496 ho engine guardian alarm

[perryk123]

hi, got an 04 496 ho thats been a bit of a trouble maker. She runs awesome, but after being run for several 2-3 hours she goes into guardian mode, and throws out on ddt:

LOW BLOCK PSI

all the readings seem fine. I am guessing its a water pressure sensor. if so does anybody know where it is, cuz i cant find it in the book. or if im wrong can anyone help.

I replaced the impellor, and found some chunks missing, also found the raw pump kinda scored up on this inside so i replaced it, thinking it might not be getting good supply, but then arent these closed cooling? I have opened up and cleaned the heat exchanger which was kinda clogged up with sand, checked themostat, pulled hoses off manifolds etc to see if there is any obstruction. She pumps good water on the hose but i know that doesnt mean much.
thanks

 

[45Auto]

Re: 496 ho engine guardian alarm

The raw water goes through the oil cooler BEFORE it goes to the heat exchanger. If your heat exchanger was clogged with sand and crap, the oil cooler is worse. The oil cooler catches all the broken off impellor pieces and crap before they get to the heat exchanger.

Pull the hose off the port (passenger) side of the heat exchanger. Pull the hose off the back end of the raw water pump. Backflush with some high pressure water through the hose you removed from the heat exchanger and it'll force the broken off impellor chunks backwards through the cooling system and out the hose you pulled off the raw water pump.

 

[rodbolt]

Re: 496 ho engine guardian alarm

low block PSI can be caused by a faulty impellor, a restriction on the suction side of the seawater pump or a defective pressure transducer on the pump assy or an air leak on the pump suction side.

 

[Fun Times]

Re: 496 ho engine guardian alarm

The water sensor is going to be mounted either on the oil cooler or on the impeller housing depending on the serial number of your engine.

My guess is the oil cooler on yours.

Also try pulling the sensor out to make sure it's clean and tight.

Here is some other information.
http://forums.iboats.com/showthread.php?p=2632556#post2632556

 

[perryk123]

Re: 496 ho engine guardian alarm

ok will try to pull the hoses off the oil cooler again n see if there is any bit of impellor or sand still there.

On the ddt she ready 2.4-2.6 psi at idle and about 15-17psi wide open on the raw water pump psi.

Also she cools at 158-162 underway, but at idle she will get upto 172 is that normal for these engines???

what tells the engine the BLOCK PSI is low? is it the raw water pump sensor or something else?

 

[45Auto]

Re: 496 ho engine guardian alarm

You don't have to pull the hoses at the oil cooler. I would backflush through the whole system from the heat exchanger back to the seapump as I described above and push any debris out the hose disconnected at the seapump.

My 2003 496HO used to read 3 psi at idle and 15-17 psi with a 4 year old impellor in it. With a new impellor it still reads 3 psi at idle but goes to 22-25 psi at anything over about 3000 RPM.

As far as I can recall temperture on mine has always been rock steady at 160. I can see how it could easily go up a little at idle for a few minutes while cooling down after a run, but I can't say I've noticed it on mine.

 

[perryk123]

Re: 496 ho engine guardian alarm

45Auto,

i pulled off the hose and tried to backflush the debris. NOTHING but clear water. I ordered a new h20 pressure sensor, to see if maybe it is faulty. I am very frustrated with her as she has been acting up. its something minor cuz at times she can run 1-2 hours with no alarm.

I pulled off the water pick up connector on the transom assembly to see if it were cracked or leaking and maybe getting air, but it was all good. checked the water pick up tube, and it looks good, i dont think its on the outside.

thanks