Engine getting hot

[stancalame]

Had a wierd day. Finally got my shifter back together and was double checking timing with boat in water but on boat lift. Water intake was below the surface. I just replaced impeller and seal in early sping and its been running great, rarely getting over 160F. I diconnected the water line that comes in from the transom and feeds the circulating pump and there is no water being delivered to the circulating pump from the impeller on the back of the upper housing. I back flshed and observed water going our the starbord side of the lower gear housing. I placed muffs on the water intake and observed water coing out of the port side wter passages, the side that feeds the impeller. So best I can tell, I do not have any blockages. The only thing I know to do is replaced the seal on the water impeller housing and new gasket. When I took of the impeller housing the oring seal was town in two places but I may have torn it when taking it off. Any ideas or coaching while I chase this problem? Any insight?

 

[stancalame]

Additionally, I notice my hoses are pretty worn but a couple of hoses are not available. Will auto hose work? The two hoses specifically that show no longer available are part 0913769 Cooler to thermostat hose and, and part 0914807Water pump to thermostat?hose. I assume the water pump to thermo is same as auto engine? I assume hose form cooler to thermo is marine specific?

 

[GA_Boater]

And you're working on a ???

 

[stancalame]

Sorry, 1991 OMC King Cobra 5.7, Model 574APERGD, Chevy 350, in a 1992 Galaxie I/O bow rider

 

[stancalame]

Any thoughts on what else could be preventing water from getting to impeller? I suppose everything has to be airtight since the impeller is self priming. I noticed that when I took impeller housing off the that the vent tube came unplegged from the housing. At least it looks like is unplagged. Does not apprear that it is broken but you tells me. Impeller housing is part 986272 sics pics of housing and close up of vent tube.

I read alot of posts on overheat with insufficient water supply to circulating pump,and someone exerienced the water tube or seals going bad in the lower housing that feeds water to impeller. If I break down the drive what seals do I need to order to replace? Looks like water tube is NLA.

Am I missing someingthing. I've confirmed water passages from intake through hose to recirc pump are open.

 

[HT32BSX115]

Any thoughts on what else could be preventing water from getting to impeller? I suppose everything has to be airtight since the impeller is self priming. I noticed that when I took impeller housing off the that the vent tube came unplegged from the housing. At least it looks like is unplagged. Does not apprear that it is broken but you tells me. Impeller housing is part 986272 sics pics of housing and close up of vent tube.

I read alot of posts on overheat with insufficient water supply to circulating pump,and someone exerienced the water tube or seals going bad in the lower housing that feeds water to impeller. If I break down the drive what seals do I need to order to replace? Looks like water tube is NLA.

Am I missing someingthing. I've confirmed water passages from intake through hose to recirc pump are open.

Howdy,

The pump primes because when at "rest" the pump is pretty much submerged. when you start out, if there's no leaks, it'll stay primed. If there's a leak anywhere between the water pickup and the pump, it'll start pulling air.
Looks like the seals are still around... I found "0986176 GUIDE & SEAL, Water tube" (#35 below) on ebay. If you think you need one of those, I suggest you buy it now!

It appears the upper seal (#48 below) is available from more than one source

If the tube is bad, you may have to improvise or find a used one.

You won't know until you drop the lower so you can look inside.

These parts don't usually leak on their own. If you've ruled everything else out, you need to look in there,

Regards,

Rick

By the way you can find the above pictures and part numbers at http://epc.brp.com

 

[stancalame]

Thanks Rick
I've done some more reasearch and talked to a marine mechanic who is familier with OMC. He tells me that my manifolds could be leaking exhaust into my colling water passages and cuasing back pressure that prevents the cooling wat from arriving at the engine. I have read on this forum and seen you tubes on testing the manifolds with acetone. From the master "Don" I read that Acetone has lower surface tension than water so it will seep through cracks that would requre 20 psig with water. Any thoughts or comments on this? Thanls for providing the part numbers. I had already begun looking them up :biggrin1:.

 

[HT32BSX115]

talked to a marine mechanic who is familier with OMC. He tells me that my manifolds could be leaking exhaust into my colling water passages and cuasing back pressure that prevents the cooling wat from arriving at the engine..

Probably not. That's an open cooling system with little or no exhaust back pressure. The least resistance for the exhaust would be right out the exhaust.If the manifolds are leaking cooling water, that water will just be blown out along with the exhaust gases.

In that case, the problem would be immediately after shutdown. Water remaining in the manifolds and risers would run back through any cracks into the exhaust ports and into any open exhaust valve causing a temporary hydrolock during the next start attempt.

By the way, tell me a little more about how your overheat is manifesting itself. Does this happen during normal operation or only when on the boat lift?

If you have the boat partially lifted out of the water, the with the water level well below the raw water pump,........I.E. with the drive ONLY in the water far enough to cover the water intake, not only will the raw water pump NOT prime and pump water to the engine, but if you tried to run it that way more than a few min, you likely have destroyed your raw water pump impeller.

The raw water pump will only prime when submerged (like when the boat is sitting at rest......note that top of the drive is nearly under water and the raw water pump would be below the surface of the water)

So before you do anything else, I would suggest that you remove the raw water pump housing and carefully inspect the impeller.

