OMC 460 cooling system issue?

[lekmedm]

Hi there!

I have a Cobra 460 (bought last year) and this weekend I replaced the impeller and all water pump parts in the outdrive with a kit, but when I started it up on muffs, I was not getting any water returning through the prop (and I'm not sure how much water was being sucked it). I'm sure the impeller was installed correctly. When I winterized, I drained all the water from the block and outdrive. I only ran the engine for a few minutes and shut it off for fear of overheating. It did not reach normal operating temperature (only about 100*F). Am I worried over nothing because I didn't let the engine run long enough for the water to circulate through, or is there a blockage somewhere?

 

[HT32BSX115]

Re: OMC 460 cooling system issue?

Hi there!

I have a Cobra 460 (bought last year) and this weekend I replaced the impeller and all water pump parts in the outdrive with a kit, but when I started it up on muffs, I was not getting any water returning through the prop (and I'm not sure how much water was being sucked it). I'm sure the impeller was installed correctly. When I winterized, I drained all the water from the block and outdrive. I only ran the engine for a few minutes and shut it off for fear of overheating. It did not reach normal operating temperature (only about 100*F). Am I worried over nothing because I didn't let the engine run long enough for the water to circulate through, or is there a blockage somewhere?

Well, there might be a blockage somewhere. Hard to say not being able to see it.

Did you look for pump remnants down stream of the pump?

yes 100* is not really long enough to even check. You should get water under the drive after you give it time enough to fill the block, manifolds and risers.... It doesn't all go out the prop. There's also "slits" in the most exhaust bellows that you should see water coming out of also.....so very little water will actually make it to the prop at idle.



you can check pump operation by removing th hose from the transom and starting the engine. There should be a fairly strong stream of water pumped from the hose. If it doesn't pump then you have a blockage somewhere between the pump and the hose connected to the transom. from the transom it should go to the oil cooler and PS cooler. you could have blockage there too.

You'll just have to check those components. If they're clear, then you may have blocked manifolds, risers, thermostat housing, heads, block, the list goes on.

If you need manifolds and risers, well, I feel for you.


Regards,


Rick

 

[lekmedm]

Re: OMC 460 cooling system issue?

Thanks for the reply, Rick. I will follow up with some diagnostics. I am being ultra careful exactly for the reason that I have the 460 Cobra which is running nicely right now, and I want to keep it that way, so I don't need overheating problems. I'd rather check 3x and ask questions 10x before I ruin the engine.

 

[HT32BSX115]

Re: OMC 460 cooling system issue?

You didn't say whether it's run in salt or not, closed cooled, etc.

Are the manifolds and risers "old"? Risers can get so clogged with rust that they can get almost completely plugged.

Since the risers are the only path for cooling water to get out of the engine, when they clog, the engine overheats because there's no flow thru the engine, or heat exchanger. (closed cooling or not)


Find the hose that comes out of the transom/gimbal.

On the Cobra, it is a 3/4" or so steel tube. (OMC gray)

There's a hose connected to it that usually goes to the PS and/or oil cooler and then goes to the T-stat housing (raw cooling) or the heat exchanger (closed cooling)

If you disconnect it and run the engine briefly you should get pretty good "flow" of water.

If the boat is in the water, you can use a small piece of plastic pipe and a long piece of hose over the gunwale to observe the flow while the engine is running. When you're in the water at rest, the raw pump is effectively submerged so there's no problem with pump priming.

When you start the engine you should have a pretty good stream almost immediately.

 

[lekmedm]

Re: OMC 460 cooling system issue?

My apologies for not being more thorough with background info...

The boat is/has been run in salt water. I have had it since last year, and everything seemed to run more-or-less ok back then. There might have been the hint of overheating under WOT, but I'm not sure. I had other issues with tuning the carb and adjusting the shift linkage that kept me distracted from any other things going on. The engine was rebuilt approx. 5 years ago (it has 200 hours on it). I don't know what that means for the manifolds and risers. How do I tell how old they are? Can they be cleaned out somehow? The system is raw water cooled. (I know, I know... everything's against me in this situation.) The boat is currently out of the water and will stay that way until I am sure of it mechanically. The marina charges $200 to have it pulled out to work on it! I want to avoid that, if I can.

 

[HT32BSX115]

Re: OMC 460 cooling system issue?

Oh boy!

Well,

I wish I (we, iBoats community) had gotten to you before you bought that boat. (same thing happened to me.....see my signature below) I was very lucky in that I found a replacement Merc engine/drive and was able to sell all the OMC stuff.....No matter.......you have it now. You need help!

