Mercruiser 5 litre 305

 Hello fellow fishers and boaties

I bought a project boat abt 6 mtjs ago and have it ready to get wet, my problem is one side of the mtr riser only gets alot hotter than the other side, i have done flow tests on what water the impellor puts through the mtr at idle revs in 20 sec abt 7 litres when i take the revs up to 1500 or higher the temp drops. Now am i worried about nothing or should i dig abit deeper. I have checked the circulation pump , thermostat and all hoses and cant see any problems anywhere. Any advice and help appreciated 

Thanks Russ


z00m's picture

Posts: 785

Date Joined: 10/05/14

How hot?

Wed, 2017-04-19 20:01

 Reading online shows the mercs normally show hotter one side than the other due to water taking the path of least resistance. Is the engine temp showing overheating? Seems the common test is that you should be able to keep your hand on the elbow for a few seconds. If not then too hot.

Given you see lower temps when revs rise this might mean your impeller is not moving enough water at idle?

Posts: 2

Date Joined: 17/04/17

 Hi thanks for the reply. The

Wed, 2017-04-19 20:13

 Hi thanks for the reply. The motor temp is fine sitting betweem 1/4 and 1/2 at idle and about 1/4 at revs. up on what tjey say the impellor should put through the motor at idle revs and what mine does is above what i read. I can keep my hand on the elbow for prob 3 or 4 secs before it gets to hot. I might just change the impellor for peace.of mind. 

Darren253's picture

Posts: 142

Date Joined: 23/07/16

Are you getting the same flow

Thu, 2017-04-20 09:33

Are you getting the same flow rate on the discharge of the manifold rather than directly out of the pump? That would be the first indication of a blocked or restricted riser...