OMC 4.3L Overheating. Read all the other threads already....

[jpwdesigns]

Hi, I've got a 1986 Starcraft with a 4 barrel 4.3L OMC v6 with a cobra outdrive. Not a stringer or king cobra. Engine sound great by the way, every thing works on the boat amazingly well for age. Only now the problem is overheating.

History:
Bought it 2 weeks ago from guy on craigslist. First time owning a boat
Took it out, overheated.
Found 2 freeze plugs bown out, end cap on oil cooler poped off, and melted impellar housing etc...

I have replaced:
Engine water pump
Thermostat
Impellar Kit and housing
Freeze plugs
Had radiator shop re solder end cap on oil cooler and pressure test it.

Result:
On muffs it works perfectly temp around 150.
In bucket or in lake temp gauge goes up until i shut off the engine.

I have tried priming the intake hose by pouring water down it till its full, and by sucking up lake water and replacing hose on thermostat housing. Makes no difference. Can not get a prime. I've flushed water from intake hose back out, from both sides behind impellor, from thermostat....everywhere. I Cant find any restriction. Like I said, on muffs it works like a champ, why wouldn't it after all, I replaced every damn piece of the water flow but alas, it doesn't work. 3 trips to the lake with the same result has me pretty dejected. I'm thinking to just take it to a mechanic and pay the piper. Last ditch effort here, if anyone has an idea i'd be grateful.

Oh, and i do have a service manual which i've studied religiously along with my forum scouring but still cant identify the problem.

 

[Gettinther]

Re: OMC 4.3L Overheating. Read all the other threads already....

Hi, I've got a 1986 Starcraft with a 4 barrel 4.3L OMC v6 with a cobra outdrive. Not a stringer or king cobra. Engine sound great by the way, every thing works on the boat amazingly well for age. Only now the problem is overheating.

History:
Bought it 2 weeks ago from guy on craigslist. First time owning a boat
Took it out, overheated.
Found 2 freeze plugs bown out, end cap on oil cooler poped off, and melted impellar housing etc...

I have replaced:
Engine water pump
Thermostat
Impellar Kit and housing
Freeze plugs
Had radiator shop re solder end cap on oil cooler and pressure test it.

Result:
On muffs it works perfectly temp around 150.
In bucket or in lake temp gauge goes up until i shut off the engine.

I have tried priming the intake hose by pouring water down it till its full, and by sucking up lake water and replacing hose on thermostat housing. Makes no difference. Can not get a prime. I've flushed water from intake hose back out, from both sides behind impellor, from thermostat....everywhere. I Cant find any restriction. Like I said, on muffs it works like a champ, why wouldn't it after all, I replaced every damn piece of the water flow but alas, it doesn't work. 3 trips to the lake with the same result has me pretty dejected. I'm thinking to just take it to a mechanic and pay the piper. Last ditch effort here, if anyone has an idea i'd be grateful.

Oh, and i do have a service manual which i've studied religiously along with my forum scouring but still cant identify the problem.

#1 Can you or have you put boat in the lake cold then remove the water supply hose coming from the outdrive , where it connects to inlet on the engine end? Start engine while holding that hose and check for water delivery in less than 30 seconds
you should have enough water out that hose to almost fill a 1-2 gallon pail. If you don't then problem is before the engine. remember that on the muffs the water is pushed to the enginethrough both pumps, in the lake it has to be pulled in by the empeller and pushed up to the engine by the same pump.

Hope this helps

 

[jpwdesigns]

Re: OMC 4.3L Overheating. Read all the other threads already....

Hi Thanks Getinther. Yes I did try that and did not get the correct water flow. I do believe the problem is on the outdrive side, or at least Pre- oil cooler. Problem is I'm sure the impeller is in there correctly but not sure what i need to be looking for now.

 

[Gettinther]

Re: OMC 4.3L Overheating. Read all the other threads already....

Hi Thanks Getinther. Yes I did try that and did not get the correct water flow. I do believe the problem is on the outdrive side, or at least Pre- oil cooler. Problem is I'm sure the impeller is in there correctly but not sure what i need to be looking for now.

possibly try running a wire down the hose and check for blockage, if nothing then i'm afraid your back to the impellerbut I do believe there is a seal or o-ring that you need to be careful of how it is assembled or your problem could be the end result

 

[jpwdesigns]

Re: OMC 4.3L Overheating. Read all the other threads already....

I can try the wire thing. I'm pretty sure my problem doesn't stem from blockages because i can backflush with no apparent ristrictions and the thing cools like mad with the muffs on. I have heard in other forum threads people talking about "sucking air" but i'm unclear where i'd go to look for leakages.

 

[Maclin]

Re: OMC 4.3L Overheating. Read all the other threads already....

On those drives the impeller drive shaft can shear under stress, it is right on the end of the main driveshaft coming into the upper housing. Unfortunately I do not know the correct procedure to check or r&r that impeller setup, but if you can turn the impeller by hand at all then it is probably not getting driven..

