New ProXS Four Strokes and Idling

[Macsimus]

Planning for a new boat and I'm very interested in the ProXS Four Stroke. One of the things I really enjoy is idling around with side-scan looking for fishy structure and cover. But, with a 250 ProXS two-stroke, I've always been hesitant due to numerous posts I've read over the years basically stating that it is not good to excessively idle the ProXS two-strokes due to carbon buildup.

Will this concern be a thing of the past with the new four-strokes or is it still a concern? If a concern, how significant?

[btsmbass]

The carbon build up is not so much the issue. Its operating temps. It's always a good idea to get the oil temps up over 200F if possible (have a smartcraft, mercmonitor, or vesselview to view oil temps). Oil temps will help evaporate the blow by from idling long periods of time and prevent "making oil". These four strokes do not run warm enough at idle to prevent blow by. After idling for long periods of time, if you have the space do a 5k rpm run for 10-15 minutes if possible. you may have to run higher rpms to get the oil temps up depending on your location. Once oil temps are up just run for 5-10 minutes with oil temps over 200F. That will keep your engine running healthy for along time.

[clayshooter100]

As long as you keep the motor maintained properly and your thermostats are operating correctly, you shouldn't have any issues. Where I live folks tend to troll on their main engines (even 2-strokes), and I regularly see outboards with hundreds of hours of idle time. Some of the outboards with the most hours I've ever seen (usually fishing charters or work boats), have 75% or more of their running hours at idle. One note, I don't recommend any extended idle time during the first 10 hours of use. Break in is important, do it properly.

[Macsimus]

After idling for long periods of time, if you have the space do a 5k rpm run for 10-15 minutes if possible. you may have to run higher rpms to get the oil temps up depending on your location. Once oil temps are up just run for 5-10 minutes with oil temps over 200F. That will keep your engine running healthy for along time.

About the only places that I can think of where that's remotely feasible is the Mississippi River, large reservoirs, or really big lakes. Of course this assumes that the wind isn't blowing hard, there isn't a lot of heavy boat traffic, there isn't a speed limit, and you quit fishing with enough daylight left to safely run that far at that speed, and you don't mind burning 10-15 minutes of gas at 5K RPM just to keep your engine "healthy". 90% of the lakes I fish are nowhere near large enough. Does Mercury really expect the average owner to do this?

If this is true, then the four-stroke is no better option than my current two-stroke.

[Wheelman]

Ran 4-strokes of a different brand in the Navy and they ran 24/7 spending a majority of the time idling, don't remember them making oil though we were in a warmer climate, just made sure it had good water psi running in the saltwater.

I don't have a mercmonitor, but was curious what normal oil temps are as cars typically try to run at 212* to evaporate any condensation.

[Triton19x2]

Merc Monitor is capable of showing engine temp but not sure about oil temp...don't remember seeing it on the one I had years ago

[Lowerider58]

It's hard to get an outboard up to temp when running low RPMs. A car is using a closed cooling system and recirculating water through a radiator but our motors are constantly taking in cool water that keeps temps down.

[06 SB]

Merc Monitor is capable of showing engine temp but not sure about oil temp...don't remember seeing it on the one I had years ago

It will not on a two stroke since that parameter is not used be the PCM. It should on a 4 stroke. The MMs are really an awesome tool and should be standard on all motor installations IMO.

[SilverFox579]

It's hard to get an outboard up to temp when running low RPMs. A car is using a closed cooling system and recirculating water through a radiator but our motors are constantly taking in cool water that keeps temps down.

True but at idle the thermostats are controlling engine temps. They only drop out once ram pressure causes poppet to open.

It will not on a two stroke since that parameter is not used be the PCM. It should on a 4 stroke. The MMs are really an awesome tool and should be standard on all motor installations IMO.

Amen to that, and yes, oil temperature IS a monitored parameter for 4 strokes if selected on the Mercmonitor (which should be reset after a repower).

[howieranger]

I don't think that there will be any problem with long idles in terms of oil dilution.

The V8 and V6 motors are controlled by a thermostat that keeps coolant temps above 130 in even cold water and they don't have popit valves.

My motor at full throttle got up to 250* f today with a long WOT run and at idle would stay above 160*f which is hot enough to evaporate off any fuel residue in the oil fairly quickly.
I haven't had the thermostat out of my motor but looking at the shop manual it doesn't look like the thermostat lifts off its seat at higher pressures like sone two stroke thermostats.
Hopefully Don will comment as what oil temps are normal etc.

[kry29]

I'm interested to hear Don's comments. For some crazy reason I have the new boat itch lol

[Hickory Legend]

Does your car or truck build up carbon when idling?

[Hookedup2]

Your temps seem way to high mine are never above 140 and stay closer to 125 when running.

[howieranger]

Your temps seem way to high mine are never above 140 and stay closer to 125 when running.

Are you talking about oil temperature or regular engine temps for the coolant? The oil temps are higher for the oil temps.

[Hookedup2]

I was talking coolant and missed your oil temps, and those are about my oil temps also.

[EuropeanAM]

Coolant Temp and Oil Temps are definitely two very different figures. Each important- but very different.

The Fourstrokes will be far less troublesome in terms of idling, as compared to previous 2-stroke or DFI engine models. Proper Maintenance, Correct Fuel, Treatments and Good Running Habits should provide with years of good service.

All of this being said- there is a common-sense factor to consider here, as well. Think of the engine's intended use when it was designed.

Some engines are intended to go fast, turn left, and go fast again. Others for everyday cruising use, still others for hard work in harsh environments.

While your new 150-400hp Fourstroke may be capable of idling for extended periods, it was really not designed to be used as a trolling motor as it's primary purpose.

Just something to keep in mind.

[RangerRic]

Don, idling 'guideline' similar for the 115 ProXS 4 str. ?
I do a fair amount of trolling for toothy critters.

[EuropeanAM]

Yes sir.