Seacore Engine Overheat

Ian

I’d also raise the drive to get intake up as far as you can. 

TonyG13

In order to try and understand where I need to look for leaks I found info from various places and tried to combine them into one basic cheat sheet I can use to learn from.

Here is what I came up with...



Orange is anti-freeze and Blue is seawater. Most documents I found call the anti-freeze side "fresh water" but I found that confusing since I boat in "fresh" water, so I'm just calling it what's in the system.

Does this look accurate for a Mercruiser 350 MAG MPI Alpha/Bravo EC Seacore?

Any corrections, errors, omissions I should make?

Dream_Inn

Looks good. #23 is the steering pump cooler.  It's typically the first place, after the seawater pump, that stuff could clog things up on the raw water (blue) side.

J3ff

What's number 19? I have leak right there... 

YYZRC

Water distribution housing. 

J3ff

YYZRC said:

Water distribution housing. 

Thanks - can it be changed in water? I assume just stuff two rags into the hoses...? 

Dream_Inn

Yes, the distribution housing can easily be changed in the water.  They tend to get brittle and crack after a while.

Liberty44140

yea you want to get that hose above the water line and then no water will come in while you change the pump. Ask around the marina for wooden plugs, will make a big difference if you can find some to plug the hoses as soon as you can. 

Look like this:

https://www.westmarine.com/buy/seafit--wooden-emergency-bungs-plugs--4641080?cm_mmc=PS-_-Google-_-GSC%3EBrand-_-4641080&product_id=4641080&creative=343879478299&device=c&matchtype=&network=g&gclid=CjwKCAjw4MP5BRBtEiwASfwAL3XTnzWOgs_DgU4YL0Megq_uzqZxB0dTZruIuuC5gMOKZylSPx8CsxoCXggQAvD_BwE

LaRea

J3ff said:

Thanks - can it be changed in water? I assume just stuff two rags into the hoses...? 

For an interesting experiment, just disconnect the hoses and leave them disconnected for a few minutes.  See how easily your bilge pump keeps up with it.  

Yes, stuff a rag into the input hose, and don't stress about it.  

YYZRC

Nice clean bilge afterward!!

Ian

Dream_Inn said:

Yes, the distribution housing can easily be changed in the water.  They tend to get brittle and crack after a while.

I did mine near end of last season, someone along the way had tweaked the blue plug and affected a “fix”. I unscrewed it and the fix de-fixed and thought I’d flood the engine room but only a trickle. Found another online and replaced no problems in water.

TonyG13

Just picked up a loaner pressure tester from AutoZone, looks brand new. I don't think many people have used it. I'll head over to the boat tomorrow to see if I can find the leak.

Great deal from AutoZone. Put down a deposit for the cost of the tool and if you bring it back within 90 days get money back in full. Basically a free rental.

Dream_Inn

Definitely great deal Tony.  I did that with a pulley remover as well.  As long as you don't break it, you don't have to buy it!

TonyG13

Agree! Hopefully I don't drop it in the water while boarding! This one is nice because it has adapters to also pressure test radiator caps - so I can do the original one on the exchanger as well as the replacement I bought.

Liberty44140

Those work well Tony, I borrowed the same kit from Auto Zone to test the heat exchanger for leaks on my Kohler 5E following a backfire a few years ago (from me adjusting the choke improperly). Great test kit. 

TonyG13

Well, none of the adapters in the AutoZone pressure test kit fit either my cap, fill top, or the overflow container. I did get one of the "universal" adapters to fit the overflow jug, but wouldn't hold a seal.

So I topped off the system. It took 1-1/2 gallons. Put on a fresh radiator cap and started her up. No active leaks that I could see, but after about 10 minutes at idle it shot from 160 to 220. Immediately shut her down.

Next step - impeller change. Hopefully that's it and it's still in one piece and I won't have to hunt downstream for pieces.

