Low Block Pressure Warning

[Jake315]

I am running a new mercruiser 350 bravo one. 16 hours on engine. Recently got low Block Pressure Warning. Water psi on digital guage shows 12 to 20 at idle, over 100 while getting up to speed, and settles at 80 psi at 3200 to 3600 rpm. Low Block Pressure sounds after 8 to 10 minutes when over 3500 rpm. Engine temp never exceeded 149 and water PSI is at 80 when alarm happens. I know this is very high. What could be problem? I removed the water sensor and cleaned it. It looks like new!

 

[alldodge]

80 psi at 3200 to 3600

Don't know where your measuring water pressure at, but if it actually has at 80 psi, there would be at least one water hose with a great big hole in it seconds after it reached this pressure.

Where are you measuring the pressure and what are you using as a gauge?

Also your in the Merc section so guessing this is a Mercruiser, but what motor and what drive, serial number are best but at least the year?

 

[Jake315]

Mercruiser 350 mag bravo one. Serial number is 2a504974. My display guage has a digital water PSI reading

 

[Jake315]

[No message]

 

[alldodge]

My bad, you did mention motor and drive, sorry the serial number narrows it down

With that serial number your motor is in the brand new or close to new.
I'm see a 0 to 100 psi digital oil pressure sender but not water pressure
Do see the water pressure switch that sends the signal of low water pressure

Most water pressure does not exceed 40 psi max

Do you have digital controls as well?
What is the oil pressure?

 

[Bt Doctur]

In my opinion there is just way too much electronics gadgets on todays boat motors. If you maintain your water pumps and impellers as you should, watch the temp gauge with 1 eye all the time, scan the volts and oil pressure and if there in the normal range just go boating. and ignore those pesky alarm modes.

 

[Jake315]

Oil pressure is in mid 40s. Can't ignore it cause it sends the boat into guardian mode, and reduces power.

 

[alldodge]

Oil pressure is in mid 40s. Can't ignore it cause it sends the boat into guardian mode, and reduces power.

Ding, ding, ding I think I have your answer. Your boat is using 2 of the same 0-100 psi senders and my guess is they are close to one another. So the plugs have been swapped for oil and water.

Look on the port side of the block down low where the remote oil filter lines go in/out of the block. Look for two of the same size senders. One close to the lines will be oil pressure and the one close to the middle of the block would be water pressure. If they are the same swap the plugs, they should fit.

The low water pressure sender is on the power steering cooler behind the motor and on top. This sender goes bad quite often

 

[Jake315]

I already took the water sensor off to inspect and clean it. It has the correct Mercury part number for a water psi sensor, so I don't think it has been swapped

 

[alldodge]

I already took the water sensor off to inspect and clean it. It has the correct Mercury part number for a water psi sensor, so I don't think it has been swapped

If your talking about the one on the power steering cooler, that is a switch (sensor) not a pressure sender. The low pressure switch is what is giving you the low block pressure warning

 

[alldodge]

The part number for a 0-100 psi sender is 881879T11, the switch is 8M6000623

 

[Jake315]

That is interesting. What is the part number for the oil pressure sender

 

[alldodge]

The reason I see them being swapped is because your oil pressure should be about 80 psi, and your water should about 40 psi

It not swapping the senders or switches, its swapping the the plug leads on those senders which feed into the PCM

 

[Jake315]

I will look into this and be back. Thanks

 

[Silverbullet555]

Why aren't you taking it to the dealer?

 

[Jake315]

I am. I just wanted to see if anyone here had a similar issue or advice

 

[Jake315]

I am. I wanted to check here if anyone had a similar issue or any ideas also .