Heat Exchanger / Cooling issue

[390Express]

Had too many issues last year to worry about the cooling system. My port motor would occasionally overheat and puke out coolant. Delving into that issue now. Engine seems like it's running great at this point.

Last fall I winterized both motors, and unscrewed the endcaps on the heat exchanger. Heat exchanger looked good, not clogged. No impeller pieces stuck in it, or anything like that. Couple tiny pieces of seaweed, no big deal.
I de-winterized the motor yesterday, unhooked the raw water pump, and ran the motor with end caps off, using the engine mounted circ pump only. I wanted to see if the heat exchanger was cracked or leaking anti-freeze into the raw water side. All good there, no leaks.

The only issue that I noticed, was the zinc on this side seems like it kind of fused itself to the heat exchanger. It's not clogging any passage, but when I remove the zinc plug, it's all blocked up. I can't get my finger in there. Should I use a drill or screw driver and open up that hole again, or wait until corrosion eats the anode and let it fix itself? The zinc on the starboard motor seems like it's completely gone. If I run aluminum zincs elsewhere, should this anode be aluminum as well? And, anyone know where to get an aluminum anode for the heat exchanger? All I see is zinc. (FWIW, I'm currently running zinc everywhere, but I plan on switching after my aft anode is done.)

At this point I'm guessing that air in my system was/is my biggest issue. I'm going to pull the hoses that are supposed to run coolant in them, and back fill them, to get as much air out as possible. The only bleed in the entire system that I see, is the small 1/2" nut at the very top of the heat exchanger. I don't see any bleed on the block whatsoever. Hopefully a new impeller and air bleed will straighten me out.

[mjk1040]

If it's truly a closed system, you have to get the air all out. Isn't there a brake bleeder like fitting around the thermostat? If not you will have to heat up the engine until the thermostat is open and coolant is flowing everywhere and add antifreeze as needed until all the air is out of the system, otherwise you will have a overheating issue.

[bud37]

Qr Bbpost At this point I'm guessing that air in my system was/is my biggest issue.

390, until you get that system pressure tested properly, you will be just guessing, wasting time and money. Seems to me this has been quite some time now and in my experience a little air works its way out over time. Good luck and I hope it is just air.

Oh and those two other tests I mentioned before in an earlier thread, for antifreeze in the oil and products of combustion in the antifreeze, then you will know for sure what you are dealing with.

[Viper]

Qr Bbpost..... My port motor would occasionally overheat.....

If you haven't replaced the impeller, then start there, and check all the other usual stuff; wear in the water pump, intake hose collapsed or kinked, no intake circuit blockage, etc. Do you have the U shaped oil cooler on the front of the engine? Those are notorious for causing raw water restrictions either from marine debris, impeller pieces, deteriorated anode, etc. If you have one of those and haven't checked it yet, that's a must. Air in the system will usually make its way through after a couple of good runs but I have heard of that taking a while sometimes.

What were the running conditions when she did occasionally overheat? Is it a full or half closed cooling system? Other than puking coolant, did you note any coolant level drop during the season? Did your coolant test okay before you put her away for the winter? A visual inspection of the HE will only reveal so much, as Bud indicated, you need to pressure test the system to be sure. Buy or borrow a rad tester. Have you performed any other tests such as a compression test? If I recall, you were having a fuel delivery issue, was this happening during that time, and did it happen again after the fuel delivery issue was resolved? Just spitting some ideas out there but there's really no sense in going any further before replacing the impeller and checking the oil cooler first, then taking her out for a good run.

BTW, don't drill out the anode port, you run the risk of ruining the threads. Use a pick to get most of the material out then chase the threads. You should then back flush so you don't push debris throughout the circuit.

[390Express]

QR_BBPOST..... My port motor would occasionally overheat.....

If you haven't replaced the impeller, then start there, and check all the other usual stuff; wear in the water pump, intake hose collapsed or kinked, no intake circuit blockage, etc. Do you have the U shaped oil cooler on the front of the engine? Those are notorious for causing raw water restrictions either from marine debris, impeller pieces, deteriorated anode, etc. If you have one of those and haven't checked it yet, that's a must. Air in the system will usually make its way through after a couple of good runs but I have heard of that taking a while sometimes.

