bassboy1
Lieutenant Commander
- Joined
- Jun 23, 2006
- Messages
- 1,884
For whatever reason, I have never bothered to take the time to learn about thermostats on an outboard. Thus, while working on a 50 hp Johnson, I have discovered a need to figure them out. What we are working with is a 1979 Johnson 55 motor, that at some point, had the powerhead replaced by a powerhead from a 1975 Evinrude 50. This motor, in it's current state, hasn't been run in years, and is in the process of being resurrected from the dead. Anyway, the '75 powerhead has no tell tale, which will change shortly. In digging around for a possible issue in the motor pumping water, or lack therof, we have narrowed it down to the thermostat, which in order to tell if it is functioning properly, a better understanding of how they work is needed.
I understand the basic concept behind a thermostat in an engine, and know very well how they work in a 4 stroke automotive engine. However, I am unsure of how they work in the case of an outboard.
The main question is do they completely cut off the flow of water, or just partially impede it. Say when you first crank the engine, and it is still at room temp, and not near operating temp, does the thermostat completely cut off the flow of water through the engine completely, redirecting it to the passage where the used water normally travels? Or, is it designed to merely impede the flow of water, but not entirely?
On this particular engine, the powerhead is currently removed, hanging from an overhead hoist in the shop. When we blow compressed air through the passage where water first enters the powerhead, it is blocked off entirely, and no air comes out any of the other water passages on the bottom of the block. Is this indication of a bad thermostat/pressure relief, or back to the original question, is the thermostat designed to shut the flow completely until the engine warms up a bit?
On a completely different not, when we go to add the tell tale, where is the best place to drill and tap for the fitting? Many mention on the top of the block, right at the base of the engine lifting ring, but I dislike that location. Can one safely install the fitting elsewhere on the motor, by tapping into one of the water jackets, or is there reason not to?
I understand the basic concept behind a thermostat in an engine, and know very well how they work in a 4 stroke automotive engine. However, I am unsure of how they work in the case of an outboard.
The main question is do they completely cut off the flow of water, or just partially impede it. Say when you first crank the engine, and it is still at room temp, and not near operating temp, does the thermostat completely cut off the flow of water through the engine completely, redirecting it to the passage where the used water normally travels? Or, is it designed to merely impede the flow of water, but not entirely?
On this particular engine, the powerhead is currently removed, hanging from an overhead hoist in the shop. When we blow compressed air through the passage where water first enters the powerhead, it is blocked off entirely, and no air comes out any of the other water passages on the bottom of the block. Is this indication of a bad thermostat/pressure relief, or back to the original question, is the thermostat designed to shut the flow completely until the engine warms up a bit?
On a completely different not, when we go to add the tell tale, where is the best place to drill and tap for the fitting? Many mention on the top of the block, right at the base of the engine lifting ring, but I dislike that location. Can one safely install the fitting elsewhere on the motor, by tapping into one of the water jackets, or is there reason not to?
