Water in drain plug but oil clean 3.7L Mercruiser 165HP 1987

[Brock.Ward]

Wait, last one...one question I do have, why would the water impeller on the lower unit effect the exhaust manifold? Why would that be the only thing getting hot? The impeller isnt connected in way to the exhaust manifold and thats the only part of the engine that is getting hot, everything else is running great and operated temp but the exhaust manifold is what starts smoking, thats why i believe its probably the thermostat isnt opening after it warms up...

 

[stonyloam]

The impeller is on the top of the gear housing (lower) when you split the outdrive. The upper section is the driveshaft housing. On a boat the exhaust must be cooled to prevent the rubber exhaust bellows (behind the engine) and rubber coated exhaust shutters and the waterpump housing from being damaged by the hot exhaust. On your 470 the water comes in from the outdrive pump, through the tube on the back of the voltage regulator (if it is still there) then into the forward tube of the heat exchanger where it goes back and forth 3 times through the tubes, then out the aft tube up through the power steering cooler (if you have one) then through the hose fitting on the side of the exhaust elbow, where it kinda goes around inside then dumps into the exhaust right about where the upper bellows connects. So if you do not have sufficient water flow things will get hot! Since the 470 is a closed cooling system it depends entirely on water pressure from the impeller pump in the outdrive for its supply of cooling water, whereas on a raw water cooled engine the engine mounted water pump helps draw the water in and push it through the system. That is why your impeller and pump housing MUST be in tip top shape and you should change your impeller every two years at a minimum. I would not worry about the thermostat at this time, chances are it is OK (would have no effect on the symptoms you observed) the impeller is way more important.

 

[Brock.Ward]

ahhh ok makes sense, however maybe I was wrong but the thing that gets hot is the exhaust manifold, its whats under the elbow or where you fill the anti freeze up. Thats what gets hot, i didnt think water circulated thru that...

 

[Bondo]

ahhh ok makes sense, however maybe I was wrong but the thing that gets hot is the exhaust manifold, its whats under the elbow or where you fill the anti freeze up. Thats what gets hot, i didnt think water circulated thru that...

Ayuh,.... That's where the raw water exits the system,...

Low or no water flow, it got Hot,....

 

[Brock.Ward]

yea but its not on the back where the water flows out its on that actual exhaust manifold that is getting hot...maybe im not following. There is coolant in the exhaust manifold by the thermostat, not water. Thats why i am surprised its getting so hot.

 

[stonyloam]

Well, how hot? You have a 165 F thermostat, and the hot(est) coolant pumps down into the heat exchanger from the manifold, so the manifold will be pretty hot. Take a look at your temperature gauge when it is running. Feel the heat exchanger. When the thermostat opens it should get pretty warm. If your water flow is not up to snuff it could start to overheat. Rather than fool with coolant side, try to get the raw water side working 100%. Even if the impeller was changed before it sat, it still needs to be done again, because the blades will take a set and loose efficiency.

 

[mr 88]

Drop outdrive or remove the lowerer half,which you have to do anyway and change impeller. The old imp. will be dry rotted or stiff and chunking apart. There is no way of checking it. The 470s' should be changed at least every other year under good conditions. If your running near sandbars etc then every year. Don;t be hating on the imp. change,show it some love and it will go smoothly.

 

[Brock.Ward]

Thanks guys, i had it running for about 20 min last night, no smoke now from the exhaust manifold. Filled it up with coolant she ran about 160-180 degrees for about 20 min but then heated up a little slowly, never really past two hundred, but some white smoke was coming out of exhaust. Engine oil looked great, so I am going to get that impeller fixed tonight pretty sure thats what it needs. Thanks again!

 

[Brock.Ward]

K guys need your help one more time. I got the lower unit off today, impeller was tore to shreds, About 3 fins were completely gone, I found 2 small pieces and thats it, I replaced the impeller off a video i found online and it says with the housing in left hand and impeller in right turn counter clockwise while installing new impeller which I did. Now my question is...where and how can I find the other pieces. Since I have had it running before I assume they are clogged up in the thermostat or where? Any help asap is appreciated as I want to get this done tonight. Thanks

 

[stonyloam]

Look under the front cap of the heat exchanger, the starboard set of tubes should catch anything that makes it out of the outdrive. They will not be in the thermostat because that is a completely separate system, only coolant flows through the thermostat. All of the raw water and impeller pieces flow through the heat exchanger.

