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Discussion Starter · #1 ·
I just replaced a set of stock Mercruiser stock manifolds with a set of CMI headers. I also installed a pressure gauge in the top the thermostat housing. At idel I bounce between 0-1 psi and about 3000 I have 2-3 psi. I changed the impeller with a stock Mercruiser impeller and housing about 10 hours hours ago. Is this low? THe reason I have a lot of steam out of the exhaust, The temp rises then the then falls once the t state opens Any help would be appreciated.
 

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On my totally stock (read thru prop exhaust) 7.4 MPI, I get off the peg at idle, and about 6 pounds at 3K rpm. Temp stays constant, and I can put my hand on the risers. Port is always cooler than starboard.
 

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If these pressure readings are on a garden hose , don't worry about it. Try in in the water. I think you will see much more.
I can't get more than 3 psi on a hose.
 

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Discussion Starter · #5 ·
The presure reading was running it in the lake today, I just pulled the impeller and all the blades are intact and look good. The fitting for the gauge is in the top of the factory 4 port tstat housing (I drilled and tapped the top plate) two of the 4 hoses I plugged, Could it be where the fitting is placed?
 

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If your bypassing the water straight to the manifolds from the stock T-stat housing, there's not much resistance, so I don't think your going to see much pressure at all if it's tapped to the T-stat housing.
 

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Discussion Starter · #7 ·
Is that amount of presure going to be enough? is there something that I can do to increase the presure?
 

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Does'nt require a lot of pressure, But it does need enough volume moving though it to remove the heat..
Once your T-stat opens up, the circulating pump will draw in more water and move it through the block and back out though the manifolds.

Are you over-heating .??
 

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Discussion Starter · #9 ·
No I wasnt over heating, the temp would rise to just over 180 then drop back down under 120 on the gauge The engine is carb'ed, Would I be better off to replace the 180 with a 140 to help keep the temp more consistant?
 

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I would run the 143, that's what I use, but my temps stay 140-145.

Do you still have the original Teleflex gauges??

The reason I ask is, I just changed my originals out, and was amazed at the difference in the readings I'm seeing now..

I thought I had all sorts of problems, water over heating, low oil pressure, etc. I was chasing problems that did'nt even exist..!! and now everything is perfect.. :bigsmile:
 

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Discussion Starter · #11 ·
All the gauges were changed out before I bought the boat, When I was running the original 454 the temp gauge would never move until the engine was shut off. Now the 502 I bought had a 180 istalled I thought that I would leave it because of the alum heads. Thanks for all the replys
 
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