What were the running conditions when she did occasionally overheat? Is it a full or half closed cooling system? Other than puking coolant, did you note any coolant level drop during the season? Did your coolant test okay before you put her away for the winter? A visual inspection of the HE will only reveal so much, as Bud indicated, you need to pressure test the system to be sure. Buy or borrow a rad tester. Have you performed any other tests such as a compression test? If I recall, you were having a fuel delivery issue, was this happening during that time, and did it happen again after the fuel delivery issue was resolved? Just spitting some ideas out there but there's really no sense in going any further before replacing the impeller and checking the oil cooler first, then taking her out for a good run.

BTW, don't drill out the anode port, you run the risk of ruining the threads. Use a pick to get most of the material out then chase the threads. You should then back flush so you don't push debris throughout the circuit.

Thanks Viper, that's the response I was looking for. The boat was idling for a little over two hours the first time it over heated, which leads me to believe that either a faulty impeller or a clogged pickup was the culprit. Now it overheats after 20-30 min. idle time. I already planned on changing the impellers this year, on both motors.

This isn't an issue that I've spent a ton of time on, I know the system needs bled, but I can't figure out the best way to do it, other than running it with the cap off, and bleed on the heat exchanger open. There's no bleed on the intake, or the housing.

Your advice regarding the zinc anode and not screwing up the threads makes sense. Do you believe I need anodes, given that it's attached with rubber mounts, and I keep it in fresh water?

I have no fuel delivery issue with the port motor. The port motor had a faulty ECU. It had bad gas, but I've worked that issue out. It still has an erratic idle, I don't know if the ECU has the idle set too low, or if there is some other issue. I did put a new IAC on the port motor, didn't change much. Idle drops down to around 500, and sputters back up to 900. I can mess with the throttle and feather it down to 500. It's supposed to be a learning ECU. I'm hoping new (proper) plugs (it has the right Champion plug in it now, but Champions seem shitty, I have AC Delco plugs to put back in it), and unplugging and re-setting the ECU fixes the issue, or conversely, run time and allowing the ECU to learn the motor corrects the same. That said, I'm not too worried about the erratic idle, it doesn't effect the performance, and it doesn't stall. I'm correcting these things in order of importance.

[390Express]

Pulled the raw water pump. It has 2-3 lobes missing off of the impeller. Kinda of what I figured. Boat would run hot at idle, and cool back down over 1200 rpm. Now... where to find the missing pieces? They're not in the heat exchanger. I believe the raw water pump goes to the Walter gear drive first, then back to the oil cooler. Is there a filter on the gear drive that could pick up the pieces? I still haven't located any thing similar. I'll do my best to back flush the system before I put it back together.

Top of the thermostat housing is where the hose to the overflow container goes. Seems like the system should kind of self-bleed through there. I've been running it at 15-20 min. intervals, without the raw water pump hooked up while the boat is on the dry, with the air bleed on the heat exchanger. Hoping it bleeds itself. So far, the antifreeze levels have stayed the same, without the motors overheating.

[tomschauer]

390, you should not run the engines without the raw water circulating. Without the raw water the exhaust temps get very high and will damage your exhaust hoses and mufflers.

[Viper]

QR_BBPOST 390, you should not run the engines without the raw water circulating. Without the raw water the exhaust temps get very high and will damage your exhaust hoses and mufflers.

++1

[Viper]

You may have done this before but can you post the engine's model number. Do you have MEFI ECMs? And what do you mean by "It's supposed to be a leaning ECU"? Are they OEM ECUs?

[Viper]

BTW, no filter in the raw water side of the Walter unless a previous owner installed something inline before it. I don't think that impeller pieces would get stuck in the drive's exchanger but anything's possible.

500 rpm is way too low for the Walter. You need to find out what's causing the low rpm.