2005 Optimax Smart Craft Water Pressure Reading Incorrect

[bunz559]

Hello board, I recently purchased a Ranger 185vx with a 175 Optimax that came with a Mercury Smart Craft. It is the older black and grey square unit. The Smart Craft water pressure reading is showing 40.7 PSI at idle and 40.8 during WOT. I am going to assume this is incorrect? The analog gauge on the dash seems to read between 4-5psi at idle and above 10psi at WOT which seems to be more in line with normal operating standards.

Question is, does my engine have a digital water pressure connection? And if so, where would I look for it? If not, what do you guys think my Smart Craft is reading/displaying?

Thanks!

1B161509
2005 Mercury Optimax 175
23P Tempest
5600
SmartCraft
No Engine Mods

[SilverFox579]

Those water pressure numbers are not correct but I cannot tell you why. I'd pull the cowl and conduct a visual inspection of all connections including the engine water pressure sensor. Don or Joe or maybe someone else will likely have other suggestions, might take a bit though as they're really busy this time of year.

[ride.race.live]

mine had the same issue... pressure sensor took a crap on mine and they seem to fail fairly commonly from what ive gathered.

Id check for obstructions but chances are from what i've seen a new pressure sensor will do the trick.... mine froze at 40.2psi If I remember right.

[bunz559]

Thanks for the responses! Where would the water pressure gauge be located under the cowl? I have a manual, but just cannot find anything on the location of the water pressure sensor. Why I'm wondering if my engine even has one for a digital reading... But at the same time, where did the previous owner plug the wires to get the high reading. LOL

[06 SB]

You do have a water pressure sensor, plus an analog system too. Follow the water pressure line under the cowl.

[EuropeanAM]

On coil plate at back of the engine. Follow the gray tubing up to the sensor, disconnect (it's a legris fitting- depress the round metal ring on the fitting to release the hose).

Turn key on with hose disconnected: If it still reads 40.X psi, you need a sensor. Not very common, actually- but use ONLY- ABSOLUTELY ONLY the correct OEM Mercury Part. Don't buy aftermarket, and avoid the junk ones on the bay or the rainforrest. Several have run that path over and over.

Our Parts Department can assist with a replacement sensor (drop them an email).

[bunz559]

Thank you for the advice. Will be in contact if parts are needed.

[ride.race.live]

but use ONLY- ABSOLUTELY ONLY the correct OEM Mercury Part. Don't buy aftermarket, and avoid the junk ones on the bay or the rainforrest. Several have run that path over and over.
).

I can vouch for this one.... I was one of those "several" that have attempted knock off parts.... didnt work out LOL.

[SilverFox579]

The water pressure sensor on my 12yr old Optimax is same one it left the factory with.

[bunz559]

I ran Don's test and looks like the sensor is no good. Unplugged the grey tube and Smartcraft still reads 40.x. Please reference to photos below and correct me if this is the wrong sensor. I had to use a crescent wrench and wrench to separate the tube from the sensor.


20200610_143719.jpg

This is the reading after unplugging the grey water line from the sensor.
20200610_143623.jpg

New question... What is this sensor or plug? It sits just below the water pressure sensor. It has a tube connected to the bottom side but no electrical plugs connected on the top side.
20200610_143732.jpg

[EuropeanAM]

You also posted a picture of the Pitot Sensor- the one you disconnected the GRAY tubing from is the Block (Water) Pressure Sensor.

Hose is disconnected by depressing the RING on the fitting, then while holding it down gently pulling the hose out of the fitting (no tools required to connect or disconnect hose).

[bunz559]

You also posted a picture of the Pitot Sensor- the one you disconnected the GRAY tubing from is the Block (Water) Pressure Sensor.

Hose is disconnected by depressing the RING on the fitting, then while holding it down gently pulling the hose out of the fitting (no tools required to connect or disconnect hose).

Thank you for clarifying the Pitot Sensor. I sent an email tonight for some part quotes referencing to this thread along with a few other maintenance parts. Will post results if this works for future references and people searching.

[bunz559]

You also posted a picture of the Pitot Sensor- the one you disconnected the GRAY tubing from is the Block (Water) Pressure Sensor.

So I finally received my parts from you guys. Mercury has been back logged on a few maintenance parts but I'm glad to be able to get to work. Question, the sensor that was sent to me is black as well, is there a difference? Will it still work in replacing the white water sensor pictured above? It seems the electrical plug prongs are the same on both sensors, unless something internally in the sensor is different, I cannot tell if it will work or not.

[ride.race.live]

Reference the part number off of the plastic packaging the sensor was in. It should read 881879A7 for the block water pressure which is a 0-50psi sensor. the Pitot sensor part number is 881879A2 which is a 0-100psi sensor which will NOT work in the place of the water psi sensor.

Part numbers verified using the merc parts catalog with your serial number.

[EuropeanAM]

You received the correct 50 psi sensor. "Color" of the current version is of no consequence.

[bunz559]

Ok, so I installed the new water pressure sensor and the Smartcraft has changed its reading. I turned on the motor with muffs and the Smartcraft is reading .7psi. I should add, my analog gauge that uses the old school grey hose reads 0psi on the muffs. I have noticed that when in the water, the analog gauge used to work between the 10 and 11psi range during WOT but would die out if anything slower than 25mph... any other suggestions because it seems both the Smartcraft and analog gauge are still not reading correctly, or they are and the pressure from the garden hose isn't enough? I even unscrewed the grey hose from the block and to see if any dirt. Cant seem to see or feel anything. It's wet but no pressure reading on either gauge.

These latest readings were on the muff with no alarms and a strong pee and with a brand new pump kit installed. Thanks for all the help up till now.

[bunz559]

So I got the boat in the water today and PSI reading changed. Gauge on dash would 0 when idling but as soon as moving it would begin reading normally. The Smartcraft would read anywhere between .7 and 1.5 psi at idle. At WOT PSI readings would jump up to 22psi. This is much higher than what is in the manual. Any ideas where to start looking into this now?

[SilverFox579]

What is Smartcraft water pressure at IDLE, no throttle applied whatsoever?

Smartcraft pressure is accurate and 22psi at WOT is fine. I'd be far more concerned with .7psi at idle, it should be between 1 - 3psi. For an Optimax, the telltale is no indicator for block water pressure as it is compressor outlet only.

[bunz559]

With no throttle applied, and just the engine on the Smartcraft is showing between the .7 and 1.X. I'm kind of stumbled as well.

[bunz559]

I think I may have found the problem. After further inspection, my poppet was assembled completely incorrectly. When I put it back in after replacement, I put it in as it came out which was wrong. I checked my service manual for proper assembly and fixed it. Hopefully this might fix my issue for wrong readings.

Could this have been a culprit?