V4 low speed overheat

My '70 85hp 'Rude just got the complete water pump/housing replacement treatment.She's pumping fine.My problem is when I idle down(1000 rpm or less) my overheat buzzer/light goes off after 2 minutes or so.It did this before the pump and housing replacement also.Upper rpm water flow is excellent from my tell-tale.(I used a hose barb and hose from a tapped hole in the upper starboard cylinder head.I think this was for a factory pressure guage.)Could my tell tale be taking too much water away at lower rpm's causing the tempature to rise? Should I re-plug this and just rely on the alarm? I went out this morning and opened up the thermostat/vernatherm housing and using Rodbolts advice,I ground a small groove in the vernatherm poppett valve.This will make thermostat open a little earlier and bleed air out of the housing right?I'm wondering if it's water deflectors in the head covers.Any advice or suggestions? Thanks,C.C.

Re: V4 low speed overheat

It very well could be the deflectors if they have never been replaced (35 yrs). Have you confirmed that it is actually getting hot by touching the head? You should be able to touch it for just a few seconds? Does the buzzer go off if you run in the water above 1000 rpm?<br /><br />Another thought - Have you had the boat in the water since you had the water pump job or are you running it only on the muffs? <br /><br />Do you know if the old impeller had any pieces broken off when it was removed?<br /><br />Finally - you mentioned an earlier post on this problem. It is best for us that you do not start a new post for the same problem. We get confused enough as it is.

Re: V4 low speed overheat

Yes,it gets hot when it's in the water,not on the muffs.I have run for 20 minutes or more at 4000 rpm and the alarm never sounds,even before the new water pump and housing were installed.It's cool as a cucumber above 1000 rpm.I really don't think it's deflectors because the heads seem to have equal heating on the upper cylinders and lower cylinders.Port and starboard banks seem to heat evenly on muffs or after hi speed runs.I flushed the water tubes when the lower unit was removed.I'll try plugging my tell tale tap in the #1 cylinder head and see if that helps.It may be possible that the water tubes into the pump housing are leaking more than they should at lower rpms too.I didn't think of that.......

Re: V4 low speed overheat

Might also want to pick up a 163 degree thermo melt stik from your dealer or boat shop and mark/touch check heads and block while test running to confirm that the temp sensor is operating properly.Temp sensor/s should kick in somewhere above 163.If the 163 stik melts during low speed test ,then you know it's overheating for sure.

Re: V4 low speed overheat

Running at a high rpm on a flushette is a good way to encounter a runaway engine situation and the thrown connecting rod scenario that follows. Not a good idea!<br /><br />On a flushette, with the water turned on full blast as it should be, you are forcing water to and thru the water pump to the engine cooling system. In the water, the water pump alone has full responsibility.<br /><br />I'd suggest that you drop the lower unit and double check the water pump installation.

Re: V4 low speed overheat

Hold up! I guess my grammar or syntax in the first post wasn't clear.I've been in the Big River when my low rpm overheat troubles occured.My little notch I cut in the vernatherm poppet disc has cured the low rpm tempature rise.(Thank you ,Capt.Rodbolt.)I just got back from 2 hours of running at all rpms and the heads stayed at a pretty constant 150 degrees-(or,thereabouts).I am very aware of running these beasts on muffs with no-load,like anything else the real acid test is on a boat in the water.I'm pretty amazed how well it runs after 35 years.Kinda' like an old warhorse.Thanks and keep on posting,C.C.

Re: V4 low speed overheat

I thought that the water should be turned ONLY a quarter of a turn on the valve when running on muffs?

Re: V4 low speed overheat

I dunno' 110johnson,I only run on muffies in janurary and feburary.,With any luck,Commander Reeves will set us straight and give us a good low-down about running on muffs in our driveways.I thought it was common knowledge,when running in your drive,on the hose,it forces water,(usually cool water.)into the pump,without exahaust back-pressure-(no load,so to speak) our goal is to get the motor to run properly,in the water,on our boat,with as little trouble as necessary.Ya' gotta' post more Joe,C.C.

Re: V4 low speed overheat

Yea, i remember reading somewhere that full water pressure is a no-no pump can not keep with the pressure!