140 getting warm at 3K

[SSTKO81]

Took my boat out today for its first trip in nearly 3 years. All went pretty well as it idled out of the cove at 1500 RPM sounding very healthy. Good temp, oil pres, voltage etc. I decided to goose it to about 3K and it was doing fine then suddenly began gaining RPMs on its own. -slowly, nothing real sudden as it went to 3500.... at this point I noticed temp had climbed to nearly 190 and was was holding. I’m not running a thermostat so this make me believe the engine may not be getting enough water (via the impeller) but how does that explain the jump in RPMs? (81 Merc 140, alpha1)
I should add, I turned the engine off and let it sit for 45 min then restarted and ran at 1500 RPM all the way back to the ramp (about 2 miles) and it’s never got over 150*

 

[achris]

150 without a thermostat is way too hot! You have problems!

First trip in 3 years. Did you do a FULL service on it before going out? You needed to AT THE LEAST, changed the drive impeller, gear oil, checked the engine alignment, greased the unis and gimbal bearing, engine oil filter, fuel filter and oil change. Full tune (including points, condenser, cap, rotor, and plugs). And having sat for 3 years, I would have drained and cleaned out the fuel tank, all the fuel lines, and stripped and rebuilt carb and fuel pump.

While the drive was off, I would have pressure tested the water pocket cover, and on the engine I would have pulled the exhaust elbow and check that and the manifold out for built up rust, and corrosion around the gasket surfaces.

But I wouldn't have stopped there. I would also have fully load tested the batteries, checked the alternator output, checked the engine was properly advancing the timing. I would have thoroughly checked the condition of all 3 bellows, greased all the hinge and swivel pins and checked the trim pump and its oil level. And while the drive was off, I would have gone through the shift cable too.

Why did the engine rpm increase as the temperature rose? Because engines are more efficient as they get hotter, it's a delicate balance between the most efficient operating temp and being cool enough to reduce the damage caused by things being too hot. And in Salt water, you need to keep the temps down to reduce the disassociation of the salt water into acid... Acid inside engines, bad idea!

At 1500rpm without a thermostat, your engine temp should have barely moved the gauge...

Chris.....

 

[SSTKO81]

Maybe I should clarify... The boat hasn't just been sitting on a trailer in my backyard for 3 years. It's been under various stages of repair and upkeep including new bearings, cam gears, bellows, gimbal, EST ignition, fuel pump, carb rebuild, etc.... The oil in the outdrive was just replaced along with the drive shaft seal, however, I hadn't considered that even without use, the rubber impeller may've simply dried up and gone bad. So I haven't changed it. In fact now that I'm writing this I think time has gotten away from me. I'm sure that impeller is nearly 5-6 years old and will need replacement. I'll replace it today and update tomorrow.

 

[SSTKO81]

Installed the new impeller on Wednesday, old one didn’t look too bad other than one fin turned backwards and some wear on the gasket plate... but I guess that’s all it takes. I’ll find out Sunday how I did....

 

[SSTKO81]

Well it’s still getting hot! Maybe worse than before. I did t get out of the cove and it was cookin. My next suspicion would be the circulation pump on the block.

 

[Bondo]

and some wear on the gasket plate...

Ayuh,..... Did you replace it, or just the impeller,......

I really doubt it's the circulatin' water pump,.....

 

[SSTKO81]

Ayuh,..... Did you replace it, or just the impeller,......

I really doubt it's the circulatin' water pump,.....

Yes. Replaced the impeller and all the associated gaskets and o-rings. Engine really sounded great other than the heat..... it’s killing me being so close, yet so far

 

[SSTKO81]

I’m trying to back flush the water system to make sure nothing is clogged in there and even with the garden hose on full Im not getting but a trickle out of the intake port.... but lots of water in every other spot on the out drive. Does that seem right?

 

[SSTKO81]

Put everything back together and reconnected the muffs to fire the engine. What I found is that I have no water coming through the exhaust system so it seems my impeller is not impelling… This is a brand new impeller. Is there some critical item I missed during installation? The only thing I could think of is maybe theGuide tube did not fit up securely around the copper intake tube… But I’m not sure how to correct that

 

[Bondo]

Yes. Replaced the impeller and all the associated gaskets and o-rings. Engine really sounded great other than the heat..... it’s killing me being so close, yet so far

Ayuh,...... Did you replace the wear plate, 'n housing,..??

 

[achris]

I’m trying to back flush the water system to make sure nothing is clogged in there and even with the garden hose on full Im not getting but a trickle out of the intake port.... but lots of water in every other spot on the out drive. Does that seem right?

Just look at how an impeller pump works. You can't push water through it, from either direction.

But we do have a clue in your procedure. (much like the Mickleson-Morley experiment. It failed to prove their hypotheses, but did prove things they weren't aware of. ) If you connected the garden hose to the hose that comes from the gimbal housing, you should not have got water leaking from any other orifice. You have a (serious) leak between the drive water pump and the bell housing.

Pull the drive, check everything.

Chris........

 

[SSTKO81]

Seems that there’s a poor seal between the pipe between the lower and upper housings. Working on how to correct that is the hard part....

 

[SSTKO81]

Final update prior to lake test. I had seated the copper pipe into the upper drive then fit the lower half into place. This resulted in a poor (see non-existent) seal between the two halves. When I refitted the halves I put the copper pipe in on the lower half lightly seated then fit the two halves together. This resulted in a (at least better) seal that allowed for water to be passed into the engine. The temp over the course of a 45 minute test on the muffs never exceeded 145. -now obviously the lake test may yield different results but this is an improvement at this time.
I almost wonder if a 1/4-1/2 in longer copper pipe may be in order.

 

[SSTKO81]

FINAL UPDATE! I took it out yesterday (finally) and everything went off flawlessly. Temp never got above 110 and I ran it up to 3500 RPM for several minutes. I couldn’t be happier!