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
I have a 1996 Catalina 36. My muffler was leaking, and the engine was also overheating.
I replaced it, and all is well.
Just my 2 cents... not an expert.
I replaced it, and all is well.
Just my 2 cents... not an expert.
Could be a couple of things: Clogged exhaust elbow as you describe, raw water pump not working properly, clogged raw water intake, clogged heat exchanger, fresh water pump nor working properly, low fresh water coolant level. Check all of these things.
In addition to the other responses, when was the last time the water pump impeller was changed.? If it's missing some blades, raw water flow would be affected as well as pieces of the impeller could be,lodged in the cooling tubes. Just a thought.
The exhaust system 'shouldn't' have anything to do with the engine itself overheating. The purpose of injecting raw water into the exhaust elbow is to keep the exhaust header cool and carry the exhaust fumes through the loop and downward (where non marine systems rely on a more or less straight path). Marine systems are somewhat contradictory to typical performance norms in diesel systems where maintain exhaust gas temps helps them flow faster... that said there still has to be some amount of system back pressure to function properly.
A secondary, but I would guess almost equally important, feature of a wet exhaust keeping the exhaust manifold cool is to keep overall temps in the engine space low. You'll notice that dry exhaust systems have insulation wrapping, and some wet systems are wrapped from the exhaust exit flange up to the point where the raw water is injected.
As pointed out by others above, if the engine itself is overheating is more likely to do with a damaged or underperforming raw-water pump as well as any component that is in line with that, including the raw water strainer. Its good you identified the build up in the exhaust elbow and cleaned it, but that same kind of salt/mineral deposit/general junk can build up in the heat exchanger (if you have one).
A secondary, but I would guess almost equally important, feature of a wet exhaust keeping the exhaust manifold cool is to keep overall temps in the engine space low. You'll notice that dry exhaust systems have insulation wrapping, and some wet systems are wrapped from the exhaust exit flange up to the point where the raw water is injected.
As pointed out by others above, if the engine itself is overheating is more likely to do with a damaged or underperforming raw-water pump as well as any component that is in line with that, including the raw water strainer. Its good you identified the build up in the exhaust elbow and cleaned it, but that same kind of salt/mineral deposit/general junk can build up in the heat exchanger (if you have one).
I changed the impeller when it first overheated - about five or ten engine hours ago. Since then the flow of raw water out the boat seems to be fine. (As I commented, what I found before that was that the fitting leading out of the heat exchange and to the muffler was clogged with salt. Among other things, that had clogged the outflow of raw water.)
I just returned from the boat just now. I ran the engine for about 15 minutes at about 1700 rpm's with the engine in gear (forward). It reached and held normal operating temperature (about 160 F.) So I can't understand what would have made it overheat the last time I took it out but not this time.
I just returned from the boat just now. I ran the engine for about 15 minutes at about 1700 rpm's with the engine in gear (forward). It reached and held normal operating temperature (about 160 F.) So I can't understand what would have made it overheat the last time I took it out but not this time.
What was the condition of the removed impeller? Any broken pieces that could be lodging or dislodging along the cooling lines? Other causes for erratic overheating could be a sticking thermostat or even a piece of plastic that may have gotten sucked in against the intake clam and latter released. Also maybe a critter swam or crawled in to the exhaust port. Check the strainer for any grasses or globs . Other than gauging the possibility and removal of broken impeller parts I would not bother doing anything but wait and see if it overheats again in the next 10 hours.
Sounds like build up/scale in the heat exchanger... Also, note the multiple examples Benny pointed out for small objects that randomly cause temporary blockage in various places. Removing the heat exchanger (which is a PITA) and taking it to a radiator repair shop is the way to get it clear of salt/scale build up or blockage, they will soak it in a de-scaler solution or cycle pump the cleaner through it. This can be a DIY job, but its a royal pain in setting up a supply of fresh water with the descaler added and then collecting the discharge and cycling back through, then rinse and repeat. Its not fun, you have to dispose of the 'brine' correctly, and usually ends up costing you more than just taking the dang thing to a radiator shop anyway. Some engines are just so much difficult to access and remove the heat exchanger than others, so leaving it in place is ideal if possible. If you do this kind of maintenance and then run through the check-list of all possible blockages and weak points, replacing clamps, hoses, and gaskets as you go you will likely find the problem and not have to repeat these tasks for several years while making your engine more reliable.
Thanks for the suggestions. When I changed the impeller the old one seemed to be fine - no broken off fins or chips that I could see.
As for the heat exchanger: Some years and about 4-500 engine hours ago the engine was starting to run hot (around 190 degrees if I'm remembering right) and I did at that time remove the heat exchanger and boil it out. At that time, it wasn't anything erratic; it consistently ran at around that temperature, and cleaning it out fixed the problem.
One alternative I was thinking: Could it be that the thermostat is going bad and sometimes sticks in the "closed" position?
As for the heat exchanger: Some years and about 4-500 engine hours ago the engine was starting to run hot (around 190 degrees if I'm remembering right) and I did at that time remove the heat exchanger and boil it out. At that time, it wasn't anything erratic; it consistently ran at around that temperature, and cleaning it out fixed the problem.
One alternative I was thinking: Could it be that the thermostat is going bad and sometimes sticks in the "closed" position?
You say that cleaning the deposits out of the exhaust elbow solved the problem for a while. I suspect that the elbow is still restricting the flow of water in the exhaust. Did you remove the elbow from the engine or just clean out where the water is injected into the top of the elbow? The reason I ask is that with my old exhaust elbow, there were deposits of scale throughout and would have been impossible to get to without removal. I did try cleaning it but decided it was best to put a new one on. It's not a project that I wanted to repeat a year later. Also, I don't think that running the engine a 1700 rpm is a good test for overheating. Your need to run it at cruise rpm, 2600-3000.
Heritage is right, what may be adequate cooling capacity at 1700 RPM might not be at 2800 RPM. A diminished flow might provide adequate cooling at lower RPM but not at a sustained cruising RPM. Diesels are heat engines and after a good run under load at cruising RPM the can get quite hot hence the recommended practice to let them cool off at idle for a few minutes before shutting down. I concur that the first cleaning of the mixing elbow might have just yielded a temporary improvement but that it might be necessary to remove it for a more thorough cleaning or replacement.