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Mercruiser Alpha one Pre '92 engine overheating, new impeller???

C

Classic78

New member
Greetings to all,

I recently purchased a relic of and old wooden hull boat (1978 Skiff Craft), 350 Chevy, MerCrusier Alpha One pre '92. I had a supposedly good marine mechanic (does repair on the side out of his house) go through and replace the regular things like gimble, bellows, shift cable. He had to pull the engine because several of the expansion plugs were corroded and leaking. He also suggested replacing the impeller while we were doing everything else, which made sense. On my first test run the engine I thought was running a bit to the hot side of the gauge in idle-to-slow running mode, but then it over overheated to red within a minute or so after I gave it open throttle. I took it home to analyse. With the lower unit in a water tub, after initial start up in idle, the the temp gauge goes into the red within 5 - 8 minutes. I know water is circulating through the system. because I see it discharge from the out drive exhaust port. I'm pretty good a trouble shooting some things, but not being a mechanic limits me where to go from here. I later found out the guy I had do the work is known to scam people and often doesn't really replace the concealed parts and pockets the money. Before tear into the lower unit myself, I just wondered what else can cause the overheat situation (for example... could be the thermostat?). Thanks in advance for anyone's advice.

Classic78
 
With the lower unit in a water tub, after initial start up in idle, the the temp gauge goes into the red within 5 - 8 minutes. I know water is circulating through the system. because I see it discharge from the out drive exhaust port.

Not really, you cant get the water level high enough in a tub. All it does is destroy the impeller
Shift into fwd, remove the drive, insert a washing machine hose cut in half into the water inlet hole and test run the motor. If temp is normal, you need a new impeller
 
Relic? no way. Skiff Craft are highly desirable and they have a cult-like following of fans. When you pull up to the dock, people look at you, not the 41 Fountain next door. They are Amish-built and are still made one at a time by hand (www.skiffcraft.com) Go look at the pics on the website. Bloody gorgeous, no? Hope yours is in good seaworthy condition. If not it's worth putting in the time and money to bring it back to Bristol condition. Like Airstream, you can send it back to the factory to have it refurbished. If you do it yourself, they have a very good consultation service and are willing to help you restore yours the right way. The engine and drive are secondary (or less) to the value. Def be worth a repower some time in the future with new engine and drive. It will outlive you and probably the next two or three owners.
Please save it. Or sell it to me!!!
 
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Okay, Thanks for the info, but I would appreciate a little clarification here. The way I had it set up, my water height was up well above the lower unit (i used a horse trough... intake was completely submerged). I guess I did not realize water entered the out drive above that point. I've also been told that if you use a hose at the intake it can give a false indication of the impeller being good, but in reality the water pressure is doing the work, rather than the water pump. Or, perhaps I'm not understanding exactly what you are saying. I also don't under if temp is normal I need an impeller. Wouldn't that mean all is good? Sorry if I seem out of it on this, but if you wouldn't mind giving me a bit more info, I'd certainly appreciate it.

Thanks again,
Classic78
 
Hey yeah, thanks for the reply. You are preaching to choir on Skiff Craft. I meant relic in loving sort of way, LOL. This is actually my 3[SUP]rd[/SUP] one. I’ve been to the factory and had one of my other ones completely restored there (those Amish boat builders ain’t cheap). Not sure yet what I will do with this one. It’s in pretty good shape, but does need some TLC. Anyway, thanks for chiming in.

Take care,

Classic78
 
If running water thru the inlet hole of the transom and the temp stays normal it means the impeller is not doing its job. If it still get hot on the hose in the water inlet you have another problem.thermostat, clogged manifolds or clogged risers
 
So if D is the inlet hole, you're right about the water level, did not have it that high. My temp gauge goes from yellow (warm up) green (normal) to red (hot) where should it be on this test?

Thanks!
 
I use a set of rectangular shaped (vs round that don't fit well) muffs on a hose to run mine in the yard. You need a REALLY big, deep bucket to do it otherwise for the exhaust puts a ton of air bubbles in the bucket, which will cause massive overheating.

Jeff
 
So I did replace the impeller... pretty sure I got it all put together correctly (everything lined and bolts tighten up good. Took it out and ran about 20 minutes in idle (no wake zone speed) temp stayed in the green. Hit the throttle and ran open for about 4-5 minutes and all of the sudden temp was redlining. Had to shut it down and hobble back to the dock letting it cool down in between runs. I took off the water distribution manifold, and was surprised to find no thermostat. Am I just really ignorant, or should there be a thermostat in there. If not, is there even a thermostat at all. If so and where is it?

