350 Mag block pressure?

[chopper_bob]

Hello all,
I have a 2013 Monterey 244FS, 350 mag, bravo 3. Only 140 hrs. Had Low Block pressure and guardian activated. Setvice engine soon. Changed pressure sensor, still happend. Pulled pump, needed impeller change. Ran it today, still get service engine soon, and it will run fine great pressure at idle and high speed, then all of a sudden, low block pressure and guardian kicks in. Pressure immediately build back up, and i can run again for a few minutes same thing happens. So, my question is, do the codes need to be reset? Is that what keeps triggering guardian mode, an old code??? New impeller, new pressure sensor, slgreat pressures for a few mins....thanks in advance.

 

[alldodge]

Pressure immediately build back up,

Howdy

Not fully understanding what your saying. The pressure is good and and guardian kicks in, or pressure does drop and guardian kicks in.

If pressure goes low and you slow down and pressure builds back up?

Also have a motor serial number?

 

[chopper_bob]

Pressure is fine, idles fine, temps all good. I can run up motor, get boat on a plane for about 3-5 mins, pressure shows 50-60 psi, then it drops to 1-3, guardian kicks in, LOW BLOCK PRESSURE. Slow boat, pressure builds right back up. Temp fine, no overheating. Same scenario over and over. After more research, when I took impeller out, it was completely destroyed...so I think some pieces got sent downstream and are clogging water supply lines. I’m gonna try to backflush.

motor s# 2A035432

Thank you for the reply.

 

[Scott Danforth]

a raw water pump wont generate 50-60 psi

are you confusing the oil pressure. if your oil pressure is dropping, you should investigate that with a mechanical gauge. if you are dropping pressure, thats not good for longevity of the motor.

low oil level will cause you to drop oil pressure

 

[alldodge]

50-60 psi, then it drops to 1-3,

Seeing pressures that high on water pressure is up there, normal is no more then 40 psi

Assuming closed cool and Bravo drive

Yes do back flush and look close at the poppet valve.item 20

https://www.mercruiserparts.com/bam/subassembly/31757/15045/230

 

[chopper_bob]

It’s open cooling. Yes block pressure gets that high, at high speed, normal 6-12 at idle. Oil pressure solid and water temp stay 150-160 throughout.

Today I backflushed. Disconnected hose from output of water pump, and disconnected hose that is down stream of pressure sensor before water enters motor. Back flushed all that, few small pieces, very small, negligible pieces of impeller and small stone/coral came out. Opened up three of the blue plugs also. Water coming out just about everywhere.w

Onto the water to test, idles fine, full power up on plane no problem. No burps at all, no misfires, nothing. THEN, less than 30 secs on plane, guardian mode, block pressure falls to near zero, boat idles, pressure pops right back up to normal idle press, and I can immediately gun her again no problem. Up on plane, then same thing, over and over. Water temp good, no overheating.

I called local marina, explained my scenario, he asked how is boat stored, I said on trailer, only 140 hours, So too soon for headers/risers etc. He said the only hose you didn’t flush is intake from outdrive to intake of water pump. And he’s right. So tomorrow I’ll flush between intake of water pump back through outdrive. There’s a quick disconnect.

 

[alldodge]

Open cooling so your thermostat housing has the poppet valve

https://www.mercruiserparts.com/bam/subassembly/31757/15045/180

 

[Scott Danforth]

I called local marina, explained my scenario, he asked how is boat stored, I said on trailer, only 140 hours, So too soon for headers/risers etc..

never assume because you dont have that many hours on the motor that you dont have rusty manifolds. you have 7 years, and if in salt, most likely time for new manifolds. pull the elbows and inspect. dont assume Rust doesnt care if you use the boat or it sits on your trailer. rust follows a calendar from day one of being splashed in salt water

just like rubber parts dont care if you use the boat or not. they last about 5 years for impellers and about 15 years for hoses.

 

[Searay205]

Moderators have the patience of a physchologist. Holy **** took 5th post to figure water pressure vs oil pressure. Normal water pressure at idle is about 3.2psig not 6 psig.

 

[chopper_bob]

Back flushed hose from pump input through outdrive. All clear.

Ill check poppet valve and manifolds. Thanks.

Im second owner, previous owner was lake boater in GA. So, salt water exposure nonexistent up until last summer. But I agree, the manifolds could still be rusty.

 

[chopper_bob]

Also, I have the ECT motor, different thermostat housing. Poppet valve location?

 

[chopper_bob]

What do you think of this? Shouldn’t all the vanes be leaning in the same direction??? I’m assuming the vanes, being rubber, would correct themselves once rotating under power???? And yes, when I installed impeller, they were, and I rotated pulley to ensure they did their job.

 

[chopper_bob]

Couple questions, 1) What is normal block pressure at 2000rpm. Mines showing 50-60 (yes block, not oil) Looks like I should have about 12-15?

2) Does low block pressure alarm get triggered with high block pressure? I read online that on the mercs, high block pressure will set off the low block sensor alarm...wierd.

3) What’s the chances the new pressure sensor I bought could be bad, rare it may be, but?

 

[alldodge]

The poppet valve (post 7 link) is part of the thermostat housing

Your not the only motor which has seen those kinds of pressure in the water system. All have bet CAT motors with poppet valves. Do a search and there are a few others here on iboats, but they have not come back to close thread so far as pressure

The vanes should all go the same direction, but with that kind of pressure the vanes may be pushed back when motor stops

 

[chopper_bob]

Thanks alldodge, I figured backpressure may flip vanes. Onto poppet valve....

 

[chopper_bob]

:joyous:

Open cooling so your thermostat housing has the poppet valve

https://www.mercruiserparts.com/bam/subassembly/31757/15045/180

You were correct, I was wrong. Part ordered, along with gasket and new spring. Local mechanic suggested take a good look into housing, a chunk of the impeller may be stuck in there. He said if you biting it to me, that’s the first place he’d look.

Also, it IS block pressure I’m seeing, on digital gauge, 50-60 psi at WOT....so, that ain’t right either. More poppet valve clues?

 

[Searay205]

Seawater pressure I referenced was from an Alpha 1 gen 2 sorry. Your bravo 3 i don't have any data.

 

[Searay205]

Before you replace manifolds search for my post on cat manifolds. very expensive $2k in parts vs $1K for the older style. my opinion since your manifolds are 40 lbs heavier than the old style and very smooth with no corners they will last long. original design from merc was 3 years or 500 hours. I running mine until 300 hours. Insanity on prices

 

[alldodge]

Also, it IS block pressure I’m seeing, on digital gauge, 50-60 psi at WOT....so, that ain’t right either. More poppet valve clues?

It has a restriction somewhere, could be in the Tee fitting item 20 or about anywhere else. If pressure was not checked with another gauge I would still think its just the sensor.

Have you checked the Y-pipe?

https://www.mercruiserparts.com/bam/subassembly/31757/15045/215

 

[chopper_bob]

Thank you all for your replies. Pulled off cap to inspect poppet. All fouled up with rocks, shells, black gunk....I should probably replace t-stat while I’m there. Maybe this is the problem?

Didnt check y-pipe, but I back flushed all that out, from t-stat through disconnected hose #13 in that parts diagram.