Oddball engine heating issue

[Getaway]

Ok, I'm usually a pretty good mechanic/trouble shooter, but this one has me stumped. On 3 different instances this past summer, I bring the boat up on plane and start cruising and notice the engine temp start to climb. In all 3 instances, I backed off the throttle, put the boat in reverse briefly, put it back in drive and the temp starts to go back down to normal, get her back up on plane and all is A-OK again.

Now, it acts like something got wrapped around the drive plugging the intake holes, but I'm positive that is not the case. It is a weird random thing that has even happened after a 6 mile run (no issue), troll for 5 hours (no issue), bring her up on plane get cruising and that is where it happened again.

This does not happen all the time. In fact, it has been about 3 weeks since it happened last and I had a few trips in between without issue. Again, I'm positive that no weeds or plastic got caught around the intake holes. It has happened in different circumstances and most of the time out in the open Lake Michigan over deep clear water.

Now, I will say, this is the first summer that I have used a Sierra water pump impeller in the lower unit. Usually, I replace my impeller every year with a Quicksilver version. I used a Sierra this year because I'm trying to combat the fact that I have to change impellers every year. Don't ask me why I need a new impeller kit every year. That is still a mystery to me, but after 6 years of owning the boat, I'm getting used to changing them every year. They seem to take a set after sitting all winter.

My initial thoughts/question... Is it possible that the impeller could cause internal cavitation in certain circumstances causing a loss of head pressure from the main water pump? Maybe after I stop, and put the boat in reverse, the caviation goes away and allows proper flow again? Seems odd, but I can picture this possibly happening.

Could it be an air pocket forms in the cooling system somewhere? Could it be a piece of crud is floating around in the cooling system and causing blockage somewhere? If so, why does it clear out when I throw her in reverse? I've checked the hoses, manifolds and don't see any weird crud/sand/debris in the cooling system.

Anybody else see this before?

Boat: 88 268DA, 454 Merc, Alpha 1 outdrive.


Thanks in advance for the input!

 

[scoflaw]

Maybe your exhaust shutters broke loose and are moving around changing positions.

 

[BillK2632]

Could it be an air pocket forms in the cooling system somewhere? Could it be a piece of crud is floating around in the cooling system and causing blockage somewhere? If so, why does it clear out when I throw her in reverse? I've checked the hoses, manifolds and don't see any weird crud/sand/debris in the cooling system.

This would be my first guess - check the water pickup hose for debris around the PS cooler and thermostat house, I bet something is floating around in there and randomly plugging things up.

Also, I wouldn't be worried about the Sierra water pump impeller, I have used them for years in my Alpha I Gen II, never an issue. I replace every 2-3yrs and they don't look worn at all, never had one fail. Now if you have just an Alpha I (plastic water pump housing) that might be a different story, but the Gen II impellers seem to be very durable.

 

[INTO WISHIN]

I had similar issues with my 80's searays. turned out to be the little bar with checkballs and springs in the therm housing. they rot or wear out

 

[INTO WISHIN]

oh, and be careful with the alpha/454 combo.

 

[Getaway]

I had similar issues with my 80's searays. turned out to be the little bar with checkballs and springs in the therm housing. they rot or wear out

Hmmm, this is the info I was hoping for. Thanks! I'll check this out tonight. Oh and yes, I'm easy on the Alpha 1. She's still original from 1988 and I plan on keeping it that way:grin:.

This would be my first guess - check the water pickup hose for debris around the PS cooler and thermostat house, I bet something is floating around in there and randomly plugging things up.

Also, I wouldn't be worried about the Sierra water pump impeller, I have used them for years in my Alpha I Gen II, never an issue. I replace every 2-3yrs and they don't look worn at all, never had one fail. Now if you have just an Alpha I (plastic water pump housing) that might be a different story, but the Gen II impellers seem to be very durable.

Thanks for the heads up on the Sierra impellers. I've had great luck with all Sierra products, but this is my first time trying their impeller. It just seems odd that this issue cropped up this year after trying their impellers for the first time so I did not want to rule that out right away.

