Mercury 850 normal head temps

[buddyp]

Looking for input on what is a normal head temp for a freshly rebuilt 1975 merc 850! I have taken readings in a barrel of constant 80 degree water...new water pump complete!

Cyl 1-160
cyl 2-150
cyl-3 140
cyl 4 120

These temps are after 10-12 minutes.
Tell-tale temp..135.

Has anyone else recorded temps for the inline 4 or 6 cyl motor?

 

[buddyp]

Re: Mercury 850 normal head temps

Ran the boat in the water..lots of water out the pee , idles great ,planes fine,ran at 3000 rpm..pee stream started to get intermitent..then started to steam.a little...ran for a total of 2 minutes...measured head temps...
cyl1-200
cyl2-190
cyl3-180
cyl4-170
As I said new rebuild new pump and housing and wear plates... replaced stock jets .074 with .078...timing checked at 25...any suggestions?

 

[buddyp]

Re: Mercury 850 normal head temps

Got smart and hooked the hose direct to the water tube...still showed heat higher than normal...loks like a divider plate issue...anyone know where to find one?

 

[Chris1956]

Re: Mercury 850 normal head temps

First of all, your timing is too advanced. Timing should be 21* BTDC at most, with today's fuel. Secondly, when you say divider plate, are you talking about exhaust baffle?

 

[Chris1956]

Re: Mercury 850 normal head temps

As you know, that motor does not have a thermostat. As such the head temp is going to be a function of the load on the motor. They run dead cold at idle, and gradually increase temp as RPM and load increase.

It is not to say thay you do not have an issue, because you certainly do.