1989 Mercruiser 4.3 LX, Alpha 1 Gen 1 Overheating

[PosessionSound26PC]

Fixed my starboard's seized gimbal bearing and on the test cruise afterwards, port started to overheat AFTER idling at dock for a good 10 minutes with temp gauges stable. We were in a no-wake zone so very low RPMs/speeds; I killed the motor around 200F. This was last fall.

It sat for a while during the starboard fix and now has sat another winter/spring so I thought it might be dirty/gummy carbs leading to lean burn (per manual this is an overheat possibility) but I also, per this forum, ran a simple test on the port water pickup pump at the outdrive by disconnecting the inlet hose to the engine's water pump and seeing if any water came out with gravity feed water and muffs attached - zilch!

I suspected the pump so I pulled the lower - pump and associated parts look ok, nothing terribly off, no broken pieces, no gouges or marks in the pump insert, the vanes had a bit of a set to them but nothing terrible. Everything looked ok and I could turn the shaft by hand. No obstructions in the lower water passageway that I could tell.

Today I pumped water backwards INTO the inlet tube at the motor to see if it would come out of the upper unit - VERY LITTLE/A TRICKLE. Most of it spilled into the bilge. I disconnected that hose from the steering oil cooler and the hose behind it that leads to the transom fitting - both hoses and cooler were clear/no obstructions.

Guess I have to pull the upper? The hose between the bell housing the gimbal housing looks ok, nothing obviously wrong. What else can it be? I can take off the plastic fitting at the bottom of the upper where water pickup tube plugs in... maybe peak in there. Just seems really weird that this circuit would be plugged... corrosion doesn't seem that bad... Any thoughts?

 

[alldodge]

Today I pumped water backwards INTO the inlet tube at the motor to see if it would come out of the upper unit - VERY LITTLE/A TRICKLE. Most of it spilled into the bilge.

Can you clarify where this is?

 

[zellerj]

The copper tube above the plastic outlet of the impeller pump fits into a rubber gromet. Check to make the rubber gromet is properly in place. Mine was turned 90 degrees which blocked the water flow.

 

[PosessionSound26PC]

Can you clarify where this is?

There is a hose that comes from the steering pump oil cooler and goes into the engine's water pump. I disconnected that hose at the water pump and pushed water into it w/ a hose. There should be no obstruction that I know of from there to the ground so I should have seen much more than a trickle...

 

[nola mike]

There is a hose that comes from the steering pump oil cooler and goes into the engine's water pump. I disconnected that hose at the water pump and pushed water into it w/ a hose. There should be no obstruction that I know of from there to the ground so I should have seen much more than a trickle...

The ps cooler is an obstruction point. Did you back flush aft of the cooler as well?

 

[PosessionSound26PC]

The copper tube above the plastic outlet of the impeller pump fits into a rubber gromet. Check to make the rubber gromet is properly in place. Mine was turned 90 degrees which blocked the water flow

@zellerj - Is this grommet at the top of the copper tube or bottom? The one at the bottom, inside the plastic pump cover, is there in the correct orientation. I have already taken the pump out of the lower unit for cleaning corrosion and re-painting but stored everything I removed in a bag - I checked the bag and that grommet is not there from when I pulled the lower. It may still be in the upper unit... but I looked up inside there earlier today and didn't notice any obstruction so either the grommet fell out when I removed the lower or it broke apart at some point and got flushed out? It would explain the overheat but not the lack of water flow in the reverse direction...

 

[PosessionSound26PC]

The ps cooler is an obstruction point. Did you back flush aft of the cooler as well?

I only pumped water into the inlet hose PRIOR to removing it from the cooler, not after. BUT, I did remove the hose aft of the cooler and checked both it and the cooler for obstructions - nothing noted. I shined my phone flashlight from behind the cooler and could clearly see the clean passage through it.

 

[alldodge]

Do flush the cooler

 

[PosessionSound26PC]

Tore off the upper unit at lunch - nothing terribly unusual right off the bat. There was some crusty buildup around the water hole between the two units, maybe salt crystals. But no big blockage. Before I pulled it off, when I tilted the upper unit down, a bunch of water came pouring out - makes me think water was getting past the blockage slowly and pooling somewhere and came out when tilted enough.

Good news is there's no sign of water/corrosion in the drive shaft area - this was my problem on starboard and led to a seized gimbal bearing. But my exhaust bellows is toast - torn at the bottom just before the clamp. Assume this has nothing to do with the blockage. Water hose behind the bell housing LOOKS ok...

Taking upper unit home for cleaning and painting and will check out the water passage - hopefully find the problem there. Don't want to have to pull the gimbal housing...

 

[alldodge]

You can leave the exhaust bellows torn or remove it. The motor will just be a bit louder then before

 

[PosessionSound26PC]

You can leave the exhaust bellows torn or remove it. The motor will just be a bit louder then before

Yeah, that's what I've read. I have a spare so might as well do it - boat's loud enough

 

[Bondo]

I have already taken the pump out of the lower unit for cleaning corrosion and re-painting but stored everything I removed in a bag - I checked the bag and that grommet is not there from when I pulled the lower.

Ayuh,..... Raw water pump parts are not cleaned up, 'n painted,....
When they're showin' any wear, 'n blemished,....
They're tossed, 'n Replaced with new a raw water pump kit,.....

 

[PosessionSound26PC]

Ayuh,..... Raw water pump parts are not cleaned up, 'n painted,....
When they're showin' any wear, 'n blemished,....
They're tossed, 'n Replaced with new a raw water pump kit,.....

