I have been having problems with my engine overheating recently. I thought that I had it fixed after cleaning the cooling tubes and replacing the mixing elbow ( it was pretty clogged). The prop is clean and there is nothing blocking the raw water intake. Yesterday I was motering into the wind (25 knotts) and waves (3-4 ft) with the engine running at 2900 RPM's and moving only at 2-3 mph when the engine overheating alarm came on. I was able to shut off the engine for a while and started it again going with the wind and running at under 2000 rpm"s without any problem. Today I motered into the wind (15-19) at 2500 rpm's without problem. The engine is a Yanmar 3GM30F in a Hunter 34. Was the engine just working too hard trying to push us through the wind and waves or do I have to look for other sources? Any insights would be greatly appreciated.
engine overheating
- Thread starter jim22335
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Shouldn't be a problem
You should be able to run a 3GM at wide open throttle ( I think 3400) indefinitely, or at 3600 for an hour or so (see manual). If the prop is too big for the negine, there would dbe smoke etc. I am not sure it should even overheat that way. Even if sailing in very warm water, it should not heat up. On the antifreeze circuit, I would check the thermostat ( just replace it). On the raw water side, I would suspect actual water flow. The shop manual gives specs as too how much water should comme out of the back of the boat. It is easier to measure how much it takes in, by putting the intake hose in a bucket!
You should be able to run a 3GM at wide open throttle ( I think 3400) indefinitely, or at 3600 for an hour or so (see manual). If the prop is too big for the negine, there would dbe smoke etc. I am not sure it should even overheat that way. Even if sailing in very warm water, it should not heat up. On the antifreeze circuit, I would check the thermostat ( just replace it). On the raw water side, I would suspect actual water flow. The shop manual gives specs as too how much water should comme out of the back of the boat. It is easier to measure how much it takes in, by putting the intake hose in a bucket!
I would check the prop too.
Jim: An over-pitched prop can definetly be a problem. You may also want to see if you have any hoses on the intake side of the pump that are soft or collapsing (restricting water flow). When is the last time you replaced your raw water impeller? Just a few things to check!
Jim: An over-pitched prop can definetly be a problem. You may also want to see if you have any hoses on the intake side of the pump that are soft or collapsing (restricting water flow). When is the last time you replaced your raw water impeller? Just a few things to check!
Raw water
The strainer may be clean, but a stick or slimball may be blocking the input. Dismantle the intake hose at the seacock and open it up to verify you have a clean arc of water coming up. If not, that's the problem. Poke a wire hanger down to free the opening.
The strainer may be clean, but a stick or slimball may be blocking the input. Dismantle the intake hose at the seacock and open it up to verify you have a clean arc of water coming up. If not, that's the problem. Poke a wire hanger down to free the opening.
Maybe a bit high on the rpm's
If a diesel should be run at 80% of full rpm's then 2900 may be a bit high for the conditions. The top end for a 3GM30F is, I'm quite sure, 3600 rpm. Therefore 2800 - 2900 rpm should be the "comfortable" range. Add the wind and waves on the nose and the engine is working a bit harder and, MAYBE, causewd the problem. I hope others agree
If a diesel should be run at 80% of full rpm's then 2900 may be a bit high for the conditions. The top end for a 3GM30F is, I'm quite sure, 3600 rpm. Therefore 2800 - 2900 rpm should be the "comfortable" range. Add the wind and waves on the nose and the engine is working a bit harder and, MAYBE, causewd the problem. I hope others agree
Jim, as Bill said, check the intake side.
Mine (H34) came with no screen on the through hull. It would suck up anything near-by. One time I had a single length of seaweed go past the strainer, all the way to the impeller. Solution? The Perko strainer became a 'yacht club sale' donation. I put a 'sand dollar' size external strainer on the hull. That was 15 years ago. Still perfect. There is nothing to add to the other posts that I can think of. Have fun, you'll find it.
Mine (H34) came with no screen on the through hull. It would suck up anything near-by. One time I had a single length of seaweed go past the strainer, all the way to the impeller. Solution? The Perko strainer became a 'yacht club sale' donation. I put a 'sand dollar' size external strainer on the hull. That was 15 years ago. Still perfect. There is nothing to add to the other posts that I can think of. Have fun, you'll find it.
Thanks for all of your input. I just replaced the impeller a couple of weeks ago and the hoses for the raw water intake this past spring. I checked the intake from under the boat but will try pulling the hose off. I will keep on looking, thanks.
Same boat same problem
For me it turned out to be the raw water intake hole was half the size it should have been because of all the bottom paint jobs. Just some thing else to check after you haul the boat.
For me it turned out to be the raw water intake hole was half the size it should have been because of all the bottom paint jobs. Just some thing else to check after you haul the boat.
Impeller
Several years ago I experienced a similar problem and discovered that an impeller had failed after only about ten hours of running time. I had purchased it from my Yanmar dealer so he readily gave me a replacement. Moral - even relatively new Yanmar impellers can fail.
Several years ago I experienced a similar problem and discovered that an impeller had failed after only about ten hours of running time. I had purchased it from my Yanmar dealer so he readily gave me a replacement. Moral - even relatively new Yanmar impellers can fail.
I don't have my service manual handy, but...
what is the possibility that the engine overheat sensor is out of whack? I hate those idiot lights for just this reason and we had a separate water temperature gauge installed in the cockpit of our 356. I wish I knew where the temp pickup actually gets its information, but you might also look into this end of the problem. Maybe there is nothing wrong with your boat but the sensor system?
what is the possibility that the engine overheat sensor is out of whack? I hate those idiot lights for just this reason and we had a separate water temperature gauge installed in the cockpit of our 356. I wish I knew where the temp pickup actually gets its information, but you might also look into this end of the problem. Maybe there is nothing wrong with your boat but the sensor system?
Is water coming out the exhaust?
If water is not coming out the exhaust, at a good rate, then the problem is in the primary (sea water) cooling pathway. Start to track down the problem. Remove the tubing from the pump input, connect a hose to it to your sink filled with water. If water is sucked up and through to the exhaust then you know the problem is between the water inlet and the pump inlet and therefore its not the impeller, its not the mixing elbow etc, otherwise vica-versa etc. Think along these lines, divide and conquer.
If water is not coming out the exhaust, at a good rate, then the problem is in the primary (sea water) cooling pathway. Start to track down the problem. Remove the tubing from the pump input, connect a hose to it to your sink filled with water. If water is sucked up and through to the exhaust then you know the problem is between the water inlet and the pump inlet and therefore its not the impeller, its not the mixing elbow etc, otherwise vica-versa etc. Think along these lines, divide and conquer.
On that note
even as we motor, I routinely check the raw-water temperature. It's easy and foolproof as far as my experience with this engine goes. When you open the engine lid while motoring, do this. First 'look' then 'smell' then 'touch' the cooling water discharge elbow at the rear of the heat exchanger. It only takes a second to test. It should be no more than room temperature. If not, it's not flowing enough raw water. Throttle down and find out why not.
even as we motor, I routinely check the raw-water temperature. It's easy and foolproof as far as my experience with this engine goes. When you open the engine lid while motoring, do this. First 'look' then 'smell' then 'touch' the cooling water discharge elbow at the rear of the heat exchanger. It only takes a second to test. It should be no more than room temperature. If not, it's not flowing enough raw water. Throttle down and find out why not.
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