Running Temp for 7.4/454 Mercruiser

[richard3rd]

Needing help, I've changed the impeller in the lower unit, changed the 140 thermo and still running around 190/200 when I'm getting up on plain, once on plain it backs down to 180. Is this the norm for these motors? The only other item to change is the water pump which has around 160 hrs on it. Any insight on this issue and the norm running temp would be awesome.

 

[Old Vet]

Mine runs between 160-170....which seems to be fairly common numbers I'm hearing from others.

 

[BonBini]

Mine stays rock solid around 145 all the time. First of the season I changed the lower pump and that alone took care of a heating issue I had... The engine temp would creep up around 195/200 after 1/2 hour or so running hard on plane (4000 + rpms). The impeller looked good, but the side thrust seal area was burnt and I presume leaking some flow.

The 7.4L needs lots of water flow from lower unit to stay cool. Did you replace the impeller and housing, or just the impeller? Also check the oil cooler for blockage, and the water line coming through the transom (the plastic bulkhead fitting will constrict down from corrosion!).

 

[fc3]

Sounds like you have an Alpha 1 drive. That drive uses a high pressure, low volume raw water pump. If it's not perfect, it's not going to cool well enough. Replacing just the impeller in these pumps is a false economy. You need to at least change a "half-kit," which is everything but the lower body. At this point, you should do a full kit and perform periodic half-hit replacements.

Best regards,
Frank