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3.0L OMC overheating issue

R

Ryanscolo

Member
Aside from the other issues I am having with the cranksshaft needing replaced or at least worked on. Which it just so happens we are going home this weekend and my dad knows the right machainc.(keep your fingers crossed) When I took the boat out last sunday before the cranshaft started knocking I was having a cooling/overheating issue. When I ran it at idle RPMS the engine would stay at 180 degrees but the second that I would get it up to speed (3 or 4,000 RPM's for 25 seconds...the temp would go up to the redzone....so I would back off, it would cool back to 180....

What should I do, my dad thinks the water is flowing through to fast.....others think its not flowing through fast enough....should I just get another thermistate? A completely other thermistate unit??

Sorry for the bad spelling, I'm doing this at work...dont want the boss to see me LOL.

Any help would be awesome!

Ryan
 
When was the last time the drive water pump impeller was changed (is this a Cobra?) those pumps kind of change characteristics as they speed up, starts off as a displacement pump and switches over to a centrifugal as it speeds up, you could have worn or cracked/missing vanes in there.
 
Ryanscolo said:
dad thinks the water is flowing through to fast.....others think its not flowing through fast enough....
Click to expand...

sorry dad. the "others" win this one.

what Bob said: impeller in the outdrive

how do you know your crankshaft has issues? a hundred different things can make a knock.
 
Well usually i say start with the impeller in the drive, replace and then run the boat still overheating do the t-stat.

In your case i would yank out the t-stat leave it out for now close up the housing and run it on the water. No more overheat you found your problem.

Now say the t-stat is good, and the impeller is good then you have a problem down stream.

But first lets do some research and you can do this on the trailer. Put water to the drive, remove the long hose that goes to the t-stat housing, from the transom, just loosen the clamp on the long hose that connects it to the t-styat housing and hold the hose straight up. Start the boat, how high is the water shooting ?

Should shoot straight up about 12-18 " Do this for about 4-5 seconds and shut off the motor.

Good water to the t-stat housing ? No there is a clog before the t-stat housing understand.

Could be the impeller broke up in the drive and is blocking the hose at the transom then you will have to get the clamp at the transom loose and remove the long hose from the transom. You can do it, take your time and think, think, think before you do anything.

Ok you have the hose off, did alot of pieces of rubber fall out ? Thats your impeller. Bad thing, bad, bad, bad thing understand ?

Clear the hose ??? No rubber pieces, good thing. Understand ?

Ok no rubber pieces put back on the hose at the transom tight clamp. Only use a screwdriver and not a socket you can destroy things.

Take a garden hose and backflush the long hose to the transom. You want to see what comes out of the drive understand maybe backflush the hose with the drive in a bucket.

The backflush wash anything out ? Only you will know and maybe your dad cause i ain't there, look see what came out.

Ok say it's clear. No little rubber pieces.

The t-stat is good or new or not in there cause you yanked it out and left the houisng with no t-stat for now and there are no little pieces of rubber clogging the t-stat housing cause you looked and put your finger in there and checked.

Whats the oil look like ?

Go ahead run the boat on the water.

Does it still overheat?

If you find rubber pieces DO NOT RUN THE BOAT ! DO NOT RUN THE BOAT !

You have a impeller in the drive that broke apart, UNDERSTAND.

We can walk you thru replacing it. It's easy.

What year is the boat you left that vital piece of info out. Don't know ?

Look at the transom numbers the last 2 will tell you the year. If you post back please include year.

Understand grasshopper ?

please post back what you find.
 
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I have a 1981 Formula Thunderbird 3.8L omc i/o with the same issue. just to clarify myself 4 hoses come off the tstat housing 1 to each manifold one to the circ pump and the inlet correct? ok pulled the inlet hose (wich is bigger than a garden hose) faced it straight up and started it up for 5 seconds we shall say 1/2 inch to an inch of water shot out of the hose. meaning the pump isnt pushing enough water correct? what is involved in replacing the pump? does the whole stern drive need to come off as the seloc says? Thanks for your input fellas
 
have a table or a large cooler or chair ready on the port side.

on a trailer lower the bow as far as it will go, and raise the drive 1/2 the way up.

Remove the very top bolts, and the exhaust and the lower will come down. place it on the table and tie it to the swim platform. be carefull of the cable don't pull on it plenty of play in the cable.

remove the 4 bolts facing u in the upper drive from the bottom and the whole waterpump and shaft will come out. you could raise the drive a little more to make it easy, i sit on a milk crate when i pull the pump.
 
ok when you are speaking of the very top bolts are you meaning the trunion caps? Oh and by the way its an 83 instead of an 81 but still a non cobra omc. just confused on which bolts to remove lol. Thanks for your help!
Bob
 
all the way on top of the drive, THE 3/8TH ONES I THINK THEY ARE.

