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Old 08-19-2017, 06:55 PM   #1
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Default Bad Day for both engines...

So two problems happened at the same time today.
First, my old engine that I haven't rebuilt yet has been running hot this summer, and it seems it runs hotter every time I take it out. Today it got hot so I slowed it down to cool off, and had the other engine going harder to keep some speed. Well all of a sudden, RPMs jumped up to 6k on that engine!

So each engine and its situation.
Hot engine- has a new water pump from this past off season. Closed cooling from a MPI 7.4L. Last week I took the 160 thermostat out, which I checked was working, and replaced it with a 140 and added a bottle of cooling enhancer fluid stuff. Under load she was running 220 and took a long time to come back down. I cleaned the barnacles from the drives and water inlets three weeks ago. I know the engine is getting weak, at least one or two cylinders have low compression. You think this could be a head gasket issue? Or should I try flushing the closed cooling because the heat exchanger might have some build up in it?

No thrust engine- prop would spin in forward and reverse, but no thrust past idle. The RPMs just go up like it's in neutral. Back at the dock, I put it in forward and then reverse, and could not move the prop in the opposite direction, the way it should be. So I don't think the prop's hub stripped and the clutches are engaging. After sitting an hour or so while we ate, I went to flush the engines at the dock. Put the drive all the way up and gave it some throttle in forward and reverse, and it seemed like it was taking the load now. So I'm confused on this because both forward and reverse are acting the same. I've had a shift cable wear through the sheathing before so I know what that's like and this isn't the same. I thought if maybe the cable wasn't adjusted right, but that would only affect forward or reverse, not both. Any ideas on this one?
I just keep seeing $$$ and time lost from family, work, and the water right now and feel sick about it...
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Old 08-19-2017, 06:56 PM   #2
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Oh, 1994 3200 with 7.4L carb engines.
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Old 08-19-2017, 10:43 PM   #3
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Ok you ran the one good engine to hard with an off balanced load, assuming BII you either spun the prop hub or engine coupler. Another possibility is broken shift cable or drive it self.

On the overheating engine what color is the antifreeze? These were raw water cooled and still have rust the water jackets that will fluff off scale, this is know to collect in the HE and block it. Remove end caps and try cleaning it out. Get an automotive radiator pressure tester and pressurize the closed cooling system to see if head gasket or other leak exists.
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Old 08-19-2017, 10:54 PM   #4
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Talked to a mercruiser guy and thinking either the engine coupler or the coupler between the upper and lower. I've made trips before on only one engine, so seems weird it would happen this time with both engines still running. Have to look and see if I can take the coupler off without pulling the engine... I'll have that and the internal drive coupler with me when I pull the boat.
The coolant is still green in the other one, but does has a lot of sediment. I pulled the end caps off, but that's the raw water side. I pushed a coat hanger through each tube, too. Will look for some radiator flush next. That engine has to get me to the boat yard...
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Old 08-20-2017, 04:25 AM   #5
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The flywheel cover has the rear engine mounts built into it and it must be removed the replace the engine coupler which is bolted to the flywheel. I do not know of a coupler in the drive it's a splined shaft that slips into the cone clutch in the upper half. Cooling down may the the couplers rubber and it will not hold up under load. Do you smell burnt rubber in the engine compartment?

Duh yes the end caps of the HE cover the raw water side, the closed side is copper tubes in the HE but these can become clogged with scale since it was a raw water engine. The HE may need to be removed and taken to a radiator shop to be flushed but first rule out all other potential cooling issues. Are you loosing antifreeze? Have you checked the raw water flow to the HE to ensure its a got a good flow rate?
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Old 08-20-2017, 04:29 AM   #6
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Yeah, I remembered the bell housing later... I'm starting to think I need to pull the prop. I never smelled burnt rubber. I'm assuming it would have been obvious?
I just ordered Barnacle Buster to put in the cooling system. I verified my raw water pump worked while I had the end caps off the HE...
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Old 08-20-2017, 05:06 AM   #7
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Yes a bad engine coupler will smell, you also said you could hear the clutch shift but no motion do the prop would be my first place to look.

Have you used an IR sensor to verify engine temps?
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Old 08-20-2017, 11:59 AM   #8
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I haven't brought my IR out because the alarm has been consistent with the gage.
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Old 08-20-2017, 12:16 PM   #9
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I think the overreving engine is a bad prop, onyou have a spare to try?

So you plan to run barnacle buster in the closed cooling? Not sure why.
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Old 08-20-2017, 12:27 PM   #10
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Yeah I'm going to go pull the prop. Hoping that's what it is, the more I think n about it.
It's called barnacle buster, but it's supposed to dissolve everything and they recommend it for raw and fresh water cooling systems.
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