OMC Cobra 5.0 overheating

[Ck111484]

My '93 Four Winns w/an OMC Cobra drive and 5.0 (Ford 302) is overheating.

Already changed the thermostat and impeller, and though it may seem a little better, it still hasn't cured it.
After running it on muffs, I pulled off the impeller housing and found this:

Water doesn't seem to be draining from that left "port" (not sure what it's called).
Is this normal?
Could it be indicative of a clogged water passageway?
Is there a way to hook up the engine itself to a water source and bypass the drive?

Any input is appreciated,
Thanks.

 

[sam60]

Re: OMC Cobra 5.0 overheating

Make sure your impeller housing liner hasn't rotated from it's proper position and the slots in the liner are allowing flow.

 

[Ck111484]

Re: OMC Cobra 5.0 overheating

Liner is brand new and hasn't moved.
Is it normal for water to not drain from the drive? Seems like it would indicate a clog...

BTW I recently overheated badly and SHREDDED the impeller; not sure if that could cause a clog somewhere?

 

[sam60]

Re: OMC Cobra 5.0 overheating

Do you have oil or power steering coolers? Remove hose connections one point at a time from transom connection and check toward engine from there to see where/ if the flow is restricted. Start at the first connection and work your way through the water flow to the stat housing for starters.

 

[sam60]

Re: OMC Cobra 5.0 overheating

My '93 Four Winns w/an OMC Cobra drive and 5.0 (Ford 302) is overheating.

Already changed the thermostat and impeller, and though it may seem a little better, it still hasn't cured it.
After running it on muffs, I pulled off the impeller housing and found this:

Water doesn't seem to be draining from that left "port" (not sure what it's called).
Is this normal?
Could it be indicative of a clogged water passageway?
Is there a way to hook up the engine itself to a water source and bypass the drive?

Any input is appreciated,
Thanks.

Another thought, have you hooked up the water with the impeller housing off to see if you have strong flow to the port side of your photo?

 

[Ck111484]

Re: OMC Cobra 5.0 overheating

So after some research, I think the fact that my impeller disintegrated means there is likely pieces of it lodged in the inlet to the power steering cooler (which is on the way to the thermostat housing ), reducing flow to the engine. This would fit the circumstances and symptoms (overheating, but not indefinitely, meaning there is probably some water flow).
Will check and report back tomorrow.

 

[Ck111484]

Re: OMC Cobra 5.0 overheating

So if I wanted to "backflush" the cooling system, which of these hoses would I remove and flush water down?

Could anyone label them for me? It would be GREATLY appreciated!

 

[Reinell-BRXL-191]

Re: OMC Cobra 5.0 overheating

The top 2 smallest hoses are the flow to the manifolds.. the second one down ( medium sized hose) goes back to the drive, and is where you would want to flush... the large one is of course the water pump hose to cool the motor

If you have the impeller pump housing off, and shove a hose in the medium sized hose on that thermostat housing, you should get water flow out of the drive

 

[Ck111484]

Re: OMC Cobra 5.0 overheating

Perfect, thank you very much!
Will do that, as well pull the hose off the PS cooler and check the inlet for debris.

 

[Ck111484]

Re: OMC Cobra 5.0 overheating

So I found a massive amount of impeller debris in the power steering cooler. Got it all cleared out with needle nose pliers, and backflushed the hose to ensure a clear passage. Better, but still overheating. Have tried 2 different thermostats, and have a brand new impeller... still getting up to a steady 195 degrees.

Getting very frustrated here. What can I check next?

 

[Ck111484]

Re: OMC Cobra 5.0 overheating

On muffs, pulled intake hose (from PS cooler to thermostat housing) and ran engine, plenty of flow there.
Pulled block drain and ran engine, plenty of water coming out, so water is running through the block.
Verified that thermostat is opening/closing in bowl of hot water.

Any ideas?

 

[Ck111484]

Re: OMC Cobra 5.0 overheating

Figure I should mention that I recently had a bad overheat that I had attributed to a bad thermostat; when I shut it down the gauge was showing 240 degrees, I smelled burning and saw a bit of white smoke (not much), then the engine wouldn't crank over... ended up being hydrolocked.
Got all the water out of the cylinders, sprayed oil fogger etc. I checked compression because I was worried that I cracked the block or blew the headgasket, but all cylinders were between 140 and 170. Water was in the oil, but I changed it and the filter before running it, and then again after I ran it for maybe 20 minutes. Don't seem to be getting any more water in; no "froth" on the dipstick whatsoever.
Performance, sound etc. also seem exactly the same as before, except I can't get the heat down.

