Assistance with engine overheating.

[Kodiak536]

Been a while, been busy working too much and not enjoying my boat. My 1999 SC2300 with Merc 5.7 liter 2 barrel carb V8 developed an overheating issue.

So, I normally run my boat once a week until warmed up...this go on for weeks because of work.

One weekend, I ran the boat with no issues. Following weekend, I had to work and decided it would be o.k to skip a week...this is about a month after getting it out of "winter storage" mode.

The very next time I ran it, 2 weeks since last run-up, engine started to overheat and alarm sounded.

But, weirdly when I rev up the engine to @2000RPM, temp started to drop, EVERYTIME.

First thought was the impeller on the pick-up pump on out drive, even though I just replaced it last season, a month before storing for winter.

Upon removing, I found 3 impeller vanes broken or about to. AH, I said to my self, that's it, problem solved.

Well, it's still overheating. Yes, it was installed correctly, yes it was lubed-up before installing and no, there were no parts missing that could've got into water jackets to clog the system...all pieces were there AND installed with vanes in correct direction, clockwise per OEM support.

Then, I removed the thermostat, found it severely corroded and partially stuck open, probably never fully opened. Nothing changed after replacement.

So, I removed the temperature sensor and wire, shorted the wire to chasis to test the gauge, no issue there. Although sendor was covered in rust and gunk.

Clean and reinstalled. Temperature got better but, still overheating. Replaced with OEM part, same issue.

Replaced the temperature sender, same condition with rust and junk. No change.

Since water circulation pump was original as I got it and severely rusted, I replaced it, since revving-up would drop the temperature, thinking may be impeller in it broke or free spinning.

All that improved the over heating alarm issue but, with brand new 160 degree thernostat, gauge still climb up past 175 degrees?! No over temperature alarm now.

But, after running for @45 mjnutes, engine started to overheat yet again!? Rev up the engine and temperature dropped way below 175 degree, as if thermostat just opened???

All this happened just because I let the boat sit one extra weekend?

I'm now thinking the riser may have some kind of clog, preventing full circulation?

Or just simply the "new" thermostat from Amazon isn't working right? Since temperature always go up past 175 degrees, as if it never fully opened?

I'm going to remove the suspected thermostat and tested on stove with hot water. Meanwhile, I would appreciate expert opinion on this matter.

Any ideas? My apologies for writing a novel. Wanted to be precise to get an accurate diagnosis.

Thanks

[Phillbo]

Originally Posted by Kodiak536

thermostat just opened???

All this happened just because I let the boat sit one extra weekend?

I'm now thinking the riser may have some kind of clog, preventing full circulation?

There is no reason to start the boat every week if you are not using it. Millions of boats go months without being started.

I would look at the risers. How old are they and are you in fresh or salt water? It may be time to replace them.

[Kodiak536]

Originally Posted by Phillbo

There is no reason to start the boat every week if you are not using it. Millions of boats go months without being started.

I beg to differ on that. My inboard-out board engine WILL seize-up from all the humidity and condensation here in NC. I know this as a fact, engine seized on me twice from letting it sit too long. Rust start in no time in the cylinder bore here.

My boat was fresh water boat from Wisconsin prior to my ownership. Now, it's strictly saltwater boat.

As for condition and state of risers? Unknown. I am finding and replacing/repairing things as I find them. There were so many "minor" issues from P.O's amateurish attempts at "repairs" to MAJOR goof-ups and darn right stupidity, like installing automotive distributor.

I was informed by the broker who I bought the boat from that these risers should be removed and inspected yearly...it's been 3 years since I bought it.

I'm trying to keep this boat "alive" for as long as possible without any major issues. So far, out drive lower was cracked, found when I was replacing the impeller on pump. Now, I got a new lower.

Engine had 350 hours on purchase, now just over 400. 50 hours in 3 years are all I managed because of lousy work schedule.

This is my "retirement toy", which I'm hoping will be between 2-5 years from now.

Thanks for your input.

[Phillbo]

If you are getting enough rust in the cylinder bore in 2 weeks to seize the engine you have big issues. I'd say you have water getting into the engine. Probably time to pull the risers.

Millions of boats sit for months on end in the humidity and don't seize every time.

[mmwjr]

I recommend you get a IR temp sensor and take readings of the thermostat housing and exhaust components, thermostat should be 160* and exhaust components ~120*. I would also perform a flow test per the Mercruiser manual, remove inlet water hose to the thermostat housing and collect water in a bucket. This takes a minute to perform and if starting with a cold engine no risk of damage. Do you keep the boat in the water? Potential for marine growth in the lower passage is possible but the flow test will confirm this.

[Kodiak536]

Originally Posted by Phillbo

If you are getting enough rust in the cylinder bore in 2 weeks to seize the engine you have big issues. I'd say you have water getting into the engine. Probably time to pull the risers.

