Mercruiser water pressure sensor [Update]

Devil_Inside

New Member
Aug 26, 2019
20
Boat Info
Proline 251
Engines
2005 Mercruiser 5.7 Horizon MPI w/ Bravo III
It appears that my water pressure sensor is faulty, which I understand is a pretty common problem. I found an older thread on another forum discussing possible alternatives for the "OEM" sensor, which costs about $140, and New Eagle was mentioned as possibly being the sensor manufacturer. I was wondering has anyone been able to figure out how to order one and from where? I am aware that there are $28 Chinese "knockoffs" on Amazon and eBay, but I am not sure if I can trust those.

Alternatively, does anyone know how to successfully bypass this sensor? Again I found multiple discussions in older threads, but thus far I haven't been able to find the correct resistor value... If anyone can shed some light I would really appreciate it.

This sensor caused my engine to go into Guardian mode yesterday at the worst possible time (crossing a choppy inlet) and it wouldn't let me go above 1200RPM.... I really don't want this happening again, and if these sensors are known to flake out, I would much rather bypass the sensor altogether and rely on my temperature gauges (analog and VesselView).

P.S. Since you guys are probably going to ask, the engine is a 2005 Horizon MPI 350 Bravo, serial 0W3285##
 
I believe it is a 90s era gm pickup oil pressure sender - I had one go out earlier this season and while it gave me the "two beeps a minute" it did not limit my power.....are you sure its the pressure sender? in the past, mine failed by reading 40+lbs of pressure - maybe yours failed by reading no pressure hence the guardian mode. There are als two temp senders in the water neck - one for the gauge and one for the computer (IIRC the 2 wire one is for the computer) if that is bad, it will limit power....and your gauge would still show normal - really no way to bypass that though as I'm sure the computer uses it for cold start enrichment too
 
Mine was reading 0psi according to VesselView and that's when Guardian kicked in. The temperature was fine - both the analog gauge and VesselView were showing normal temps, albeit there was a difference of ~10* F between the two.
 
I just changed mine last week with a cheap knock off. It works great. There is only 1 to 2 lbs of pressure in the tube that its connected to. The smart gauge now reads 39lbs of pressure. The alarm is silenced and that all I care about. Just watch your temp and you'll be fine.
 
It appears that my water pressure sensor is faulty, which I understand is a pretty common problem. I found an older thread on another forum discussing possible alternatives for the "OEM" sensor, which costs about $140, and New Eagle was mentioned as possibly being the sensor manufacturer. I was wondering has anyone been able to figure out how to order one and from where? I am aware that there are $28 Chinese "knockoffs" on Amazon and eBay, but I am not sure if I can trust those.

Alternatively, does anyone know how to successfully bypass this sensor? Again I found multiple discussions in older threads, but thus far I haven't been able to find the correct resistor value... If anyone can shed some light I would really appreciate it.

This sensor caused my engine to go into Guardian mode yesterday at the worst possible time (crossing a choppy inlet) and it wouldn't let me go above 1200RPM.... I really don't want this happening again, and if these sensors are known to flake out, I would much rather bypass the sensor altogether and rely on my temperature gauges (analog and VesselView).

P.S. Since you guys are probably going to ask, the engine is a 2005 Horizon MPI 350 Bravo, serial 0W3285##

There was a good discussion about this on iboats a while ago...
https://forums.iboats.com/forum/eng...to-mercruiser-sea-water-pressure-sensor/page3

-Kevin
 
I just changed mine last week with a cheap knock off. It works great. There is only 1 to 2 lbs of pressure in the tube that its connected to. The smart gauge now reads 39lbs of pressure. The alarm is silenced and that all I care about. Just watch your temp and you'll be fine.

I am probably overthinking this, but wouldn't the high pressure reading also cause the engine to go into Guardian mode? I know that there is a high limit, but I don't know what the threshold is. I suppose if you aren't getting any alarms that means it's probably happy.
 
