2016 Mercruiser 6.2 Guardian Mode Hell. Low Block Water Preassure, pleaseeee help!

[Alexander Augustin]

Hello Newbie here at the forum. Looking for help, lost in oblivion...

I recently purchase a Sea Ray 2016 Sundancer 280 with a Mercruiser 6.2 300 with Bravo III.

Shotly after enjoying for a few months, the guardian mode started to become active after 3000rpm, not sure if is relevant, but it started to happen after the boat tilted a little and I used the trims to stabilize it.8

It keep doing it after that everytime at 3000 rpm when the low block water preassure alarm activated and it goes into guardian.

Now I'm at the 2nd mechanic and thousands of dollars behind without resolution to the problem.

First attempt.
Computer scan gave the following fault

Active Trouble Code List:1
SPN 521328 merc fault #328 - guardian active

After this we took the boat of of the water
- new water preassure sensor
- new prop ( needed it)
- water pump kit replace

The boat worked fine one day, the next day, after a little titl again and medium speed, same alarm. My first mechanic said he had diverticulitis so we had to find a new one.

Second mechanic:
Scanned boat again, he sent the report to Mercruiser and they said; water preassure sensor, we changed the sensor, no result. Mercruiser next instructions were to change the water pump (apparently changing the kit was not sufficient). New water pump, new sensor again!!! No problem resolved.

Now he is recommending taking the boat out of thr water again, but no silver linning.

Right now psi is 2-3 at neutral, 4-6 at idle, but it wont go up and guardian will ignite at 3000rpm, psi never goes above 6.

Please if someone has experience something different, help will be very much appreciated.

Best.

 

[scoflaw]

Sounds like blockage before the pump

 

[hughespat57]

Fresh or saltwater?
Two things can happen before the pump

The outer drive house has a bend that can get weak and suck down, newer hoses have a plastic insert there now.

Bravoitis a corrosion problem where the hose comes thru the transom.

Do you have a thru hull sea valve for a generator or A/C pump near by?
If you do can you route a hose from that to engine pump as a test?

If it runs well off a sea valve it’s a restriction

 

[Scott215]

Following

 

[Alexander Augustin]

Fresh or saltwater?
Two things can happen before the pump

The outer drive house has a bend that can get weak and suck down, newer hoses have a plastic insert there now.

Bravoitis a corrosion problem where the hose comes thru the transom.

Do you have a thru hull sea valve for a generator or A/C pump near by?
If you do can you route a hose from that to engine pump as a test?

If it runs well off a sea valve it’s a restriction

 

[Alexander Augustin]

Thank you hughespat57, its salt water, and there is a generation near the engine, I'll comment this to the texhnician.

The corrosion could be a direccion as the steering cooler (right where the sensor plugs in) had it. We also changed it.

 

[Alexander Augustin]

Thank you hughespat57, its salt water, and there is a generation near the engine, I'll comment this to the texhnician.

The corrosion could be a direccion as the steering cooler (right where the sensor plugs in) had it. We also changed it.

 

[paulswagelock]

I think you will find a blockage in the lower unit or transom assembly. You needed a new prop, did you bottom it out in sand/mud and that got sucked into the lower leg and is blocking the water path? Salt water - odd for that motor, but the transom assembly gets corroded and blocked, restricting flow.
I agree with others, it sounds more like a restriction before the pump and your mechanics are focusing from the pump forward.

 

[Alexander Augustin]

We are trying hughespat57 recommendation today. I'll let you know the conclusion today.

Thank you everyone for you helpnso far.

 

[Bill Curtis]

When the pressure sensor is removed, there is a very small hole in the fitting that allows the pressure into the sensor. In salt water, those do block up with scale / crap. See if that hole is clear under the sensor.

 

[Korkie]

+1 on all of the above. Low pressure = restriction before the pump, high pressure = restriction after the pump. We had same overheat issue, ours was caused by bravoitis, installed thru hulls for both our motors, blocked off inlet for outdrive and added drive showers. We now have strainers and catch all the crap that was going thru the motors from the drive sea water supply.

 

[Alexander Augustin]

Thank you Korkie,

I just want to highlight that we have not had a high temp reading. Only the guardian mode activation. Psi reading have also not been consistent. I was also wondering, going through the 3rd preassure sensor in less than 6mo. Can restriction before the pump or tranmission coolant cause this.

Ps the trans coolant was change because the inlet where the sensor had a lot of that green corrosion. The mechanic mention its due to the electrolitis in the marina.

We still due to do the bypass redommended.

Ill.let you all know the results on that.

Thank you all for the support.

 

[Alexander Augustin]

Hello all, It painful to say that we tryed hughespat57 recomendatuon with the marina hose and the outcome is the same.

As soon as the engine hits 2800rpm the water preassure drops below 6psi.

The saddest part is that his comment is, "we are back to 0" he is recommending taking the boat out of the water again, but without a plan on what to do. Any suggestion???

 

[Espos4]

Has the water inlet at the inside of the transom ever been removed to inspect for a collapsed inlet hose (aka bravo itis)? If not, it should be done.

Has the out drive ever been removed and split open to check the water passageways?
Removing the lower unit from the upper may reveal barnacles and other growth.

