Mystery Cobra Impeller

"Recently I encountered a &#34

"Recently I encountered a "short" impeller for my 1987 2.3L Cobra. This impeller's blades are only about 1/2 as long as a standard impeller. I have some evidence that it was intended for either 1987 or 1990 applications (I have also always wondered why the Sierra catalog only shows the standard impeller and enclosure as good for 1988 - 1990 2.3L; not 1987!) The p/n is 986465, vs. the standard impeller p/n 983895.

Does anyone know the history and/or application of this mystery "short" impeller? I have been burning up a lot of standard impellers and housings since I've owned the boat (and know full well about cleaning out the system when one disintegrates); perhaps I should be using this "short" part instead?"

"I'm not sure why but that

"I'm not sure why but that impeller 986465 was only used in the small Cobra's 2.3 and 3.0 in 1990, of course all the rest of the water pump parts are different as well so that impeller shouldn't work with yours unless someone has changed the other parts as well? See this link for an exploded view of a 1990 2.3 upper case http://www.dougrussell.com/partscatalog/volvo_omc/index.cfm?fuseaction=comp&grou p=757&GroupList=741,742,743,744,745,746,747,748,749,750,751,752,753,754,755,756, 757,758 and see this one for a 1987 2.3 upper case http://www.dougrussell.com/partscatalog/volvo_omc/index.cfm?fuseaction=comp&grou p=338&GroupList=322,323,324,327,328,329,330,331,332,333,334,335,336,363,338,339"

"Thanks Bob, sure enough, the

"Thanks Bob, sure enough, the 1990 shows the short impeller graphic and p/n. My 1987 2.3L has always had the standard impeller, but I seem to burn them up constantly despite keeping the outrive trimmed down and in deep water. In looking into impellers I encountered the short version.

I'm wondering if there exists a design issue whereby the standard impeller is a bit large for water flow within the 2.3L, causing overheating of the impeller. Perhaps by 1990 OMC recognized this and reduced the impeller surface area. Thoughts?

I'm thinking of trying the 1990 impeller / liner / housing to see what happens.

Still interesting too that Sierra only shows the standard impeller as 1988 - 1990 for 2.3L; starting to look like that's an error in their catalog and should in fact say 1987 - 1990."

"I understand your theory but

"I understand your theory but not sure what to tell you, I also verified the same info on the Bombardier site which has the old online data from OMC and only 1990 shows the smaller impeller for 2.3 and 3.0 Infact I checked 91 and 92, they no longer made the 2.3 but they went back to original impeller for the 3.0??? Unless you stumble upon an OMC mechanic that may remember this anomaly it may remain a mystery "

"As a follow up, Tom Smith at

"As a follow up, Tom Smith at Tom Smith Marine (www.tomsmithmarine.com) informed me that the short impeller was introduced to limit water flow on the 2.3L only. He stated the t-stat housing was also changed. Apparently the standard impeller had more water flow than the 2.3L needed, such that the motor couldn't get up to temperature in some cases. Mystery solved?"

"Thanks for the feedback David

"Thanks for the feedback David, another piece of OMC trivia to file away upstairs for future use!"