Thanks again in advance!
 
There is supposed to b one.

Look for diagrams on your motor, on the parts breakdown area (on this site, where you got to buy parts), and you'll see what you need and where it goes.

Jeff
 
Re: "....So I did replace the impeller..."
Was the old one intact? If not, the missing pieces could have migrated to a bad spot.

Re: "... missing T'stat"
If its truly missing this is indicative of a very likely previous overheating problem that P/O tried to fix by removing the t'stat. BTW, the function of a t'stat is to make sure the engine runs warm enough... not cool.
 
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Old one was disintegrated down a bit, but mostly still in tact. What is my next step? I'm assuming my impeller replacement job was done correctly or hopefully good enough for the rest of the season. Is there anyway to flush the cooling system for clogging. I noticed 3 of the 4 upper hoses (3/4'') felt like they had hot water inside when I squeezed them. 1 of the 4 felt fairly cool tonight after I put in a t-stat. Still overheated after 10 minutes or so.
 
I am still overheating. Can anyone tell me if there is a flushing method for clogged exhaust manifolds and/or risers without disassembly? the port side exhaust discharge sputters and sprays water, while the starboard exhaust discharge seems to flow nicely.

Thanks,
Greg A
 
Raw water systems are not kind to thermostats. They can stick shut, and I've had one that even came apart.
If ya haven't done it yet, I'd check the thermostat and put it in a pan of water with a thermometer.
Heat the pan and watch it.

Of the water hoses on one side get warm, and the other side doesn't- pull the cold ones and look inside.
Other than pulling manifolds off, there isn't much else to do.
 
Update. I did remove the port side riser and manifold. I thoroughly examined the parts, and pressure sprayed both parts completely, re-assembled and the same overheating occurred. I took them apart again, and remembered I just happen to have an old riser from the another 305 Chevy I previously owned that was never needed. I installed that part and Viola issued resolved. As I looked closer at everything, the old part had the wrong gasket that actually covered the flow through water channel. Anyway took on another test run and no more overheat, but now the engine just shut down after running Idle 10 min. It ran smooth for about 10 min and then I heard a fairly high pitch squeal coming from the lower area close to the crank shaft, and then it shut itself down before I could get to the key. It would not turn over again for a few minutes and then it did again, but I was afraid to run it anymore. I paid a supposed boat mechanic to do a lot of things that I had to re-do. Changing the impeller and oil to name two things. Now I am wondering if the oil he had me get was the wrong grade and type. HE told me to get straight 50 weight. Any help will be greatly appreciated.
 
Do yourself a favor and lose this mechanic. You may have seized the motor . change the oil and filter to 20w-50 or 25w-40 . cut the oil filter open for examination, remove the electric oil sender and install a mechanical gauge to read oil pressure.
 
Bt Doctur... I owe you a BIG thanks! I drained the 50 weight out, which was clumpy and thick, put in new 20w 50 and new filter. Fired her up and purring now. I ran Idle for 20 minutes, revving every so often... temp stayed in the green, no clanks or squeals. I just hope no major internal damage occurred.

Thanks again
 
Update... not good! So I felt confident enough to take the boat out for some fun on the lake with my kids thinking all my known issues were handled. We ran about 1 1/2 hours various speeds, tubing, cruising, etc. The engine was very responsive from the throttle, temp stayed in the green towards yellow range, and the out drive seemed to performed flawlessly. I keyed the engine on and off numerous times for tubers to enter and exit the water. After the vary last shut off, I went to re-start and just got a growl with no turn over (new battery fully charged). That was all I got for the rest of the day and had to be towed back to the dock. I am at a loss as to where to begin. Is it possible my engine seized from the improper oil that was in it. I probably had less that 1/2 hour of run total run time with that oil. However, I was over heated a couple times from the water flow blockage that I finally found.
As Always thanks in advance for anyone's help

78Classic
 
A bad alternator ( or a loose belt) will let your engine run until the battery goes dead. Check state of charge of battery.
 
