Boiling coolant - 1981 Mercruiser 470

Joined
Jul 13, 2012
Messages
6
Hi all,

I have a 1981 Mercruiser 470 with a seawater cooling system, which I bought two seasons ago and has been running well. All I have done is had the starter rebuilt.

Yesterday, my engine temp got really high (off the gauge), and I see steam coming from the engine bay. I'm assuming it is boiling coolant. My first thought is the thermostat, my second is the water pump. I still have plenty of coolant in the reservoir, which leads me to believe it is not a leak. The engine also runs very well, which leads me to believe it is not a head gasket issue (but I can be wrong on that).

Anyone have any thoughts on this, anything can help.

Thanks!
Andrew
 

stonyloam

Vice Admiral
Joined
Mar 13, 2009
Messages
5,827
Re: Boiling coolant - 1981 Mercruiser 470

Your FIRST thought should be the impeller in the outdrive. You will need to replace the impeller and housing at the least. Maybe shutters too.
 
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