If it's disintegrated, you'll need to replace it and locate all the debris downstream. (if you have an oil or power steering cooler, some or all of the pump debris may be lodged there.

 

[stancalame]

Now you have my wheels turning. THe problem did occur when the boat was lifted and only intake in water. However I did connect muffs with hose and didnt get prime. I pulled impeller and thankfuly all good. I'll reinstall but the rubber oring is quite flat and not sure it wil seal. I'll givei it a shot and see what happens. Thanks for the explanation on the exhaust. I was hoping it was not the issue becuase it not in my very marginal budget. I'll post back with results.

 

[Lou C]

A couple of small points that may be important:

​when I replace a Cobra impeller, I will run the boat on the water muffs with the plastic cover that goes on the rear of the upper drive off, and make sure there is no water leaking round that gasket, if so then air could also be pulled in....
​also, that vent hose, and the fitting in the impeller housing must be open, (blow out with compressed air) because I think that it helps allow the pump to prime, by letting air OUT and water IN when you submerge the drive in the water....

​What the mechanic said, about exhaust gas heating the cooling water does not make sense, unless it was a closed system, where you could have that as a potential issue. In an open system, the cooling water is quickly exiting the exhaust whenever the engine is running. HOWEVER, it is possible for a leaky head gasket to put hot gases into the cooling water and this for sure can cause hot running. With an open system this can be hard to diagnose, because you can't just look in the recovery tank for bubbles like in a vehicle with a closed system. I actually rigged up a way of doing this, using a spare thermos housing, the hoses for the manifolds and 2 funnels (to keep the cooling system completely full) when I was researching my water in the cyl issue and it was pretty simple and told the tale right away.....
I took the 'stat out of this housing
then put 2 lengths of hose on the nipples that would feed the manifolds
​Taped them together so that they stood straight up
​stuck a funnel in each one
Filled them up with water
​started engine and let it come up to about 150* (checking exhaust to make sure it did not get too hot)
​shut off engine. in a few secs got a lot of bubbles on the starboard side, a bit less on the port, this to me showed that exhaust gases were getting into the cooling water, from either a blown HG or cracked head. Dis assembly showed it to be the former.....

 

[Lou C]

here's a crude pic, that I copied off the net (haven't put all my old pix of my engine on my new computer yet).....

 

[HT32BSX115]

Now you have my wheels turning. THe problem did occur when the boat was lifted and only intake in water. However I did connect muffs with hose and didnt get prime. I pulled impeller and thankfuly all good. I'll reinstall but the rubber oring is quite flat and not sure it wil seal. I'll givei it a shot and see what happens. Thanks for the explanation on the exhaust. I was hoping it was not the issue becuase it not in my very marginal budget. I'll post back with results.

As usual, LouC is SPOT ON!

One other thing you might consider is......If the risers haven't been removed and the (riser) gaskets replaced, you might consider doing it. AND if you're operating in salt, you should absolutely do it.

After time those gaskets can leak (always at the wrong time) once the gaskets are off and the surfaces clean, you can use a "straight edge" to check for flatness. because if they're not flat, they could leak after new gaskets are installed. ( I even used a belt sander to clean up both surfaces. BUT be careful! you can quickly take too much off!!)

Also, you can inspect the raw water cooling pasages (what you can see) to determine how clogged both the manifolds and risers are since the point where they come together is usually pretty narrow.

Lou didn't you post some "rusty" and "not-so-rusty" riser pictures on another post sometime back for a comparison?.

 

[Lou C]

Yep I did, gotta put all my old pix on my new 'puter that I finally got after my 2009 Dell quit connecting to the 'net (horrors, it had windows vista on it) lol....

 

[bruceb58]

Now you have my wheels turning. THe problem did occur when the boat was lifted and only intake in water.

That's your issue. The water level needs to be over the pump when the boat is not moving. Hopefully, that didn't ruin your impeller.

 

[stancalame]

Well I feel pretty dumb but I learned a lesson. As you indicated Bruce, I lowered pump in water and prest, water circulation. I happen to have the old seal that I'd kept from last time and with a good coating of OMac gasket compound I was able to entertain my friends on the lake! Now that I think about it it make total sense.

I also realize that I need to drain that pump housing in winter. I've had the boar 3 years and never drained it. I'm lucky living in North Texas where we do t get much freezing weather. Thanks for all the help from the group. The other benefit is that I read the entire section in my manual on the cooling system. I have a much more comprehensive understanding of the he cool I g system. The boat has s running as good as it has ever run.

I think I do ha ea blown power valve on carb but I'll pick up on the other string I have going.

Hope you all had a safe and festive 4th! It's great to be free to work on my boat and be on the lake!

 

[Lou C]

When you winterize it, an easy way to get the water out of the impeller, is to:
​1) put the drive all the way down
​2) disconnect the raw water intake hose at the thermos housing, point it down in the bilge to drain
​3) Hold the hose up, put a funnel in it and fill the hose with -100 Marine antifreeze till it comes out the drive water intakes
​4) some people will hit the starter for a split second to turn the impeller a tiny bit to make sure all the water drained, I have never done that and we get freezing weather down to zero F and have never had a problem with water cracking the plastic housing.....