Fresh Rebuild Getting Hot

[911S]

I have a ?89 Mercury Black Max V6 135 HP that I rebuilt the powerhead on over the winter. Got it on the water a few weeks ago and everything is running great except for the fact that it runs really hot at idle. As soon as I bring the rpm?s up the temp goes down to 140 but at idle it climbs slowly up towards the 200 degree mark and would keep going if I didn't bring up the rpm's. I never let it get that high for long. I changed the water pump during the rebuild and then changed the impeller again but didn?t help. Would the ?popit? valve have anything to do with the temp at low rpm? Seams from what I?ve read it opens at higher rpm to let more water in, which seems to be what is happening. Any ideas? Thanks!

 

[fpdiver]

Re: Fresh Rebuild Getting Hot

Sounds like you Thermostat is stuck. On many outboard (not sure on yours) there is a T-Stat and a poppit. The T-stat opens once tempeature gets high enough. The poppits opens on high pressure from high RPM, bypassing the T-Stat.

this would explain your scenario.

 

[j_martin]

Re: Fresh Rebuild Getting Hot

Sounds like you Thermostat is stuck. On many outboard (not sure on yours) there is a T-Stat and a poppit. The T-stat opens once tempeature gets high enough. The poppits opens on high pressure from high RPM, bypassing the T-Stat.

this would explain your scenario.

Or the poppet's hanging open not allowing the block to fill at idle......\


What's your tell-tale doing? What is the water pressure doing?

BTW, a water pressure gauge is cheaper than even one missed guess on parts.

hope it helps
John

 

[911S]

Re: Fresh Rebuild Getting Hot

thanks for the reply's the t-stats are new.....the tell tale is a steady stream.

don't know how to check the water pressure....John can you tell me how?

 

[j_martin]

Re: Fresh Rebuild Getting Hot

thanks for the reply's the t-stats are new.....the tell tale is a steady stream.

don't know how to check the water pressure....John can you tell me how?

Install a 30 dollar water pressure gauge. Hooks up to the pipe plug right behind the flywheel on top. I wouldn't run a v6 without one.

I suspect your water pressure is real low at idle, indicating that the water pump or delivery tube system needs service. Gaskets under pump, pump housing, seals, and the tube itself are all suspect at this point.

hope it helps
John

 

[911S]

Re: Fresh Rebuild Getting Hot

Thanks John, I'll get a pressure gauge and hook it up, what kind of pressure should I expect to see?

Ted