OMC 4.3 Cobra overheating. Help.

[Jode]

First trip of the season motor over heated while idling within 30 minutes.
Have tried all of the obvious trouble-shooting solutions. Changed pump housing and impeller. Installed new thermostat. Separated top and bottom drives and inspected grommets, seals and tube...all looked OK. Checked to make sure impeller shaft was turning and it was. Ran water through all inlets, ports hoses and exhaust...no blockage. Water flows fine out of inlet hose to thermostat when the muffs are used. When I put the boat in the water, the water flow through the inlet hose is sporatic or not at all. Totally baffled Any suggestions would be greatly appreciated.

Thanks in advance
Dwight

 

[Howard Sterndrive]

Re: OMC 4.3 Cobra overheating. Help.

water can get in, but can it get out?

corrosion in the exhaust manifolds can restrict water exiting and taking the heat out with it...

 

[indybleck]

Re: OMC 4.3 Cobra overheating. Help.

There was a thread on here earlier some one had the same problem, check some of the past threads, you checked the grommets on the tube, is the impeller housing good? Sometimes on the muffs the water is forced through the lower instead of the impeller pumping it through.

 

[Jode]

Re: OMC 4.3 Cobra overheating. Help.

water can get in, but can it get out?

corrosion in the exhaust manifolds can restrict water exiting and taking the heat out with it...

I have good flow in and out. I am wondering if there could be back pressure from the motor that is restricting water flow in from the impeller?