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AQAD31a back-up cooling intake

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chrispoulton

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Hi, I have a 1989 AQAD31a coupled to a 290A-DP drive in my boat (1969 Coronet 21 Explorer II). being an insurance broker I see various claims for damage caused by overheating after plastic bags or similar block the water intake grills in the drive unit, and am considering a secondary water intake in the hull bottom, which would connect to the rubber hose (the one that runs from the transom shield inlet valve to the steel intake pipe below the raw water pump) via a custom-made t-piece. My question is: since the water pressure going into the raw water pump is effectively going to double, could this cause any damage to the water pump, or any other items in the system? My intention here is to keep sea water flowing through the system in the event of the outdrive intakes being blocked.
Last question, is it possible to get a temperature alarm that sound long before the standard item? i.e. at a lower temperature of say 90 degrees C? Thanks everyone.
 
glen_adolph said:
All you need to do is get a temperature switch that fits the tank with the 90 Deg C rating. VDO and Stewart Warner both have them. The temperature switch simply compleats the circuit at the set temperature.
http://www.vdo.com/generator/www/co...erature_switches/temperature_switches_en.html
http://www.stewartwarner.com/Catalog/swtemp.html
Click to expand...


Thank you Glen. Much Appreciated. Do you have an opinion on the additional water intake, thru-hull, between the transom shield and the raw water pump? Thanks.
 
Keep in mind you are dealing with a suction line... your model transom shield on the port side might have a bronze valve controling intake from the rubber S hose to the drive. Common problems result from lack of suction caused by air entering the hose, then to the pump, causing it to cavitate losing suction power. Make sure the valve if equipped is working in good order and the inlet is not clogged and hose connections are tight. Also check the other connection point
on the drive for corrosion and possible leakage. Given all is ok your plan to T and bypass this circuit has been used by me living in the north for winterizing purposes after haulout. My concern from a insurance perspective is you are might create a possible syphon situation should something let go. Insure the T connection has valves on the outdrive and thru hull connection and you are using a good thru hull and valve. It is important your hose not collapse so use appropriate hose and double clamp. IMHO
 
All you need is properly working factory alarm system in the panel. Plastic bags do get stuck on the drive, and with alarm sounding at 205F (i think thats ~95C) you are well below boiling point, and just slowing down will quickly get engine temp into 170F or less since there is no load/heat. You are overthinking it. However an additional gauge or alarm/buzzer can easily be installed in-line with hose anywhere in raw water circuit (just before exhaust elbow is best). By the way you can have 10 raw water intakes plumbed before the raw water pump (suction), but the pressure after the pump will always be the same.

I have seen raw water pressure gauges, they are pretty useful and after you learn what standard system pressure reading is, they will show higher pressure (there is an obstruction reducing diameter where water passes) or lower pressure (leak/air). This is to keep an eye on the health of the raw water cooling circuit.
 
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stringer_bell said:
All you need is properly working factory alarm system in the panel. Plastic bags do get stuck on the drive, and with alarm sounding at 205F (i think thats ~95C) you are well below boiling point, and just slowing down will quickly get engine temp into 170F or less since there is no load/heat. You are overthinking it. However an additional gauge or alarm/buzzer can easily be installed in-line with hose anywhere in raw water circuit (just before exhaust elbow is best). By the way you can have 10 raw water intakes plumbed before the raw water pump (suction), but the pressure after the pump will always be the same.

I have seen raw water pressure gauges, they are pretty useful and after you learn what standard system pressure reading is, they will show higher pressure (there is an obstruction reducing diameter where water passes) or lower pressure (leak/air). This is to keep an eye on the health of the raw water cooling circuit.
Click to expand...


Thanks stringer_bell, that info is fantastic and exactly what I needed. I will install the additional intake after the seas and use a good-quality 316-grade stainless steel thru-hull fitting, seacock and t-piece. I will also look for the raw water pressure gauge you mentioned and put this in the hose running from the transom shield valve into the new t-piece.
Many thanks once again.
Chris
 
I agree with Stringer_bell. Keep the factory alarm and make sure it works. Keep your insurance dues paid and pay attention to the buzzer and gauge. Being on that end of the busniess, it is easy to forget that there are a whole lot more units that never have that problem.
 
No need for a T piece, just put your water pick up through a standard thru-hull and strainer, then abandon the pick up in the drive. No more plastic bag problems. I have a pair of Volvo D3's set up exactly like this. It is a much better system for all sorts of reasons and causes no issues vs the many we have had on a similar boat with standard stern drive pickups.
For early warning of heating issues I would suggest getting a temp probe that fits into the exhaust system just past the elbow. I have them (with programmable alarms) on one of my boats and you can monitor the complete operation of your cooling system by noting how the temps change over time. You can actually see the impeller wearing, heat exchanger getting blocked over a period of time etc etc as well as getting an early alarm should anything suddenly get blocked or fail.
 
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