Re: 470 Mercruiser
I assume you have a closed cooling system although that is not mentioned...if so, there is probably inadequate circulation of raw water cooling through the heat exchanger and/or to the exhaust elbow. Since you mention the problem begins and worsens at 2000 rpm+, I would tend to check raw water cooling flow first.<br /><br />In the typical 470 set up, the 'radiator' cap is located above the thermostat, but if heat is resulting from failure of the exhaust to be cooled adequately, in addition to the coolant, you'll experience the condition you describe because the exhaust elbow is overheating more than the heads or block as a result of the heat source coming from the exhaust. In other words, if your temp gauge shows somewhat higher than normal temp, but coolant is over flowing because the exhaust elbow is excessively hot, the issue is inadequate exhaust cooling. This can be caused by:<br /><br />1 - Worn lower unit impeller (causing poor raw water circulation). Typically, temp becomes problematic at higher rpm's.<br />2 - Restriction in heat exchanger<br />3 - Restriction in raw water flow to exhaust elbow.<br />4 - Restriction of raw water flow within the exhaust elbow.<br />5 - Exhaust restriction in exhaust elbow, or post exhaust elbow. <br /><br />With the closed cooling system and the symtoms you describe it may not be as serious as indicated by some of the others. I experienced this issue when my lower unit impeller broke up. It can happen when the primary over-heat source originates in the exhaust elbow rather than from the heads or block.
: When i get it to about 2000 rpms water began to come out of the radiator cap. Its brand new. I looks fine. I sems as if i heard of this before. What is the problem... It is not going into the overflow..<br /><br />Skybizzer