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  #1  
Old 01-13-2008
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Overheating - air lock?

Yesterday I had my Pearson 27 hauled for a bottom cleaning and to check for a fouled prop - blowing black smoke under load and struggling to get above 3 knots. As suspected, the prop was covered in barnacles and once she was back in the water, zipped through the bayou like a greased weasel.

I had some engine work done in October after an incident involving a stuck valve (head removed, valve seals replaced, head gasket replaced, etc). When I got the boat back in early December she was overheating, traced to some blockage by scale in the hot water circuit. Almost the entire coolant system was checked - heat exchanger removed and serviced, thermostat replaced, raw water intake hose replaced, etc and so forth. The hot water loop is completely out of the coolant circuit now until I have some hardware replaced.

So everything was finally running smoothly - no overloading of engine, no exhaust smoke, clear raw water output. Took her out on a shake down run out into Lake Pontchartrain, the first in 3 months.

I motored out to a marker roughly a mile offshore, no problems whatsoever - smooth, clear exhaust, temp gauge at low end of 165-195 operating range - if even that high - at nearly 6 knots (hull speed is 6.4) I rounded the mark and headed back in (into the wind) and after a minute or so the temp slowly started to creep up. It then shot up to about 220. I cut the engine and after a few choice words to nobody in particular, went below and flipped up the pressure valve on the cap. Quite a bit of air came out, very little coolant into the expansion tank (which was about halfway between the cold and hot marks). I went above, waited a minute or so, started up the engine, and watched the temp gauge literally plunge back down to around 140, where it more or less stayed all the way back in.

Raw water flow appeared to be fine (brand new impeller), so besides an air lock in the fresh water/coolant system or some other temporary disruption of flow, does this sound indicative of anything else?
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Last edited by phallo153; 01-13-2008 at 12:45 PM.
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Old 01-13-2008
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An airlock is a distinct possibility, since you obviously had the system open and apart (maybe a time or two).

When you removed the HW tank from the cct did you connect the two hoses together to keep that loop in play? If you dead-ended the two heater hoses you may have affected the circulation path.
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Old 01-13-2008
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Quote:
Originally Posted by Faster View Post
An airlock is a distinct possibility, since you obviously had the system open and apart (maybe a time or two).

When you removed the HW tank from the cct did you connect the two hoses together to keep that loop in play? If you dead-ended the two heater hoses you may have affected the circulation path.
Sure did, I removed the two heater hoses and put on another length of hose, about 12", as a loop on the inlet/outlet to the HW heater.
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Old 01-19-2008
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I'm not that up to speed with fresh water cooling, to be honest. Has this problem persisted?
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Old 01-20-2008
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I'm not that up to speed with fresh water cooling, to be honest. Has this problem persisted?
Haven't been back out yet Jason, it's been so damn nasty. May try to take it out tomorrow morning if I make it over.
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