As long as your lower unit is submerged, does it matter whether your idling or underway? Thanks
As long as your lower unit is submerged, does it matter whether your idling or underway? Thanks
I'm not sure if you're referring to the actual lower unit gear case, or your water pickup for the impeller. I'm going to assume you're talking about the impeller. If you're idling the amount of water being circulated by the impeller is less, but the engine isn't producing as much heat because its not working as hard. It's all proportional to what rpm the motor is running at. With that said it's important to replace the impeller on your motor every couple of years to keep it working efficient as possible and to avoid overheating issues.
Twice I have forgotten to change the water pump and impeller when I should have and have had my hot horn go off when idling. If I bumped the RPM's up and ran a little faster, the water pressure on the lower unit was enough to circulate enough water and cool the engine and stop the hot horn.
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I had the same experience . First sign of worn water pump.. Have also seen the reverse where I had to slow down from higher speeds to mid range to keep from overheat. Simple lack of maintenance can ruin a dayOriginally Posted by Jeff Hahn
Just idling my motor temp is 156. Has been so since new and impeller changed annually. When running hard about 100. Motor is getting much better water flow when on your plane
2024 Phoenix 818
2024 merc 175 pro xs 3B411947
I guess what I'm really asking is if it is harmful to idle around at a low rpm. When I'm mapping or searching for schooling fish I sometimes will do this for extended periods. Last year I got a temp warning horn after which I changed out impeller and tstats. I'm afraid to repeat that scenario. BTW, water pressure gauge doesn't work.
No it isn't, some that use trolling as a presentation do it for hours. I have done the same when recording sonar logs for mapping.
Even if you don't have a functioning water pressure gauge, you still should have the telltail water jet.
Wayne Purdum
Charlottesville, Va.
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First, get the water pressure gauge working. Next, find out where you're reading water temp from. If the temp sender is mounted on the block of the motor (most are mounted on the heads) then you're also reading ambient air temp under the cowl along with motor temp. Obviously, while idling, the air under the cowl isn't circulating so the temp indicates rising. When running, that air is circulating, being replaced by outside air and the ambient temp goes down. If you're reading in a "water jacket" with a sending unit, then you're reading true water temp and the faster if circulates (picking up fresh water from the cooler lake) the better it decreases. All this to say you can tell more from the water pressure gauge and reading water pressure then relying on the temp gauge while idling. The temp gauge is needed when you first crank on cold mornings to keep from "cold seizing" the outboard.
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You should also service/inspect the pressure release valve. If its stuck open, a lot of times just from one little grain of sand motor will overheat particularly at idle speeds.
Good info on location of temp sensor. Air flow could indeed be a reason that temps drop at speed. Though would not extra water flow be another?
2024 Phoenix 818
2024 merc 175 pro xs 3B411947
If you have a Mercury Optimax then you need to get a MercMonitor. This removes a lot of guess work. How do you know the water pressure gauge is not working? Because it reads zero? Maybe there is a blockage/restriction somewhere.
To Davidsa.... it your motor temp is 156 at idle then you have a problem. It should rise to 130-140 and then cycle down to 120 and then repeat. I believe you have a t-stat that is not working, i.e. not opening all the way or not opening at all. When you run and the temps drop that is because the poppet valve opens and that bypasses the t-stats.
George Brock
2015 920 Pro/XP
2015 Mercury 250 Pro/XS
Twin 8' Powerpole Blades
All good info ..
My T-stat opens at 136 according to my gauge.
Also beware that on some motors the tateltell is not a guarantee that things are all good.
It's a 2008 Evinrude 115 Etec. And thanks for all the replies. I'd love to replace the pressure gauge but when I lay on my back and look up under the console I don't see the gauges. There is like two layers of fiberglass and I can't see how to separate them to access the gauges.
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