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Help! Both engines overheating ! Help !

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Old 08-01-2010, 10:37 PM
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Default Help! Both engines overheating ! Help !

Ok guys here is the scenario....1999 Donzi 38ZX with 525SCs. Boat has been running perfect with no issues on Lake Lanier. Last weekend we spent the night on it and when we awoke we had drifted a little bit closer to shore than we were. I thought I was far enough away and deep enough water but apparently I wasn't. In fact, I could have been in some sandy silt. Anyway, we cranked up and took off. Not 90 seconds later, both engine alarms went off and I noticed the water temp gauges were at 190+degrees. I jumped in and checked the intake on the lower units. They appeared clear. Got a tow home. Called my service guy and he came out and replaced the impellers with the results being the same. He then came out and replaced both thermostats and back flushed from intake hose of the water pump out to the lower unit. There was some sandy residue surrounding the thermostats. Same results. Now I feel certain that I sucked up a S%#T load of crap. Now every time I have changed impellers, I change the impeller, plate, housing, etc. Come to find out, he did not change the housing. So he is coming back to redo those. He said they weren't scorched bad that is why he left them. Although we flushed the bottom hose and out the drives, I can't help but think we could have flushed more of the system. Is there a safe way to flush more? Where else can I have a blockage? It is pumping water out of the exhaust but it must not be circulating enough in the block. The hoses out of the thermostat housing are warm so I feel they are opening like normal. We love this boat. It is perfect for us and our three kids. Any ideas on what else it can be ? I am worried that he will replace the housings and nothing will change. Then what?
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Old 08-02-2010, 05:57 AM
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Don't forget the oil & power steering coolers. I would take the whole cooling system apart and flush it thoroughly and install NEW pumps. IMHO

Good Luck
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Old 08-02-2010, 08:26 AM
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You may wish to invest in two large sea strainers to prevent further problems in the future. Perko. com has large strainers. your choice.
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Old 08-02-2010, 08:40 AM
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I can not imagine that boat does not have sea strainers with 525's in it? If so did you clear them out? It is possible that if you do have them and did not clean then the new water pump is messed up as well. IMO if there is any scoring at all you need to change the houseing. You may have to pull your coolers to clean them out. Lots of times unless your hose has lots of preasure it will not flow enough. You can also pull your block drains and see if you are getting any sand out of them.
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Old 08-02-2010, 09:08 AM
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Yep. No strainers on it. Good idea about the block drain. Hopefully things will improve after reinstalling the impeller and housings. I'll research the oil cooler stuff. Any more info on a more complete flushing ?
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Old 08-02-2010, 10:53 AM
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you have the exact same set up i have, the drives are HP's with the low water pick ups at the bullet (not the later dual bullet and side pickups used later). I boat in a silty area as well and it does not take much to block up passages in the drive. Pull the intake hose off the raw water pump, attach a garden hose and clamp it down good then back flush the drive. I've had it happen several times and have gotten pretty good at clearing the system out in the water.

you can also back flush the cooler by pulling the feed that comes up just under the blower snout. Attach a garden hose there and make sure the hose is off the raw water pump so you can get a good flow through the cooler. Once you are sure the cooler and drive are free of silt and the pump is functioning properly any silt that made it into the engine should clear itself under normal use. No large debris can make it past the oil cooler so i wouldnt worry about big clumps of anything getting that far up. Been through this dozens of times.

I dont have strainers and to be honest I'm not sure how well they would work under these circumstances.
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Last edited by glassdave; 08-02-2010 at 11:02 AM.
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Old 08-02-2010, 11:49 AM
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I thought there was a thread before about how to try and strain sand/silt, if I remember everyone said the sea strainers that come on most new PB don't strain sand.

Is this correct?

Is there a strainer that does?

Last edited by Wildman_grafix; 08-02-2010 at 01:06 PM.
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Old 08-02-2010, 12:37 PM
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do you have some kind of transom mounted flush valve that allows you to flush the engines without putting the muffs on the drive?

If so could it be letting air into the system and breaking the suction
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Old 08-03-2010, 09:10 AM
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Pull the petcocks out of the blocks and check for sand with some wire....Sea strainers will not stop sand....Been there
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Old 08-03-2010, 11:23 AM
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Sand and silt will go everywhere and get stuck. The best thing to do to be 100% sure that most of it gets out is pull every hose one at time and backflush. Also, I would pull a couple of your bottom exhaust hoses and flush the manifolds or headers, depending on what you have.

Then after its all back together, Pull the block drains and run the engines on the hose with the drains out. Shove a coat hanger way into the holes with them running.
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