Aqua_Aura

If it's heating that quickly and it suddenly happened the first time, it would seem like an impeller. They are not difficult to change 👍

YYZRC

Aqua_Aura said:

If it's heating that quickly and it suddenly happened the first time, it would seem like an impeller. They are not difficult to change 👍

Great choice of words.  Not "difficult", just painful, frustrating, time consuming, and unnecessarily terribly designed/located!

Aqua_Aura

It's probably harder in the Mercury, I guess I didn't think about that. The Volvo was very easy to do as it is just attached to the harmonic balancer. Take off two hoses a couple of screws and pull it off. 

YYZRC

The Volvo impeller swap is bliss. 

212rowboat

i'd also be worried about a blockage... 

TonyG13

Installing new impeller tomorrow. Buddy said to also change oil in case it got cooked. Good advice?

212rowboat

With modern oil the fuse isn't lit until after 240*.... 

TonyG13

Since I couldn't squeeze down and do a Gumby, I had my mechanic change the impeller yesterday. It luckily was not fried or disinegrated...

It was very flexible, not stiff like a new one. Topped off anti-freeze on closed side and installed new radiator cap. Put in a total of 3 gallons since overheat. Still wondering if as @212rowboat said that loose radiator cap could also have been a contributing factor since it seemed loose when I went to check it after the first event.

Ran both engines to have something to compare to and here are my temps with times every 2 minutes from start and RPM:

Port     Stbd     Time     RPM
77        77       Start      Idle
117      113    +2:00     Idle
135      129    +4:00     Idle
156      149    +6:00     Idle
167      160    +8:00     Idle
163      167    +10:00   Idle
160      160    +10:00   1500
162      162    +12:00   2000
160      160    +14:00   2250
167      162    +16:00   Idle

Left it idling for about 15 more minutes before shutting down.

Last week, it shot up and overheated at about the 10 minute mark. Not today.

Do these numbers look within normal limits? Problem solved? Anything else preventive to look at?

Ian

I don’t have seacore but look pretty typical to me. A few degrees delta could be the sensors. 

212rowboat

The delta is most likely the thermostat... they aren't precision things, but they are close enough... youd think after all these years something better would be introduced,  but... well... theyre good enough.  Also don't forget that delta could simply be an air bubble somewhere in the system that hasn't burped. 

Re: loose cap
Usually in an overheat the cap blows... its kinda made that way and the reason theyre not threaded... it could easily be the cap, or the cap could be a casualty.... either way, caps are consumables and once one has done its job, it's time to retire it.  

You could have sucked up sand that has since cleared, you could have had air in the system that was reluctant to burp, you could have had a bad cap... run it and find out... oil is good to 240 before it starts to break down... for every pound on the closed system you raise the boil point 3* (so add 35* to 212* at sea level with a 15# cap) so your engine is capable of handling 220 to 230 easily and without damage.  It won't go that hot instantly... when you alarm it will be at 182*, but you're still good... if it climbs to 190 bring the boat down, disengage gear, throttle up that engine (in neutral) and see if the temp goes down (max flow of sea pump at around 20-25gpm and no load on engine)...

if it DOES cool back down, you've got a flow problem... if it doesn't, you've got an obstruction problem.  The sea pump doesn't produce ample flow at idle for a hot engine, but touching 1200 or so RPM (above the 650 or so at idle) will near the bottom of the suitable flow range for a hot engine.

Obstruction other than obvious includes thermostat or rusted risers/elbows disallowing exit of water.... flow issue includes circulation pump on engine in addition to hoses kinked... 

Now youve been initiated.... you know what to look for.  

TonyG13

I definitely appreciate the initiation - and education! I think I now have at least a base knowledge level on the cooling system.

Thanks for all of the advice and explaining it at an elementary school level! I try to read and keep up on some of the other threads you guys comment in and they are at doctoral levels.   

YYZRC

Does your water pump have the replaceable wear plates? If not, any scoring on the brass housing?