1989 mercury over heat

[steven88venture]

im posting for my dad he has a 1989 200 merc black max on a 83 19ft bullet runs perfect but starts over heating at idle and low rpms but still has between 3 and 5 psi water pressure any ideas wat the deal is

 

[Faztbullet]

Re: 1989 mercury over heat

Does he have a low water pickup on lower unit? Does it do this at start up or after a run?

 

[steven88venture]

Re: 1989 mercury over heat

no it dosent have a low water pick up and it dose it any time

 

[gss036]

Re: 1989 mercury over heat

Check the thermostats, they should be opening at 143 degrees. Do you check for a water pressure drop when you get up to about 3000 rpm, that is a ball park area for the poppet valve to open. 3-5 # at idles is about where it should be and up to about 10-12# at upper rpm.

 

[j_martin]

Re: 1989 mercury over heat

I drove through a rotten mass of whatever one time. Mine did that till I pulled the exhaust cover and picked the junk out of all the little passages.

They tend to run a little warm at idle. It could be just that the overtemp sensor is drifted out of spec and is touchier than it should be.

hope it helps
John