omc overheat

[kpoly]

GM 305 overheats on muffs. Antifreeze still in engine and manifolds, leaving me to think raw water pump not working. Replaced impeller in outdrive. Not sure how to test for defective water pump. Thoughts? Thanks.

 

[southkogs]

What vintage OMC we talkin' 'bout here kpoly?

If you disconnect the hose coming up from the stern drive while on muffs, do you have water coming up the line?

 

[kpoly]

1985 Stringer, mechanical. Will check on the supply hose coming from the outdrive. What is acceptable amount of water thru this hose?

 

[southkogs]

Stringer will act a little different - your impeller isn't so much drawing water as it is moving it. The Stringer is designed to be completely submerged, so the water flow you're getting to the engine is being pushed from the hose as much as from the impeller.

First thing before you do anything else - grease your swivel bearing on the front of the Sterndrive. If you're not getting the right seal from the seat and grease, exhaust gas can get into your water flow. There's a reasonable chance that's what's happening to you.

Next, you can disconnect the hose going to the thermostat housing. At 500/600 RPM, you should fill up a gallon bucket in about 35-40 seconds. I would think this would be better tested with the drive submerged at the lake.

Do you have a hose connection on your pivot cap (where the drive connects to the intermediate housing)?

 

[kpoly]

Do not have a pivot cap on the hose coming from the intermediate housing. Put new belt on, new impeller and still at idle it creeps up to an overheat situation. Is this normal? When I had it on the water the temp would go down if I ran the boat at higher rpms but when I went back to idle, once again the temps began to rise. How do you test for a water pump, which is original to the boat?

 

[Scott Danforth]

if you have antifreeze in the motor and manifolds, I will assume a full system. did you clean out the heat exchanger?

Also, is this a factory unit? I did not think the stock stringer raw water pump moved enough water for a full system heat exchanger.

when you replaced the impeller, did you replace just the impeller, or the complete raw water pump assembly? did the old impeller have all its blades, or were there missing blades?

 

[kpoly]

I'm not sure this boat has a heat exchanger. No blades were missing from the impeller when I replaced it. No water in the oil. I replaced the entire impeller housing, along with the impeller. Will look to see how much water is being drawn on the muffs at the t-stat housing. Wondering is something could be blocking the passage from intermediate housing to the t-stat.