Yamaha f 250 proper temperature range

[Rooster 1961]

Fellow fishermen, my F250s run at about 60 to 75% on the Yamaha engine monitoring system. Closer to 75% or 3/4s of the way to the right on the gauge during cruise between 4 and 5k RPMs. I’m running a Robalo R305. Is this normal or too hot? Had the impellers and engine 100hr service last summer. The motors have 550 hrs on both.
Thanks In advance.

 

[seasick]

I don't know what 60 to 75% means.
When you serviced the pump last season what were the readings then and what were they before the maintenance.
Does your gauge have the option to display actual temps?

 

[g0tagrip]

I have twin F250s on my Marlin and they run about one to two increments to the right of straight up on the temp gauge when running at 4200 RPMs. I'd say that it is about 60-70 % on the gauges. My engines have 1942.2 hours on them. I am getting ready for the 2000 hour maintenance; timing belts, tensioners, plugs, etc.

 

[Doc Stressor]

Those gauges are not very precise and the "normal" temperature range varies from boat to boat. My 3.3 F250 used to run 2 marks from the right. Then suddenly it started running only 1 mark from the right side. Never had a problem. The overheat buzzer will go off if are really at a dangerous temperature. It triggers at around 195 degrees. Remember that automotive engines normally run at over 200 degrees.

 

[seasick]

The best way to check temps and I do this every season is to use a contactless infrared thermometer. You can get a usable one at HD or similar for about 30 bucks.
With the cowling off, you run the motor and using the thermometer, measure the temp of the thermostat housing. It's not critical where you point the laser beam but make sure that you point to the same spot on all the t-stat housings.
You are looking for two things: higher than normal temps ( or colder than normal) and a significant difference between cylinder banks ( if there are two of course)
I can't tell you exactly what temps you should see. Over time you will learn. Most thermostats open in the range of 145 to 165 or so.
In the absence of a thermometer, you can put your hand on the t-stat housing or head cover as the motor warms up. You will be able to feel if there is a big difference but note that at some point the metal may become too hot to touch!
If the t-stats heat up differently , one cooler than the other, it could mean that one side is hot OR one side is colder than it should be. Having a few reference measurements over time will enable you to determine if things ate too warm or too cold.

Many years back, I was in a store listing to two fellows argue about who's boom box was louder. One of them said, mine is so loud, they numbered the volume know from 1 to 11 instead of 1 to 10.
My point is that 65-75% doesn't mean a lot when you don't know what it represents in absolute values. Those kinds of displays drive me nuts.

 

[Jened1840]

Fellow fishermen, my F250s run at about 60 to 75% on the Yamaha engine monitoring system. Closer to 75% or 3/4s of the way to the right on the gauge during cruise between 4 and 5k RPMs. I’m running a Robalo R305. Is this normal or too hot? Had the impellers and engine 100hr service last summer. The motors have 550 hrs on both.
Thanks In advance.

FYI as per sim Yamaha where the sensor is for the gauges (nnea2000) is the hottest part of engine on the f250. As per shop manual, overheat alarm is at 248 degrees Fahrenheit. On my gauges, my 2007’s fluctuate between 1/2 and 3/4, my axiom unit shows between 195 and 199 degrees. I was told this is completely normal

 

[Doc Stressor]

The alarm goes off well before 248 degrees. Each cylinder bank has its own thermoswitch that establishes continuity at 183-194 degrees and turns on the alarm. Depending on the rpm, the engine can go into limp mode controlled by the ECM. The alarm will stay on until the temperature drops below 180 degrees.

The engine temperature sensor continuously decreases resistance as the temperature increases. This is the sensor that is connected to your temperature gauge. All of 3 these sensors are located in the water jacket near the top of the cylinder bank. As long as you aren't getting an alarm, you are OK.

 

[Hookup1]

I don't have everything in front of me for my F150's but I'm sure it is similar for the F250. Garmin and other units will show approximate/relative (not absolute) temperatures. Maybe on an alternate engine screen you get better info or adjust the defaults. Bottom line is its a guide.