I do not want to scare you. But you NEED to know that you have a sterndrive system that has very limited support (parts & service) available. That engine/drive combination was only offered from 1987-1990 and OMC went away in about 1999 or so. The "After-Market" supports most other OMC stuff pretty well. They don't support the 460 King Cobra too well at all...



The manifolds for your 460 are very scarce. Doug Russell Marine does have manifolds I think........ There may also be someone actually making them now. 2 years ago they simply weren't available.....as was the coupler. Both are complete show-stoppers!

That's an ebay link above. click it and you'll see the ebay auction they have for manifolds. It's been there for a long time and they always indicate that there's only "2 available" If you intend to use that boat in salt and the manifolds are 5 years old it would be VERY prudent to have a spare set of manifolds on hand. If they leak they'll ruin the engine in short order (if it sits for any length of time before being repaired)

Your risers may also be plugged with rust as I indicated earlier. [No. They cannot be cleaned, they must be replaced] I don't how available risers are. (I just sold my nearly new set of risers recently) I don't have but a few parts left (power steering stuff) I sold everything else removed from my Four Winns Liberator.

My suggestion to you is that, if you intend to keep the boat and use it in salt (raw water cooled) you need to get new manifolds and risers NOW. If you don't need them right now you could need to replace them in a few short years.....and they may not be available then....


In either case, if your risers have not been removed and checked recently, it might be a good idea to remove them and check for blockage. Get some new riser gaskets. They must be replaced anytime the risers are removed for any reason.

Do a search here, there a several threads where people ask how "long will my manifolds/risers last", raw water, salt, etc.

They'll go quite a while when used in salt, if flushed immediately after use.

If you leave it in the water for extended periods of time, they don't last as long...

If you have an emotional attachment to the boat, start looking NOW for a good condition Mercury or Volvo engine/drive to replace what you have. That's your best bet in the long run.....

Sorry about that,


Rick

 

[lekmedm]

Re: OMC 460 cooling system issue?

Yep, I know all about those issues (now). In all honest, I don't know if I'm going to keep the boat. I'd like to see how this season goes. I'd just like it in good working order.

One thing I might add to the condition of the boat/engine is that both the previous owner and I dock the boat on a river and not in salt water all the time, so on the way back to dock the whole cooling system gets flushed out with fresh water.

 

[HT32BSX115]

Re: OMC 460 cooling system issue?

Running thru fresh water last... will definitely help with engine/manifold/riser corrosion in the long run but it doesn't eliminate it altogether (like closed cooling might)

You may still have rust blocked risers..... which could cause an overheat condition....it's a slow process.....the blockage increases as the rust slowly closes off the discharge.......You will sometimes get hot-spots on the risers indicating where the cooling water is NOT flowing.....


Since you really didn't run it long enough to determine if it is indeed overheating, you should run it with a known source of water before you start taking things apart.

Also make sure you have a good raw water pump and all the hoses to the engine are clear of debris.


If it was starting to overheat at WOT, it could be the raw pump ( or raw pump remnants clogging the water passages), or a clogged raw water pickup etc....and the clogged risers as indicated above.....


Regards,


Rick

 

[lekmedm]

Re: OMC 460 cooling system issue?

Well, I finally had a chance to go to the boat and continue this saga...

So as I might have mentioned before, I have rebuilt the stern drive water pump. This time I disconnected a hose from the PS line and can confirm a good steady stream of water coming through (at least I think it was a good stream - it's not like it was gushing all over the place). I let the engine idle for several minutes, but when it reached 200*F this time, I shut it down. It is my understanding that at idle such an engine should be at 160 - 170*F. What are the odds that the thermostat might be stuck or opening very late? I am trying to eliminate all possibilities before I consider the dreaded manifold replacement option. Could I toss in an automotive t-stat to test, or do I need a marine one? Could there be an issue with the water pump on the engine? If the manifolds are still suspect, would removing the end caps and checking water flow help in diagnosis without taking apart the manifolds?

 

[HT32BSX115]

Re: OMC 460 cooling system issue?

Those manifolds have END caps? (those aren't log style manifolds are they?)

(you mean the rubber caps on the back of each manifold?)

Do you know how old the manifolds and risers are?

If you have GOOD water flow, you're zero-ing in on this.

The T-stat could easily be the problem (the t-stat housing could also be plugged with the last impeller failure remnants too!)

You don't have to replace it with an auto type to check it. just remove it and run without it briefly to see if it makes any difference.

