phebus

I have a 496HO, and I'm getting a double beep approx once a minute while at idle. Hooked up to a scan tool, and it read that the port side manifold was getting hot, and temp gauge on dash goes to approx 180* at idle, while it is approx 160* while at speed. I have replaced the impeller every year since new, and I've never had one come apart. I replaced it earlier this year, and I am going to replace it again, but I feel I may have sucked up some sand, and may need to flush the system. Is there a specific area that tends to lead to the port manifold getting hot, or is it just indicitive of low flow and effected the most?

Any suggestions on the best way to flush out the system would be appreciated.

Dave_N

The port side manifold is always the first thing to get hot on a 496 when the sea water flow is reduced. If you have a scan tool, check the pump pressure, if it's low it may be the pump, if it's normal you may have a restriction somewhere.

If it appears to be a restriction, I would check the heat exchanger first.

Dave

phebus

Is it best to flush the heat exchanger by backflushing through the hose, or to remove the end caps and flush?

turnerrd

If your looking at the front of your motor remove the large hose that comes into the heat exchanger on the bottom right side. This is the intake to the exchanger. Hook your garden hose to it and it wiil back flush all the way to the sea pump. You'll want to pull the outlet (top hose I believe) from the pump to allow any particles to get out.
To clean the heat exchanger remove the end caps single nut/bolt and gently pry off the end caps and rubber seal. I used a long piece of stiff wire and ran it through all the tiny holes in the exchanger core. You'll be able to tell pretty quickly if your clogged or not. Make sure you put the rubber seals back in the same way they came out.


Also check the hose that feeds your port side manifold from the exchanger. It may be clogged.

Let us know what you find.

phebus

Backflushed the bejeebers out of everything, and did it ovr a bucket so I could see if anything came out. Water was clear, and I saw no evidence of any sand or debris. Pulled end caps from heat echanger, and flushed it out as well. Lined the end cap gaskets back up, but now it leaks, so I'm off to see if anyone local has gaskets. Took water pump apart, and there was no scoring in pump body, and the impeller looked fine, but of course I will replace it while I have it apart.
Hopefully when it is all back together, it will run cool.

turnerrd

One more thing to check.
If your manifod looks like the one in attachment with the water rail on the bottom take a look at (part 23) the fitting for the hose that goes into the bottom of the water rail. It is made out of brass and the water rail is aluminum (dissimilar metals) and it can actually corrode to the point that it restricts water flow. Just a thought. My understanding was that there was a recall on these early on.

Try pulling one of the top hoses off your port manifold and the bottom hose off and flush it. See if it flowing good.

Pwrbt33

iTrader: (2)

Ditto on the rail problem.

John S.

bcolmsted

U may have a bad sensor or connection on the heat sensor thats on the sea water pump..Had the same alarm symptom, 2 beeps every min..Temp gauge never went past 175 however.If u disconnect that sensor connector at the pump, u will get the very same alarm.

phebus

The alarm only sounds while I am idling, and the temp gauge is around 180*, while under way, the temp drops to around 160*, and there is no alarm. So, I don't think it's a false alarm, and I feel it's due to a lack of water flow, or lack of pressure. I flushed everything out real good yesterday, and put a new impeller in, so I'm anxious to try it, and see if the problem has been resolved.

Raylar

You need a scan tool to read your pump system pressure. If you have low pressure, it will be lower at idle and could make for a hot manifold and a high temperature sensor fault on the engine. Remember just replacing the impellor will not always work if the housing is scored or just worn to much. The Merc manual will give you a system pressure range.

Ray @ Raylar