8V53 Over heating

[Full Moon]

1969 Convertible with Detroit 8V53s. Port engine runs fine at normal cruise setting, 2150 rpm. Slow down to idle or 1100 rpm and it over heats. 200 degrees and climbing. Checked water flow, equal both sides. checked impeller, it is OK. Changed coolant. still does it. Next is to pull heat exchanger but it was suppose to have been pulled and cleaned last Fall with not much use since then.

Any advise for something we haven't tried?

 

[MikeP]

Are the temp readings with the oem electrical gauges? If so, check with a manual gauge to verify it's actually a temp issue, not a gauge issue. Electrical gauges can do weird stuff...

 

[workingonadream]

I agree with mike p check with a infrared temp gun this would be quicker than installing a set of mechanical gauges. I don't think its your exchanger as the opposite should happen. it should run cool at idle, but run hot under load. the temp gauges on my boat are off by 20 degrees compared to the mechanicals I installed. good luck

 

[Full Moon]

I agree with both, new gage and sensor last fall but no problem until now. We are going to try the infra red thermometer to confirm.