Overheating: 1988 OMC Cobra 4.3

[kmeintjes]

I have a 1988 4 Winns Candia with a 4.3 liter V6 OMC Cobra sterndrive. I don't use it much, but it has been well maintained and I have had it for 10 years.<br /><br />The other day the engine overheated. I had been towing a kid on a tube (small, inland Michigan lake) for about 10 minutes when the temp gage went from normal to pegged in a minute or two. I shut it down immediately, and towed it to shore. It is now out of the water.<br /><br />I expected to have to replace the impeller on the stern drive pump, but it is in excellent condition. (I replaced it 3 years ago). What now? What are the steps to minimize cost and tearup of the engine?<br /><br />A friend says the power steering heat exchanger is likely plugged. I would prefer not to tear into it. It is impossible to reach at the back of the motor compartment. Now that the stern drive impeller is out, can I back flush the ps heat exchanger from the hose on the thermostat housing? Would the pressure of a garden hose be too much?<br /><br />We have zebra mussels in our lake. Can you clean out the water intake passage that runs through the outboard unit?<br /><br />The easiest cheapest part to replace is probably the thermostat. Should I have done that first?<br /><br />From what I can read, the next, most drastic step would be to remove and clean the exhaust manifolds.<br /><br />Thank you in advance for any advice. As you can see, I suspect there is a blockage in the cold water intake. Can I test the delivery of cold water to the thermostat housing?<br /><br />Keith, in Michigan

 

[liner85]

Re: Overheating: 1988 OMC Cobra 4.3

Sorry to ask the obvious... but did you check the alternator/water pump belt? (I'm only asking since I had a similar experience on an older mercruiser. I hastily replaced the impeller, only to find a snapped belt was the cause of overheating...)

 

[Bondo]

Re: Overheating: 1988 OMC Cobra 4.3

Now that the stern drive impeller is out, can I back flush the ps heat exchanger from the hose on the thermostat housing? Would the pressure of a garden hose be too much?<br />

Ayuh,.... That's a Great place,+ way to start,.....<br />Try to recover the Waste that's expelled, just to See what comes out......<br />I suppose you could pour some bleach down the same line to kill/flush the Zebra Mussels out,... But,... I've got them at My Dock,+ haven't seen or experinced any Issue from them........<br />

Can I test the delivery of cold water to the thermostat housing?

Ayuh,....... Just remove the same hose you're going to use to Back-Flush the line for a short time with the engine Running,......<br />You should get a Steady, Solid water flow.....<br />

From what I can read, the next, most drastic step would be to remove and clean the exhaust manifolds.

Ayuh,......... That'll be the Next place to look,.........<br />They tend to Clog where the Manifold water flows into the Riser,....<br />Pull the Riser/Elbows 1st,..... You can tell from there if the manifolds need replacing.......<br />Being that you boat in Freshwater,.... I Doubt that's your Problem...........<br />

I expected to have to replace the impeller on the stern drive pump, but it is in excellent condition. (I replaced it 3 years ago).

I'd replace it Anyway,.......<br />And,... Inspect the Housing Very Carefully,..... To only take a few small scratches in the upper,.. or lower housing face to loose Alot of pumping capacity..........<br /><br />Good Luck,+ Welcome to the forums here at iboats.com.............

 

[kmeintjes]

Re: Overheating: 1988 OMC Cobra 4.3

Originally posted by liner85:<br /> Sorry to ask the obvious... but did you check the alternator/water pump belt? (I'm only asking since I had a similar experience on an older mercruiser. I hastily replaced the impeller, only to find a snapped belt was the cause of overheating...)

Thank you. Yes, the belt is intact. It may be that the engine water pump is defective, but that is not my first theory.<br /><br />Keith

 

[kmeintjes]

Re: Overheating: 1988 OMC Cobra 4.3

Bondo,<br /><br />Thank you for your quick and helpful reply. Do you think the thermostat could be stuck?<br /><br />Keith

 

[Lou C]

Re: Overheating: 1988 OMC Cobra 4.3

That is a possibility as well. As far as the Cobra impeller, it is easy to change on the rear of the upper unit. When I do them I change the housing and wear plates and all gaskets. Make sure the plastic housing seals well (the gasket has to fit into the groove in the housing). It can be tricky to get back in. I'd check to make sure the line from the transom shield to the thermo housing is clear. Next test the thermostat. Should be a 160 degree stat held into the housing by a rubber ring that fits into a groove in the thermo housing. I'd also look carefully at the water intake screen if you have a marine growth problem. The manifolds are the OMC one piece units. You are in freshwater so it is not likely to be the cause, but you can feel the upper section while the engine is idling on the water hose, they should be warm at most, not hot. You can test the impeller by putting the boat in the water, temporarily disconecting the thermo housing hose from the transom at the thermo housing, and hold it up while someone starts the motor just for a minute, it should shoot a stream of water several inches up in the air. The last thing is the circulating pump on the front of the engine, that can be checked as well but they don't often go bad unless it is leaking from underneath the water pump pulley.

 

[lakelivin]

Re: Overheating: 1988 OMC Cobra 4.3

I've got a 16 year old 4.3L Cobra, and last time I had the drive off noticed a large piece of rubber at the bottom of the exhaust pipe near the transom. Turned out to be one of the fleppers that had broken & worked it's way down. <br /><br />It didn't cause any problems with my boat cause of where it ended up (got 2 new ones on order). But given the age of his boat, is it possible that one or both of his flappers broke off & is/are blocking the exhaust water flow? Could that cause such a quick & severe temp increase?

 

[Haut Medoc]

Re: Overheating: 1988 OMC Cobra 4.3

If it winds up in the wrong place it can......JK

 

[javsam]

Re: Overheating: 1988 OMC Cobra 4.3

all good points,also check your plugs their may be one that melted the electrode something that can happen during overheating.<br />javsam

 

[Fix a Floot]

Re: Overheating: 1988 OMC Cobra 4.3

Ok I Just fixed a OMC 5.8L had over tep issues 1st replaced low unit water impeller next termo in yoke next checked engine water pump found gaskest seeping, replaced only gaskets pump was fine next pulled oil cooler tadah! there it was rubber impacted in inlet had to use tool to remome no back flushing would had done the trick FYI. engine ran cool with boat at rest but when you put it under load over heat PROBLEM FIXED