Mercruiser 3.0 with Alpha 1 overheating on plane

[dupre68]

I have a 2001 Sea Ray 180 BR with the Mercruiser 3.0 and Alpha 1 stern drive. My battery ran dead the other day because my kids left the key in run position with radio on. I charged the battery with a 12V 10A battery charger while still in the boat. All seemed good. I am not sure if the battery issue is related here but mentioning it as it is the only odd thing that has happened prior to my problem. I took boat out to lake yesterday and noticed that when running wide open on plane the engine overheated to over 200 degrees. I shut it down and let it cool. I could hear what I think was the water boiling. When cooled I started it again and at idle it would stay around 170 which is normal for my boat. When I then tried to open it up again I could see the temp gauge rising so I went right back to idle and pulled boat out of water. I am reading online that it could be the tstat or the impeller. The boat only has 135 hours on it. It had 98 hours when I got it and was in great shape. We put the additional hours on it over the last 4 months. Any ideas? Is there any videos on how to change the tstat?

 

[alldodge]

Re: Mercruiser 3.0 with Alpha 1 overheating on plane

:welcome: to iboats

Looks like you need to replace the impeller in the outdrive.

 

[squarehead]

Re: Mercruiser 3.0 with Alpha 1 overheating on plane

alldodge is right, kids listened to radio plus listened to engine running. impeller is history

 

[Volphin]

Re: Mercruiser 3.0 with Alpha 1 overheating on plane

LOL I'd use it as an excuse to get my lawn mowed for quite some time!

 

[dupre68]

Re: Mercruiser 3.0 with Alpha 1 overheating on plane

Thanks for quick reply. Does it make sense to check the t-stat first prior to replacing impeller? What causes impeller to go? I usually turn engine over prior to trailering the boat out of my garage. I turn key until engine kicks over then immediately shut it down. It literally never runs more than a half second. Also, forgot to mention that the oil pressure was low when engine was over 200. (like 30 psi instead of 40 which was more normal)

 

[Volphin]

Re: Mercruiser 3.0 with Alpha 1 overheating on plane

The oil pressure went low because of the heat. Very normal for the situation. I'd change it. The t-Stat should be OK, but you can easily pull it and test it. Never EVER run your engine without using water & muffs. That's what did in your impeller my friend. Even a second or two dry run will eat em up. Looks like you have to mow your own grass now too.

 

[ktbarrentine]

Re: Mercruiser 3.0 with Alpha 1 overheating on plane

Dont jump so quick on to the impeller fault... (yet). I did not get the impression from this that the kids left the engine running....just left the key in the "on" position....

If your impeller is bad , or going bad, you will also see this at idle and no-wake speeds. Typically when you see your temps start to rise when leaving the dock (low speed, no-wake speed, prolonged idle at dock), increaing the speed will generally cause the temp to drop back down. That is what I see when I know it is time to replace the impeller.
Not to say that you may not have a bad impeller, but there are other things to check for high temps at high speeds, too. And there are ways to check for a bad (or marginal) impeller using muffs in the driveway without having to take it apart (yet - but if you dont know when it was last replaced, then by all means, replace it!)).
Just sayin.
Sometimes high temps at higher RPMs is caused by something blocking the cooling flow (like pieces of old impeller or garbage in the power steering cooler. (and yes, poor flow from a worn impeller).
Why do feel the need to "turn the engine over prior to trailering the boat out of the garage"? A "bump" is typically ok, but it only takes a few seconds of running the impeller dry to fry it.

 

[frantically relaxing]

Re: Mercruiser 3.0 with Alpha 1 overheating on plane

Trouble shooting facts:

There's no way the kids overheated the engine while idling in water. And it wasn't running anyway, which is why the battery went dead...

A dead battery has zero zilch nada to do with a bad water pump impeller...

The temp is normal at idle, gets hot underway, as stated by the OP. Normal temp at idle indicates thermostat is fine.

Sitting idling, an impeller with say, 4 blades missing, will still pump enough water to keep the engine at normal temp.

Under way, with 4 blades missing the impeller simply won't pump enough water, and the engine will eventually start getting hot.

Conclusion: impeller is bad.

 

[stonyloam]

Re: Mercruiser 3.0 with Alpha 1 overheating on plane

Running an engine for a second or two, while not the best procedure is not going to cause much if any damage to the impeller. Running for 20 or 30 seconds is another story. I have a sneaking suspicion that the kids did more than just turn the key on, they may have started the engine and ran it for long enough to damage the impeller. If the thermostat were not working the engine would continue to overheat when you slowed down, so chances are that your impeller is shot. I would suggest that you remove the whole outdrive to replace it. Two reasons, it is a lot easier to get the outdrive back together on the bench and it will give you a chance to check and lube the gimbal bearing and the U-joints. While you have it apart check for melted plastic parts, including shutter parts in the exhaust, check the impeller for missing blades. From now on it would be a good idea to put on a set of muffs when you give the engine a test start at home (which is a good idea IMHO). Good luck.