While it's out you can throw it in a pan of water and see if it opens all the way at around 160* or so.

Holley 4bbl 4160 marine carb

(HEY, I still have mine..... It's going on my 55 Ford F-600 Y-block V-8!)

 

[lekmedm]

Re: OMC 460 cooling system issue?

Those manifolds have END caps? (those aren't log style manifolds are they?)

(you mean the rubber caps on the back of each manifold?)

Yes, those rubber caps on the back of each manifold.

Do you know how old the manifolds and risers are?

No idea. The engine was rebuild approx. 5 years ago and has 200 hours on it. I have no good guess as to the manifolds and risers.

If you have GOOD water flow, you're zero-ing in on this.

The T-stat could easily be the problem (the t-stat housing could also be plugged with the last impeller failure remnants too!)

You don't have to replace it with an auto type to check it. just remove it and run without it briefly to see if it makes any difference.

While it's out you can throw it in a pan of water and see if it opens all the way at around 160* or so.

That's the first thing I'll check. However, if it turns out that the t-stat is not the issue, is there a way to diagnose those manifolds without actually taking them off. I'm not afraid to remove them, I just want to save myself some trouble if possible.

Thanks for the help, Rick.

 

[HT32BSX115]

Re: OMC 460 cooling system issue?

However, if it turns out that the t-stat is not the issue, is there a way to diagnose those manifolds without actually taking them off. I'm not afraid to remove them, I just want to save myself some trouble if possible.

Not really....

ALL the cooling water for just about about ANY (pleasure boat) marine engine exits thru the risers or manifolds/risers. (if you're closed cooled [full system] it's risers only)


So, if the risers or manifolds are closing down with rust, the flow of cooling water will be reduced until a point at which the flow is essentially stopped.

The risers and manifolds really must be removed to inspect. Also to prevent riser gasket leaks, you really should remove the risers once in a while (every few years) to replace those riser gaskets (and if they're old, INSPECT).

I didn't after I got mine and the riser gaskets started leaking. Every time I shut down the engine a small amount of water would leak back into the exhaust manifolds (both sides) and into an open exhaust valve.

It wasn't much water but it only takes a few cc's of water in a cyl to hydro-lock an engine.

Since it wasn't much I could crank the engine and it would eventually start. If I let it sit over night the little bit of water would leak past the rings and the next day it would start normally.

When I pulled the engine to rebuild and separated the risers and manifolds, I discovered that the riser gaskets were leaking slightly. It doesn't hurt a thing when the engine is running. Only when you shut it down does the water leak back. The water in the risers and manifolds slowly goes down right after you shut down. Otherwise more would leak past the gasket.

In anycase, since I was going to completely rebuild the engine, my plan was to buy new risers and manifolds since you shouldn't put used "stuff" on a new engine, and keep the manifolds and risers on had as spares since I knew they were "scarce".......

I found out quickly that (for a 460) they weren't scarce, they weren't available!


Regards,


Rick

 

[lekmedm]

Re: OMC 460 cooling system issue?

Hey Rick, do you know anything about these aluminum manifolds from Hardin Marine?

 

[lekmedm]

Re: OMC 460 cooling system issue?

One other thing... How about these exhaust adapters that claim to let you bolt on big block Chevy aluminum manifolds to a Ford big block? Any thoughts about these?

 

[HT32BSX115]

Re: OMC 460 cooling system issue?

Ahh yes. I do know about those things!

I was very close to trying them.....couple that with the coupler problem and you'd have a fortune in an engine and drive and REALLY be tied to it!!



If you take the coupler/flywheel modification (a little short of $500......the Hardin Marine manifolds at $1900

(and the shipping/gaskets/etc/) you're at about $2500 in round numbers + same old engine and drive ( & some internal parts are also still scarce for the drive)

There was someone on this forum about a year or 2 ago that tried the adapters and Chev manifolds (or was going to) and said they wouldn't work all that well....(he didn't say why) You have to get aluminum manifolds to go on the adapters which still isn't cheap.


It wouldn't be bad if Sterndrive Engr had a ready to go Cobra drive.....(I hear they will eventually but I'm willing to bet that it's going to be for all engines EXCEPT the 460 King Cobra.......and it would still be bad because you'd still need a coupler and manifolds.)




I paid $5000 for my 454+Bravo III.

