I have a 2qm20 original sea water engine converted some years ago to fresh water. Need a new thermostat, will the one shown for the fresh water engine fit in the manifold housing position
Mike
Mike
Thermostat
- Thread starter chusansail
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Mike, if it is the factory conversion, the manual says that the thermostat will fit but the opening and full open temp set points for the fresh water cooled one are higher. The thermostat for the raw water cooled engine are 42C (108F) opening and 52C (126F) fully open.. for the fresh water thermostat, 71C (160F) opening and 85C (185F) fully opened.
Those are big differences in temperature. Anyone have any reasons why the engine would require such a difference for respective cooling systems?
Never worked with raw water cooled unit but I would guess the reason is to avoid having various carbonates drop out at the higher temperatures. Create a real mess in there after a while.
Further to my original post, I am in the Bahamas at the moment probably cannot get a thermostat. The one in the engine at present is stuck closed. Although the motor never gets hotter than 185f( fresh water cooled unit) would it be better to run without a thermostat, or keep the broken one in.
Mike
Particulates dropping out.. exactly.. doesn't normally happen in the heat exchanger because the temp of the seawater is a lot cooler than 140F, which is around where the dropping out commences.
Chusansail, it sounds like ya don't have too much of a problem .. I would not take it out.. If it is stuck closed, I would drill a hole in the valve plate to make sure that it is OK..a 3/16" or 1/4" hole should do.
Chusansail, it sounds like ya don't have too much of a problem .. I would not take it out.. If it is stuck closed, I would drill a hole in the valve plate to make sure that it is OK..a 3/16" or 1/4" hole should do.
It seems that for some years you may have been running with a raw water thermostat. If you find the engine has been running good during the warm up stage just go ahead and replace it with another. I'm not 100% sure for the Yanmar engine but discarding the thermostat may cause the water to circulate to quickly not allowing it enough time as it passes through the heat exchanger which could allow temperature to build up to the point of overheating.
Are You Sure You Have a Problem ................
As shown in the manual, the full open temperature of the stat occurs at 185 deg. F which is what you are presently showing.
Looks as if you have a perfectly good thermostat on your "( fresh water cooled unit)" so why change it ?
Don't hesitate if you require any further engine specs, however it's going to cost you some photos of what you're doing down there. I spent three years working in the Bahamas on a cruise ship destination island and it was the greatest job I've ever had.
............. because with the advantage of having the factory service manual in one hand and a rum and coke in the other, it looks like you're right within specs.
As shown in the manual, the full open temperature of the stat occurs at 185 deg. F which is what you are presently showing.
Looks as if you have a perfectly good thermostat on your "( fresh water cooled unit)" so why change it ?
Don't hesitate if you require any further engine specs, however it's going to cost you some photos of what you're doing down there. I spent three years working in the Bahamas on a cruise ship destination island and it was the greatest job I've ever had.
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Joining in on this thread probably after the horse has left the gate, but I would like to add.
I've got a raw water to anti-freeze converted 2QM20 on my 1980 Cherubini Hunter 36. Still runs like a charm.
Unfortunately, my QM series Yanmar manual is on my boat, so I don't have the official references handy.
Reading through the original post and the replies, I am not clear what type of conversion Mike has. (But question for Mike -- is your 185F operating temp actually measured, or your assumption?) I'm mentioning because the conversion type does determine the physical size of the thermostat that can be used. My conversion I believe was often done by Hunter (or their dealers) in the Cherubini era since a few other owners through my years on SBO forums have also mentioned the same set-up. Rather than an official Yanmar kit that puts the exchanger on the engine and changes the thermostat housing, the other type of conversion, as on my boat, was to install an external-to-the-engine heat exchanger (mine is mounted on a nearby bulkhead), add a bracket to the side of the engine to which is mounted an external second pump which becomes powered by the alternator belt, and re-route the engine's normal raw water flow to a self contained anti-freeze circulation arrangement. The in-engine "raw water" pump now does the duty of pumping anti-freeze though the external exchanger and back to into the engine's thermostat housing for constant re-circulating through the engine. The added external pump serves to move sea water through the exchanger and then to the exhaust elbow. For this type of conversion, the original sea/raw water thermostat housing remains. And only the lower temperature sea/raw water thermostat will fit. The high temp ~180F type has a different size and shape. I think Yanmar purposefully made the two sizes different so that owners would not operate a sea water cooled engine at the higher temps. As noted already, minerals and salt in the sea water precipitate out at temps much over 140F. The water cooling channels will quickly clog up. Besides then causing the engine to over-heat, the channels buried within the cast iron of the engine block and head really can't ever be gotten clear again. Engine ruined.
