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Play Dough
RO# 29135
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 Posted - May 14 2012 : 17:28:04
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The motor is 1989 5.7L Alpha 1 Mercruiser Sterndrive. Use is in Lake Michigan. For the second year in a row, the port motor overheated at dead idle. ANY increase in rpm cools the engine. The impellers are 2 years old and replaced as normal maintenance every 3 years and never show any excessive wear. Last year the mechanic changed the thermostat which solved the problem for the year (approx 100 hours of use), plus one use this season. My local Sea Ray dealer thinks it's the impeller. Because the symptoms are identical to last year, I'm leaning toward the thermostat. One other possibility that I was told about is to check the inlet to the power steering cooler to make sure there's no obstructions there. Any other advice? Seems odd that a thermostat is good for only one year.
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Homeport: Ludington, MI
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jtybt15
RO# 3300
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Posted - May 14 2012 : 17:43:09
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Did they replace the impeller housing? Gotta do that every time you replace the impeller.
The impellers on alpha I and older models have impellers that can go bad real fast. There's also the chance of blockage anywhere in the cooling system. How old are the risers? The raw water exits are very small can get blocked with sand...which can also do damage to the whole pump.
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Charlie
There is much to be said, in a world like ours, for taking the world as you find it and fishing with a worm.-Bliss Perry, 1904
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Homeport: Ca
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littlebookworm
RO# 27413
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Posted - May 14 2012 : 18:18:28
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When they replaced the impeller, were any pieces of the old impeller missing? Did they go searching for them? Check the oil cooler; pieces often get stuck in there, blocking water flow. Hy
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Homeport: Eastport, NY
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Play Dough
RO# 29135
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Posted - May 14 2012 : 18:35:20
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Usage is very clear freshwater and I try to do preventative maintenance. Impellers have been changed at 3 year intervals. Every impeller changed has shown some wear but nowhere near any failure. Boat is serviced by the local marine service in the area. I have no reason to believe the work done was anything but what would be considered normal. All engine parts are original to the boat which is not unusual in the Great Lakes. I don't know of many boats that have had a manifold replacement.
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Homeport: Ludington, MI
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Sandy
RO# 1159
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Posted - May 14 2012 : 23:24:37
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Like Charlie said.
If you just change impeller at 3 yrs ( most would tend to do that every year as preventative maintenance and to do a proper check) but the not the even slightly scored housing/wear surface, the pump will not draw water at low rpm .At low rpm the impeller vanes contact the housing and need a tight seal surface to create necessary suction to pump. At higher rpm the impeller vanes bend & may not even rub against the housing surface but rely on impeller speed to push a lot of water & that creates it's own suction. You may have other issues but your description is classic for worn wear surface in a RW pump housing.
You can test the thermostat in a warming pot of water and a candy thermometer. But it sounds like it is working fine once it gets some water supply at slightly elevated engine rpms.
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| Sandy |
Edited by - Sandy on May 14 2012 23:27:42 |
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Homeport: The Vineyard
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jtybt15
RO# 3300
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Posted - May 15 2012 : 00:50:18
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Yeah, 3 years is too long between changes. 2 years is the accepted outside between changes.
Thermostats, even new ones, can be 'sticky'. Drill 2 3/16" holes in the thermostat to allow water flow when still cold and air to burp out. If you have air trapped right at the thermostat, it can insulate the bi-metal spring that activates the thermostat so it will get hotter than it should...but it should fix itself after first opening.
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Charlie
There is much to be said, in a world like ours, for taking the world as you find it and fishing with a worm.-Bliss Perry, 1904
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Homeport: Ca
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Play Dough
RO# 29135
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Posted - May 15 2012 : 06:46:14
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Well, the impeller may very well be the issue, but I assure you that it is a rarity to have annual impe
ller replacement on boats moored in the Great Lakes. Salt water usage might be different. I have no experience in that arena. It was the impeller that I was positive would be the culprit last year which is why I hired the marine service to repair the issue (thinking the boat would need to be pulled). Instead, I paid $130 to replace a thermostat which solved the problem. Time will tell what the problem actually turns out to be. Thanks for your input.