There was a good discussion about this on iboats a while ago...
https://forums.iboats.com/forum/eng...to-mercruiser-sea-water-pressure-sensor/page3

-Kevin

Thanks, Kevin. I have read this thread several times, and any others I could find on the subject. That's how I discovered that the sensor is most likely being distributed by New Eagle and it appears to be manufactured by Woodward

https://store.neweagle.net/product/sensor-pressure-50-psi/

Unfortunately I haven't been able to purchase one because I dont have an account
 
OK, so the plot thickens - I replaced the sensor with an OEM Mercruiser sensor, and my pressure readings are still kinda low. According to VesselView, I am only getting 0.4psi to 0.7psi at idle, about 2psi @1000rpm, 4-5psi around 1500rpm, etc. No alarms or Guardian mode this time around, but I only ran the boat for a short period of time, at the slip.
I went to Home Depot and I bought a cheap 0 to 15psi gauge, and a couple of fittings, and I installed it in place of the sensor. My readings went up ~1psi, so at idle I was getting a reading of 1.4psi to 1.7psi, about 3psi @1000rpm, 6psi @1500rpm and 8psi @2000rpm.
I don't know how accurate the cheap $10 gauge is, nor do I know how accurate the new pressure sensor is, but even the higher values shown by the gauge are kind of low aren't they?

This motor is new to me and thus far I've only ran it for about 2 hours total (everything from idle to WOT), during which time the temperatures stayed normal according to both the analog gauge and VesselView. This engine replaced a raw water cooled 1995 Mercruiser 5.7 TBI/EFI, which I ran for 6 years and over 800hrs, and it too never had any overheating issues so I don't think the problem is "Bravoitis". I am embarrassed to admit that I never checked what's behind the water outlet while I had the motor out, but at the time I hadn't even heard about "Bravoitis".
The impeller and wear plate are brand new, and so is the water distribution housing, and water hose (transom assembly to raw water pump). While I had the raw water pump apart I didn't notice any excessive scoring inside, but then again I probably wasn't paying as close attention as I should have as I wasn't aware of that known issue either....

I am really not sure what to make of this, but I think I should do a flow test as a next step. I recall reading about a target value of ~7.5qts water for 15 seconds of runtime as a baseline - does that sound about right?
 
OK, so the plot thickens - I replaced the sensor with an OEM Mercruiser sensor, and my pressure readings are still kinda low. According to VesselView, I am only getting 0.4psi to 0.7psi at idle, about 2psi @1000rpm, 4-5psi around 1500rpm, etc. No alarms or Guardian mode this time around, but I only ran the boat for a short period of time, at the slip.
I went to Home Depot and I bought a cheap 0 to 15psi gauge, and a couple of fittings, and I installed it in place of the sensor. My readings went up ~1psi, so at idle I was getting a reading of 1.4psi to 1.7psi, about 3psi @1000rpm, 6psi @1500rpm and 8psi @2000rpm.
I don't know how accurate the cheap $10 gauge is, nor do I know how accurate the new pressure sensor is, but even the higher values shown by the gauge are kind of low aren't they?

This motor is new to me and thus far I've only ran it for about 2 hours total (everything from idle to WOT), during which time the temperatures stayed normal according to both the analog gauge and VesselView. This engine replaced a raw water cooled 1995 Mercruiser 5.7 TBI/EFI, which I ran for 6 years and over 800hrs, and it too never had any overheating issues so I don't think the problem is "Bravoitis". I am embarrassed to admit that I never checked what's behind the water outlet while I had the motor out, but at the time I hadn't even heard about "Bravoitis".
The impeller and wear plate are brand new, and so is the water distribution housing, and water hose (transom assembly to raw water pump). While I had the raw water pump apart I didn't notice any excessive scoring inside, but then again I probably wasn't paying as close attention as I should have as I wasn't aware of that known issue either....

I am really not sure what to make of this, but I think I should do a flow test as a next step. I recall reading about a target value of ~7.5qts water for 15 seconds of runtime as a baseline - does that sound about right?


Not sure of the spec. either, but the first thing I would do with respect to the Bravoitis concern, would be to pull the hose off that comes from the transom fitting and see what kind of flow you have going to the pump.
 
There's nothing wrong with your cooling system, those psi numbers are normal and your motor is running at a normal temp.
 
According to the mechanic I spoke with. There is only 1 to 2 lbs of pressure in that tube. Your boat is in range. As long as your not overheating your good to go.
Don't over think this.
 
My Mag 350,s run about 4-5 PSI at idle. Earlier this year I had a time when 1 motor would barely make 1.5PSI at idle. I verified the reading with a mechanical gauge. I pulled the seawater pump and found the face of the bronze housing scored so I installed a new OEM pump. No change in pressure

Thought it through and I swapped the bypass valves (poppets) and springs between motors and the low pressure moved to the other engine. Then I ordered a new poppet and spring and a week later things returned to normal without replacing the parts.

