1990 OMC Cobra 3.0 overheating @ low speed

ryanscolo thats the problem i was having i cleaned out the rust inside the manifolds where the water exits at i am going to test tomorrow or sat and i will let you know how it turns out

hey folks,

did anyone ever find any resolutions to this? I have a 1988 Bayliner Cierra Sunbridge 2455, with a "new" 5.7 OMC, cobra outdrive....SAME PROBLEM. This boat has cost me thousands, and I took it out last Friday, had no problems. Monitored cooling, oil pressure, etc the whole day, never missed a lick. Yesterday, my wife and I went to the marina to take it out, and being a new motor, I started it at dock while we loaded our cooler, fishing tackle, etc, and noticed it was getting warm. 10 hours later, I was still at dock, had hoses to tstat housing on and off a thousand times, removed outdrive impeller, etc, never could get it to pump water of any substantial amount. I did not try putting it into gear, as my boat is surrounded by other boats, and if I leave the dock, I better be "sure" because the vessels around me cost well in excess of $100k, dont want any accidents. I am suppose to meet the mechanic monday morning where he will tow me to loading ramp to take boat to his shop, but after reading this thread I cant help but wonder if in forward gear, my cooling problem will vanish as well? Any help you can give would be fantastic. This is motor #3 since I have owned this boat. First motor was junk when I got the boat, second motor was a salvage from donor boat, and now $4000 later its a "new" reman. motor. Really really dont want to put any more engines in this boat.

I too have had the same problem. Sporadic waterflow coming from the outdrive. Very frustrating. I think I have solved it, since I have now been running for a week with good consistent water flow.
I have stinted the hose which connects the transom through pipe to the articulating outdrive by running a smaller diameter hose through it from the transom through pipe. Pushing my stint past the bends and a tighter obstruction in the original, possibly collapsed hose. I then cut off the stint at the transom through pipe, sewed dental floss through it, and tailed the dental floss over the through pipe, fastening it with the transom to tstat hose, [neccesary because the inner/stint hose wants to move out of the obstruction/collapsed hose with the water flow].

Sorry guys, I'm a newbie and experiencing the same problem on our boat that we bought 3 weeks ago, everything was working fine until 2 days ago we took the boat out for a fishing trip but after running it for over 30 mins the engine starts to overheat wether idling or running speed, don't know where to start and ended up in this sites, very helpul and a lot of info. My question is can you service or remove the impeller if the boat is dock at the marina, we dont have a trailer to take it to a dry place, any suggestion, any help is greatly appreciated, thanks.

trilight said:

I too have had the same problem. Sporadic waterflow coming from the outdrive. Very frustrating. I think I have solved it, since I have now been running for a week with good consistent water flow.
I have stinted the hose which connects the transom through pipe to the articulating outdrive by running a smaller diameter hose through it from the transom through pipe. Pushing my stint past the bends and a tighter obstruction in the original, possibly collapsed hose. I then cut off the stint at the transom through pipe, sewed dental floss through it, and tailed the dental floss over the through pipe, fastening it with the transom to tstat hose, [neccesary because the inner/stint hose wants to move out of the obstruction/collapsed hose with the water flow].

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You have to remove the plastic cover to get to the impeller housing. Undo the cover bolts and remove the impeller. Lightly grease the new one with petroleum jelly and install with a slight twist. I start the twist at about 90 degrees to the left off from the keyway so that when it gets in there it will seat on the drive key properly. You'll see what I mean. If necessary, you can take the boat into shallow water and do it in your bare feet. OK to tilt the drive all the way up to ease access. Been there. Best to keep a spare impeller somewhere in your on board spares kit. In operation the impeller is water lubricated, so no need for tons of grease.

o2batsea, thanks for your reply, we're going to take boat into a shallow water anh hopefully will be able to solve the overheating issue with this boat. Last night I read the reply over and over to familiarize myself with this unit. BTW what kind of material is this impeller made of and do they have a threaded part or a keyway that holds it in place into the shaft, thanks again.

o2batsea said:

You have to remove the plastic cover to get to the impeller housing. Undo the cover bolts and remove the impeller. Lightly grease the new one with petroleum jelly and install with a slight twist. I start the twist at about 90 degrees to the left off from the keyway so that when it gets in there it will seat on the drive key properly. You'll see what I mean. If necessary, you can take the boat into shallow water and do it in your bare feet. OK to tilt the drive all the way up to ease access. Been there. Best to keep a spare impeller somewhere in your on board spares kit. In operation the impeller is water lubricated, so no need for tons of grease.

Click to expand...

Impeller is either nitrile or butyl rubber. Not sure which. Probably butyl. It has a vee shaped keyway on the forward end of the impeller's hub. Only goes on one way, so it it's a go/no-go fit.

Stupid question. What is the purpose of the small vent hose? It was broken off the housing on this one and sprayed all over the place through the 3 bolted cover. Got a new housing with the fitting on it and will replace the hose but what is it's purpose?

Did you ever fix the overheating problem? I just bought a boat last fall, I put a reman jasper engine in it, new water pump, New impeller kit including housing. And I am overheating at idle and slow speed.