Was thinking that I dodged a bullet and didn't damage anything; now with it still overheating I'm not so sure...

 

[bruceb58]

Re: OMC Cobra 5.0 overheating

You may have burnt up you exhaust flappers and they are now laying down inside your exhaust tube. Also, if you boat in salt water, your manifolds could be blocked up causeing not enough water to flow.

 

[Ck111484]

Re: OMC Cobra 5.0 overheating

Forgot to mention, I pulled the risers to inspect them as well as the exhaust flappers, and the flappers were missing, which I'm hoping is what caused the hydrolock; I installed new ones. I suppose it's possible that an old flapper is blocking the exhaust...

How can I check water "output" through the exhaust?

 

[sam60]

Re: OMC Cobra 5.0 overheating

So I found a massive amount of impeller debris in the power steering cooler. Got it all cleared out with needle nose pliers, and backflushed the hose to ensure a clear passage. Better, but still overheating. Have tried 2 different thermostats, and have a brand new impeller... still getting up to a steady 195 degrees.

Getting very frustrated here. What can I check next?

So, you're not willing to isolate, clean and check each component in the direction of flow or you've already done that and everything looks great and your still overheating? How's the impeller housing and liner? Are the in & out slots where the should be or has the liner spun?

 

[Ck111484]

Re: OMC Cobra 5.0 overheating

So, you're not willing to isolate, clean and check each component in the direction of flow or you've already done that and everything looks great and your still overheating? How's the impeller housing and liner? Are the in & out slots where the should be or has the liner spun?

As far as I can tell, everything is clear. Pulled the water inlet hose from the thermostat housing and have plenty of flow there; pulled the block drain and ran the engine and have plenty of water coming out there; pulled the risers, replaced that flappers, and stuck a hose down into the y-pipe and plenty of water seemed to be coming out of the drive. Anything I'm missing?
The impeller, cage and gasket are new; I have a new housing coming just in case, however during testing I have had the cover off on the drive to expose the impeller housing and don't see any water leaking out or hear any air being sucked in.

However, now that I think about it, I just remembered that the little valve on the impeller housing that the little hose attaches to was clogged and water wasn't coming out, but I unclogged it and now it shoots out. Not sure what that little valve does.

 

[Ck111484]

Re: OMC Cobra 5.0 overheating

I also noticed that the impeller housing was hot to the touch today, however everything in the housing looks fine.

 

[sam60]

Re: OMC Cobra 5.0 overheating

You pulled the risers but what about the exhaust manifolds? Circ pump is good? How was the new stat in the pan of water with the stat and a thermometer to check if it was good new?

I'm not an expert, but until you go through each component and check, having "decent flow with a garden hose" isn't solving your problem.

Just trying to help as I've had the same issue.

 

[Ck111484]

Re: OMC Cobra 5.0 overheating

It's okay, you can give it to me straight

Didn't pull the manifolds because I figured the condition of the risers would be somewhat indicative of the manifold's (risers were perfect), and the boat has never been in anything but freshwater so I feel that the likelihood of the exhaust components needing replacement is very unlikely.

The circulation pump is currently under speculation, but from what I've read, they don't really go bad and if they do, you know it because they either leak or the belt breaks. However, it does seem like it could make sense. Is there anything to look for in particular to see if the circ. pump is bad?

Tomorrow I plan on buying an infrared heat gun to verify that the high temps are "real", and replacing the PS cooler to thermostat housing hose with a clear one to see if I'm ingesting air somewhere.

 

[sam60]

Re: OMC Cobra 5.0 overheating

You might be surprised at how clogged the tubes in the exhaust manifolds can be from "fresh water", Mine where down to about a 3/8" passage. I took a piece of all thread and opened mine back up. Then I cleaned them up more by CAREFULLY using Iron-Out.

These are fed by the hoses from the stat housing. Pull the exhaust manifolds after you have the new gaskets on hand.