 

[Brock.Ward]

just did that sprayed water thru heat exchanger exhaust out let and voltage cooler thing no pieces...im lost.

 

[johnzonh]

The impeller is in Merc Manual #6 page 3B-8 for the diagram. I have the same. easy to get to and pop out... plenty of youtube videos out there on where it is located under the water pump housing. even if it looks 'ok' replace it anyway.... probably has at least developed a 'set' (shaped in direction of rotation) for the peace of mind... replace it.. water pump gasket kits are dirt cheap.

I had resurrected a 3.7 1987 last year from a guy who forgot to pull the drain plug out of the boat before winter...so I dug out 2 feet of solid ice. found out that the exhaust manifold gasket was shot...so when I fired her up every bit of antifreeze in the so-called foolproof closed system went right into the pistons... into the oil... mixed up... came out the top of the breather line from the valve cover ....and the whole back end of the boat was covered in goop. LOL your post about the water in the pan reminded me of that sorry guys

 

[Brock.Ward]

lol well its not doing that it runs great and now I replaced water impeller im about to run it again just want to know im safe from the extra debree from the impeller...

I shot water thru the heat exchanger out the exhaust and all no other pieces, only thing I can think of is they went towards the power steering or are lodged in there which isnt hooked up so i dont care.

 

[Brock.Ward]

got impeller changed, ran it, was smokey inside by exhaust I am just hoping thats cause its been so long since water was thru it and it had crap in it, wife said she saw some black water coming out and it did stink....i am assuming just needs to clean out a bit since it was sitting for four years and prolly was pretty hot since the impeller was shot last time i ran it....

 

[stonyloam]

I shot water thru the heat exchanger out the exhaust and all no other pieces, only thing I can think of is they went towards the power steering or are lodged in there which isnt hooked up so i dont care.

That is not quite the right way to do it. The larger pieces would have been carried through the tube th the heat exchanger and would have been trapped at the inlet of the first set of tubes on the starboard side under the front cover here: https://www.mercruiserparts.com/Show...HEAT+EXCHANGER flushing from the inlet out the exhaust will not remove the debris. The best thing to do is remove the front exchanger cover and remove any impeller pieces (if any) that are there. Any pieces that made it through that first set of tubes probably went all the way through and out the exhaust. If you are careful, you may be able to reuse the gasket. Don't worry, there is only raw water under the cover. Better safe than sorry.

 

[Brock.Ward]

guys back to this issue, got it all running again, new impeller installed lots of water coming out of exhaust looks like it running great, however, the exhaust pipe behind the manifold going down it heating up and smoking bad. At first i noticed the blower plastic was burning off it which could be it still from residue but i dont want to take my chances as i hear crackling and popping so i shut it down. The engine was only at 160-170 and wasnt heating up anymore, any ideas on why it would smoke other than now just burning off the residue, what should the temp be on that exhaust elbow? Any help asap would be appreciate as i am trying to get this going before weekend.

 

[Brock.Ward]

Water flowing from exhaust, new impeller, but exhaust elbow and downpipe smoking

Makes a cracking sound and smokes a lot...noticed blower tube was touching it and melting which could have cause it but it didnt seem like it was getting better when i removed it...water seems to be flowing great, should you be able to touch it by finger quick when water is flowing well? what else could cause it to get that hot but engine is not overheating

 

[GA_Boater]

Which of the 6,000,000+ Mercruiser models are you working on?

 

[Brock.Ward]

Mercruiser 3.7L Alpha one 1987

 

[Bondo]

however, the exhaust pipe behind the manifold going down it heating up and smoking bad. At first i noticed the blower plastic was burning off it which could be it still from residue but i dont want to take my chances as i hear crackling and popping so i shut it down.

Ayuh,.... Got a Picture, yer not makin' alota sense,.....