I still run 170'sh on plane and about 175-180 at idle. From what I've gatherted that is not all that unusual for a 496 and most of them run at about 170. One thing I did learn after reading the service manual in more detail is that the thermostat only starts to open at 160. It never fully opens until 185. I've heard that guardian mode kicks in at 180. This doesn't make sense though why would guardian mode kick in before the thermostat is all the way open? I know my guage has been at 180 before at idle and I have never gotten the single beep and flash to indicate guardian mode.
Does any one know if the sending unit for the guage is the same one that the computer reads off of? If it is a seperate circuit then maybe I need to change the sending unit for the guage.
Also how could I go about hooking up a dash mounted water pressure guage (Livorsi/Gaffrig) on a Velocity? I'm thinking of eliminating my drive trim guage since I have a mechanical indicator and the fact that Velocity never hooks them up to start with, just there to fill the hole.