Earlier this year I was working a elevated temperature on one engine. Turns out that engine was normal because of a stuck open thermostat on the other engine. Replaced thermostat on "hot" engine - still hot - replaced the thermostat on "cold" engine" (obviously stuck open) and now both run the same temp +/-.

Head temp sensor controls overheat. This isn't really what your temp indicator shows but it controls the alarm.

Water temp sensor thru thermostat is what the displays show you.

 

[seasick]

Since your cooling system is 'open', not pressurized, the water can not get to 248 degrees,
As Doc mentioned, the thermo switch will kick on way before that. My 2 stroke runs normally a lot cooler than you were told is normal. Those t-stats kick in at about 145 degrees.
Also, on my motor a high temp alarm will not put the motor in limp mode.

 

[Marlinmark]

I’m looking at buying a boat that thermal probs we’re disabled as they weren’t not able to determine cause after several mechanics.
their theory is that it is the “computer” and that is cost prohibitive to replace.
what is the “computer” and could it be starting to fail and if so what does that mean for a 1997 208?

 

[DennisG01]

I’m looking at buying a boat that thermal probs we’re disabled as they weren’t not able to determine cause after several mechanics.
their theory is that it is the “computer” and that is cost prohibitive to replace.
what is the “computer” and could it be starting to fail and if so what does that mean for a 1997 208?

Can you please clarify some things?

What is a "thermal probs"?

What "cause" where they not able to determine?

I'm not following why you are asking what a computer is. You used one to write your question! If the engine is fuel injected, it uses a computer to control that, amongst other things.

Reading through your post, I'm not sure I even understand what you are asking?

 

[Marlinmark]

I’m apologize for being unclear as I am not super clear on the issue myself.
the owner said there are two thermal probes that send temp signal to “computer”. The boat was thinking it was in high temp condition and went into “limp mode”. They had mechanic go out and measure temps while running and didn’t see any problems so they disconnected them. My question is what does it take to replace computer and where does it reside?
I’m thinking it is all within the outboard motor but is that right?

 

[DennisG01]

OK, that's starting to get clearer!

The computer (ECM) would be on the engine... what year/make/model engine do you have?

Assuming for a bit that you have at least have a Yamaha - it's on the aft side side of the engine.

Continuing with the assumption... although this part is pretty common... you're going to find you have thermostats and water temp sensors. It "sounds" like the sensors are flaky and are sending a bad signal to the ECM. From what you've written it sounds like you need new temp sensors, not an ECM.

Not for nothing... and please don't take offense... but with what you've written so far, it sounds like your best bet is to get a new mechanic and pay them to fix it, rather than working on this yourself. It's not a bad thing to put bread on someone else's table.

 

[seasick]

I agree with Dennis, maybe you didn't understand what the mechanic said or possibly the mechanic doesn't know what he is doing.
Get a second opinion.
What motor is on that boat. If it is an original OX66 model, there aren't many things that cause limo mode. In addition, any good Yamaha mechanic would have a Blinky light for the OX model or the Yamaha Diagnostic terminal for other models. Those tools would tell him what caused the alarm.

 

[Marlinmark]

OK, that's starting to get clearer!

The computer (ECM) would be on the engine... what year/make/model engine do you have?

Assuming for a bit that you have at least have a Yamaha - it's on the aft side side of the engine.

Continuing with the assumption... although this part is pretty common... you're going to find you have thermostats and water temp sensors. It "sounds" like the sensors are flaky and are sending a bad signal to the ECM. From what you've written it sounds like you need new temp sensors, not an ECM.

Not for nothing... and please don't take offense... but with what you've written so far, it sounds like your best bet is to get a new mechanic and pay them to fix it, rather than working on this yourself. It's not a bad thing to put bread on someone else's table.

 

[Marlinmark]

I appreciate your info and patience.
It is a 1997 Yamaha 2-stroke
The owner said the thermostats were replaced and they spent $2k on trouble shooting with no success from two mechanic shops. He said watch for water coming from starboard side and you’re ok…
I just don’t want to get stuck 10 miles out.
I suppose I’m answering my own concern but will speak with his mechanic today.
Pricing a used 175 4 stroke looks like $10-15k…
Thanks again and I hope to be a GW owner soon!