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Coolant loss

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donmega

Member
"hi I have a 4.3 mercruiser v6

"hi I have a 4.3 mercruiser v6 fresh water cooled. It started to heat up more than usual over the weekend after some hard runs (tubing). the temp usually sticks at 150, but yesterday climbed up to 170 so I eased off and let her idle to cool down... it only seems to really climb if I really throttle it, but it takes a 5-10 mins of hard running to make it climb. I do think have a slow coolant loss somewhere but I dont see any visible leakage from under the motor... is this normal to have minor coolant loss over time? i did top it up once before a few months ago and the temps been fine... I havent checked the overflow tank and Ive never overheated it."
 
"You didn't say how old th

"You didn't say how old the boat was but it could be due for a new thermostat and or impeller. What ever the cause it is one that should be corrected before some real damage happens. Coolant loss from a sealed system can only leak out in a limited amount of places like a head gasket, hose, coolant jacket, heat exchanger, water pump seal, intake gasket, etc. If the oil is clear of coolant it could be a leaking intake allowing the coolant to enter the cylinders.

A check of the plugs will sometimes show if coolant is being burned. Most times the plugs will be white in color if coolant is burning in the fuel mix.
As stated before a pressure test may help tell if there is a leak but even with a pressure test a leaking head or intake gasket is hard to find. Also as stated, the heat exchanger is a good place to start more so if this is a salt water boat. Could have a small leak in the exchanger.

Just a few ideas, hope you find the cause."
 
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