I always let my engine idle for a bit before I shut it off. Even though I have flaps on my thru hull exhaust ports, I never suddenly chop the throttle... Plan/drive ahead!!!! as much as possible. If you need to stop your boat suddenly at speed in an emergency, there is a maneuver I learned in a US Powerboating course. Take the course and learn it. I was able to take that course which at the time was "bundled" with a "Mark Set Boat Handling" course compliments of US Sailing, their affiliate. USSailing/Powerboating graciously donated a number of seats at a combined Boat Safety/Mark Set course ( a 4 day course into 2 days) as their contribution towards mitigating the damage to the yacht clubs on Barnegat Bay by Hurricane Sandy the summer after Sandy. Due to the club locations, all clubs sustained substantial damage ( one was totally flattened). FYI, "Mark Set Course" refers to small boat activities both before and during a sail boat race, including the unique assistance/rescue requirements of small racing sailboats. Just a plug for them :) http://www.uspowerboating.com/.

Taking your state minimum (if you have any) boat safety course is not enough. When I took the course, one of our other YC club members also had a USCG Masters License, while mine (active at the time) was only used casually, the other Captain used his every day at work in New York harbor. We both felt we learned something about boat handling beyond the sail boat race specific issues.

Sorry for getting waaaay off topic.
 
Bob:

Ever meet Sam Fuso? He's a USCG Auxiliarist (from my old flotilla) who trained those guys who responded to the famous Sully incident on the Hudson.

Jeff
 
So this reply is about year old now... But I did end up having the hydrolock situation last summer. Unfortunately, I did not realize it for about a week. Once I realized what had happened, I removed the plugs, turned the crank by hand about 30 revolutions, dousing the cylinders thoroughly with penetrating oils, and lubricants with evaporating additives. I also changed the oil. The engine fired right up and has been running pretty well since then, but everyone tells me it's on borrowed time once the water intrusion happens. Since then my flywheel has gone bad in a couple places, so now I need to pull the engine. I've located a 305 long block marine engine for a pretty good price, but I think my engine is actually a short block 305 that was replaced before I owned the boat (it did not have the brass expansion plugs) . So that is the set up... 3 questions, 1 - if you were me would you keep or replace the engine (money is an object... I don't have much)? - 2 if I do replace, can I dress the new long block with most of the same components of what I believe is a short block chevy 305 with marine components (water pump, fuel pump, distributor etc.)? 3 - this is going show my ignorance, but do I need to pull to remove any of the out drive components before pulling the engine? Thanks to all for your input.
 
Classic78 said:
....I did end up having the hydrolock situation last summer. ...... The engine fired right up and has been running pretty well since then, but everyone tells me it's on borrowed time once the water intrusion happens.

I've located a 305 long block marine engine for a pretty good price, but I think my engine is actually a short block 305 that was replaced before I owned the boat (it did not have the brass expansion plugs)

1 - if you were me would you keep or replace the engine (money is an object... I don't have much)?

2 if I do replace, can I dress the new long block with most of the same components of what I believe is a short block chevy 305 with marine components (water pump, fuel pump, distributor etc.)?
Click to expand...

You certainly might have corrosion based gremlins that are just waiting to shred the engine......Or......you got lucky and there is no water damage. Here's the thing, you've run the engine too hot several times, it has squealed and ground to a halt, you've run the wrong oil, and then there's the question of exactly how old it is. In other words, the water intrusion is just one of many unknowns and you're on borrowed time for many reasons.

Does the source of your longblock 305 require a useable core return? I don't think I'd cut my boating season short to change an engine that might be walking toward the grave. If it's run okay so far, you might as well keep running it and get all the life you can out of it. What's the worst that can happen? You run a short time longer and it croaks anyway.....or it just keeps running until the end of summer??? When boating season is over, pull in the shop, yank the engine, and then install your reman long block.

Long block just means the engine was delivered with heads, valve train, cam and timing gears/chain already assembled. Sometimes tehy come with valve covers, timing cover, oil pump, and oil pan installed. Short blocks are usually just the block with crankshaft, rods, and pistons installed. In the vast majority of cases even with a long block you have to use your own intake, valve covers, timing cover, and oil pan.

If all of your parts match up, then the long block is a pretty straight forward swap.
 
I have salvaged many many engines that either have sucked in water causing hydro lock or were completely submerged (fresh water only).

Have not seen one fail after the fact due to the water intrusion. Keep the oil clean and filter changed for a few oil change cycles Like twice a season or every 50 hours vs once a season and every 100 hrs.........Use quality oil, 20-50 name brand, 25-45 mercury oil or as many including me, mobile one 15-50 (walmart ~$26.00 for 5 qrt jug).

If it runs well continue until it does not.........No need to chase a ghost that does not exist!!

If you find a spare block then get it prepped in case. Other wise run it like you stole it!!
 
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