lagasse@biomed.UUCP (Robert C. Lagasse) (05/17/85)
Outboard engines use a rubber impeller as a cooling water pump and from what I have been told by several outboard mechanics is that this part will burn up and turn into little rubber bands in seconds if the engine is not immersed in water while running. Once this part fails, the engine will overheat and (probably several minutes later) set off the high temperature "hot" horn (which only the larger engines are equipped with) indicating that the pistons have or are about to seize. You are supposed to keep an eye on the little "water indicator" hole that pisses into the water while the engine is running assuring you that the rubber impeller is still turning O.K. OMC (Johnson/Evinrude) sells a water pressure gage which mounts on the dashboard and comes "with tubing" so I suppose you have to run a hose from the engine to the gage. Still, you have to keep an eye on the gage. I have installed a fluid pressure switch at the engine by cutting the hose that runs to the "water indicator" and inserting a tee connector to feed the switch. A pair of wires run up to the dashboard where a piezo buzzer is mounted. The buzzer sounds for a few seconds on start-up until the water pressure rises which clicks the switch contacts open. The power is tapped from the "ignition on" + lead so all is quiet when the key is off. This also lets me know when I have left the key on without the engine running. Any comments ?????? Bob Lagasse Biomed Eng. MGH
rls@ihu1g.UUCP (r.l. schieve) (05/17/85)
> Outboard engines use a rubber impeller as a cooling water pump and from what > I have been told by several outboard mechanics is that this part will burn > up and turn into little rubber bands in seconds if the engine is not > immersed in water while running. Once this part fails, the engine will > overheat and (probably several minutes later) set off the high temperature > "hot" horn (which only the larger engines are equipped with) indicating that > the pistons have or are about to seize. You are supposed to keep an eye on > the little "water indicator" hole that pisses into the water while the > engine is running assuring you that the rubber impeller is still turning O.K. > OMC (Johnson/Evinrude) sells a water pressure gage which mounts on the > dashboard and comes "with tubing" so I suppose you have to run a hose from > the engine to the gage. Still, you have to keep an eye on the gage. > I have installed a fluid pressure switch at the engine by cutting the hose > that runs to the "water indicator" and inserting a tee connector to feed the > switch. A pair of wires run up to the dashboard where a piezo buzzer is > mounted. The buzzer sounds for a few seconds on start-up until the water > pressure rises which clicks the switch contacts open. The power is tapped > from the "ignition on" + lead so all is quiet when the key is off. This > also lets me know when I have left the key on without the engine running. > Any comments ?????? > Bob Lagasse Biomed Eng. MGH Sounds like a good idea but you may be a bit paranoid. I know how expensive outboards can be but I also know that they are more durable than most dealers would have you believe. I do have a question about the water pressure gauge OMC provides. Is it a go/no go indication or is it calibrated in PSI. I haven't had to change the water pump on my 140 hp yet but I have on smaller OMC engines and what often happens is several of the impeller fins or blades (whatever they are called) break off. The pump still functions but at reduced capacity. Having seen this happen it seems wise to periodically replace the impeller but I do admit I had a lot more confidence tearing into a 20 year old 18 hp than a relatively new 140 hp with a replacement value somewhere around $6000. Rick Schieve
mike@amdcad.UUCP (Mike Parker) (05/17/85)
In article <53@biomed.UUCP>, lagasse@biomed.UUCP (Robert C. Lagasse) writes: > Outboard engines use a rubber impeller as a cooling water pump and from what > I have been told by several outboard mechanics is that this part will burn > up and turn into little rubber bands in seconds if the engine is not > immersed in water while running. Once this part fails, the engine will If you have an outboard ( or fro that matter inboard ) engine that has been in storage for a period of years. In my case a brand new Volvo marine engine that had set for 2 years. The impeller may have died of "dry rot". For what they cost it help to have a spare around the first time you start such an engine. > I have installed a fluid pressure switch at the engine by cutting the hose > that runs to the "water indicator" and inserting a tee connector to feed the > switch. A pair of wires run up to the dashboard where a piezo buzzer is > mounted. The buzzer sounds for a few seconds on start-up until the water > pressure rises which clicks the switch contacts open. The power is tapped > from the "ignition on" + lead so all is quiet when the key is off. This > also lets me know when I have left the key on without the engine running. > Any comments ?????? > Bob Lagasse Biomed Eng. MGH Nice idea, wish it was mine. The volvo has an analog temperature guage but you don't see the problem until you're miles from home and hot. Mike
lagasse@biomed.UUCP (Robert C. Lagasse) (05/20/85)
Reply to Rick Shieve @ AT&T Labs: The OMC water pressure gage is uncalibrated. I have seen one since I wrote the original article. The installation instructions tell you to note the normal position of the needle for your engine when running and any future deviation of this reding could indicate a problem. Apparantly, the gage is for use with all sizes of engines. Bob Lagasse Mass. Gen. Hosp.
tj@utcs.UUCP (tj) (05/29/85)
This sounds like a very good Idea. I have never seen the "horn" on a motor but Mercury motors (don't know if all models) have a thermal switch that is mounted on the block that cuts off the ignition when it overheats. (A horn CAN be ignored...) I personally fried a 75 horse motor due to lack of water cooling. A water deflector plate was missing on the lower unit. I started the motor and checked that water was flowing, it was... great I says... I roared off into the never never only to discover that at high speed the deflector is needed to properly fdeflect water into the cooling system. When I slowed, water then returned to the system and turned to steam as it hit the cylinders... They didn't crack, but they was fried... A guage would have helped. I can also say that the owner before us told us that he personally had fried a pump impeller by running it dry. Rubber is just rubber... t.jones