While I’m not 100% convinced, I suspect that the poppet can get cocked and jam in the open position. When it’s open, there is very little restriction to flow.
 

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Not sure of the spec. either, but the first thing I would do with respect to the Bravoitis concern, would be to pull the hose off that comes from the transom fitting and see what kind of flow you have going to the pump.

I don't believe it is Bravotitis because I've never had overheating issues with my previous motor and it was raw water cooled. The new to me 2005 Horizon MPI motor is fresh water cooled, and for the 2 hours that I ran it, the temps also stayed normal.
I do plan on checking the flow from the sea water pump as per the Mercruiser service manual. I basically need to connect a long hose to the outlet of the pump, bring the engine to 1000rpm and measure the volume - it should be minimum 7.5qts per 15seconds

There's nothing wrong with your cooling system, those psi numbers are normal and your motor is running at a normal temp.
According to the mechanic I spoke with. There is only 1 to 2 lbs of pressure in that tube. Your boat is in range. As long as your not overheating your good to go.
Don't over think this.

Unfortunately I have been reading a lot of conflicting information regarding the PSI values at idle however, when I spoke with Mercruiser tech support, I was told I should be getting around 2psi at idle and 7 to 14psi at cruise. In my case the pressure sensor is reading only 0.3 to 0.7psi at idle, and the mechanical gauge is reading 1psi higher than that. Frankly I don't really care what my PSI values are, since pressure is merely a resistance to flow, however I don't know how low I can go before the ECM freaks out and puts the engine in Guardian mode - that's the only reason I am chasing this ghost.


My Mag 350,s run about 4-5 PSI at idle. Earlier this year I had a time when 1 motor would barely make 1.5PSI at idle. I verified the reading with a mechanical gauge. I pulled the seawater pump and found the face of the bronze housing scored so I installed a new OEM pump. No change in pressure

Thought it through and I swapped the bypass valves (poppets) and springs between motors and the low pressure moved to the other engine. Then I ordered a new poppet and spring and a week later things returned to normal without replacing the parts.

While I’m not 100% convinced, I suspect that the poppet can get cocked and jam in the open position. When it’s open, there is very little restriction to flow.

Can you please tell me where is this bypass valve (poppets) you speak of? I definitely want to check it out. A screenshot from the Mercruiser part catalog, or similar, would be very very helpful, if you could post it. Thank you so much!
 
Mine are raw water cooled so it could be different but they are under that 3 bolt cover with the belt routing on it.
 

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OP don't have a poppet valve motor and his motor shouldn't be at 5 psi at idle either
 
So, long story short, had a water pressure sensor go bad, engine went into guardian mode, replaced sensor with the Amazon one for 20 bucks i think. Worked well..... for the first 3 days anyway. Was showing 30 psi at idle. No way. The pump is about flow, not pressure, anyway sensor goes bad after a few days and I'm stuck again. Spend the next few days thinking it was more than what it was, and ending up rebuilding the raw pump. Still the same problem. So, went and purchased the sensor from merc, 155 bucks. She reads 2.5 at idle and has been well for a few months now.
 
Went through similar scenario, gardian mode, mech replaced both sensors, still poor readings, did raw water pumps on both engs, reading on port sensor is pinned at 37.5, starboard was more in the 15.0 @ 3200 rpm, 3.0 at idle initially and for a lot of the summer. Last weekend the one that fluctuates accordingly dropped to 5.0 @ 3200 and 1.9 at idle. Not happy again.
 
Well I am getting a new sensor under warranty and I will see what the new one reads once it arrives. I also ordered another 0-15psi gauge from a different manufacturer so hopefully between the two pressure sensors and the two pressure gauges I will be able to establish some sort of a quorum.

I am also planning on checking the output of my sea water pump as per Mercuiser's procedure. I will report my results in the next 2-3 days.

Hopefully I will be able to get to the bottom of this before the weekend.
 
The water pressure sensor is a total joke for a pleasure boat. They didn't put them on boats 20 years ago, and them old boats run just fine. If your temp is good all is well, going into guardian mode not so much fun.
 
I like it actually. It gives you a warning before trouble arrives. Particularly when an impeller is deteriorating or a suction screen is restricted.
 
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