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Old 08-30-2015, 08:20 AM   #21
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Let's be clear. NO engine should overheat at wot if the cooling system is working right and if it is reaching rated rpms. If it is not reaching rated rpms due to over propping, a dragging transmission (unlikely) then you are producing maximum power but the raw water pump and coolant pump are not operating at their maximum which reduces cooling capability. But I suspect that even if you were over propped by 300 rpm a clean cooling system would not overheat.


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Old 08-30-2015, 10:57 AM   #22
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For about $100 or so you can purchase an EGT gauge to stick in the exhaust that will allow you to operate with out overloading.

I actually have one, but haven't installed it yet. I have so many projects I can't seem to get organized.

What is the range of EGT I should operate in?
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Old 08-30-2015, 11:14 AM   #23
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Gauge reading vs infrared thermometer

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Originally Posted by djmarchand View Post
Let's be clear. NO engine should overheat at wot if the cooling system is working right and if it is reaching rated rpms. If it is not reaching rated rpms due to over propping, a dragging transmission (unlikely) then you are producing maximum power but the raw water pump and coolant pump are not operating at their maximum which reduces cooling capability. But I suspect that even if you were over propped by 300 rpm a clean cooling system would not overheat.


David

Is this a clue? I noticed, somewhere on the murky LA ICW, that the engine temp started rising a bit over 180 even at 2200-2400rpm. I stopped and cleaned out the engine strainer. There was some seaweed (not much) and a few minnows in there. After cleaning the temp went back to 180.

The amount of stuff in the strainer didn't seem like it should have choked the RW flow and raised the engine temp IMO, but I'm not very knowledgable. But maybe the RW cooling system is clogged somewhere downstream, so even the slightest restriction at the strainer causes the engine temp to rise?

The impeller is new, but I didn't install it. Had a tech do it in FL before I started my trip. However, this sametech also was supposed to change the trans oil and I'm not sure that got done based on my black trans oil and trans problems 1/2 way through my trip home. Or maybe the trans is going out. I don't know.

I really don't have a good baseline to operated from on this boat, so I feel like I'm chasing my tail at times trying to figure stuff out.
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Old 08-30-2015, 12:29 PM   #24
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A pretty good rule of thumb is that thermostats tend to operate in a 10F band. So at low cruise, somewhat above idle, tstat is nearly closed, but modulating. Go to high power and it is nearly open, but still controlling. This high power coolant temp should not be much more than 10F higher.

While electric gauges are notorious for being inaccurate, they usually are pretty good at measuring temp rise. So if you see a 10F rise from slow to high cruise, probably ok. In cardude's case, he's seeing like a 30F rise. That's too much.

Cardude: When running full power, what is the temp of the wet exhaust pipe well downstream of exhaust mixer? If like above 40F rise above sea temp, sounds like restriction somewhere in sea water system.

Barnacle buster cleans can help, but if there are old impeller vanes or old dead zincs in the coolers, you gots to actually clean them out physically. Then later cleans can be barnacle buster.
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Old 08-30-2015, 01:02 PM   #25
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A pretty good rule of thumb is that thermostats tend to operate in a 10F band. So at low cruise, somewhat above idle, tstat is nearly closed, but modulating. Go to high power and it is nearly open, but still controlling. This high power coolant temp should not be much more than 10F higher.

While electric gauges are notorious for being inaccurate, they usually are pretty good at measuring temp rise. So if you see a 10F rise from slow to high cruise, probably ok. In cardude's case, he's seeing like a 30F rise. That's too much.

Cardude: When running full power, what is the temp of the wet exhaust pipe well downstream of exhaust mixer? If like above 40F rise above sea temp, sounds like restriction somewhere in sea water system.

Barnacle buster cleans can help, but if there are old impeller vanes or old dead zincs in the coolers, you gots to actually clean them out physically. Then later cleans can be barnacle buster.

Ok. Thanks. That gives me some things to check. I might try to get a buddy to go to the boat with me today so I can take some temps at different RPMs while he drives.
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Old 08-31-2015, 07:00 PM   #26
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Already almost 180

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Thermostat. Gauge is correct.

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Downstream exhaust.

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WOT

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Thermostat.

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So I got full rated RPM but it shot up to 200 pretty quickly. When I brought the rpm back down it went back to 180 but took awhile.

No black smoke. No big vapor trail.
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Old 08-31-2015, 07:02 PM   #27
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Scenery

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Old 08-31-2015, 07:48 PM   #28
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I prefer the scenery to those ugly engine pictures.


But seriously I think that you are marginally ok. At 180 and moderate rpms the thermostat is partially open. At wot it is wide open and no longer modulating. That is probably ok as long as it stays at 200 and the alarm doesn't go off.


But you are close to overheating.


David
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Old 08-31-2015, 09:33 PM   #29
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Quote:
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I prefer the scenery to those ugly engine pictures.

But seriously I think that you are marginally ok. At 180 and moderate rpms the thermostat is partially open. At wot it is wide open and no longer modulating. That is probably ok as long as it stays at 200 and the alarm doesn't go off.

But you are close to overheating.

David
Cardude,

David is absolutely correct. The factory optional alarm panel for your engine triggers the high engine temp alarm at 95C (203F). The description of that alarm and what it means is below.

For the engines that have the more conventional instrument panel with both gauges and alarms, the alarm sensor is 100F (212F). The parts detail is below.

Finally, the factory gauges are redlined at 100C (212F).

No matter which method you use, David is right. My own experience with several JH Yanmars has been 180F at normal operating speeds and 190F at WOT, a 10F spread. Any time it went higher, it meant it was time to find out why, which is what you are doing. Good luck
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Old 08-31-2015, 10:15 PM   #30
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I prefer the scenery to those ugly engine pictures.


But seriously I think that you are marginally ok. At 180 and moderate rpms the thermostat is partially open. At wot it is wide open and no longer modulating. That is probably ok as long as it stays at 200 and the alarm doesn't go off.


But you are close to overheating.


David

Yeah. The scenery was good. 😉
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