My engine has been overheating. I thought I'd found the problem before - the angle piece from the heat exchange for the raw water to exit towards the muffler was clogged with salt. I cleaned that out and it seemed to solve the problem, but then it overheated again. Is it possible that the muffler is bad? (Note: The engine has about 1100 hours on it and the muffler is the original one.)
Overheating: Muffler the cause?
- Thread starter John R
- Start date
Can you give us the make of engine ? If there is a mixing elbow of some description, that's always a favorite source of blockage.
At 1100 hrs, the engine is just broken in and don't ask me why, but the interior of plastic mufflers seem to stay clean without buildup.
At 1100 hrs, the engine is just broken in and don't ask me why, but the interior of plastic mufflers seem to stay clean without buildup.
Possible but not likely. I would consider more plausible another build up obstruction perhaps inside the heat exchanger or pieces of a broken impeller which could have lodged in engine passages or the exchanger. Nevertheless start diagnosis from scratch with no misconceptions; I would divide the cooling system into sections to facilitate spotting where a flow obstruction might be. Checking water flow at the raw water pump's output port may indicate if the system up to that point may be sound, don't know what engine you have but will assume you have a belt driven stand alone pump. Remove the outlet hose and crank the engine to observe flow, if good move on but if low backtrack checking flow through the intake valve, check any strainer, check the inside of the hoses for buildup, check the impeller vanes and make sure the rubber portion is strongly attached to the metal bushing. Moving on check out flow at the engine before it enters the heat exchanger; once again if all is well move on but if not bench test the thermostat to make sure it is opening at the temperature specified for your engine. Probe for any impeller pieces. If all is well lets now check for outflow at the exchanger, if it is low you will need to employ some long and thin brushes to clean it or flush it, if all is well move the out flow of the mixing elbow. If low clean or replace the mixing elbow. At this point all is left is the muffler and the exhaust thru-hull fitting. First check that the fitting is not fouled by marine growth or some critter that crawled in it. If the problem persists and is now isolated to the muffler then replace the muffler but odds are you will find your obstruction way before that. Good luck.
My engine was overheating, seaweed in the seacock. How is your stream? Do you have water squirting out the back as the motor is running? How does your stream compare to the younger boats? If you have adequate water flow, than either the motor is making too much heat or the heat exchange is inadequate. When did you change the raw water impeller last?
John,
Do a search on Good Old Boat, They had an article about some folks heading through France and this was happening. It was some sort of raw water mixing elbow (obvious I don't own a diesel, huh). A $40 part (he actually had the spare on board) , 20 minute fix that took days of fretting to discover. Once replaced, he cut the elbow in half to show the problem. Nasty!
Do a search on Good Old Boat, They had an article about some folks heading through France and this was happening. It was some sort of raw water mixing elbow (obvious I don't own a diesel, huh). A $40 part (he actually had the spare on board) , 20 minute fix that took days of fretting to discover. Once replaced, he cut the elbow in half to show the problem. Nasty!
I once had a hose failure. It looked great from the outside, but inside was a flap of rubber that only reduced the flow when the throttle was advanced. Then stayed that way until the engine was stopped. It was a bugger to find. In my case it was the hose that feeds the raw water pump from the screen. Naturally it seemed to appear while we were out for a 23 night vacation. I managed to locate some hose that was too big to jury rig a fix. I replaced it with proper hose when we got home.
Ken
Ken
The engine is a Universal 35 hp. I changed the impeller after it overheated the first time. Everything seemed ok after that... until it overheated again. I took a look at it before I left the dock that time, and the raw water flow out the back of the boat seemed fine, but I can't swear to it later, when it overheated. As I said, then the other day I ran the engine for about 15 minutes at 1700 rpm with the transmission in gear, and no overheat. The flow was fine the entire time. One thing I'm wondering: Could it possibly be the thermostat -- that sometimes it sticks closed and sometimes it opens properly?
John, a thermostat should cost you all of $17 from a tractor store. Have you considered just changing it? Like reefing: if you think you should... 
If you have a stuck thermostat CLOSED, you'll have hi engine temp in short order of about 10 minutes!!
If you have a thermostat stuck OPEN, it'll take the engine much longer to get up to 160 degrees operating temp - hence it'll take longer to get hot water in the heater.
If you have a stuck thermostat CLOSED, you'll have hi engine temp in short order of about 10 minutes!!
If you have a thermostat stuck OPEN, it'll take the engine much longer to get up to 160 degrees operating temp - hence it'll take longer to get hot water in the heater.
Here's another thought...
How old are your hoses? In addition to other things mentioned, the old hoses tend to become more pliable and as a result may collapse restricting water flow when they heat up. They may look OK but aren't.
Also, besides the raw water pump, check the condition of the engine water pump. A loose belt may not be turning it as should be and/or it may have a bearing that is beginning to fail.