My anti-freeze Yanmar operates in the ~130F range --just as with a raw water unit.
Mike, I might be at my boat today and if so I will bring my manual home. If you still want info, respond again to this thread, and like Kloudie did, I can photo the relevant pages for you.
My layman's understanding of thermostats is that they are designed to fail so that the coolant water will always flow. Better to run with an under-temped engine than one that overheats severely I guess. If my impression is correct, then I would think that just leaving your suspected bad thermostat in the engine would be OK. And considering you are in warm waters, and the heat exchanger won't be 100% efficient, you are likely to have some engine temp increase anyway.
You do know about the engine propulsion sub-forum on SBO? You might find some diesel mechanics over there.
Joining in on this thread probably after the horse has left the gate, but I would like to add.
I've got a raw water to anti-freeze converted 2QM20 on my 1980 Cherubini Hunter 36. Still runs like a charm.
Unfortunately, my QM series Yanmar manual is on my boat, so I don't have the official references handy.
Reading through the original post and the replies, I am not clear what type of conversion Mike has. (But question for Mike -- is your 185F operating temp actually measured, or your assumption?) I'm mentioning because the conversion type does determine the physical size of the thermostat that can be used. My conversion I believe was often done by Hunter (or their dealers) in the Cherubini era since a few other owners through my years on SBO forums have also mentioned the same set-up. Rather than an official Yanmar kit that puts the exchanger on the engine and changes the thermostat housing, the other type of conversion, as on my boat, was to install an external-to-the-engine heat exchanger (mine is mounted on a nearby bulkhead), add a bracket to the side of the engine to which is mounted an external second pump which becomes powered by the alternator belt, and re-route the engine's normal raw water flow to a self contained anti-freeze circulation arrangement. The in-engine "raw water" pump now does the duty of pumping anti-freeze though the external exchanger and back to into the engine's thermostat housing for constant re-circulating through the engine. The added external pump serves to move sea water through the exchanger and then to the exhaust elbow. For this type of conversion, the original sea/raw water thermostat housing remains. And only the lower temperature sea/raw water thermostat will fit. The high temp ~180F type has a different size and shape. I think Yanmar purposefully made the two sizes different so that owners would not operate a sea water cooled engine at the higher temps. As noted already, minerals and salt in the sea water precipitate out at temps much over 140F. The water cooling channels will quickly clog up. Besides then causing the engine to over-heat, the channels buried within the cast iron of the engine block and head really can't ever be gotten clear again. Engine ruined.
My anti-freeze Yanmar operates in the ~130F range --just as with a raw water unit.
Mike, I might be at my boat today and if so I will bring my manual home. If you still want info, respond again to this thread, and like Kloudie did, I can photo the relevant pages for you.
My layman's understanding of thermostats is that they are designed to fail so that the coolant water will always flow. Better to run with an under-temped engine than one that overheats severely I guess. If my impression is correct, then I would think that just leaving your suspected bad thermostat in the engine would be OK. And considering you are in warm waters, and the heat exchanger won't be 100% efficient, you are likely to have some engine temp increase anyway.
You do know about the engine propulsion sub-forum on SBO? You might find some diesel mechanics over there.
First, the thermostat for your QM is very different from a thermostat for a GM.. If you look at the picture I posted, it shows coolant going around a movable plate which is just below the "arch" on the thermostat. That plate is what regulates the water temperature by opening or closing the coolant flow. First. be sure that the thermostat is at fault by putting it into boiling water.. if the passage opens, you probably don't have a thermostat problem. If it doesn't move, then drill a hole in that plate to let more coolant through. Do not remove the thermostat for normal running because that will affect the coolant pump performance. The "arch is the part looking left in the bottom two pix and looking up in the top two pix of my post. Again his is stuff pertaining to the factory fresh water system.. if it is not a factory system, my info may not be correct..
The carbonates in raw/sea water will quickly precipitate out of solution at near 155°F forming 'scale' in the cooling system (.... or 'rocks' if near an undersea volcano vent). If the raw cooling water never exceeds ~150°, fouling with carbonates is minimized. ;-)
The unit is faulty so I'll do as you recommend as getting a newark here is a problem
Thanks again
Thanks again
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