Both of these can only be done with the boat out of the water.

 

[hughespat57]

Can you provide the Mercruiser serial number please?
I want to see if your system has the spring loaded bypass valves.

 

[Alexander Augustin]

Mercruiser engine sn# 2A459152
Drive sn# 2A326775

Thank you

 

[hughespat57]

These 2016 with the air drain system and possible flush kit are a plumbers nightmare...

1. On suction side - if it has the flush kit that is on the inlet side of the sea pump, be sure all the fittings are tight or it could suck air in.
2. if no flush kit there is a quick connect instead, same be sure it is secure and the o-ring is in place or it could suck air.
3. after the pump (now on pressure side) before the oil cooler for the steering is a strainer. Has this been checked? This is after the pump but before where I believe the sensor is?

for reference all this is raw water...

 

[hughespat57]

Somewhat scratch the above that strainer is after the sensor, it seems Mercruiser added it as a last ditch to protect the drain valves from debris/grit that might clog or damage them. If this were clogged we would see a high pressure reading.

This plumbing is so complicated with the drain system and FWC vs RWC I can see why the mechanic is at a loss to trouble shoot. I found several flow diagrams from the builder installer guides, but they are simplified and leave out some key on engine components. I am doing a drawing from the parts books to show flow; should have it soon. I see a number of components that could cause bypass issues if failing.

These next generation engines are going to be challenging. All the usual MPI/ECM/Sensor issue we have seen. But now add complex cooling/drain, dual oxygen sensors, catalyst, DTS (fly by wire).

To recap:
As has been said the most common issues are on the suction side BEFORE the pump. clogged intake, collapsed hose, transom (Bravoitis). But the OP bypassed all these by using the Sea Valve for the generator. The only issue here is that generator inlet could be a little undersized, or it is also restricted by growth or such.

Low pressure AFTER the pump is rare but not impossible.
Usual suspect is the pump itself, but OP has had the pump replaced. (note the pump housing now contains air operated drain valve and Mercuiser has had two designs)

Other than the pump it would have to be a LACK of minimum restriction. Sea water pumps are positive displacement, for every revolution they must move a specific quantity of water. A large restriction can prevent water flow and cause the pump to overheat and damage the impeller. But with NO restriction it just moves water and will be essentially at 0 PSI. So the ECM system has a calibrated minimum pressure/rpm curve it is looking for the pump working against a known system restriction.

At the most basic level the system restriction is based on the diameter of the hoses and fittings which will pass only so much water at a given pressure.

When I finish the drawing I will go over the components that maintain that restriction and if stuck "open" could allow water to bypass in a manner that reduces the system restriction and would show as "low pressure".

 

[hughespat57]

Wow is all I can say...
So this is the normal water flow

And this is with drains open

 

[hughespat57]

So final observations:
The water pressure sensor is being used to verify acceptable water flow, because real flow sensors are more difficult and expensive to implement. To use pressure as an indicator of good flow it has to be against a known system restriction and will vary with RPM.

The principle device that maintains a minimum system restriction at any given RPM is the "poppet valve".
Mercruiser introduced these around the same time as the ECM with water pressure sensor for pretty obvious reasons, it was consistent when any given engine design might have more or less hose/fitting restrictions.
We see these as "bypass valves" on earlier MPI. In RWC engines it also is used to bypass the block when the thermostat is closed so as to allow ample water for the manifolds and exhaust. In the FWC all water flows thru the heat exchanger all the time, so it only servers as a calibrated restriction. In fact Mercruiser has two different Poppet valves with different springs "black" for RWC and "stainless" for FWC so they must have different pressure values.

So what can cause to little restriction on the pump side for the ECM to become confused.
1. If either drain system were stuck open, but you would visibly see water running into the bilge.
2. The check valves for the drain system could allow some water to bypass the heat exchanger, but they appear rather small so not sure they would trigger the ECM. But possible worth taking apart.
3. The poppet valve is open, ether because the spring failed or debris or other part failure. Water will still flow and the engine should not run hot, but it would confuse the ECM.

I have professed two things on this site when doing diagnostics:
1. Check the simplest things first
2. Every test must prove something specific, or disprove something specific, otherwise the test has no real value.

Simple things:
Check the suction side completely, most common problems.
If there appears to be good water flow when running on the hard, and no actual signs of overheating. Check the poppet and the check valves.

Hard things, test:
Pump pressure, big c clamp and two pieces of wood or angle about 6" long.
Make as a clamp on the water line to the poppet valve.
Close the hose down about 50%, run and check pressure reading @ about 2000 RPM,
Close down clamp more pressure should rise, (don't go crazy you don't want to blow out something)

Really hard test:
2. The installer guide specification says the pump should be able to flow 28GPM @4000 RPM.
The only way to test this properly is in the water or with a water supply that you confirm can supply 30GPM.
Warm the engine up first.
You have to take the hose off the heat exchanger and attach a 1 1/4" hose long enough to go to a barrel that is at least 15 gallon. That you have marked at 14 gallons. Start the engine and a stop watch immediately bring to 4000 RPM. Barrel should fill in 30 seconds, shut down.

If the pump can make pressure and the pump can move water the problem is after the heat exchanger.