New Owner with questions
 

Just bought 1978 V20 Steplift with Mercruiser 470 I/O.

Does anybody know where to get a manual? Also what is the normal operating temperature of the Merc 470? I took mine out on the water and it was running at around 160 at idle and 200 on plane. And how do I replace the raw water impeller/where is it located? Any answers will help. Any tips on care or what to expect to break would be appreciated. Thanks!

Any Mercruiser dealer or online you can get the manual of that motor, it will run around 100 bucks if not mistaken. The impeller is inside the lower unit, you have to lower/remove it in order to get to the impeller.

Thanks! I found a manual and bought it. Waiting for it to come in. Don't suppose you would know the temperature range?

Welcome to the site DBG. Great bunch of guys here with a heap of knowledge about these boats and boating in general. Congrats on your purchase. Send pics :)

According to my manual, it lists the thermostat at 160. Getting up to 200 is pretty hot when you consider boiling temp is 212. Did you make sure it is pumping water? I am thinking impeller change real soon...


welcome to the family,

rkc

Yeah the impeller change is next on the list once I get the part. It's getting good raw water flow from what I can tell. Of course this is a new boat to me and I cannot tell what's typical. I think there might be a buncha junk in the fresh water system. I'm going to flush it out today and see if that helps. When I come off plane, the temperature climbs dramatically. Any ideas? I'm thinking possible blockage in the fresh water system.

If you are getting good raw water flow, then it may not be your impeller. Is there enough antifreeze in it? Maybe its the thermostat.

Word of advice: If someone else chirps in, they will probably be more knowledgeable than myself. I am not a mechanic and a relative newbie.

However I am not just taking a break from changing my oil pan.

rkc

Yes you are :p Get back to work.. the water is calling you!!:you::you:

Unless my mind is playing tricks on me I seem to recall somewhere in my years of boating that the waterpump impellers on outboards and I/O's do very little work while on plane.

I think I recall reading somewhere that the force of the boat moving thru the water causes water to be injected through the intake holes in the lower unit and the force is so great that it actually partially bends the impeller out of the way and goes up into the motor by itself. In fact, if you look carefully at the intake holes you will see that they are chamfered in such a way so as to channel the water into the intake at speed. If the intake plate was put on backwards during a cleaning (a common mistake) then the water will not be forced into the motor during high speed running. It will work fine at low speed when the impeller is doing all the work, but not at high speed. In fact, that's the reason the makers of outboards don't use a solid impeller like you would see in a sump pump. The soft rubber can flex and get out of the way at high pressure, thereby making more efficient cooling.

I don't know if this is your problem, but it's a quick easy check. Just look at the intake plate(s) on your lower unit and make sure that the holes are facing forward so that water is scooped up as you travel through it. If they are facing backwards then you just found your high speed cooling problem.

Thanks for all the tips. I think it must have been the fresh water cooling system. This morning I drained it, flushed it, and replaced the coolant. I put her on the hose, warmed it up, and let it run at high RPMs for about five minutes. Then revved it a coupla times. The needle stayed in place right around 160. On to the next issue...

When coming down to idle after running her at high RPMs the engine dies. Any ideas? Thanks!