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Cold running Merc inboard

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"This is raw water cooled &#4

"This is raw water cooled (no heat exhcanger )and it will not come up to operating temp. The engine runs fine, but infrared readings at the thermostat housing read 105-107F at 3000rpm. I have tested the stat (160)and it checks out to spec, but the temp never gets up to where it would come into play.I have a good mechanic who thought there might be a problem with the stat housing,but that checks out OK. We replaced the plates between the risers and manifolds with ones that restricted water flow, but there was no change. I bought the boat a year ago, and it has always run cold. I thought that it had a bad stat, but obviously this was not the case. Any ideas on this would be greatly appreciated. By the way, if I run it up to 3600+- for a couple of minutes and bring it back to idle, the temp will briefly rise to 120-130, but then returns to 105-107 as soon as I throttle up.Help."
 
"George I had the opposite pro

"George I had the opposite problem, the temperature reading was too high and it turned out the instrument was wrong. Check the gauge."
 
"On my Chryslers, at one time,

"On my Chryslers, at one time, water was leaking around the t-stat. The pocket the t-stat fit in is a bit rusted, so the t-stat wasn't water tight when closed. I cured that by making up a sheet metal plate and riveted a new t-stat to it. Perhaps this is your problem?

Jeff

PS: In simple terms, too much water is flowing through the block for some reason."
 
"George,

I would check to b

"George,

I would check to be sure you have the correct thermostat housing installed. Merc has used several different designs since 1977, and the water flow also varies depending on model. Some of those things are a plumber's mightmare. But unless the laws of physics have changed, if that water in the block is not moving, it will get hot. For some reason the water is not staying in the block. Get the service manual, check the flow chart and check the hose configuration. You have water passing through the system and bypassing the thermostat. Good luck, Rick"
 
George
I agree with Rick. My

George
I agree with Rick. My old engine was a 1977 305 Chris-Craft Chevy. The risers and manifolds had been replaced with Mercruiser log style but they retained the CC T-stat housing. The motor would never come close to 110. A lot of housings look similar. Be sure to check to see if the existing housing is the correct one for your application.
Joe
 
"George, First make sure the h

"George, First make sure the hoses from the thermostat top cover are connected to the exhaust elbows, not the manifold or riser. The hoses that make a X pattern on the thermostat housing, the rear set should go to the stern end of the exhaust manifold or riser block and the front pair to the forward end caps of the manifold. As well under the thermostat cover you should be using the gasket with the matching notch in it. 24-48818. I see you replaced the plates between elbow and manifold. There are applications where they use a vented and non-vented version. Do you have riser blocks under the elbows? If so they should be the vented style. If no riser they should be the non-vented. My bet is the hoses from the top thermostat cover are plumbed to the manifold. Good Luck"
 
Thanks for all your suggestion

Thanks for all your suggestions. I have a feeling Harve may be on the right track.

Now I have to find the time to get to the marina and check it out!
 
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