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I have been running my A4 for the last 7 years with the manual bypass, installed between the Tee and the thermostat housing, and I have never seen temps over 120, even with the bypass fully open. Would moving the valve to the T-stat outlet give better control over the temperature? It seems like that would mimic the action of the thermostat in restricting flow and allow me to dial the temperature. Would that overheat the exhaust manifold? Any thoughts or comments welcome.
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I'd check the thermostat first. It may somehow be stuck in the open position.
Also you could use IR thermometer to be sure the gauge is not lying.
If you have a original "three legged" thermostat it is a "double action" thermostat - that is as the thermostat opens it allows more water to flow through the engine and less water to go around the engine ie the "bypass".
Many members are happy with a cool running engine.
ex TRUE GRIT -
tsell..yep..it could overheat the exhaust side. I would not restrict the flow headed into the manifold, and I would not move the bypass. Have you confirmed your t-stat works by boiling it on the stove? Where is the boat, and what are the typical water temps? Edit - I see Vermont..sorry..Last edited by sastanley; 08-21-2020, 05:45 PM.-Shawn
"Holiday" - '89 Alura 35 #109
"Twice Around" - '77 C-30, #511 with original A-4 & MMI manifold - SOLD! (no longer a two boat owner!!)
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I do not have a thermostat installed, and have had significant carbon on the plugs. Since I just did the head gasket yesterday, I had a chance to have a good look at the valves, and the carbon build up on them, along with the top of the combustion chamber made me start to think about optimal operating temps, and how to achieve them without a thermostat. For sure I am concerned about the exhaust manifold temps.Comment
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Huh? That's the reason FOR a thermostat.Originally posted by tsell View PostNeil
1977 Catalina 30
San Pedro, California
prior boats 1987 Westsail 32, 1970 Catalina 22
Had my hands in a few othersComment
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I think cooler engine temps will produce that carbon build up. I am running 180-190° in summer (Ches. Bay water temps are high 80's), but I am FWC.-Shawn
"Holiday" - '89 Alura 35 #109
"Twice Around" - '77 C-30, #511 with original A-4 & MMI manifold - SOLD! (no longer a two boat owner!!)
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I found Don’s excellent explanation of the thermostat in our engines in the tech tips, which definitively answered my musings.Originally posted by sastanley View Post
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I ran for 34 years with no t-stst @ 130* and my stock plugs were always a creamy chocolate color as they should be. An engine can be adjusted to run at most any temp. It is the fuel air mix that causes black and sooty plugs as well as proper timing not necessarily a low temp! I did run a bit to the lean side and never any trouble.
Dave Neptune
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