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jshane37

Regular Contributor
Hello all!! Was wondering if a

Hello all!! Was wondering if anyone could help me with an overheating problem. 1986 Alpha drive 190 h.p. (4cyl). Good flow of water from impeller into heat exchanger. Replaced thermostat and still runs very hot. Only overheats when boat is under heavy load. Does great at idle and slow speeds. Anyone please?
Joe
 
"Check your heat exchanger to

"Check your heat exchanger to make sure you are getting a good flow of water not only to it but through it, if not it will overheat.

Chers
Peter C"
 
"Hello Peter.... Yes I checke

"Hello Peter.... Yes I checked the flow of water into, and out of the heat exchanger and I get a great flow of water. Higher stream as the RPM's are greater. Not really sure what to check next. I ran great today at about 3500 RPM's, but when I gave it some throttle the temp went through the roof and overflowed into the coolant reserve tank."
 
"If the heat exchanger has hot

"If the heat exchanger has hot coolant going in, is it cooler coming out? Yes? Then it's working.

If the temp is not cooler coming out of the exch. then you need to remove the scale and rust buildup inside it. Is the belt tight on the engine circ. pump in the front?

If exchanger is good, I would suspect your riser is plugged with crap and rust. Easy to remove and clean with acid. Also check the flapper below the rubber exhaust elbow to see if it is moving freely. Spray some carb cleaner on each end of the shaft to remove any carbon buildup."
 
"Thanks for the direction Guy,

"Thanks for the direction Guy, I will give those a try today. One thing though..wouldnt it be raw water rather than coolant going through my heat exchanger? Will give those others a whirl."
 
"Joseph
Engines that are equi

"Joseph
Engines that are equiped with a closed cooling system are cooled with fresh water circulated through the heat exchanger. Fresh water in the system is cooled by the raw water which flows through the heat exchanger and is discharged out the back of your boat.
The fresh water section of the cooling system is the pressurised closed section of the cooling system, like your car.
Think of the heat exchanger like the radiator in your car but instead of air flowing across the cooling fins of the radiator to cool it, you have raw water being pumped across the cooling tubes in your heat exchanger to do the same job.
So you have fresh and raw water inside your heat exchanger at the same time but hopefully not mixed together.

Cheers
Peter C"
 
"Peter and Guy
I think that I

"Peter and Guy
I think that I have a better understanding of how the cooling system works thanks to you. Today I checked the "flapper" as suggested and though it seemed a little worn, it seemed to swivel back and forth nicely. The flapper was folded almost in half though, is that normal? Imagine a rubber letter "V" and thats what it looks like. Also, I pulled the riser and anti freeze tank and both seemed ok, other than a little rust. Small chips of rust in the riser that rattled around that I managed to get out.
Guy~
I checked the drive belt for the cool pump and it has little slack in it. Probably less than a half inch. I also took the 2 bolts off of the cover and inspected the "wheel" to the pump and it seemed to be fine. In fact I bumped the engine and the wheel spun nicely on the pump. I will pull the heat exchanger tomorrow and see if there are any obstructions that would prevent the water from moving through freely.
Thank you both for your input thus far.
Joe"
 
"Replace that bent flapper bef

"Replace that bent flapper before it falls down into the exh. pipe. It has to be straight to keep raw water from backwashing into the engine exhaust. Exhaust pressure keeps it open. If you stopped the engine at 4500 RPM, it is possible for the backwash at the back of the boat to enter the engine when it hits the stern.

Get a stiff tubular wire brush and run it through all the openings of the riser. Take the riser to the carwash and clean it with the wand. It will be messy but the pressure wand will clean out any loose crap."
 
"Would a faulty flapper cause

"Would a faulty flapper cause the engine to over heat though? This thing looks like it has been worn for some time and the engine ran fine last season. Also, how in the heck do you get that flapper out of the exhaust tube to replace it? I see that it is held with two pins but dont see how to pull them."
 
"If the flapper is not allowin

"If the flapper is not allowing it to turn with the exhaust flow so its flat surface is parallel to the pipe, it becomes a blockage to exhaust movement--YES!

Remove the rubber exhaust hose from the pipe. Use a soapy water to reinstall the large hoses."
 
"Will do Guy, thanks. How doe

"Will do Guy, thanks. How does that flapper come out of there though? I have figured out how to take the large rubber exhaust hoses off, but not sure how to get the flapper out of the metal (tube) housing. Suggestions? Ideas? Links on how to remove?
Thanks in advance"
 
"Also, imagine that you take t

"Also, imagine that you take that flapper and fold it in half, thats the permanant form that it has in the exhaust tube. It moves freely to the touch, (left and right) and I would assume that because of its shape, it only blocks half of the tube at a time. I guess I am not picturing in my head how it could be a blockage because of the current shape."
 
"In its current shape, only ha

"In its current shape, only half the exhaust pipe is avaiable for the engine to breathe. Try breathing out out one nostril during a marathon."
 
look at the blowup drawing. I

look at the blowup drawing. I believe the bushing holds it in place from the outside with the hose over the bushing
 
"One nostril during a marathon

"One nostril during a marathon....Guy, you have a way of putting everything into perspective. Thanks and will replace that flapper today.
Joe"
 
"Question: If the impeller is

"Question: If the impeller is faulty, maybe only lost one or two fins, is it possible for the engine to stay fairly cool when idled at the pier? I can run it at about 3000 RPM's while not in gear and the temp never creaps above 160-170. Would the prop in motion cause water to be drawn away from where the impeller needs to "drink it"? Just curious."
 
