30L 1992 Overheating at low speed help

"I have a 17 ft long Sunbird b

"I have a 17 ft long Sunbird boat. It come with a 3.0L GM cobra and OMC unit. This boat runs wonderful but lately it has been running hot when cruising at low speed. The temp. drops down to normal when I accelerate the engine. Also, it does not overheat when I plug the hose in the unit at home. What is going on? Does anyone know what might be the problem?
Thanks"

"I would suspect not enough wa

"I would suspect not enough water flow at low speed and most likely the water pump impeller in the drive unit. There is a test you can do (boat in water not on muffs) which is to remove the input water hose from the thermostat and hold it up about 15 inches above the transom mount over a bucket. Start the engine and check for at least 2 to 4 inches of a water head coming out of the hose, if not you could have an obstruction (old pieces of an impeller) in the system or the impeller itself is worn out? You may also have a power steering cooler on the line? It may have an obstruction in it as well."

"Thanks Bob,
I checked the im

"Thanks Bob,
I checked the impeller and looks fine (How can I tell if it has worned out?). But I noticed that the O-Ring is missing piece of it and I could see that water leeks a little. Could that be the problem?
One more thinh, at least I know it is not the power steering cooler because my boat does not have power steering.
Thanks for your comments and advices"

"I would replace that o ring f

"I would replace that o ring for sure, if it's leaking water it can also be sucking in air. If you don't know when the last time the impeller was changed I would get a water pump kit and change it, the o ring and the rest all at the same time. At least then you'll know exactly what's been done. I would also get a service manual, the best one is the OMC factory manual that you can usually find on ebay, you need to know your year or at least the engine model number."

"If that O-ring is on the inle

"If that O-ring is on the inlet side of the pump, then it's allowing it to suck in air instead of water. Very bad!

Jeff"