 

[Maclin]

Re: OMC 4.3L Overheating. Read all the other threads already....

Sorry, more doom and gloom to dispense, but freezeplugs popped out means a hard freeze and the passages inside the block are probably cracked, and will fill the crankcase with water as the engine heats up and those come under pressure. Those plugs are really casting plugs and not "feeze" plugs, and cannot really save anything. After casting and the engine is in use they simply become an indicator that the block went thru a hard freeze.

Have you checked the oil? or changed it yet?

 

[HCMQA]

Re: OMC 4.3L Overheating. Read all the other threads already....

It really sounds like the raw water pump
Take impeller housing off and have a helper briefly bump the starter. does it spin?
Make sure you look at a parts picture/blow up of the order of things when putting the housing back together.

My guess is the impeller is not turning. Could the wrong one, installed incorrectly and sucking air, or the drive shaft is broken.

 

[jpwdesigns]

Re: OMC 4.3L Overheating. Read all the other threads already....

It really sounds like the raw water pump
Take impeller housing off and have a helper briefly bump the starter. does it spin?
Make sure you look at a parts picture/blow up of the order of things when putting the housing back together.

My guess is the impeller is not turning. Could the wrong one, installed incorrectly and sucking air, or the drive shaft is broken.

Hi, Thanks for the comment.

I'm sure the impeller is turning. every time i've pulled the housing since installing on Friday it's been in a different spot. So it is rotating.

Drive shaft is ok. I can drive the boat when in the water. It runs fine except for the cooling issue we're working on.

I double checked with the store I bought the impeller from to make sure it was the correct for my boat and he assured me it is correct. It also is identical to the burned one I pulled off before installing the new one. I also obeyed the manual explicitly when installing the impeller and housing except i did not remove the Adapter and the stuff behind it. See pic:


This is a video also showing where the water is coming out during idle with muffs. Is it normal? http://youtu.be/Kfm3Ig0_us8

 

[jpwdesigns]

Re: OMC 4.3L Overheating. Read all the other threads already....

Sorry, more doom and gloom to dispense, but freezeplugs popped out means a hard freeze and the passages inside the block are probably cracked, and will fill the crankcase with water as the engine heats up and those come under pressure. Those plugs are really casting plugs and not "feeze" plugs, and cannot really save anything. After casting and the engine is in use they simply become an indicator that the block went thru a hard freeze.

Have you checked the oil? or changed it yet?

Well, i'm not an engine expert but i've done a fair amount of work on engines and from all i can tell and from what it sounds like and since there is no water in the oil i'd say that the block is fine.

 

[jpwdesigns]

Re: OMC 4.3L Overheating. Read all the other threads already....

On those drives the impeller drive shaft can shear under stress, it is right on the end of the main driveshaft coming into the upper housing. Unfortunately I do not know the correct procedure to check or r&r that impeller setup, but if you can turn the impeller by hand at all then it is probably not getting driven..

I can not turn the impeller rod by hand. going to go check it with the starter bump and housing off as recommended by HCMQA just to be double sure....

 

[jpwdesigns]

Re: OMC 4.3L Overheating. Read all the other threads already....

Here is the test for the impeller drive shaft. Turning like mad. http://youtu.be/mEiZ8zGBq4o

Here is also a new development. This time when I took off the housing the impeller is obviously not in there right. first time to see it like this in like 4 times taking it off and checking it. What's that about?

For some reason the water from muffs is re-positioning the blades of impeller i think.

 

[jpwdesigns]

Re: OMC 4.3L Overheating. Read all the other threads already....

Another odd test.

I lowered the outboard into a bucket up to the anti-cavitation plate, put the muffs on started her up. Waited until it was normal running temp, 180 ish. Pulled off the muffs with outboard still in tub of water and it kept cooling normal no rise in temp. Put my hands on the intakes and could feel the suction. Next I turned off the engine and waited a couple of minutes. started it up and this time it wouldn't cool.

So, its not getting primed by itself.

I also thought it strange that I was getting significant air coming from the little exhaust tube which normally connects to the impeller housing. While the engine was running during second part of this test...the fail... I pulled that little hose to see if there was any water coming out of the impeller housing drain like normal. This time nothing was coming out but the tube on the outboard side, not the impeller housing side was blowing air from exhaust i guess. I don't see how that should be happening because when running with the muffs water is moving out of the impeller housing.

 

[Maclin]

Re: OMC 4.3L Overheating. Read all the other threads already....

On one of your youtubes I saw the impeller shaft turning. That is part of the driveshaft itself, and is what I was worried about, so that is good. Just double check all of the washers, orings, etc. in the impeller pump housing. It appears to be getting water if it is shoved into the grates under pressure, so my guess is that something is not kosher with the impeller housing innards and sealing.

 

[daman4469]

Re: OMC 4.3L Overheating. Read all the other threads already....

