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briang0

Regular Contributor
"I have a 1/2 FWC Chevy BB 409

"I have a 1/2 FWC Chevy BB 409ci. When I purchased the boat 3 years ago it had a setup that had no room for a thermostat. The engine ran cool I would have to let it warm up for about 30 minutes before leaving the dock. Last year I installed a used thermostat housing off a 454 BB. Plus new manifolds and risers, and a new tranny cooler. Now the engine warms up a lot faster and generally runs at 160-170 degress. The one strange thing is the temp gauge will go up to 200 degrees right before the thermostat opens then drops right down and holds after that. Is this normal? I have nothing to go by since berfore the change the temp never got above 140 unless there was a problem. I made several cooling line changes not sure what the previous owner was thinking. The only thing that is not perfect is the bypass hose doesn't come off the water pump near the thermo house it comes off about 6 inches away at another port on the water pump. I didn't have any trouble last year but I like to have things right. Comments??"
 
"I'm not familiar with a 4

"I'm not familiar with a 409 BB. There is/was a 366, 396, 400, 402, 427, and of course, the 454 and now, larger. In any case, where exactly is the water temperature sensor? I will notice that the manifolds do get quite hot before the thermostat opens, at which point the temp heads back down as circulation improves. If you don't get any steam out the cap during warm up, I tend to think this is a non-problem."
 
What type of system was used o

What type of system was used on the 454 that donated the housing? Where is the thermostat come from?

where is the temp sender located?
 
It came from a fresh water coo

It came from a fresh water cooled engines the temp sender is in the intake manifold about 4 inches from the housing the thermostat is 160 degrees and is new. There are 2 lines coming from the housing to the heat exchanger for antifreeze.
 
I've seen t-stats do that-

I've seen t-stats do that--my starboard engine does now and then. Okay 'long as the temp drops. I suspect the stat is sticking somehow.

Jeff
 
"If you want to check it, ther

"If you want to check it, there is a simple way. Remove the theromstat; put a pot of water on the stove; put the thermostat in the pot of water; and begin to heat it slowly. Notice the temperature of the water. If it is a 160 degree thermostat you should see some movement of the thermostat at about 160 degrees. Continue to heat the water and see if the opening of the thermostat is smooth. If it opens all at once it is sticking. Even though it is new, in that case I would change it.

Just a suggestion,

Chuck Hanson"
 
"Congrats on keeping the dinos

"Congrats on keeping the dinosaur roaring.

The few i've seen have the bypass hose coming off the top of the water pump and connect back up at the front of the intake, just like the Mark IV's. This could be a factor.

The sender being in the manifold, not in the t-stat housing, is not "marine" standard. The peak temp before t-stat opening could be coupled.

was the t-stat a marine part? Sometimes, there are little differences that will separate a marine part from an auto part.

If the temp-spike-before-opening happens all the time, and it cools while running, I'd live with it. If it happens sometimes, I'd keep digging. Get one of those handheld IR temp guns - it's money well spent"
 
"It could be that the exhaust

"It could be that the exhaust crossover in the intake manifold is heating the nearby water passage, causing the momentary spike. One of those good times to use a IR temp gauge and measure around there during warm up."
 
The tstat is not a "marine

The tstat is not a "marine" one so I'll put a marine one in. I can move the temp sender to the thermo housing since it had one in place when I installed it but used the one that was already connected. I'm not 100% sure where the by pass hose goes into the housing after 4 boys my mind is not what it use to be although I don't have to lift anything when they are around. I'm building a to do list for April since there is about 4' of snow around the boat right now and more on the way this week.
 
"brian;

thru the friend-of-

"brian;

thru the friend-of-a-friend loop, rx'd suggestion to check www.348-409.com for lots of specifics on these items. Understand it is auto focused, so check there for the basics and check back here for the marine-specific.

The few that I saw had the hose going from the pump back into the cooling passage on the intake. I would think you could use the t-stat housing if the fittings are in the correct location.

good luck"
 
Here's an update. The byp

Here's an update. The bypass hose goes from the water pump to the thermo housing and the temp sender is in the intake manifold. Is the consensis to put the bypass hose to the intake manifold and the temp sender in the thermo houseing?? I just installed a new 160 degree marine thermostat and new gaskets one gasket has the little brass eyelets in it.
 
that'd be my vote for the

that'd be my vote for the routing.

the gasket with the brass grommet is to ensure electrical contact betwen the manifold and the tstat housing in case you have a sensor or switch in the housing.
 
Here's an update. I moved

Here's an update. I moved the temp sender from the intake manifold to the t stat housing and moved the bypass hose to the intake manifold. I fired her up and after a little longer warm up the temp came up to 160 and held. I can't run the rmps up to high on land because my well can't keep up with the raw water pump. Right now things look good I'll know better in a couple of weeks when I put her in the water. Thanks for all help...
 
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