Running a little warm at an idle

F

frosh coach

Member
exMember
Joined
May 7, 2007
RO Number
26203
Messages
207
I have twin 1994 mercruiser 5.7 FWC motors with alpha 1 gen II drives. The engines are set up with a thru-hull intake for each motor. The intake on the drive is capped off (drive cools it's self).
Just put the boat in last weekend for the season. My starboard engine runs around 175В°F at an idle. when I run the boat, it runs great at 160В°F (they both do). I changed the impeller on the engine mounted water pumps last year. Where should I start? Should I do an impeller, can it be the pump is going?

Thanks
in advance.
 
the scoop is forcing more water when running. At idle only the pump is causing flow. I would start at the pump. When you replace the impeller did you find all the missing pieces?
 
Bruce - I did find the pieces. The impeller was actually in pretty good shape. That's why I'm wondering if it's the pump starting to go.
thanks for the reply
 
The intake on the drive should never be blocked off. The water that circulates thru the intake system adds to the cooling of the drive.

Do you have the drive pumps in the drive installed. If you have a bravo style pump, you can remove the drive pump components and 'T' the drive intake into the thru hull intake. The added benefit is that neither intake can get clogged by debris and shut down the whole cooling system...unless you go thru a large kelp forest or the like.
 
Charlie - You're correct, I worded that wrong. The intakes on the drive work (for cooling the drive). The hole inside the boat (on the transom assy) is capped.
 
Is the 175* at idle underway or perhaps mostly just in N sitting at a slip where the water can get warmed by the boat's exhaust?

I don't think 175*F at idle is anything to get too concerned about since it's a safe temp level. But then my FWC Crusaders have 170* t-stats and your FWC engine would likely have 160* t-stat and that is a 15* difference over the t-stat on yours , if that is confirmed with an IR gun at the temp sender location.
(Teleflex notes their gauges can read up to a maximum of 15*F off. http://www.jamestowndistributors.com/userportal/document.do?docId=842 )

But "generally speaking", if temps drop to thermostat specs at higher rpms there is no undue RW flow restriction issue , but there may either be a little scoring of the RW pump housing wear surface or there could be just a small suction air leak.
 
as others have noted, lack of water flow at idle. start at the intake scoop and strainer and work back. the water is either not getting pulled in, or there is a restriction somewhere so that it needs more pressure from movement to overcome the restriction. possibly all of the above.
 
Thanks everyone for your reply's.

Sandy - The 175°F was at the slip and as I was leaving the slip at an idle. Once I brought it up to 1500-1800 in neutral the temp went back down. I'm going to remove the hoses from the water pump and back flush. Good thing is on plane she runs right at 160°F.
 
Is the slip by any chance backed up to a bulkhead or otherwise somewhat contained more than if it was out near the end of a longer dock with a little more flow around it? If so, I imagine your exhaust has just been warming the intake water and would be nothing to worry about.

It's always good to back flush, as I do on my boat at least once a season, but you aren't reporting a flow restriction issue since that would be more of a problem at higher rpm .
 
Ok guys I'm still having this issue but only when the starboard engine is at less than 1200 rpm. As soon as I give it a bit of throttle, the temp drops to about 165°F. Runs like a champ while on plane. I'm leaning towards three things... The sending unit (I already swapped gauges), the impeller on the engine raw water pump (which was replaced last year with the housing), or even the pump its self. Any thoughts?
 
If the actual temp has been confirmed a bit high at the sender location with an IR temp gun, I believe the most likely causes for low-rpm -only elevated temps are usually scoring of the pump wear surfaces and/or the impeller tips( since the impeller tips only contact the wear surfaces at low rpm to create suction) , or a slight suction air leak before or at the pump. Suction air leaks often have near-finite maximum inflow so once increased-rpm pump demand exceeds that limit, the % of air to water in the flow keeps dropping toward negligible proportion. And water hoses may even seal better to fittings with loose hose clamps for instance, under greater pump suction.
...Maybe... t-stat( does yours have holes for air purging and quicker response to engine coolant temps?). But you do indicate the impeller & wear-surface housing is only a year old (then again, a lot can happen in very short time) .

If temps drop to 165*F above 1200 RPM in Neutral , then the obvious underway intake scoop benefit can be discounted as making most of the difference you are seeing.

You clearly do not have a restriction issue. And not really much of a temp issue either on that FWC engine, though I understand the desire to have both engines idle at the cooler temp so as to not be niggled by the gauge reading.
 
You must log in or register to reply here.
Back
Top