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454 Mag Overheating - Help!

Old 06-27-2012, 11:06 AM
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Default 454 Mag Overheating - Help!

One for the collective...

So I have my new to me Formula. '89 242 LS, 454 Mag, Bravo. Engine runs great with the exception of an overheat condition.

Here are the facts:

Engine idled a little warm at first but thought that it was typical "on the hose" warming up. It once got to about 190 on the hose (high idle) but I thought not much of it. Took the boat out, and within about two miles of running, the engine would creep up to 200. Not good. If I kept the engine running well under 3k rpm, it seemed to creep up very slowly. Going back to idling would keep the temp around 150. Found trash in the oil cooler from a bad impeller (new one installed... forgot to clean out the line). Still overheating. Water flow from the sea water pump is enough to flood the bilge quickly (at least at idle, though I tried this same test on the hose at home with higher speed and lost water output and it was pulsing... not enough water at the hose probably).

Got the boat back home, and found that the thermostat had some issues. Removed the thermostat, and ran on the hose. Ran it particularly hard on the hose (of course no load), and the engine wouldn't go above 130. Thought it was fixed (needed a new sleeve to install the thermostat... left it out to test). Took the boat out Father's Day. Again, same issue, though not as quick to overheat.

I went back to the boat the other day and pulled the manifolds. I thought they were good, but lots of scale flaking off on the exhaust side with some evidence of water intrusion. They have to be replaced. I also pulled the circulating pump and its inspection plate. The bearing is shot but the vains apear ok from what little I can see.

I need to get this figured out. I am using IMCO risers on the stock manifolds. The risers are ice cold running on the hose... manifolds hot.

Any ideas?

Thanks!
Tom
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Old 06-27-2012, 11:17 AM
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How many salt water hours on the boat total? Sounds to me that you have years of scaling built up blocking passages. check all ins and outs of block and manifold.

your risers are cold and mani hot because the thermo housing runs water straight through to the risers when thermo is closed.
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Old 06-27-2012, 12:19 PM
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also, you may want to get a mirror to the inlet side of the oil cooler. You just might have old impeller jammed into the cooling tubes enough to restrict flow
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Old 06-27-2012, 01:36 PM
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also the hose joint at the transom. that is where the hose is at it's smallest. junk can pile up at the fitting in transom. blow it out backwards. put hose on pump inlet hose and blast it out thru drive.
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Old 06-27-2012, 03:12 PM
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I will go through everything again in terms of hose routing between the transom and the thermostat housing. It's possible that there could be some material wedged into the oil cooler. I back flushed it, but something could still be in there. We'll see.

I noticed that there was a good amount of steam coming from the exhaust when trying to get on plane (before it was showing an overheat). And to me anyway, it seems that there just isn't the volume of water coming out of the exhaust that I would expect (boat has the silent thunder platform... and the plugs are installed).

Oh, and the boat was purchased in Florida, and then made it's way up to the Annapolis area. Lots of salt I'm assuming. The whole pakage has 485 hours on it.
Hoping to get this figured out quickly.
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Old 06-27-2012, 03:44 PM
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ok that changes things a bit. You need to def check the freshwater hose coming from the drive to the transom. I'm betting you cant get your pinky in it where it enters the transom. Not an easy project to do with the engine installed. remove the elbow inside the boat and see how small the passage is for water to come in.. I would still get an inspection mirror to the inlet of the oil cooler too..
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Old 06-27-2012, 03:46 PM
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A friend mentioned this to me already... I had the hose off and looked at that. My pinky goes in fine though I can't really get that far into it to really check the elbow. I know this is supposed to be a pretty big issue on early Bravo set ups. If there was a problem at the transom, would it pump enough water to basically flood the bilge in a matter of a minute?
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Old 06-27-2012, 04:16 PM
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I would check all areas u can on the block first. If you still have the recir pump off those two outlets are good places to check, dig in there with a screwdriver and see what u find. Also with the thermos housing off check the intake for blockage. Check the exhaust, and the outlets of the risers.
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Old 06-27-2012, 04:28 PM
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I know the intake looked good. But I am going to dig around some. I have some engine brushes too that I can use to get into the outlet from the transom.

Water slowly heating up definitely points to a blockage/flow issue IMO... agreed?
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Old 06-27-2012, 05:01 PM
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if the boat has seen allot of sandy areas the block could have sand in it. we see it in our area once in awhile and have to flush them out real good.
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