What should my temperature gauge be reading?

[poconojoe]

2003 185 Bayliner with 4.3L carb and alpha one gen 2.
Boat is docked in a slip on lake Wallenpaupack.
My first full season with a power boat.
The last few times I shut the engine off, I got a little detonation, run-on or dieseling (what ever you want to call it), so I was suspicious that there was too much heat.
It always seemed to run a little below 175 so I thought that was normal.
When looking up which thermostat is needed for my 4.3, I've only found a 160 degree stats.
I don't know what t-stat is in there now, but if it's a 160, what should my gauge be reading? (given my gauge is somewhat correct)
I want to use it for a couple more weeks, but I'm getting paranoid because I don't know when the impeller was changed last.
I'm definitely changing the impeller and t-stat as soon as I pull the boat out.
Should I just bite the big one and pull the boat now and not take any chances?
The gauge never went past 175 degrees. Is that too high? The lake water is currently 65 degrees.

 

[alldodge]

2003 185 Bayliner with 4.3L carb and alpha one gen 2.
Boat is docked in a slip on lake Wallenpaupack.
My first full season with a power boat.
The last few times I shut the engine off, I got a little detonation, run-on or dieseling (what ever you want to call it), so I was suspicious that there was too much heat.
It always seemed to run a little below 175 so I thought that was normal.
When looking up which thermostat is needed for my 4.3, I've only found a 160 degree stats.
I don't know what t-stat is in there now, but if it's a 160, what should my gauge be reading? (given my gauge is somewhat correct)
I want to use it for a couple more weeks, but I'm getting paranoid because I don't know when the impeller was changed last.
I'm definitely changing the impeller and t-stat as soon as I pull the boat out.
Should I just bite the big one and pull the boat now and not take any chances?
The gauge never went past 175 degrees. Is that too high? The lake water is currently 65 degrees.

Most often "run on" is caused by incorrect timing and/or to high an idle. If carbon is built up it can also cause the issue along with a carb leaking fuel. Your engine should have a 160 degree thermostat. Running at 175 on plane is fine. If after coming off plane and idling for a short while your temp so go down some. If the temp doesn't go down this could be telling you that you need another impeller. So long as your engine does not exceed 190 your OK. That being said that is if your gauge is accurate (If it reads 175 and it actually is 185 or 190).

Your impeller is the one cheap item which has the ability to destroy your engine. not knowing the status of it is rolling the dice. Now the Gen 2 drive impeller does last much longer then the Gen 1 but the knowing is still the same issue.

 

[poconojoe]

Thanks for the input. Yesterday it read spot on 175 when on plane doing 25 mph. Came down to a slow go just above idle and the gauge went down to just under 175. Darn analog gauges are just too general in their readings. The gauge has 100 then two lines and then 175. I would be more coomfortable with a digital gauge. Would that be just a swap of the gauge itself or is it more than that to upgrade to digital?

 

[alldodge]

Thanks for the input. Yesterday it read spot on 175 when on plane doing 25 mph. Came down to a slow go just above idle and the gauge went down to just under 175. Darn analog gauges are just too general in their readings. The gauge has 100 then two lines and then 175. I would be more comfortable with a digital gauge. Would that be just a swap of the gauge itself or is it more than that to upgrade to digital?

Most digital gauges take the same analog signal and translate to digits. The accuracy of the gauge remains the same only the visual appearance changes. If you want accuracy change to a mechanical gauge, but that would be a long cable. With the gauge barely moving I would suspect the gauge or sender.

 

[DaveG55]

Get an IR temp gun, they're not that expensive, and shoot the engine at the sensor and t-stat housing. That should tell you if the guage is reading correctly and/or how far it's off. Quick, easy check to get a reasonably accurate temp.
You can also pull the sensor and t-stat and test them on the stove. In a pot of water, using a good thermometer, heat the water and watch where the t-stat opens. The sensor check is much the same except you measure its resistance as it heats and compare that to what it should be.

 

[achris]

All that said, my 4.3MPI stays the same temperature regardless. It's a 160 degree thermostat, and it reads just a hair under the half way line on the gauge. My gauge doesn't even have ANY numbers, but the gauge is only there as a guide, not an absolute. What you are looking for is consistency, not an absolute value. If you want to know what the temperature actually is, as already said, get a mechanical gauge or a proper calibrated digital gauge (and you'll be paying considerably more than the current unit)....

As long as your gauge is consistent, and you maintain the engine, you shouldn't have any problems.

Run-on can also be caused by trying to shut down the engine immediately after a hard run. Let the engine idle for a minute or so to allow cylinder temperatures to come down....

Chris.....

 

[stonyloam]

As a rule a gauge will be accurate to +- 1/2 of the smallest increment. In your case 25 degrees. So your "real" temperature could be anywhere between 162 and 187. What you might do is change the impeller and then take it for a test run. Note the temperature and mark the gauge face. That will be your "standard" temperature. Any deviation from that would be a sign of a problem. My gauge has read 140 for the last 25 or so years, as long as it stays there I know it is OK.

 

[poconojoe]

Sounds good stonyloam. This way I'll have a base reading marked right on the gauge. It will be very obvious if something is going wrong. Great idea!