Mercruiser 5.0 MPI no water pressure but cooling okay

[klopf]

Engine: Mercruiser 5.0 MPI year 2010
Sterndrive: Alpha one gen. 2
Gauge: Merc. Monitor
Water inlet: Only from the bottom of the boat through raw water pump. No impeller in the drive
Cooling: Closed cooling

First observation
Steady alarm when increasing RPM. Alarm turns off when reducing RPM. That went on for about 10 min. After that - no alarm and I did a trip for about 2 hours mixed speed. Temperature okay.

Next observations
I did a diagnose with my Rinda tool, and the alarm was about Low Water Pressure, Overheating and Guardian Mode. Water Pressure readings is 0.14 psi, which is to low.

Last observation
At idle the Water Pressure is at 0.00 psi on the Merc. Monitor


Then, the question is: Since I have had no problems with cooling, do you expect the Water Pressure sensor to be faulty?
Or would you change the impeller in the water pump?
Or maybe something else?

Regards
Thomas

 

[camalot]

You would have a Bravo drive if you have a sea pump and throu hull pick up, what can happen when the pump is not working as intended is your have exhaust manifold over heat but the engine will still show good on the gauge. What code did you Rinda give you, this will give you a good idea whats going on. If you have the brass water pump look for scoring before rebuilding.
If there is any scoring don't just replace the impeller it won't be much better than before.

 

[thumpar]

You would have a Bravo drive if you have a sea pump and throu hull pick up, what can happen when the pump is not working as intended is your have exhaust manifold over heat but the engine will still show good on the gauge. What code did you Rinda give you, this will give you a good idea whats going on. If you have the brass water pump look for scoring before rebuilding.
If there is any scoring don't just replace the impeller it won't be much better than before.

I can tell you for sure the engine will not stay cool if the seawater pump is not working. Ask me how I know.

 

[alldodge]

Then, the question is: Since I have had no problems with cooling, do you expect the Water Pressure sensor to be faulty?
Or would you change the impeller in the water pump?
Or maybe something else?

Howdy Thomas

The water pressure switches go bad quite often, but can also happen when there is a bad ground or corrosion on the contacts. The sensor is part number 8M6000623 and there should be no Teflon tape or anything else used when replacing.

That said, if you have not replaced your impeller as others have mentioned, this should be done prior

 

[klopf]

Thanks guys.
I will for sure replace the impeller as it's a couple of years since the last time.
Actually it's not an easy job as the water pump is sitting in a spot difficult to reach.
Do you have any experience removing the two hoses on the aft of the pump?

 

[thumpar]

Just loosen the clamps and wiggle the hoses off. For me that is the easy part.

 

[alldodge]

Do you have any experience removing the two hoses on the aft of the pump?

Yes, I'm sorry to say. To change it on my Formula I have to remove the, alternator and outdrive lube bottle, then I get to hang upside down. The inverted position is so much fun "NOT". :facepalm:

As with most mechanic work, you need to decide what needs to come off to give enough room to get at it, comfortable is best but not always able to achieve. Once the clamps are off, might need a hose pick to break it loose. If you can I would recommend removing the pump t wok on it, I don't because it is a bear to remove.

Oh and pay close attention which hose is on top, the hard wall hose or soft

 

[thumpar]

I remove the pump on mine but it will depend on the boat configuration which is easiest.

 

[klopf]

You would have a Bravo drive if you have a sea pump and throu hull pick up, what can happen when the pump is not working as intended is your have exhaust manifold over heat but the engine will still show good on the gauge. What code did you Rinda give you, this will give you a good idea whats going on. If you have the brass water pump look for scoring before rebuilding.
If there is any scoring don't just replace the impeller it won't be much better than before.

No, actually it's an Alpha drive. I have throu hull pick up.
Error codes:
BLK PSI LO, Overspeed and Guardian.
The Water Pressure was 0.33 psi

 

[klopf]

Just loosen the clamps and wiggle the hoses off. For me that is the easy part.

For me, that's the hard part. The hoses are stuck and very hard to work on. I'm looking for tools to help me do the job.

 

[klopf]

Anyway - the main problem still could be the sensor. Do you know if it's possible to test whether the sensor works or not?

 

[alldodge]

Anyway - the main problem still could be the sensor. Do you know if it's possible to test whether the sensor works or not?

The testing of the switch has come up many times and as yet there is not a clear way to test it. The PCM 555 manual only shows the connections and what the pressures should be when running, but no exact figures to diagnose. The manual just says if found faulty then replace. As before they have been a real issue. The failure rate for the part is shown as 2x10M cycles

 

[klopf]

I finally had the sea water pump removed and inspected the impeller. It's as good as new, and it can't be that causing 0.0 psi readings. I replaced it anyway. Next step is to clean the water pressure sensor and maybe replace it. Have any of you experience with cleaning/replacing the sensor?

 

[alldodge]

Many folks have replaced the sensor. They do go bad, only set for 1 bar. When installing a new one, don't use any Teflon tape or dope, just put it in as-is

 

[klopf]

Many folks have replaced the sensor. They do go bad, only set for 1 bar. When installing a new one, don't use any Teflon tape or dope, just put it in as-is

Thanks

 

[achris]

You would have a Bravo drive if you have a sea pump and throu hull pick up,....

No, any engine fitted with a closed cooling system will also be fitted with an engine driven raw-water pump, Bravo style, but retain the Alpha drive. Closed cooling HE needs more throughput than the Alpha pump can provide. The engine mounted pumps are capable of at least twice the volume as the Alpha style pump.

Chris.....