 

[BRG25]

Re: Mercruiser 3.0 with Alpha 1 overheating on plane

The impeller should be replaced every couple years as a maintenance item. If you don't know when it was last replaced, get it done, it's not that expensive. Why do you guys debate this stuff?

 

[CharlieB]

Re: Mercruiser 3.0 with Alpha 1 overheating on plane

Was the boat on the trailer when the kids left the radio on?

Were the keys IN the boat, could they have started it without water? Just to hear how 'cool' it sounds?

Any time temp begins to rise the OD should be removed and the water pump inspected. EVERY TIME.

If the impeller is over 2 years old and the vanes have much of a 'set' in them, replace it. If there is heat damage, melted edges, that's a no brainer, replace it.

Check the upper housing for warp, if the upper and lower housings do not seal perfectly then as the boat rises and gets on plane the water column in the housing drains out, leaving the pump itself out of the water. If the uper and lower housing do NOT seal then the pump begins to suck air, cooling fails and the motor heats.

Lastly, closely inspect the stainless cup and lower plate, when a circular 'ring' gets worn into either/both parts from the raised 'ring' seal on the sides of the impeller, then the seal between the two begins to fail. Here again, on the upper side,, can allow air to suck in while on plane and reduce cooling.

 

[ktbarrentine]

Re: Mercruiser 3.0 with Alpha 1 overheating on plane

Sitting idling, an impeller with say, 4 blades missing, will still pump enough water to keep the engine at normal temp.

Under way, with 4 blades missing the impeller simply won't pump enough water, and the engine will eventually start getting hot.

Conclusion: impeller is bad.

My first experience with a bad impeller: The vanes were all there, but had taken a "set" (hadnt been changed or ran in quite some time). The boat started to overheat while idling in a no-wake zone. Increasing the speed out of the no-wake zone brought the temp back down nicely. replacing the impeller (of course) fixed it.

 

[natispotatis]

Re: Mercruiser 3.0 with Alpha 1 overheating on plane

Ktbarrentine, I'm curious how you test for a bad impeller with muffs in the driveway. What procedure do you use? I might have an issue with mine and would like to know. Thanks!

 

[stonyloam]

Re: Mercruiser 3.0 with Alpha 1 overheating on plane

, I'm curious how you test for a bad impeller with muffs in the driveway. What procedure do you use? I might have an issue with mine and would like to know. Thanks!

You don't! You pull the outdrive and change it!

 

[ktbarrentine]

Re: Mercruiser 3.0 with Alpha 1 overheating on plane

Ktbarrentine, I'm curious how you test for a bad impeller with muffs in the driveway. What procedure do you use? I might have an issue with mine and would like to know. Thanks!

This is pretty much a go-no-go check and not a "take it to the bank" check (absolutely not quantitative)..... but, when I put on my muffs and turn on the water faucet, I have significant amount of water flowing (leaking) out around the muffs, because a "good" impeller wont let water past it while it is not turning, so the water has to go somewhere (I should note here that I have the water inlet hose disconnected to the PS cooler when I try this...then reconnect it before starting the engine). Once I start the boat up, the water leakage around the muffs drops off significantly because the water is now moving to the engine through the running impeller. This tells me I should be good to splash the boat.

The "take it to the bank" test is the one done with the boat in the water per the written instructions (flow measured from a disconnected hose over a fifteen second test at specific RPM - can really only be done in water).

I do, however, always follow the philosophy of changing my impeller every two years unless I see some reason to do it sooner than that. (and the test on muffs only really tells me if I have gross problem with the impeller, like missing blades or severly set bladeswhich I havent seen as long as I do the two year change-out).

 

[AviatorJim]

Re: Mercruiser 3.0 with Alpha 1 overheating on plane

I went through the same thing on my pre-alpha drive. Changed the impeller a couple times, water pump. Eventually I got to the point of replacing all my hoses with clear ones. And I saw that as soon as I was on plane water stopped coming up from the drive leg. Turned out to be the gasket under the lower housing has shrunk and cracked. So once I planed out hot exhaust was drawn in rather than water. Replacing the upper and lower housings, gaskets, impeller, and that melted plastic tube fixed me right up.
--Jim