Check those risers....and take that thermostat out! Mine gave me problems for years, even when I would replace it, and I removed it a few years ago. Runs nice and cool ever since, with no cooling issues. Some may disagree, but I chased that issue around for a long, long time and thermostat removal solved it.

 

[jpwdesigns]

Re: OMC 4.3L Overheating. Read all the other threads already....

Check those risers....and take that thermostat out! Mine gave me problems for years, even when I would replace it, and I removed it a few years ago. Runs nice and cool ever since, with no cooling issues. Some may disagree, but I chased that issue around for a long, long time and thermostat removal solved it.

.

Are you saying that removing your thermostat solved a problem of getting your impeller primed? Because that is my issue. I can start my engine on muffs, pull them off with the outboard still in a bucket up to the anti cavitation plate and it will work well. I can even turn off the engine and start it again 30 seconds or so later and it will still work. If I wait 10 min it will have lost prime and not be able to suck up the water. My issue is with prime. Not thermostat as far as I understand it. If you're saying i can yank the thermostat and get prime easier i might try it.

 

[sea wolf]

Re: OMC 4.3L Overheating. Read all the other threads already....

Pull the impeller housing & pry off the satinless steel plate. It it's warped or scored badly, replace it. Sometimes u can turn that plate around & reuse it but if it's warped, forget it. Match up the plate with the impeller housing with the o-ring gasket in place. If there's a gap, the plate is warped which will cause the pump to suck air. Do not remove the t-stat as someone suggested.

 

[HCMQA]

Re: OMC 4.3L Overheating. Read all the other threads already....

Water is coming out of all the correct places when you are on the muffs because the hose is pushing the water in.

simply your impeller is not priming.

Warped case, backer plate etc allowing air in.
rubber seal not in correct place when installed
inside of impeller not fitting properly to drive shaft impeller drive end so it is not turning. Look inside your current impeller and make sure it has the triangle indent that fits over the drive shaft.

Another thing is when the engine is running with the muffs on and you pull that little hose off the side of the impeller housing water should be coming out of there like a gun. If you give it a little gas it should really blast out of there. That fitting is basically a tell tale of sorts and it will let you know that the impeller is doing its job.

The reason you can take the muffs off while in the bucket is now the engine water pump is doing the work. After a 10 min soak it loses its prime.

Water and exhaust only come out of the prop hub when you really get on the the throttle.

Lastly 180 is a little high do you have an auto stat in there? It should be 160. You should only get to 180 after a bunch of WOT runs towing a tube full of drunks.

 

[jpwdesigns]

Re: OMC 4.3L Overheating. Read all the other threads already....

Pull the impeller housing & pry off the satinless steel plate. It it's warped or scored badly, replace it. Sometimes u can turn that plate around & reuse it but if it's warped, forget it. Match up the plate with the impeller housing with the o-ring gasket in place. If there's a gap, the plate is warped which will cause the pump to suck air. Do not remove the t-stat as someone suggested.

Sea wolf, thanks for the comment. I think i'm ok there because the plate is brand new with gasket behind it and sealing compound on both sides of the gasket. I bought a complete impeller kit with the housing.

 

[jpwdesigns]

Re: OMC 4.3L Overheating. Read all the other threads already....

Water is coming out of all the correct places when you are on the muffs because the hose is pushing the water in.

simply your impeller is not priming.

Warped case, backer plate etc allowing air in.
rubber seal not in correct place when installed
inside of impeller not fitting properly to drive shaft impeller drive end so it is not turning. Look inside your current impeller and make sure it has the triangle indent that fits over the drive shaft.

Another thing is when the engine is running with the muffs on and you pull that little hose off the side of the impeller housing water should be coming out of there like a gun. If you give it a little gas it should really blast out of there. That fitting is basically a tell tale of sorts and it will let you know that the impeller is doing its job.

The reason you can take the muffs off while in the bucket is now the engine water pump is doing the work. After a 10 min soak it loses its prime.

Water and exhaust only come out of the prop hub when you really get on the the throttle.

Lastly 180 is a little high do you have an auto stat in there? It should be 160. You should only get to 180 after a bunch of WOT runs towing a tube full of drunks.

Hi HCMQA. Thermostat is this one http://www.iboats.com/Mallory-Thermostat-Kit-9-43156/dm/view_id.365177 Maybe there's some other issues of corrosion or something that is slowing down circulation but i'll get to that once i can get the bugger to reliably start cooling. Probably will need to pull the manifolds etc...

interesting thought about the engine water pump doing all the work once started in the bucket. I wonder if I can test that theory to see if the impeller is doing anything. I just have a hard time accepting that it could be the impeller cause the whole kit is brand new. any idea how i could test for air leaks? Drop the back end in the lake and disconnect the intake hose from thermostat housing and blow while someone looks at outboard to see where bubbles come from? From visually inspecting the impeller housing and oring its perfect. no water ever escaping from around the housing either.