"I'd say that would only o

"I'd say that would only occur if the water temp in the lake was 35-40 deg. F. If you lost one or two fins, it would not last long plus the rubber chunks would block the water passage."
 
"See thats whats not making se

"See thats whats not making sense to me. The temp of the water in the river is around 65 F. I pulled the heat exchanger and all surrounding hoses today and found them to be in remarkable condition. I did find part of a rubber fin (about a quarter of an inch) that I suspect came from the impeller. It was laying around in the heat exchanger. The part that doesnt jive though is that I get a great circulation of water from the impeller, and the boat never got above 170 degree's while idleing at the dock for several moments. At one point the thermo even kicked open and the temp dropped to about 160. BUT, as soon as I plane the boat off, and give it some throttle, the temp peaks and the engine shuts down. This problem makes a rubics cube look like a walk in the park...ugh"
 
"If you have an impeller break

"If you have an impeller breaking up, you need to replace it right away. The rubber fin you found is a telltale sign of possible other pieces jammed in some part of the cooling system. That may be the problem you are having--insufficient raw cooling water flow at higher RPMs. When you pull off the old impeller, see how many pieces are missing and try to find them by back flushing the raw water portion of the cooling system. Did you get the flapper replaced?"
 
"Not yet Guy, gonna make a one

"Not yet Guy, gonna make a one stop shop tomorrow and pick up a new impeller and flapper. Do you have any links for replacement of the impeller? I found one for the flapper with my subscription to Seloc, but cant find any help for the impeller. Is it something rather easy to accomplish? Also, how do you back flush the system?"
 
"Joseph.
Time for a cold show

"Joseph.
Time for a cold shower !!!!
You are puting far to much thought into this and are in danger of over analysing it.
Any water pump given a particular set of circumstances will cavitate. Particularly when it is missing some fins.
DO AS GUY SAYS !!!!!!!!!!!!!!
Pull the leg, replace the pump, launch the boat, give it some stick and see what happens.

Cheers
Peter C"
 
"The impeller is pretty simple

"The impeller is pretty simple. You will need some 2-4-C lube and apply per instructions.
Tonight, pull off the plug coving the trim tab and squirt some blaster or liquid wrench inside it. Tomorrow tilt the OD upward to work on it. My SELOC manual covers it pretty well. It should be in your subscription. Look under removal of the lower unit. PLACE GEAR SELECTOR IN FORWARD. Scribe a position mark on the trim tab and remove it. Next, loosen the five nuts on the cavitation plate and remove them while holding the LU. Drop it down and off. It's heavy. Remove the O-ring if there and the slinger gasket at the base of the shaft. Unscrew the pump cover and pry off the impeller--it is held in place with a tiny key; save it. Inspect the bottom half of the pump housing--if it looks like it got hot--melted--go buy one and replace it. If he SS can is scored, replace it also. Replace the impeller by lubing it with soapy water and fold the fins into the can--don't for get the key--and put on the top and water tube. Replace the slinger gasket. Tape over the splines to install a new O-ring if equipped.

When installing the LU, align the water tubes and the shift tube in front and make sure the little O-ring is in place on the cavitation place--hold it in place with a little grease.
Have the two side nuts ready and install once it is halfway connected together; now finish connecting the two sections--don't force them--it all should slap together at once. If not, take it apart and try again."
 
"Hello Guy and Peter,
Ok, bet

"Hello Guy and Peter,
Ok, between juggling work and play, I have managed to change the thermostat, flapper, and impeller...and a few gaskets along the way. Reading the Seloc manual, I believe that I put it back together correctly (lower unit). No spare parts anyway. Two questions though. While running the earmuffs on the lower unit with water flowing, I get a fairly steady stream of water that squirts from the lower area of the shift shaft arm. The water seems to come from the lower unit pump.
Secondly, the manual says that the short arm of the shift shaft must face forward when mating the upper gear housing to the lower unit. This doesnt seem to make sense because it barely seats in the metal slot on the upper gear housing. Shouldnt the long end sit in there? Seems to fit better with no slack."
 
"If the stream of water you ar

"If the stream of water you are talking about comes from the starboard lower side of the OD nose, then that is normal.

It WAS in forward when you R&R the LU? If the manual states as you said, leave it like that if it works. Maybe one of the other gents can confirm what you are asking."
 
"The water seems to be coming

"The water seems to be coming straight up from the area where the shift rod sits, as if it is coming from where the lower unit and upper housing meet. I just wondered if putting that new impeller on, would it somehow cause a forced stream of water to escape through that area."
 
"Joseph;
The only place you s

"Joseph;
The only place you should be getting water out besides the prop opening, is two outlet ports on the lower corners of the the transom assembly, near the transom. They are at about 5:00 and 7:00 o'clock, about 1/2" diameter. YOu should get a good flow of water out of each.
Rod"
 
Did you forget the itty bitty

Did you forget the itty bitty little O-ring on the starboard side of the lower cavitation plate?
 
"Just wanted to say thanks to

"Just wanted to say thanks to everyone that replied to my posting. Replacing the impeller, flapper and thermostat solved my over heating problem. Not sure if it was one thing or the other, but the combination of suggestions solved my dilemma. Special thanks to Guy and Peter for their input."
 
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