How old are your hoses? In addition to other things mentioned, the old hoses tend to become more pliable and as a result may collapse restricting water flow when they heat up. They may look OK but aren't.
Also, besides the raw water pump, check the condition of the engine water pump. A loose belt may not be turning it as should be and/or it may have a bearing that is beginning to fail.
Have you recently replaced the hot water heater in your fresh water system? Or worked on it? A long shot, but if you have and the hoses weren't bled to the point where enough coolant wasn't flowing your engine could over heat too.
Thanks for the other suggestions. Keep in mind one thing: It seems to overheat only sometimes. So, for issues like bad hoses - wouldn't it overheat always if the hoses are bad? Same for the elbow? As far as the engine water pump - excuse my ignorance, but I wasn't even aware of that one. A slipping belt sounds like a possibility -- maybe it slips sometimes and at other times not, or maybe only after running for a longer period of time?
Elbow is where heated water is injected into exhaust flow. Water reacting with exhaust precipitates CARBON out of the stream and can block the flow. Engine may work sometimes and overheat if stressed, or if other particulates hit narrowed passage.
Randomly overheating? When you say the engine overheats do you mean the alarm buzzer starts screaming? Next time you go out after the engine has reached operating temperature just touch the valve cover so that you can get a feel for the normal temperature and then when the buzzer next goes off go ahead and touch it again. If the engine is overheating the temperature of the engine's valve cover will be considerably higher and almost too hot to the touch. If the buzzer is sounding and the temperature of the engine feels like normal you could have found your culprit. You could have a faulty sender or the wiring harness from control panel to engine could have started getting chafed peeling insulation from the wires and randomly closing the circuit. If the overheating is for real perhaps something is bein overlooked about the conditions when it happens. For example a strong opposing current will induce a larger load on the engine causing it to run hotter and if the engine already has a diminished cooling water flow it will not take much to cause overheating. We once ran a boat for about an hour with the buzzer going. We did it because it was starting to get dark and we needed to clear a Pass in unfamiliar waters. To our advantage the boat was equipped with a temperature gauge and we could see that temperature although elevated was remaining constant. We also new that the buzzer will sound well in advance of a damaging temperature. We had sucked in a plastic bag that someone had disposed off and it was only partially blocking the flow. There is always an explanation, it is just that sometimes is not very evident.
Get an infrared thermometer. Even a cheap one is a very useful tool to track overheating problems. Record the baseline temperatures of various areas of the engine when running under cruising load at normal temperatures and compare that when you have a problem. Also measure the cooling water flow (calibrated bucket, watch and calculator) and compare that with the flow/RPM tables in your motor manual.
So, here's the deal: I thought I'd found the problem - the belt seemed loose. I tightened it up and the next time I went out, there was no wind so I motored for four hours or so and the engine ran fine. Problem solved, right? Wrong.
Yesterday I went out again. At first it was fine. I went outside the Golden Gate Bridge and ran into adverse current on the way back so cranked up the engine again. This time, it overheated. One thing I realized: This time I was in fairly rough seas. I hung over the stern and observed that the waves were high enough to wash up and over the exhaust outlet. It seemed to me that in this case, no raw water was coming out, only exhaust. The temp gauge was registering up at the top, so I shut it down.
An hour or so later, I was back inside the Bay where the water was calm. After awhile I cranked up the engine again. I only ran it at low speed so maybe that was the difference, but in the calm water it didn't overheat, and I could see raw water being expelled. Is it possible that the muffler is bad? Could that cause it to overheat, and could that be related to no raw water being expelled in a rougher sea state? (Note, again: This is a Universal 35 HP engine with a little over 1100 hours on it. To my knowledge the muffler has never been changed.)
Yesterday I went out again. At first it was fine. I went outside the Golden Gate Bridge and ran into adverse current on the way back so cranked up the engine again. This time, it overheated. One thing I realized: This time I was in fairly rough seas. I hung over the stern and observed that the waves were high enough to wash up and over the exhaust outlet. It seemed to me that in this case, no raw water was coming out, only exhaust. The temp gauge was registering up at the top, so I shut it down.
An hour or so later, I was back inside the Bay where the water was calm. After awhile I cranked up the engine again. I only ran it at low speed so maybe that was the difference, but in the calm water it didn't overheat, and I could see raw water being expelled. Is it possible that the muffler is bad? Could that cause it to overheat, and could that be related to no raw water being expelled in a rougher sea state? (Note, again: This is a Universal 35 HP engine with a little over 1100 hours on it. To my knowledge the muffler has never been changed.)
As I explained in my original post, I already replaced the impeller. And if it were the pump, then why does it not overheat sometimes, like when I run it in calm water? (I looked and saw that raw water was being expelled then.)