The lower and the exhaust housing will drop be ready. There is a very large dipstick hole 3/4 i think.

If your alone you can stick a little cooler under the skeg to hold it.
 
Ok got the water pump out trouble is it looks like its in pretty good condition.im gonna replace it just cause I have it apart though. Any other ideas?
 
make sure you use plenty of blue permetex around the body of the actual water pump housing, make sure you get the tru bolts sealed also.

Check the splines on the water pump shafts and use SPLINE GREASE.

Ok how does the t-stat look. For now you can remove it and run it without a t-stat.

Still over heating? Remove the riser, it clogged up ?

With the riser off look down the exhaust tube, have a flapper / shutter broke off and is clogging the exhaust?

With the drive fully up shine a light up the large exhaust hole, got a flapper stuck up there.

Look in the back of the drive got the flapper stuck in there.

Ok before removing anything, put water to the drive, remove the long hose coming from the transom that enters the t-stat housing hold it straight up, start the motor how high is the water shooting, steady stream ? 3-4 seconds is all you need to see it, shut off the motor.

Good water to the t-stat, means you have a blockage at the t-stat or after, no good water to the t-stat means the blockage is before the t-stat.

Understand ? If not reply and i'll go thru it again maybe i wasn't clear with something won't be the first time.

And if you want send me a e-mail with a # i'll call ya.
 
Ok got the water pump kit and goodies today figured out the direction of the shaft so I can put it all back together and bam stopped again.. The big o-ring that comes with the kit doesnt fit anywhere the tech drawing has it listed in between the impeller plate and housing. well It doesnt seem like that is right its to big to fit there the inner diameter of the o ring is bigger than the circumfrence of the plate.any advice?
 
yeah because that o ring is looks it fits around the impeller housing. ok permatex on both sides of the stainless impeller plate how bout where the impeller housing meets gearcase?
 
don't need it on the ss plate on the inside. where it meets the top put a good amount or really the bottom cause it goes in the bottom is where the ss plate goes.. The housing where it splits and yes all around the housing where it meets the drive. Thru bolts.

It's a g-d damn powerful pump, Known weak link that is so powerful can pump into the gear oil.
 
ok new pump sealed installed and pumping water but still doesnt seem like enough from the the t-stat inlet so i traced the inlet hose back to what looks like a filter?took the hose off of the transom side of it and there is definetly more flow out of that hose 3-4" compared to water just rolling out with the hose facing up at the inlet. Boy the seloc says the shaft rotates clockwise lol but not wich way your looking at it....had to have someone watch the ball gear while I hit the starter a few times to find out when looking at it from the rear at the bottom of the upper gear case it rotates counter clockwise had to figure wich way to install the impeller vanes....gonna check the tech diagrams to find out what this filter looking thing is lol.
 
i got no f--king idea what that filter is throw it in the garbage.

Don't you dare put it back on. You sure it's not a heat exchanger ?

Power steering fluid cooler maybe ?
 
Any heat exchanger i hate, hate, hate, on boats.

Did i say i hate them ?

In saltwater i hate them twice as much.

HaH leave it off. What is your boat used in cause you didn't put up a location.

Did i say i hate when people don't put a general location up.
 
lmao ok im in ohio and freshwater only but I was looking at the original owners manual and saw some records from Key Largo! nice place but kinda salty lol not sure how long it was there but the guy said the motor had only 15 hours on it from being completely rebuilt and then one day it started overheating at high Rpms and had dumped so much money in it already and he just winterized it and put in storage.
 
Ok Im beleiving the water pump wasnt my problem in the first place... You know the hole where the grease fitting is for the swivel housing? Im gonna take a shot and say water isnt supposed to come out there huh?
 
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ok while searching for answers on the information superhighway I came across one of your threads that you were helping someone on. The drive has to be fully down to pump water? please tell me im an idiot and this is why its not working lol. it wasnt all the way down when I tried it but it wasnt all the way up either.
 
I pmed you back I was so disgusted after seeing it not pumping again so I took the leg off again but then thought about it and stopped ill put it back on when I get out of school and test.
 
ok 3 pm i'll call got it in my cell phone. I will repeat over the phone what i write in the post.

The stringer drive must never be run in anything but the full down position.

The stringer drive must never be run except with water going to the drive.

Merc is the same but even less able to take running without water going to the drive.
 
Ok I have found out just how hard it is to find manifolds for this boat lol. Bought 2 used risers that look in beautiful condition for 75 a piece. Manifolds are proving harder to find, Doug russel marine has them for 835.00 for one side and 353.00 for the other :-( thats all I could find so far. keep ya posted
 
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