Overheating slowly

[hazelheckler]

Mercruiser 228 305 cid chevy. 1978 sea ray

When run on muffs or in the bay at 1000 rpm never overheats but when throttle is advanced to 2500 rpm or over the temperature gradually climbs into the red and won't come down till throttle is reduced to near 1000 rpm.

New water pump kit installed (seawater supply), checked flow 2.5 quarts 15 seconds at input to circulation water pump.

Removed thermostat, no difference.

Removed all hoses and was able to blow through them, manifold inlet and exhaust outlet (except exhaust elbow outlet) too far back,,,

When I plugged up the exhaust manifold inlet hose and exhaust elbow inlet hose and blew air through the exhaust manifold outlet hose pressure built up. Shouldn't there have been no back pressure? Wouldn't the pressure go right out the exhaust hose on the exhaust elbow?

What should I try next?

Thanks,,,Mike

 

[NHGuy]

Re: Overheating slowly

Do you have open cooling or is it some type of heat exchanger?

 

[hazelheckler]

Re: Overheating slowly

No heat exchanger just raw water in and raw water out,,,

 

[Bondo]

Re: Overheating slowly

Mercruiser 228 305 cid chevy. 1978 sea ray

When run on muffs or in the bay at 1000 rpm never overheats but when throttle is advanced to 2500 rpm or over the temperature gradually climbs into the red and won't come down till throttle is reduced to near 1000 rpm.

New water pump kit installed (seawater supply), checked flow 2.5 quarts 15 seconds at input to circulation water pump.

Removed thermostat, no difference.

Removed all hoses and was able to blow through them, manifold inlet and exhaust outlet (except exhaust elbow outlet) too far back,,,

When I plugged up the exhaust manifold inlet hose and exhaust elbow inlet hose and blew air through the exhaust manifold outlet hose pressure built up. Shouldn't there have been no back pressure? Wouldn't the pressure go right out the exhaust hose on the exhaust elbow?

What should I try next?

Thanks,,,Mike

Ayuh,.... Pull the elbows, 'n see what ya got,....

Waters comin' In,... 'n it's gotta be able to get Out,....

 

[MarkSee]

Re: Overheating slowly

Ayuh,.... Pull the elbows, 'n see what ya got,....

...elbows?...oh that's right:facepalm:, that's what we use to call RISERS which sit on top of a SPACER (if applicable) or not, which then sits on top of the MANIFOLD. Got it. :laugh:

Mark

 

[Bondo]

Re: Overheating slowly

...elbows?...oh that's right:facepalm:, that's what we use to call RISERS which sit on top of a SPACER (if applicable) or not, which then sits on top of the MANIFOLD. Got it. :laugh:

Mark

Ayuh,.... You caught that conversation too, eh,..?? :lol: