Mercruiser 228 got hot, but was it too hot?

Josephmcg

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Aug 15, 2017
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cruisin through my harbor, for a good 15 mins before heading out into long island sound, all gauges were good, cruised across the sound probably about a 1-3 minute ride , pulled back on throttle was cruising just a little off plane for maybe 2 min, looked down and my temp was super high, I'd say 220 tops. So I shut everything down, opened the hatch and let her cool, both exhaust manifolds were hot, the coolant tubes on the top of the engine were hot, although I could touch them I couldnt hold my hand on them for long. Nothing smoked or smelled funky. Waited til she cooled to 160, started right up, starting cruising at 5-10mph and temp went back to normal 140, heading back in the whole time doing 10mph tops and engine ran fine, sounded fine, and temp stayed a consistent 138-140. I know I have to go check some things out because something isn't correct, but do you guys think I've done any damage and where should I start to diagnose? Any help would be greatly appreciated

Thanks guys
-joey
 

Josephmcg

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Aug 15, 2017
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Forgot to mention, engine is a mercruiser 228, chevy 305 small block, with a 2 barrel carb, raw water cooled, alpha 1
 

Lou C

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I don't think 220 would hurt it esp since you caught it fast. What I'd do is check the exhaust hoses and flappers, and then maybe do a compression test. Check the oil for water. Probably fine, you may have picked up something on the lower unit. Might want to check your raw water flow with the boat in the water. How old is the exhaust system? In the region you boat in (LI Sound) raw water cooled exhaust should be replaced every 5-7 years to be on the safe side. When the risers get clogged up you can have high temps like that.
 

achris

More fish than mountain goat
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Tough one. Depending on what caused the overheat will direct you in the remedial work. But it looks like you don't know... If it was a plastic bag on the water intakes, then you need to check the water pump impeller, housing and base, water pocket cover, exhaust shutters and all the rubber in the exhaust path. If it was debris caught in the thermostat, then just pull the thermostat and clear that. As water would still have been flowing through the system, all those other things will have been fine.

Chris........
 

Josephmcg

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Aug 15, 2017
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Thanks guys for your support, the exhaust manifolds and risers were done within the last 2 years, I'm going to head down to the boat in about an hour to see if I can figure anything out, again thank you
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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if it got hot, there was no water flow. your flappers are most likely burnt along with your rubber exhaust hose (rated at 250F)

you may or may not have done further damage, however like Chris says, pull the drive and get to the impeller. while your in there, I would simply change the impeller and raw water pump.
 

CamaroMan

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Mar 18, 2016
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if you do the impeller, u can find the hose coming from the transom tot he front water pump, and see how long it takes to fill a bucket.. however since it rn fine at 140 afterwards it it a bit odd.. perhaps a plastic bag wrapped around the water intake, but that is so rare!

You might have a small crack in the water hose coming up form the outdrive which might still supply water ..



Bit of a hack way but this might give an indication:
When u remove the lower leg to do the impeller.. plug the copper water pipe going up into the upper (make sure its in and seated) and block it with a rubber stopper. Find the hose that comes from transom to water pump in front of motor (usually about 1-1/2 or 1-3/4"), remove it and fill with water.. see if the level goes down. if so u have a water leak somewhere between the motor and the outdrive (bad).

Obviously the pump puts out more pressure than just gravity but it might show u something. Tilt the drive up and down a little - this will flex the water hose and possibly reveal a leak..
 

Josephmcg

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Aug 15, 2017
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Hey guys thanks for all the support, I went down and checked everything out I could without pulling the drive, everything seemed fine, so I raised the out drive, and cleaned the lower unit where the water inlet is, there wasnt anything major blocking the inlet or anything but i figured why not. Since then I've taken the boat out 4 or 5 times without a problem. Temps are always on point and boat runs great.

I know I should pull the drive and check the impeller but the boat is coming out of the water in the next week or so, and I plan on doing alot of upgrades and repairs to her then. I think I may have just had something like sea weed or the very very rare situation of picking up a bag, although in long island sound you never know what you're going to come across.

Again thank you guys for the support I greatly appreciate it!
 

Lou C

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Is the boat docked or moored in salt water? If so there is a chance you had some barnacles growing up above the water intakes in the water passage. I have had this problem and have split the drive a couple of times to clean them out. While the boat is still in the water, why not do a raw water pump output test, that will tell you for sure without taking anything apart.
 

Josephmcg

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Aug 15, 2017
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Hey guys. So it's back to getting hot while on plane, the boat is docked in salt water, how do I do the raw water pump test? Also what other tests can I do to rule other things out? I can idle and cruise around my harbor without any issues, once I get underway say above 15-20mph, temp starts to creep up, once she gets around 180, I back off to a stop then start cruising slow again, and the temp comes right back down to normal temp
 

Lancer76

Petty Officer 2nd Class
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Jul 23, 2017
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Sounds similar to what I just went through - same symptoms. For me, it was bits of impeller clogging the water intake tube, so engine was not getting adequate flow. for what it's worth, I could not simulate this condition on the hose; only on water. Once the impeller pieces were removed, the problem was solved. I was told that flow from the stern drive to the thermostat housing (when hose is removed) should bubble out of the hose 5 inches. However, I am not certain at what RPM that occurs.
 

Josephmcg

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Aug 15, 2017
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So what did you do remove the house from the stern drive to the thermostat at the thermostat? And flush water in through muffs on the outdrive? To remove all pieces? Or what would I have to do to see if that inlet house is clogged?
 

Maclin

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May 27, 2007
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Overheat at speed can be a symptom of clogged exhaust manifolds or risers, especially so in salt water.
 

Josephmcg

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Aug 15, 2017
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The manifolds and risers were done in the past 2 years, but i think im going to have to do them again if that's the case, should I upgrade to the newer ones with the riser in the center or find old style one's with the riser on the back of it ?
 

Lou C

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It is far more likely that you have a low raw water flow into the cooling system, than clogged risers because they are only 2 years old. Usually you don't start to see clogging there till about 5 years. I would look up the spec Merc uses to measure raw water flow, and do that test with the boat in the water. If its low then its time to remove the drive and do the impeller, plus look at all the places where old impeller bits can get lodged (transom water hose, thermostat housing, manifold and riser feed hoses). When replacing the impeller, check the water intakes for marine growth. This is a problem I had till I removed that screen that OMC put in the lower units on the Cobra drives, barnacles would grow right on it. I made a clean out tool out of stiff wire and I can rod out the water intake holes and the area just above it even with the boat on the mooring by tilting the drive all the way up. If its never been cleaned out, or not in the last 3 seasons or so, you'd be surprised what can grow in there. I boat in the same region as you do (Long Island side of LI Sound) and this is a common problem. My mechanic says the clean out should be done about every 3 seasons if the boat is moored or docked in salt water. My temps were getting close to 185 before I cleaned it out and after that, it went back down to its usual 160.
 

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Lancer76

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Jul 23, 2017
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So what did you do remove the house from the stern drive to the thermostat at the thermostat? And flush water in through muffs on the outdrive? To remove all pieces? Or what would I have to do to see if that inlet house is clogged?

First I dropped the lower unit and checked the impeller, the impeller housing and inlet to the impeller. Also checked the water pocket on the bottom of the upper housing. After replacing the entire pump and reassembling, I still had an overheating issue. My next move was to removed the upper and lower outdrive and remove the gimbal housing. This provides access to the water hose between the outdrive and the transom. I took that off and found debris (in my case impeller peices) that clogged about 75% of the hose ID. While I had everything apart, I replace the gimbal bearing, water hose, and bellows.

If you drop the lower unit, undo the raw water hose at the T-Stat housing, and run a garden hose into the raw water hose, you can check to see if there is a restriction between the engine end of the raw water hose and the outdrive. With my situation, I was getting backpressure out the raw water hose when backflushing through the outdrive. The water was not free flowing through the system. However, after I removed those chunks of debris mentioned above, there was no backpressure and the water flowed freely from the engine end of the raw water hose, through the transom, and out the upper end of the outdrive. While I was not able to dislodge the debris with the backflushing, perhaps you can, if that is in fact your issue.
 

Josephmcg

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Aug 15, 2017
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Do you have to pull the entire out drive off to access this raw water hose? I did hear of a guy on this forum not sure who it was though that apparently replaced that hose with a new one without having to take the outdrive off, and apparently it was easy he said?!
 

Josephmcg

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So hose #1 Is the hose we are speaking of right?
 

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Lancer76

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Well, to be clear, I speak of 2 different hoses. One is on the outside of the transom, and runs from a through-transom fitting to the upper unit of the outdrive. It is not on your diagram. That one is hard to get at. Need to pull the outdrive.

The second hose, is Hose 1 on your diagram. That hose runs from the inside portion of the through-transom fitting to the T-stat housing and is the raw water intake hose. This second hose is the one that I would remove at the T-stat housing and back flush with a garden hose after removing the lower unit of your outdrive. That's also the same hose you'd remove at the T-stat housing to check how much flow you are getting from the outdrive when the boat is running.
 

Lou C

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With these open, non pressurized cooling systems, they depend on a large volume of cool water in and out of the cooling system. Anything that lowers that volume will cause cooling issues. The main culprits are:
impeller, worn, wear plate, same
​old impeller pieces stuck in hose or thermo housing, or PS cooler
sticky thermostat
​clogged exhaust risers
bad water tube gaskets in the lower unit
​air leaking into suction hoses (more common on engines with the impeller on the engine, not in the drive)

​Boats moored or docked in salt water will have an additional issue with the marine growth in the water intakes and in the water passage above them. Just like inboards that have a thru hull pick up that are made so that they can be cleaned out by a diver. I would recommend that if you moor or dock the boat in salt water, when you take the drive apart to replace the impeller, paint the inside of the water passage with antifouling paint for aluminum.
 
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