Motor heating up

[zul]

I've had this boat for 2 years, it always warms up to 165 and stays put. It's been real steady and reliable. (420 hours)

Last week, changed the oil (Quicksilver 25w-40), oil filter and included BG MOA high mileage oil additive:

https://www.amazon.com/BG-MOA-110-E...id=1530277611&sr=8-5&keywords=bg+oil+additive

Within 3 miles of running on the lake, it's heating up to 170. So I've been shutting down for a few minutes waiting for it to cool down. I can run slow laps and various speeds including a little WOT on this small test lake. Mostly just cruising speed 22-25 mph. Keeps heating up to 170. I can hold my hands on the heads for 8-9 sec, but it's HOT to the touch.

At first plane, the oil pressure went up to 75. (Previous years it's always been @ 60.) On this test run, after a few miles, the oil pressure went back down to approx 62 and stayed there for the rest of the test run (about an hour). Hmm??

The oil looks good (color) and the exhaust manifolds are warm.

I don't think the oil additive should have an effect of heating up? So I'm trying to rule that out. I've also got new plugs in, but don't think that would change anything?

Ideas? Causes? Thermostat?

 

[Scott Danforth]

when was the last time you did a raw water pump service?

 

[harringtondav]

Put flush muffs on it and observe the water flow from the two exhaust holes at the bottom of the gimbal transom plate. Start the garden hose at about 1/4 flow and increase it to around 1/2 flow until the exhaust water flow maxes.You should be getting at 1-1 1/2 Gal/min exhaust flow at idle. If not, Scott Danforth probably has the answer above. Also, oil pressure is always higher with cold oil, and drops as it heats up. I wouldn't worry about that one.

 

[Scott Danforth]

Put flush muffs on it and observe the water flow from the two exhaust holes at the bottom of the gimbal transom plate. Start the garden hose at about 1/4 flow and increase it to around 1/2 flow until the exhaust water flow maxes.You should be getting at 1-1 1/2 Gal/min exhaust flow at idle. If not, Scott Danforth probably has the answer above. Also, oil pressure is always higher with cold oil, and drops as it heats up. I wouldn't worry about that one.

no....the impeller pump flow is 10gpm at 1000 rpm topping out at 19gpm at about 1800 rpm. from there the pump cant flow any more, however the boat is usually moving

never run a motor on muffs without the hose on full. you need the pressure to get the water forced up to the raw water pump as they are not self priming

garden hoses at best with a 3/4" hose and 100 psi in a residental (not well pump) situation can provide about 15 GPM. which is why you never run more than 1500 RPM on a hose

 

[harringtondav]

My pump output was a guess based on observing the water going down to the curb.

See attachments from my Merc 4.3 manual. My O/D puts out 3.3 qts. in 15 sec. 3.3 GPM. So much for my estimation. But 10-19 GPM?? My city water tap delivers exactly 5 GPM. Also please note the muff flushing instructions. I believe the full garden hose flow concern is over pressurizing the rubber impeller and causing the vanes to take a reverse bend. So I stand by my advice. But the point is if you don't get much flow from the exhaust, the seawater impeller is shot.

 

[alldodge]

170 degrees and .... I can hold my hands on the heads for 8-9 sec, but it's HOT to the touch.

This gets me thinking maybe your motor is not getting to 170 degrees, maybe a gauge issue. Ever try a IR temp gun to see what it shows at the thermostat housing?

 

[Bt Doctur]

after 2 years you need a new impeller , try that first.
with a 160 stat, 170 is not really abnormal during a long run

 

[zul]

Thanks for the input!

The SEI drive is 80 hours new, installed and broke in last year.
I was starting to think that the outdrive install could have left me with reversed vanes/fins on the impeller but then I remembered that I did one previous test run where the temp went up almost immediately (like it did on test run #2).

Puzzling.

I'll put the muffs on it when I can to see if water is working properly.