Thermostat

[dennis5112]

Brands Marina, Port Clinton, Ohio installed a rebuilt Atomic 4 Motor in my Pearson 28, 1975 Sail Boat. When they install the thermostat the motor is too near the thermostat. When they remove the thermostat, the motor runs at the desired temperature. We are still looking for the cause of the increase in temperature. Dennis5112

[bayway27]

Please help me to visualize your problem. "When they install the thermostat the motor is too near the thermostat"?? I ask this because I believe that the thermostat is only located in it's housing in the block.

[Don Moyer]

Dennis,

In working with your excellent marina mechanic (Rich), we may be getting close to the answer on this perplexing issue. It turns out that the temperatures at all locations on your engine are perfectly normal with a thermostat installed except for one small place in front of the head just beside the temperature sending unit. The temperature of the block just below this location is normal. Fortunately or unfortunately, your cockpit gauge is faithfully indicating the temperature of this tiny hot spot in the
head just beside the sending unit.

We sent a replacement head for Rich to install which presents the same indications.

This morning we ran a test on another Atomic 4 in our own shop and we get the very same indications; e.g. a very small localized spot of 200 degree + temperature indication just below and to the right of the sending unit. Since we use a manual temperature gauge with its probe extending an inch or so in from the front of the head, this higher temperature is not registered on our gauge. Our gauge measures the composite temperature of the water moving through the area of the thermostat.

Our assessment is that a reinforcing rib in the water jacket of the head that extends from the area just above the combustion chamber of the front cylinder to the very front of the head conducts the high temperature of the combustion chamber to the front surface of the head, and accounts for this small area of elevated temperature.

The obvious question is; if this condition is normal, why don't all late model heads indicate high temperature? At this point I don't have that answer. I'm waiting for a call from the marina to offer to send them one of our sending units and gauges to try.

Don

[Jesse Delanoy]

Don,

Have you experienced a similar condition with your MMI aftermarket heads?

[Don Moyer]

Jesse,

Yes. Our aftermarket heads have the very same reinforcing rib inside the cooling jacket. On this particular engine, the original head was an MMI aftermarket version which had the same indications as the OEM head we sent for a replacement.

Don