1996 27 scr on the verge of over heating

[Eddy M]

Good day. i replaced my 7.4 merc. 2 seasons ago w/ a rebuilt gen. 5 block ,built by a local speed shop... at the same time i installed a merc. 1/2 fresh water cooling system, w/ new merc. manifolds N risers n elbows. since day 1 the overflow tank almost fills it self from the block when run for 45 min @ 3200 rpm , then when ideling the temp. gos from a steady 170 to 200 , But the overflow tank wont drain back in to the heat exchanger, untill i crack the h.e. cap. HELP, please.. and the tank is mounted as high as it can go.

[mmwjr]

What outdrive do you have Alpha or Bravo? I have only seen a few HE's design to work with the Alpha lower volume water pump.

What temp setting is the t-stat?

"when run for 45 min @ 3200 rpm , then when ideling the temp. gos from a steady 170 to 200"
How long does it stay at 200? Lower rpms means pushing less coolant so a short temp rise is normal. Is the exhaust getting hot as well? Use a handheld IR temp sensor to measure.

Is the engine still hot when you are opening the HE cap? The coolant should flow back once the engine cools.

[Eddy M]

Originally Posted by mmwjr

What outdrive do you have Alpha or Bravo? I have only seen a few HE's design to work with the Alpha lower volume water pump.

What temp setting is the t-stat?

"when run for 45 min @ 3200 rpm , then when ideling the temp. gos from a steady 170 to 200"
How long does it stay at 200? Lower rpms means pushing less coolant so a short temp rise is normal. Is the exhaust getting hot as well? Use a handheld IR temp sensor to measure.

Is the engine still hot when you are opening the HE cap? The coolant should flow back once the engine cools.

thks. for any input.