Millions of boats sit for months on end in the humidity and don't seize every time.

Understood and I agree. Engine had "siezed" twice, enough to think starter gone bad but, removing the plugs and manually rotating were enough to rotate and start the engine each time...first time, I replaced starter not knowing that.

I'll remove and test the "new" thermostat and go from there. I will update as I progress.

Thanks for your input.

[Kodiak536]

Originally Posted by mmwjr

I recommend you get a IR temp sensor and take readings of the thermostat housing and exhaust components, thermostat should be 160* and exhaust components ~120*.

That was my thought, after removing and testing the thermostat.

To answer your question, my boat stays on the trailer in my driveway, only see water when we go out, 3-4 times a year.

Like I said initially, I skipped one weekend of running the engine and next time, it over heated.

NEVER had this problem before in past 3 years I had the boat, which is what's confusing to me and have me baffled.

Engine run just fine, better in fact since those components got replaced but, overheating(gauge showing 175+ and rising until revving it up) still happen.

Issue is NOT immediate, it happened last after running over 45 minutes @175-180. Thermostat seem to open very little for a 160 rated.

When it did show sign of temperature rising, I revved it up to @2000 RPM, temperature started to fall and all of a sudden, it dropped drastically as if thermostat finally opened. I shut it down when it dropped and came here for assistance.

Thermostat is HIGHLY suspicious at this point so, it's coming off, run without to see and if no issue, I will test it in hot water. I can still return it for replacement/refund.

Thanks for assistance, will keep this post updated as I progress in troubleshooting.

[Phillbo]

Originally Posted by Kodiak536

Understood and I agree. Engine had "siezed" twice, enough to think starter gone bad but, removing the plugs and manually rotating were enough to rotate and start the engine each time...first time, I replaced starter not knowing that.

That's not 'siezed' you are getting water in your cylinders some how and the motor is hydro locking. I've never heard of humidity causing enough condensation to hydro lock a motor but then, I live in the desert.

[mmwjr]

Originally Posted by Kodiak536

That was my thought, after removing and testing the thermostat.

To answer your question, my boat stays on the trailer in my driveway, only see water when we go out, 3-4 times a year.

Like I said initially, I skipped one weekend of running the engine and next time, it over heated.

NEVER had this problem before in past 3 years I had the boat, which is what's confusing to me and have me baffled.

Engine run just fine, better in fact since those components got replaced but, overheating(gauge showing 175+ and rising until revving it up) still happen.

Issue is NOT immediate, it happened last after running over 45 minutes @175-180. Thermostat seem to open very little for a 160 rated.

When it did show sign of temperature rising, I revved it up to @2000 RPM, temperature started to fall and all of a sudden, it dropped drastically as if thermostat finally opened. I shut it down when it dropped and came here for assistance.

Thermostat is HIGHLY suspicious at this point so, it's coming off, run without to see and if no issue, I will test it in hot water. I can still return it for replacement/refund.

Thanks for assistance, will keep this post updated as I progress in troubleshooting.

Did your helm temp gauge read lower in the past? Mine has always read around 175* with a 160* thermostat yet using an IR sensor I get about 156* on the thermostat housing.

[mmwjr]

Originally Posted by Phillbo

If you are getting enough rust in the cylinder bore in 2 weeks to seize the engine you have big issues. I'd say you have water getting into the engine. Probably time to pull the risers.

Millions of boats sit for months on end in the humidity and don't seize every time.

I’m in the mid Atlantic area and I have only seen humidity cause enough rust on cylinder walls to lock an engine if the spark plugs were left out for a few years and we have 80-90% humity here in the summer.

[Kodiak536]

It could've been that my starter were going out, who knows how old it was.

There was a small leak on that side from the riser hose, which was dripping water on starter area.

I git until Aug 1 to return the thermostat, I'll test things out this weekend.

Thanks for your input.

[Kodiak536]

So, this morning I got out there on my boat to removed the new thermostat that I bought from Amazon, supposedly an OEM replacement from QuickSilver for this engine.

Ran the boat without thermostat and had ZERO temperature issue, stayed well below 175 degrees @1200 RPM, in gear and out, ran fine and never approached 175 as it did before. Ran nearly an hour or so, barely above the line half way to 175...whatever that is.

Took the new thermostat in to the house and got a pot of water going with thermometer in it. Heated water to @160, suspended it in the water as direct by the manual and thermostat didn't open. @168, it started to open and fully opened @178 degrees.

So, I guess Amazing Amazon sent me the wrong part! I guess I'll need to find another rated for 160. Next time, I'm testing it before installation to save me the hassle and headache.

Appreciate all the help people! I will, at later date, remove the risers and inspect them like I should've been doing past 3 years though.