Maybe your exhaust shutters broke loose and are moving around changing positions.

I'll double check these, but they were new a couple years ago. Hope they are still in tact!

 

[Tacoma290]

Another item to check for is debris in the heat exchanger. I had the same symptoms as you describe, and there was debris(stringy debris from a mollusk) that the impeller had passed to the heat exchanger; the debris fouled the exchanger enough that the heat would creep up as full plane, then go back to normal at 1500 RPM or less.

 

[Getaway]

Another item to check for is debris in the heat exchanger. I had the same symptoms as you describe, and there was debris(stringy debris from a mollusk) that the impeller had passed to the heat exchanger; the debris fouled the exchanger enough that the heat would creep up as full plane, then go back to normal at 1500 RPM or less.

Thanks! No heat exchanger on my motor. Direct lake cooled. I will be checking more closely for debris. It just seems odd that it only happens once in a while and as soon as I stop and put it briefly in reverse, the problem is cured. Weird. Like a head pressure or cavitation problem, but I've had the boat for 6 years and it has only happened 3 times in the past 2 months...

 

[CliffA]

Maybe your exhaust shutters broke loose and are moving around changing positions.

+1.....to me this is the most logical cause since the problem temporarily goes away when you are in reverse.....when the boat moves in reverse the force of the lake water pushing against the exhaust dislodges the stuck flapper and the hot exhaust water is allowed to exit the engine and the engine cools down....then the overheating problem reappears when going forward because the engine exhaust water is forcing the flapper to get stuck again and blocks the flow.....

cliff

 

[Getaway]

+1.....to me this is the most logical cause since the problem temporarily goes away when you are in reverse.....when the boat moves in reverse the force of the lake water pushing against the exhaust dislodges the stuck flapper and the hot exhaust water is allowed to exit the engine and the engine cools down....then the overheating problem reappears when going forward because the engine exhaust water is forcing the flapper to get stuck again and blocks the flow.....

cliff

Thanks Cliff. Thats making sense to me. I know they are supposed to close off to keep cold water from rushing into a hot motor. That being said, they are also problematic. Mine were broken when I pulled the motor to have it rebuilt about 5 years ago. I wonder if the new ones are already having issues.

 

[scoflaw]

Thanks Cliff. Thats making sense to me. I know they are supposed to close off to keep cold water from rushing into a hot motor. That being said, they are also problematic. Mine were broken when I pulled the motor to have it rebuilt about 5 years ago. I wonder if the new ones are already having issues.

Doesn't necessarily mean it's the last set that was installed, could be old ones that were never removed

 

[SloBurn]

I had similar issues with my 80's searays. turned out to be the little bar with checkballs and springs in the therm housing. they rot or wear out

This also happened to mine, stretched the springs out and now it's fine.

 

[Getaway]

This also happened to mine, stretched the springs out and now it's fine.

Did it cause the motor to heat up to 220+ or just run warmer?

 

[Getaway]

I had similar issues with my 80's searays. turned out to be the little bar with checkballs and springs in the therm housing. they rot or wear out

Progress report. Ok, so far, the cooling system looks clear. The exhaust shutters are still like new and are functioning fine.

I pulled that checkball assembly out and stretched the springs and put it back in. Those did not look like anything was wrong, but I did it anyway. Have not run the boat since, but will try this week.

Question, what do those things do? Not really sure why they are there.

 

[Getaway]

Ok, I've done some research and found the little check balls act like a radiator cap on a car. They are meant to build a little pressure in the cooling system. If the springs break or are too weak, they will allow for a constant bypass of water and may not give the engine good coolant flow causing overheating at higher RPMs.

Also, a good mechanic just told me he has seen thermostats not completely open or open erratically and cause issues like this. My thermostat is at least 6 years old and maybe older. Not sure if my engine rebuilder reused the old one or gave me a new one when he rebuilt my engine in 2010......So, I'll be changing the thermostat and giving her another run.

Fingers and toes crossed...