I'm at the end of my rope! My Yanmar @7 HP disel is overheating on a regular basis. Here's what I've done to fix the problem(with no success):replaced worn impellar, flushed out hoses(for broken bits of the impellar blade), changed the oil, changed oil filter, cleaned raw water filter, plenty of antifreeze/coolant, changed fuel filter, and checked to see if raw water is being pulled in and discharged(okay). Anyway...the engine STILL overheats and coolant goes flying everywhere. I'm so frustrated I could just hire a mechanic! Any advice would be much appreciated! Scott
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Jim Logan
Yanmar Overheat Problem
If you read the archives at this site, you will find that a very common reason for overheating is a clogged injector elbow in the exhause system, usually caused either by long use or running a relatively low rpm - clean or replace the elbow and see if that fixes your problem. Also, have you checked the seal on the cap on your coolant tank?
If you read the archives at this site, you will find that a very common reason for overheating is a clogged injector elbow in the exhause system, usually caused either by long use or running a relatively low rpm - clean or replace the elbow and see if that fixes your problem. Also, have you checked the seal on the cap on your coolant tank?
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Walt G.
Overheat Problem
If you haven't changed the thermostat, try replacing it. I'm not familiar with your particular engine, but I assume it has a thermostat. You might initially try running the engine without a thermostat to see if it still overheats. If it doesn't the thermostat is your likely problem. Another possibility is that your heat exchanger is plugged on the engine coolant side -- try to check it out visually or by feeling if there's a significant difference in temperature in the cold water input and output hoses. Lastly, ensure you don't have high spots or loops in your engine-side coolant hoses that could be creating pockets of air which sometimes restrict the flow of engine coolant. This was a problem I had when I added a hot air heater to my engine. Good Luck.
If you haven't changed the thermostat, try replacing it. I'm not familiar with your particular engine, but I assume it has a thermostat. You might initially try running the engine without a thermostat to see if it still overheats. If it doesn't the thermostat is your likely problem. Another possibility is that your heat exchanger is plugged on the engine coolant side -- try to check it out visually or by feeling if there's a significant difference in temperature in the cold water input and output hoses. Lastly, ensure you don't have high spots or loops in your engine-side coolant hoses that could be creating pockets of air which sometimes restrict the flow of engine coolant. This was a problem I had when I added a hot air heater to my engine. Good Luck.
A little confused.
Scottie: I assume that you have a 3GM20F (27hp)? You also mentioned that the "coolant goes flying everywhere". Not sure what is up here. I have never seen a drop of coolant around my engine. If you are seeing coolant outside the engine maybe, just maybe you have a head gasket leak. This would definetly cause overheating. Also mentioned was the heat exchanger, wondering if there is a blockage here that is causing pressure build up? Assuming that the mechanic is not too far from your marina a service call may be in order. $75 could save you several thousand if you end up frying the engine.
Scottie: I assume that you have a 3GM20F (27hp)? You also mentioned that the "coolant goes flying everywhere". Not sure what is up here. I have never seen a drop of coolant around my engine. If you are seeing coolant outside the engine maybe, just maybe you have a head gasket leak. This would definetly cause overheating. Also mentioned was the heat exchanger, wondering if there is a blockage here that is causing pressure build up? Assuming that the mechanic is not too far from your marina a service call may be in order. $75 could save you several thousand if you end up frying the engine.
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SteveC
Scottie, how old is your engine and ...
what kind of hours are on it. If its an older model with high hours on, i would think it's heat exchanger related. However, I would first try the thermostat tests suggested because it's easier... Sounds like all the other things are working OK. Also, if you are running at a higher throttle then normal, you may also have the mixing elbow partially corroded causing the engine to work harder.
what kind of hours are on it. If its an older model with high hours on, i would think it's heat exchanger related. However, I would first try the thermostat tests suggested because it's easier... Sounds like all the other things are working OK. Also, if you are running at a higher throttle then normal, you may also have the mixing elbow partially corroded causing the engine to work harder.
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SteveC
One after thought....
you mentioned flushed out bits of hose...... Some of these tiny bits may have clogged the tiny tubes within the heat exchanger, reducing flow... I personally have never disassembled mine, but the manual instructions don't seem difficult, but it is a little work.
you mentioned flushed out bits of hose...... Some of these tiny bits may have clogged the tiny tubes within the heat exchanger, reducing flow... I personally have never disassembled mine, but the manual instructions don't seem difficult, but it is a little work.
