1987 50 hp overheating

[Whitefeather1968]

My '87 50 hp has an occasional overheating alarm whenever it idles for more than 5 mins. I can get it to stop if I put it in gear a take off after about 10 seconds. There is a good stream of water coming out of the tell tale.I replaced the impeller about 3 years ago. I'm thinking it's probably a thermostat issue but wanted to hear from the experts first.
I should also mention that the VRO system was taken off about 10 years ago and I premix my gas.The alarm is a constant buzz so I know it's the overheating alarm. All input is very much appreciated.

 

[ondarvr]

Most likely the thermostat.

 

[juno pierrat]

getting to the thermostat is difficult, bottom two blots!, had same problem, removed water cover and replaced thermo, still had same problem, removed head and water cover together and found that much easier, found hole in head gasket down close to thermo, possible freeze damage
will try to post pic, but if you have money for a head gasket its much easier to remove head and work on the whole assembly. sorry pic is to largre

 

[oldboat1]

Good suggestions. I would manually check the head temp as well -- IR gun is useful. It's possible the temp switch is acting up (top of the head I think on VRO models). Have to assume for safety the warning is accurate, but should check. I would do that first.

 

[Whitefeather1968]

Thanks for the advice.
I went ahead and bought a new thermostat and gasket today. I figure it hasn't been changed in the 10-11 years I've had it so might need to replace it anyway. I got it pulled apart with little resistance and realized I forgot the cover gasket. So back to the marina again.
My only question is, Is the plastic valve with the spring directly over the t-stat the water bypass valve? Does it matter how it sets back in the head? It looks like its has a notch in it and I'm not sure of the way it sets in the head.
Thanks again

 

[juno pierrat]

the service manual says The tapped side of the relief valve should face the rubber grommet. Gasket sealant on both side of gasket . torque to 60 - 84 in. lbs.

 

[Whitefeather1968]

Well I went ahead and replaced the thermostat and gaskets and put it in a tub of water. Same thing after about 5 mins, the overheat alarm goes off so I check the heads by using the hand method. It was hot. I went ahead and replaced the water pump today, put it in the bath, and now everything is running cool no alarm and noticeable temperature change on the heads.
I did notice that there is water squirting from between the lower unit and the midsection. There is no gasket there and I've rechecked the bolts for tightness. I also noticed water coming from the front part of the foot near the the top next to the midsection connection. It looks like a orifice is there but I'd have to remove a piece of that corrosion preventing material. I've got a video if needed. I've never noticed it before so I'm wondering if I've got to pull that foot off again or is this this normal?
Thanks again.

 

[juno pierrat]

yes its very normal

 

[oldboat1]

agree -- sounds normal. Also sounds like good progress.

don't mean to nitpick, but thinking you may not have that lower unit dunked quite far enough (want a minimum of 6 inches or so above the impeller).

 

[Whitefeather1968]

Thanks guys. I got it on the lake yesterday and was happy. It seemed like everything was working fine. Tried to duplicate the idle and low rpm cruising and it never got hot. So job well done fellas. Thanks again

 

[ondarvr]

It's always nice to here what the outcome was, many times you never hear back from the person to know exactly what solved the problem.