I sold all the OMC Cobra "stuff" for about $3000 over the course of 2 years piece by piece.....making my engine/drive cost about $2000 in round numbers.
(now I did add closed cooling [$700], buy a set of props[$600] and buy a new Teleflex CH1700 throttle quadrant and cables($250)

I didn't have to get the closed cooling....so my swap out cost was about was still less than $3000. (I did all the labor)

You have no really easy choices. I don't know any other way to put it. All the above "things" are going to set you back anywhere from $2000-3000. and you still have to contend with the engine and drive. If you had to rebuild the engine you could easily get $2000 in it just for a longblock.

If you needed to rebuild the drive (there's still people that claim to be able to rebuild King Cobras) that would probably set you back about $2000 or more to get a rebuild with a decent warranty. (we're up to about $6000-7000 so far... not counting any labor)

Here's an example of a new engine/drive on ebay for a couple $K more.

I didn't buy new. I found a boat that was damaged by a tree falling on it from Craigslist. I have since looked once in a while there and found several more in the last couple of years.

There's a lot of choices out there. Your best one may be to get it running and cut your losses.



Your mileage may vary....

Sorry about that,


Rick

 

[lekmedm]

Re: OMC 460 cooling system issue?

Hi Rick (and everyone else keeping up with this thread ). So I pulled off the risers and manifolds, and sure enough, they're clogged up.

I was wondering if you ever saw these adapters. I believe they are stainless steel, which means I could bold on regular manifolds instead of aluminum ones. For the $550 + $400 to $600 for a 454 manifolds/risers kit, I could do the setup for up to $1200 and have a lower cost in the future is I need to change the manifolds again in a few years. I'll remind everyone again that I have a raw water cooling system, and I'm running in salt water. Original manifolds are supposedly again in production since last year, but risers are not and others fro, say, Osco would have to be made to work with the OMC original manifolds. The OEM manifolds are going for around $700+ a piece right now.

I am becoming partial to trying out this option with the adapter plate if it will let me use standard manifolds.

I'm not sure about your info concerning couplers and flywheels, and how that pertains to my situation. I realize other parts to my setup can also be rare/impossible to find, however, that's not my current situation. My outdrive is in perfect condition. I just drained the oil, and it was clear even though it was darkened from use.

 

[HT32BSX115]

Re: OMC 460 cooling system issue?

Yes those were the adapters that the guy was talking about. (Maybe he'll see this and comment...)

The coupler doesn't pertain to your situation except to say that it is an absolute show stopper and you have to pull the engine to change it (I don't think anyone is making them so you would have to go with the company that's modifying the flywheel and using a different one if yours failed....they do fail once in a while but I will say, mine went 20 years....that's a good thing....)

I'm not saying that you can't use those adapters. They might solve the riser problem since you'd be using risers that would bolt to the BBC manifolds that you'll be using with the adapters.

You will have to sort of re-plumb to match up with your Y-pipe or thru hulls though...

That shouldn't be all that hard if you have some rubber pipe/fittings etc to work with...You may have to do a little fab work....

None of this is impossible. ......

Good luck,


Rick

 

[seattle2855]

Re: OMC 460 cooling system issue?

Hi Rick (and everyone else keeping up with this thread ). So I pulled off the risers and manifolds, and sure enough, they're clogged up.

I have the same set up as you (OMC 460) and have an open thread dealing with the same problem. My risers were pretty clogged up too with rust. Using a couple of small screwdrivers I was able to open them up pretty well. I know this isn't a long term solution, but it's better than nothing.

To clean out the riser, I would scrape the insides of the risers with a screwdriver. I'd also twist the screwdriver back and forth to break the rust pieces up so they were small enough to come out. Then I'd lift it up and shake out all the flakes of rust. I also had to do this around the water outlet side. Make sure the little v cut outs on the flange are open too. I spend about 90 minutes on each riser and they look pretty decent now.

There's still the risk that the risers have an internal leak, but they looked ok upon inspection.

I'd done this same "cleaning" on the manifolds and risers a couple of years ago and they've worked well until recently.

 

[stevetriton]

Re: OMC 460 cooling system issue?

Im installing new manifolds on my 460 from hitek marine these are stainlles steel.they have outsourced manufactureing so prices are more resa nible .MARINE PARTS SOURCE has originals in stock.N ew couplers are available . I LOVE MY 460.

 

[seattle2855]

Re: OMC 460 cooling system issue?

Im installing new manifolds on my 460 from hitek marine these are stainlles steel.they have outsourced manufactureing so prices are more resa nible .MARINE PARTS SOURCE has originals in stock.N ew couplers are available . I LOVE MY 460.

Can I ask what is cost of those hitek manifolds are??