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Les Andersen
Ropes End
Scottie, If the "coolant goes flying everywhere" is from the raw water side after the exchanger then I would bet it is the exhaust elbow. When the same thing happened to me it was because the raw water from the exchanger was being blocked at the elbow. The pressure would build up, the alarm would go off because of insufficient flow through the system, and finally the hose between the exchanger and the elbow would blow off resulting in lots of raw water spraying all over the engine. This generally hapens when running at 2500 + rpms for 1/2 hr or longer. You can run at low rpms for much longer because there will be enough water flow to maintain the lower engine temp. There will be water in the exhaust but it will be less than normal for the rpm. Kind of hard to notice a constricted flow out the exhaust. When the hose lets go you can notice the change in exhaust noise but its easy to miss. A quick fix wold be to remove the hose from the fitting at the elbow and look to see if there is a constriction. This comes from calcium deposits from the raw water against the hot exhaust. If there is, you can usually break it out with a nail, coat hanger etc. See of your engine runs better afterwards. If that fixes it then change the fitting. It is usually a 90 degree threaded hose fitting and can be found at most hardware/plumbing store. It is easier/cheaper than changing the elbow. Sometimes the fitting is so corroded into the elbow that removal is impossible but worth the effort. I carry a spare elbow because it can be changed with a cressant wrench and easier than trying to fool with the elbow in a pinch, But, eventually the elbow will need to be replaced. Really cures you from running the engine at low rpms for extended periods of time. It the problem is on the internal/anti-freeze side of the system then radiator cap, thermostat, back flushing are the normal procedures. Good luck Les Andersen s/v Mutual Fun
Scottie, If the "coolant goes flying everywhere" is from the raw water side after the exchanger then I would bet it is the exhaust elbow. When the same thing happened to me it was because the raw water from the exchanger was being blocked at the elbow. The pressure would build up, the alarm would go off because of insufficient flow through the system, and finally the hose between the exchanger and the elbow would blow off resulting in lots of raw water spraying all over the engine. This generally hapens when running at 2500 + rpms for 1/2 hr or longer. You can run at low rpms for much longer because there will be enough water flow to maintain the lower engine temp. There will be water in the exhaust but it will be less than normal for the rpm. Kind of hard to notice a constricted flow out the exhaust. When the hose lets go you can notice the change in exhaust noise but its easy to miss. A quick fix wold be to remove the hose from the fitting at the elbow and look to see if there is a constriction. This comes from calcium deposits from the raw water against the hot exhaust. If there is, you can usually break it out with a nail, coat hanger etc. See of your engine runs better afterwards. If that fixes it then change the fitting. It is usually a 90 degree threaded hose fitting and can be found at most hardware/plumbing store. It is easier/cheaper than changing the elbow. Sometimes the fitting is so corroded into the elbow that removal is impossible but worth the effort. I carry a spare elbow because it can be changed with a cressant wrench and easier than trying to fool with the elbow in a pinch, But, eventually the elbow will need to be replaced. Really cures you from running the engine at low rpms for extended periods of time. It the problem is on the internal/anti-freeze side of the system then radiator cap, thermostat, back flushing are the normal procedures. Good luck Les Andersen s/v Mutual Fun
PS:
The elbow is about $90 and you need a gasket too. Low rpm's and salt water make the conditions worse. I have alway run my engine in the 2500-3000 rpm range and have never had this problem, but we are in fresh water most of the time. If you have not checked this out you need to. If you can get the hose off you can use a mirror and a flash lite to look up in there and see. You can also just put your finger up in there and you are probably going to be able to feel the coke (carbonized soot).
The elbow is about $90 and you need a gasket too. Low rpm's and salt water make the conditions worse. I have alway run my engine in the 2500-3000 rpm range and have never had this problem, but we are in fresh water most of the time. If you have not checked this out you need to. If you can get the hose off you can use a mirror and a flash lite to look up in there and see. You can also just put your finger up in there and you are probably going to be able to feel the coke (carbonized soot).
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