No problem, just need assurance

[jklnhyde]

My 1987 SeaRay Seville 19 cuddy(3.0L Cobra) runs just perfect and without a hitch, but there are two issues that I have a hard time accepting.
First, the temp gauge registers about 140 when putting away from the dock and regardless of how long at idle, it still rises no more than a quarter of the way. When I get on the throttle, the temp climbs to 175 and stays there or just slightly above, regardless of how long I continue at WOT.
Is 175-180 degrees good for an 3.0L OMC?
Why does the same Mercruiser engine specify a 140 thermostat and OMC specs a 160?

Next issue: at WOT (roughly trimmed, on glass-smooth water, just me and 1/2 tank of fuel), the boat climbs steadily to 32MPH @ 3800RPM. With a bit more finessing the trim, it moves to 33MPH @ 4000RPM.
I know the 3.0L should rev to 4400-4600RPM, but my throttle is maxed at the control and the carb linkage cannot go any further. The engine sounds rougher than I think it should, but has worked fine this way. The prop is a Vortex MI aluminum, 13.25x17.
Any suggestions?

 

[rndn]

Re: No problem, just need assurance

If the engine is properly tuned and in good running order and your tach is operating correctly, you need to drop to a 15 inch prop. For long engine life you really don't want to run your engine outside of the suggested rpm range.

 

[chiefalen]

Re: No problem, just need assurance

That boat right now is perfect. You could if you want to verify the rpms.

You should not be running at w.o.t for to long and really i rarely do. 3500 is what you should be doing in that ole girl.

Why does merc want 140 and omc want 160 same motor, got me.

As long as you never go over 185 your perfect. Gauge might not be right.

We both have 21-22 year old boats get out and enjoy it.

Prop you could go to a 15 buy one on e-bay and keep the other one as a spare on board. I always keep a spare prop on board as so should everyone.

Good luck

 

[Lou C]

Re: No problem, just need assurance

I agree that you shouldn't run an I/O at more than 75% of max rpm as a regular thing and crusing at 3200-3500 will give max engine life, but you have to get to the bottom of this issue. In my 1988 OMC factory shop manual, for the 3.0 installed in a 16-19 ft boat they list a 13" diameter prop with a 19" pitch. A 13-1/4 x 17 is listed for a 17-20 ft boat so you are not too far off. The other things than can cause lower than expected RPM are a lack of full spark advance and fuel restrictions. I'd make sure your fuel filters, anti siphon valve and gas tank vent are OK as well. When was the last time it got a full tune up, these old OMCs had points n condenser ignition and they need regular maintenance. My old 1988 4.3 4bbl will pull right in the middle of the max rpm range in calm water, with the standard 14-1/2x19 prop.

As far as the temp, you are really not overheating, my 4.3 with the same 160 stat runs right at 160 pretty much all the time, unless the water is very cool or I am running on plane for a long time, then come off plane and it will spike up to 175 then comes right down after idling for a minute or two. I'd just replace the thermo to be in the safe side and check the tightness of the water pump belt. The cooler running at idle (120-140) and slightly higher then thermo open point temp on plane (175) suggests a slightly sticky thermo, that's what mine does when it needs to be changed. I put in a new one each season here in salt water. As a maintenance item, when was the last time the inpeller in the drive was done? They can last a while if you don't run in sandy shallow water but it's a good idea to change them every 2 seasons.

 

[jklnhyde]

Re: No problem, just need assurance

Thanks for the replies.
The engine just got a major tune up; I'm a mech, so I won't launch unless I'm 100% certain the boat is good. I put a Pertronix ignition and coil, new plugs, belts, fuel hoses, cap and rotor. I agree that there could be a minor restriction in the fuel flow, and I still plan on replacing the 2 fuel filters and the water separator since they're cheap enough.
As for the anti-siphoning valve-where is it and how do I check it?
On the cooling side, I'm glad my temp is stable where it's at, but I do have a new water pump that I was going to hold off installing, so that, and a new thermostat might do the trick.

Thanks!

 

[danond]

Re: No problem, just need assurance

It's rare that the engine water pump goes bad in a freshwater boat. Replace the impeller in the drive, if you haven't in a year or two. It takes $20 and 30 minutes. Totally worth it.