So this is my 3rd season with my Sho 250 . My eng temp for the first three years have been 142-145 top end temp . Yesterday I ran it I was seeing 147- 149 . This was with water temps at upper 40s and air temps low 50s . What temp is getting close to being to hot for these motors .
Have you ever changed the water pump?
12 lbs 9 oz caught on 4/28/1975 Lake Eufaula
Your not even close to any kind of overheat issue. I think horn sounds at 180-190Originally Posted by skennedy
Mine runs higher temps on a long wide open throttle run. I have run temperatures higher than you have indicated many times. I have my engine temperature displayed on my Lowrance unit. Once on a very long WOT run I ran a significantly higher temperature. Water pressure was normal. I sent in an engine oil sample and it came back normal. So I agree with the statement above that you don’t have an overheat issue with your engine.
2015 Ranger Z520C Yamaha 250
301* F.
Those are all normal numbers.
As stated above, fish will be floating before the water is to hot.
Thanks guys .
My SHO is flashed, but on a long WOT run I see ~200 degrees on the Lowrance NMEA. It will run 145 most of the time even during short WOT runs. But if I run WOT for 5+ mins, temps start to climb and can go to 190-205. Water pressure is 18-20 psi. I talked to Hydrotech amd they’ve seen similar on a flashed engine.
Taylor so if you're seeing 200+ degrees with your flashed engine how is your horn not sounding or does the flash raise the alarm temp setting. I've recently had an issue which I posted about with my 250 sho overtemp and I wonder if the alarm temp is as low as 180-190 or is it higher. I hope it is set low enough so that an alarm is really just that, a warning and no damage is done and that is gives us enough time to shut down before damage. Does anyone know for sure what a factory engine alarm temp is set for?
The horn sounds when the engine temperature reaches 302 degrees Fahrenheit.
See post #5.
Ok, I saw and noted post #5 but in my opinion it isn't clear that it is stating the temperature the horn sounds. To me it is addressing the question of what temp is getting close to harming the engine which is a very different question from what temp the horn is set for. 300+ degrees is a pretty normal threshold for cylinder operating temperature. I'm a general aviation pilot and generally it gets our attention if we see head temps over 380 degrees F and we like for them to be in cruise flight around 300 in aircraft piston engines. If the horn doesn't sound until the cylinder head gets to 302 degrees F then I'm not surprised that there isn't much time from the sounding of the horn until melt down!
The first question was "What temp is getting close to being to hot for these motors ." I replied 301*F. As that is the temperature that is closest to the motor being too hot.
The motor is then too hot at 302*F. That is the temperature that the warning horn will sound when the motor is too hot.
A cylinder head at a temperature of >400* F is a long way from a block temperature of 302* F IMO.
In addition to the engine temp sensor tripping at 302 deg, I believe the two thermoswitches trip at ~190 deg. The difference is that the two thermoswitche are in a different place on the engine from the temp sensor.
The only thing you can monitor via NMEA is the temp sensor. I’ve never had an alarm when it goes to 200 which aligns with the 302 setpoint. However, I have had high temp alarms (probably from the thermoswitches) when in shallow water and the water screens get plugged up. In that case, I never see more than 150 deg on the temp sensor, but I suspect the thermoswitches are tripping due to temps closer to the cylinders going >190 due to lack of cooling water flow.
At at least that’s how I understand it, but would appreciate clarification if I’m wrong.
The first question was "What temp is getting close to being to hot for these motors ." I replied 301*F. As that is the temperature that is closest to the motor being too hot.
The motor is then too hot at 302*F. That is the temperature that the warning horn will sound when the motor is too hot.
A cylinder head at a temperature of >400* F is a long way from a block temperature of 302* F IMO.
Your understanding is correct.
Thank you. Do you know what exactly the temp sensor and thermoswitches are monitoring. I was curious if the temp sensor was monitoring more of oil temperature and the thermoswitches more the water jacket temperatures. I know the thermoswitches trip quickly if you lose cooling water flow (clogged intake idling through shallow ponds) but temps on the temp sensor never rise. However at WOT when I have tons of water pressure, the thermoswitches never trip but I see the temp sensor rise. My guess was there’s a ton of cooling water going through the water jackets cooling the heads, but the cooling lines for the oil cooler are pretty small.
I noticed the oil cooler design changed from the early SHOs to the more recent models (one less outlet hose on the recent models). I was thinking maybe Yamaha was trying to increase oil temps to help get the rings to seat? This is all just speculation and I noticed the different oil outlet lines while comparing my oil cooler plumbing to my service manual. The port circled in red is the one I don’t have on my 2017 SHO.7837686D-7780-4089-BC89-26525DAAE21C.jpeg
The thermosensor is monitoring block temperature at one point while the thermoswitches are monitoring block temperatures at two other points.
Even though the thermosensor is not physically far from one of the thermoswitches they have widely varying set points for the alarm to sound.
I would tend to agree with you that the thermosensor is more closely monitoring oil temperature whereas the thermoswitches are monitoring water temperature. Yamaha does not tend to provide any guidance with respect to theory of operation.
I don't think the oil cooler redesign was related to the propensity of the 4.2 block to be difficult to get the rings to seat. Just a guess. Again, Yamaha does not like to tell anyone outside of Japan the real reasons for why they do what they do.
I don’t trust the accuracy of the NMEA interface (145 NMEA and 270 engine recorded temp) For sure check your water pump impeller replaced. I experienced a similar increase in temp and the impeller needed replacement. Here is a link regarding the SHO temps.
Here is the link http://www.bbcboards.net/showthread....aha+water+temp
I had the water pump changed and saw the same temps before and after. As noted, I run 18+ psi water pressure. I also changed thermostats and flushed all the cooling lines to make sure nothing was plugged. Hydrotech told me they saw 230 deg on Waynes flashed SHO.
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