Optimax 115 Temp drops when running

[ChrisPage227]

Just took my boat out for the first trip of the year and noticed a cooling issue. It is an '06 Optimax 115, SN 1B498653, Model # 1115D73HY. When i started it I let it idle for a few minutes. Water temp was 55 , air temp was in the low 60's. Temp was steadily climbing up to around 130 when I started to drive away and the temp was dropping pretty immediately. I watched it go from 120-130 right down to 80 fairly quickly when i was running at around 4000 RPM. If i throttled back into idle or near idle the temp comes back up. Is this a pretty straightforward case of the thermostat being stuck open? Or should I be evaluating something else? Water pressure according to the smart craft gauge was around 5 at idle, 10+ at 4000 RPM.

[JOE54]

temps should always drop when boat is underway/normal

[06 SB]

What you are watching is completely normal. I have seen running temps down in the low 70s in the winter. A thermostat that is stuck open will never get to the initial 120 degrees at idle. Once running it will drop and it should return to above 120 degrees when you return to idle.

Also, water pressure should be 1-3 PSI minimum at idle and 15 minimum at WOT. Any RPM in between does not have a corelating PSI value.

[ChrisPage227]

What you are watching is completely normal. I have seen running temps down in the low 70s in the winter. A thermostat that is stuck open will never get to the initial 120 degrees at idle. Once running it will drop and it should return to above 120 degrees when you return to idle.

Also, water pressure should be 1-3 PSI minimum at idle and 15 minimum at WOT. Any RPM in between does not have a corelating PSI value.

Thanks for the info. I was only providing those water pressure readings to give some context that the water pump appears to be working ok. I almost never take it to WOT so I was just reporting the info I had :-). I'm glad to hear this is normal but should I be concerned about running for extended periods of time with the engine temp in the 70 degree range?

[SilverFox579]

Thermostats only control temperature at or near idle speeds, once the poppet opens, thermostats are out of the cooling circuit. You need not concern yourself with engine coolant temp on plane, it will vary dependent on several factors, load, power demand, and biggest one of all, surface temp.

I fish a lot in winter and have seen Smartcraft coolant temps for my Optimax in the 60s with surface temps in the upper 30s and low 40s. My practice in those conditions is to watch for 2 complete thermostat cycles at idle speeds, gradually accelerate as coolant temp begins to rise after thermostat closes 3rd time taking at least a mile to reach cruise rpm.

[bassfisher444]

What you are watching is completely normal. I have seen running temps down in the low 70s in the winter. A thermostat that is stuck open will never get to the initial 120 degrees at idle. Once running it will drop and it should return to above 120 degrees when you return to idle.

Also, water pressure should be 1-3 PSI minimum at idle and 15 minimum at WOT. Any RPM in between does not have a corelating PSI value.

According to the service manual 11-14 psi wide open is fine. 20210119_220857.jpg

[06 SB]

According to the service manual 11-14 psi wide open is fine. 20210119_220857.jpg

True statement, BUT if you watch your water pressure in a turn, it will drop several PSI. If you are at 15 or above, the water pressure will still be in that range. So, WOT in a turn I will still be above the minimum. 15psi is a commonly accepted minimum, not just my personal one.

[ChrisPage227]

Continuing on with this topic, took the boat out again yesterday and let it sit idle with the plan to let the engine heat up until the thermostats opened, and then go from there. It idles for like 10 min and the temp never got above 116. I eased until taking off and ran about the lake for like 5-10 min, the temp came down as expected, and then when i got where I was going i wanted to see what would happen with the temp so i brought it into neutral and idled and again the temp never climbed above 116-118. NOW i feel like the thermostat may be stuck open or not functioning properly. So I sat there idling for like 10 min and i heard a single beep and got the "check engine" light on my smartcraft gauge at which point I immediately shut the engine off. But when i restarted the engine now warnings, no beeps, no message on the gauge anymore. Not sure what it was trying to tell me honestly.

Basedon the temp not going up at idle I will now pull the thermostat and have a look at it. If there is something obvious I am overlooking that I should also do I issue a big thanks in advance for the insight!

[EuropeanAM]

What was your Water Pressure at idle? Very important question....

[ChrisPage227]

Water pressure was between 3-4psi at idle

[JOE54]

parts breakdown shows it to use 143 thermostat

[SilverFox579]

NOW i feel like the thermostat may be stuck open or not functioning properly. So I sat there idling for like 10 min and i heard a single beep and got the "check engine" light on my smartcraft gauge at which point I immediately shut the engine off. But when i restarted the engine now warnings, no beeps, no message on the gauge anymore. Not sure what it was trying to tell me honestly.

