Operating Temp range

[JohnD]

454 gas. Had overheating issues.. thought fixed. Flushed system, new impeller, new thermostat (140 degreee).

What is reasonable range between idle / trolling rpm 900-1100 rpm temp and running temp (3200-3800rpm)?

I just ran boat - idle approx 155-160 degrees, running 3400-3800 rpm temp went up to 175.. almost 180 (where I will shut it down). Temp drops very quickly back when I come off plane.

fyi - water temps 87 right now!! I recall she always runs a little warm when water temps are high.

any thoughts apprciated. johnd

[Little Dandy]

Is your boat fresh water cooled?

My FWC boat has 170* thermostat. Typically I see 175* off the gauge and around 178* when running hard. Not to steal your thread, but how accurate are the gauges?

I believe that raw water cooled boats run cooler. I'm sure someone will correct me soon if I'm wrong on that.

[hammerhead]

I have volvo 330hp fwc in a 28 with jackshafts, My port engine runs around 175 running hard and about 160 idle, my starboard engine runs 180 hard and about the same for trolling and idle, make sure that the 140 is the right therm, or when the water cools down the engine will never run get up to operating temp.Harry

[JohnD]

operating temps

Thanks. Yes FWC. Factory had 160 thermostat in. We just replaced and my mechanic said take it to 140 to get it open sooner.
As to gauge accuracy.. I don't know, guess next thing to check.
johnd

[hammerhead]

If you flushed the system, then I would check the risers, when was the last time they were replaced??

[JohnD]

operating temps

Replaced the risers 4-5 years ago with Stainless.
Based on what you all are saying I think the issue is simply very high water temps in the river. gonna try a few more ideas this week if I get time.
Thanks for the ideas and questions. johnd

[spoolsout]

JohnD,

We were having a similar problem recently except we were overheating at lower RPMs. Ended up being a thermostat. Our mechanic also used a 140 thermostat. Have you checked the heat exchanger for blockage? Mechanic told us that if a heat exchanger is blocked the boat will tend to overheat at higher RPMs. At 900-1100 RPMs we are at about 150-160 at cruise we are 160-170 port tends to run a little warmer. Think it may be the guage. We have twin 1995 454 mercs. Hope this helps.

[JohnD]

operating temps

Thanks for more thoughts and your temps.
Cleaned heat exchanger.. a little bit of eel grass came out.
I've always run 160-170 steady... and this week in the river I'm running 170 up to 180. It may just be the river is so warm (87*).. guess I need to get offshore into cooler temps and see if any change.
Mostly just need some time off work to enjoy the boat - that's the biggest issue still.

johnd