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Old 07-28-2013, 04:01 PM   #1
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Default ongoing overheating problems

I replaced the thermostat after my last post and the temp seemed to stabilize so I thought the problem was solved.went out the 4th of july but was close to home and didn't even get up to cruising speed.All OK .Then I went on vacation.Last saturday 4 of us went out just for a run .got about a mile away (temp guage at 150 160)..watched the temp the entire time .At a sudden loss of power we turned for home.temp still reading good.started making tapping noise .put it in neutral engine cut out . opened hatch engine HOT water boiling in thermostat housing.
The problem is ..we cant find the smoking gun...outdrive Impeller looked ok (will be replacing it anyway) pulled the circulator pump and opened it up and that doesn't look bad either!? I'm very upset and stressed out to be having all this trouble with a boat that i just bought

What else should I be looking for

96 2400 scr alfa gen 2
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Old 07-28-2013, 05:02 PM   #2
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Exhaust Risers and manifolds. If these are blocked the water flow is restricted. First replace impeller, IMHO inspecting is a waste of time if you go through all te work to pull it out why not spend the ~$30 and put a new one in. They are only good fo 2 years after that asking for trouble. If impeller doesn't fix then pull a riser and inspect.

Get yourself a infered handheld thermal gun and measure temps on t-stat, risers, manifolds, ... looking for hot spots.

How many hours are on the engine? Exhaust is good for no more than 500 typically but this depends on fresh vs. salt water, flushing the engine helps but in the end everything wears out.
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Old 07-28-2013, 05:43 PM   #3
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obviously a raw water problem,not to worry as you can trouble shoot water flow with a garden hose.

So,
1. hook up your outdrive ears, and pull the hose off the inlet hose on the raw water pump. See if you have garden hose water coming out. (note: all stock engines are RH right hand or counter clockwise rotation, maybe sure the input water like is on the bottom of the raw water pump, and not reversed).
2. Hook up raw water pump again, and check flow at fuel cooler plastic plug.
3. check flow at thermostat housing. (make sure thermostat is not installed backwards).
4. pull cooling hoses of manifolds and check for flow.

see if its runs cool on the garden hose....
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Old 07-28-2013, 05:53 PM   #4
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Pas when you are sawing raw water pump I am assuming you mean the circulating pump on the front ofhe engine, his boat has an Alpha so the raw water pump is in the outdrive.

Therefore:

1. hook up ears to O/D remove water inlet house from transom assy to t-stat to check water flow.
2. Being a 96' don't think he has EFI but has a carb so no fuel cooler.
3 and 4. are kind ofthe same as water to manifolds come from t-stat housing. Most t-stats can not be installed upside down by design. Crown goes up and if upside down bottoms out before flang is flush with housing.
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Old 07-29-2013, 10:39 AM   #5
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After some more checking I think the tstat housing may be bad (one piece)...The incoming water is not going to the circulator pump . I am going to check it this evening
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Old 07-29-2013, 11:48 AM   #6
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Here is a diagram of the cooling system. This is for a bravo application, since you have an alpha the hose going to the water pump in this diagram will go directly to your transom housing.

cooling system.jpg
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Old 07-29-2013, 02:21 PM   #7
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This is a little confusing. Water was boiling? 212F. Temp. guage read 150-160f? I think normal operation is 175F. Inspecting the impellor should be fine. If there are missing fins or there is cracking in the rubber, then replace it. Otherwise it should be fine. Either the fins are there to sling water or they are not. Cracking indicates the fins are going to fail in the neat future. Better to replace it before it fails than chase through the system for all the rubber parts.

Risers and manifolds can also cause overheating issues. As does blocking pick ups.
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Old 07-29-2013, 04:39 PM   #8
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Shrew I agree that if the fins are all there and have no signs of cracks the impeller is probably Ok but after draining the gear lube to seperate the lower half of an Alpha drive you are spending ~$20 for new lube why not add another $30 and not have to worry about it for 2 more years.

Open systems are pretty simple need to verify no blockage from input to output (debris in pick up, rust scale in engine & exhaust) , working pumps (raw and circulating), good t-stat.

Was water boiling? I have seen closed systems that were low on coolant where the temp guage showed normal yet the system boiled over. Best I can tell is a air pocket formed near the temp sensor giving false reading.

Either way sounds like it was having issues. Just hope no engine damage occured since he mentioned a low of power.
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Old 08-11-2013, 10:48 PM   #9
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It gets worse . Installed new water pump in lower unit. Checked everything for blockage .Checked Circulator pump. Bought an infrared thermometer . Finally had a chance to take her out today. We put her through the motions and everything looked good.Got back to the dock left it running .Opened the hatch to do one more temp check....WATER in the hole... at the rear of the motor there was water running out mixed with oil...shut it down .....2 gallons of oil water in the crank case....I GIVE UP.
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Old 08-12-2013, 12:19 AM   #10
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time for a compression test, as you might have a blow head gasket, not to big of a deal.

You could have a cracked block or leaking manifolds.

time to get a mobile mechanic in to look it over.
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