That tells you your engine failed to reach at least 120° within 5 minutes idle time AND that you have a thermostat problem, it's stuck open probably due to debris. Shutting engine down and restarting silences the alarm but doesn't resolve the cause. Remove, inspect, and clean.

[06 SB]

Chris, for future reference, shutting off then restarting a motor will never solve a problem. It can however mask one that could prove to be catastrophic to your motors health.

I also believe you have a System Monitor. If you upgrade it to a Mercmonitor, it will give you plain language alarms vice a check engine light so you will know what is causing the alarm.

[EuropeanAM]

^^^ +1

Good idea to remove the thermostat and poppet valve and plan to replace them while apart. If EITHER of them is permitting water to bypass (due to debris, sticking, or other failure) the engine will run cold.

Had your water pressure been higher than 6 psi at idle, there might have been a different problem involved.

[ChrisPage227]

@SilverFox579, thanks for the info on that warning and the advice.

@06 SB, Thanks and understood. I only shut the motor off on impulse when I heard the warning beep and saw the thing pop up on my gauge. I had assumed the warning light would be back on when I started it back up but it was gone so I eased it home with my eyes glued on the gauge. And yeah the gauge that's on there is an old basic SC1000 system monitor, I am going to look into upgrading.

@EuropeanAM I am emailing your parts dept now for thermostat and poppet valve parts, and thanks for the advice btw. In regard to the mercmonitor, as I mentioned above I have one of the old style SC1000 gauges, its a round gauge with the small square LCD read out. Its hooked up to the engine via one of the blue CAN wires, do I need to do anything different with the wiring/connection to swap it out for a mercmonitor gauge? Or is it as plug and play as I am hoping. And aside from having to rely on your phone having battery life, is there any appreciable downside to opting for the Vesselview mobile system instead of an actual mercmonitor gauge? I'm gonna have your guys quote those for me, just need to make a decision on which one I suppose. Thanks again.

[SilverFox579]

Chris my boat was rigged with the System Monitor when new. All you should need, if you decide to add a Mercmonitor, is an inexpensive adapter cable which makes the install plug and play. Can contact European Marine to help with your decision process on which would be better for you.

If you want to order or price Mercury Engine Parts or Accessories

[EuropeanAM]

+1... Read through the information Rhonda sends you, and make a choice on what system will serve YOUR wants and needs best.

Each has it's own pros (and cons), but they're ALL better than the antiquated unit you're using currently.

[Grizz86]

Phil, I just ordered the Mercury vesselview for my '04 Optimax. I've never had an issue with it till this past weekend. I had no idea what the noise was at first. I had never heard an engine alarm go off before. I think it was the two stroke oil tank float failure - low oil alarm. ??? I had quit keeping my tank full up as it was leaking when traveling - tilted way up. It's always stored down - vertical. The motor kept running, never dropped rpm's etc. It was getting dark and I had about 15 miles to run to the ramp when the alarm first went off. Engine wasn't hot, pee stream was good, no water in fuel issues etc. My oil tank was down when I got home. ???? It shouldn't have been as low as it was. TBD. 2004 Mercury Optimax 90hp ELPTOSW OT944831.

[SilverFox579]

Should really keep one topic per engine, so suggest you copy your post above and open a new topic with a description of the alarm tone telling us if it was a steady tone or beep pattern. The 1.5L Optimax is a bit different in some respects than the larger hp models which have remote tanks for oil supply.

[ChrisPage227]

Continuing on with this topic, took the boat out again yesterday and let it sit idle with the plan to let the engine heat up until the thermostats opened, and then go from there. It idles for like 10 min and the temp never got above 116. I eased until taking off and ran about the lake for like 5-10 min, the temp came down as expected, and then when i got where I was going i wanted to see what would happen with the temp so i brought it into neutral and idled and again the temp never climbed above 116-118. NOW i feel like the thermostat may be stuck open or not functioning properly. So I sat there idling for like 10 min and i heard a single beep and got the "check engine" light on my smartcraft gauge at which point I immediately shut the engine off. But when i restarted the engine now warnings, no beeps, no message on the gauge anymore. Not sure what it was trying to tell me honestly.

Basedon the temp not going up at idle I will now pull the thermostat and have a look at it. If there is something obvious I am overlooking that I should also do I issue a big thanks in advance for the insight!

So my water pressure at idle was 6.5 today. What other problem should I be looking into with water pressure rhat high at idle? It was about 14psi at wot