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Homeport: Ludington, MI
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Brite Idea
RO# 12714
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Posted - May 15 2012 : 10:38:53
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1989 5.7L Alpha is a pain in the butt once it starts giving you overheat problems but I'll give you some areas to look. If it were my boat I'd order the Alpha water pump kit that comes with the housing and change it every year. I'm trying to help without sending you on a parts changing trial and error but it's been my experience like Charlie says those old Alpha water pumps can go bad in an instant and it doesn't take much believe me.
Ok, the thermostat could be bad, I change them every third year and I have experienced bad ones right out of the box so test it before you install it! Is your thermostat housing the one with the stupid little check balls? If so they could be hanging up. This next one is a maintenance issue but how old are the manifolds and risers because if they are old and the water flow is blocked the water pump can't overcome the blockage so you experience over heating.
When the water pump is replaced be sure to remove the water pump base and clean out the passage below, I once had so many tube worms grow in there the water pump wiped out because it couldn't suck up any water.
Please keep us up to date on your progress and hopefully you'll post good news.
Rob
Rob
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Homeport: Copiague, N.Y.
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starfishkiller
RO# 16333
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Posted - May 15 2012 : 11:53:57
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As a former owner of a merc outdrive powered boat, I will echo what others have said about replacing the water pump anually. Merc sells a kit with the upper housing, base plate, impeller, gaskets, small o-ring for oil gallery, etc. That should be purchased every fall, and installed as part of the drive removal, bellows inspection, spline and u-joint greasing, oil change, etc.
As far as thermostats, I learned through the school of hard knocks, to remove the thermostat in the fall, fill the block with anti-freeze through the opening, and then replace the thermostat housing without the thermostat. In the spring I would start the engine on muffs, without the thermostat. Really flush the cooling system out with fresh water, and then replace the thermostat with a new one. On multiple occasions, I cheaped out and reused the old thermostat, which led to spring time overheats.
Manifolds and risers do go bad in fresh water as well. I also know this from my own experiences with overheated engines, clogged risers, etc.
This was all on a boat that was used in fresh water only. Be careful about ruling stuff out, just because the boat is used in fresh water.
YMMV
eric
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Homeport: Budd Lake, NJ
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Play Dough
RO# 29135
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Posted - May 16 2012 : 18:30:42
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I decided to conserve my valuable boating weekends and just have the mechanic go down and check out my overheating problem. I was close to having the correct diagnosis. It was related to the thermostat. I don't know all the details of the hardware, but a couple springs or something under the thermostat had become clogged with debris. Zebra mussels were the debris item that stuck in my mind from the message I received. Anyway, a few parts are being replaced at less than $20 in parts and I'll be on the water this weekend.
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Homeport: Ludington, MI
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Sandy
RO# 1159
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Posted - May 16 2012 : 21:44:43
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Ahh.... I believe that Mercruiser uses pressure activated bypass valves , apparently similar to O/B poppet valves with spring, ball and seat, in the RWC engines.
Sounds like happy news for getting back OTW. 
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| Sandy |
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Homeport: The Vineyard
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SCORPIO
RO# 4810
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Posted - May 17 2012 : 06:01:59
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Next time you have the boat out of the water, take a good look at the hose that runs from the leg to the transom. It connects to the hose that feeds water to the T-stat housing. I had new hoses installed by a professional when my bellows and gimbals were changed. Turns out that hose is a bit long and kinks at the bend. It produced the same problem you describe, heating at low rpm, cooling as soon as you bump up the throttle. I chased this problem for most of 2009, replacing everything I could in the boat without pulling her. On haul out, I saw the kink had gotten worse. Apparently at low rpm it restricts flow but as you up the rpm, pressure increases, forcing open the hose enough to flow sufficient water. I replced those hoses on both drives with wire reinforced exhaust hose, problme solved.
To help check this, trim your drive all the way up at idle and see if the temps drop, if so, that hose is likely the culprit. Trimming up strightens the hose a bit.
Hopefully the T-stat housing/balls are your issue. I replced mine but that didn't fix it for me.
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| Chris USPS AP |
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Homeport: Lewes, Delaware
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Play Dough
RO# 29135
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Posted - May 19 2012 : 17:05:49
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Items 3 thru 6 were replaced. Ran the boat this morning and all is well.
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Homeport: Ludington, MI
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Overheating at idle.