Sorry Bondo - poor wording on my part. I meant I took the pump out so I could clean and re-paint the lower unit...

 

[PosessionSound26PC]

Disconnected the hose aft of the steering oil cooler from the plastic fitting in the transom assembly. I was able to pass a 6ga battery cable (5/16 OD) through the fitting, through the water hose that connects to the gimbal housing and out the hole in the gimbal housing (both upper and lower units are currently removed). Other than a little dust, nothing noticeable came out and it wasn't hard to pass the wire through other than at the initial kick in the plastic fitting. I don't think there's an obstruction in there, or anywhere that I can find. Very frustrating.

Could the copper tube between the units have come loose from the plastic water pocket cover and allowed water to spill out before it could go up to the engine? Doesn't explain why I wasn't able to back flush more than a trickle but maybe I had a kink in my hose that prevented enough pressure... I was using one of those shrinking coil-up type hoses... I think I'll re-run that back flush test tomorrow with a real hose. If that checks out, then something else happened to keep the pump from getting water into the engine when I tested that - like the copper tube being loose, or its seal... I assume my gravity feed set-up was ok? I had a 5 gal dispenser on the swim platform so similar pressure/head to being in the water, but not the pressure of a garden hose...

Feels like I'm chasing my own tail...

I don't store the boat at home and the storage yard has no water - I have to bring my own and pump it w/ a generator. The damned city turned off the faucets for flushing motors for "environmental" reasons...

 

[alldodge]

This would have been good to know sooner

I don't store the boat at home and the storage yard has no water - I have to bring my own and pump it w/ a generator.

Doesn't explain why I wasn't able to back flush more than a trickle but maybe I had a kink in my hose that prevented enough pressure

Could be but can you take your boat to another location, like even home and work on it there?

 

[PosessionSound26PC]

This would have been good to know sooner




Could be but can you take your boat to another location, like even home and work on it there?

Not home, street and driveway too steep :-( Maybe a friend's house but not any time soon.

I will re-try the generator/pump/hose setup tomorrow for back-flushing and see how it goes. Didn't find any clogs of any kind and impeller pump looked fine as I mentioned earlier.

When I get the upper and lower back on, I will try some sort of pressure testing - any hints/ideas on that?

 

[alldodge]

Don't know how to test upper elbow, but lower and place rubber piece between Man and elbow to pressure test lower Man

 

[kenny nunez]

Low speed or idling heating is sometimes caused by a blockage in the by pass hole in the thermostat housing. Are the manifolds completely free flowing? Have you looked closely at the plastic cover in the bottom of the upper housing, it should show no appearance of melting.
With the boat in the water and idling remove the hose from the drive pump at the thermostat housing and try to hold back the flow by holding the hose in one hand and with the palm of your hand over the outlet. You should not be able to stop it.
This may sound stupid but is it really getting that hot? A sending unit could be the problem.

 

[PosessionSound26PC]

Update and answers to Kenny Nunez questions:

Brought a proper hose to the boat (see previous comments) and re-tested back flow/flushing from the inlet hose to the engine's water pump back out to the bell housing - solid stream of water, no blockage at all. At least that particular water passage is clear.

Kenny, my overheat seemed a bit sudden to be blockage but maybe it's possible if a large piece of rust came off and blocked the by-pass hole? In any case, I have since removed, cleaned and re-painted the thermostat and checked all connected hoses, replaced the thermostat and gaskets and re-installed. I knew from work on starboard that you can't really see the by-pass hole w/o drilling out the rusted-in plug so I didn't worry about it (it wasn't an issue on starboard so... fingers crossed). If all else fails, I can poke a bore scope camera in there.

I do not know about the manifolds other than previous owner had never changed them out but he was fresh-water only and starboard's were pretty decent when I replaced them last year - have not taken port's apart and didn't wish to until end of this season but we ran at the dock for a good 10 minutes w/o issues, prior to the overheat. I will re-test out of the water after getting my outdrive back on, hopefully later this week and check the flow.

The plastic water pocket cover inside the upper is fine - no melting, good shape. I am replacing the gasket since I removed the cover to look for blockage in the pocket.

Your engine water pump test sounds good - will do after re-assembly. I hope it's not the water pump!

As far as temp, I watched it go to 200F in the no-wake zone outside the dock area and then decided to cut the engine. Possible it's the sender if everything checks out, but it would be weird for it to all of a sudden die right there and then... Could have been a piece of kelp or a plastic bag but didn't think to check for that at the time.

Will re-assemble outdrive this week and hopefully test impeller pump by end of week. Thanks!

 

[PosessionSound26PC]

Just an update to bump the thread while I wait for the final re-assembly and test:

Replaced port exhaust bellows that was all torn up. First time doing this and got the expander tool. Went ok, not too bad of a hassle. Lots of corrosion on the gimbal and bell housings - will be taking apart this winter to clean and re-paint.

One weird thing while prepping port exhaust bosses: my fingers ran into a severed continuity wire on the inside of the gimbal ring. Wasn't sure where this connected to on the bell housing so looked at starboard and saw a screw next to a hole on the port side of the bell housing. But that screw, its hole, and the other hole are all missing on the port side. No idea where this was connected but assume I need to connect in order for mercathode and anode to work properly? Will take a look for another connection point I may have missed but very odd...

When I pulled the lower unit a while back, also found that the lower oil seal on the upper unit was shredded. I will be replacing today and will hopefully have the cleaned and repainted upper unit back on today.